Showing 1–50 of 547 results for author: Das, B

The Fundamental Lemma of Altermagnetism: Emergence of Alterferrimagnetism

Authors: Chanchal K. Barman, Bishal Das, Alessio Filippetti, Aftab Alam, Fabio Bernardini

Abstract: Recent years have seen a proliferation in investigations on Altermagnetism due to its exciting prospects both from an applications perspective and theoretical standpoint. Traditionally, altermagnets are distinguished from collinear antiferromagnets using the central concept of halving subgroups within the spin space group formalism. In this work, we propose the Fundamental Lemma of Altermagnetism… ▽ More Recent years have seen a proliferation in investigations on Altermagnetism due to its exciting prospects both from an applications perspective and theoretical standpoint. Traditionally, altermagnets are distinguished from collinear antiferromagnets using the central concept of halving subgroups within the spin space group formalism. In this work, we propose the Fundamental Lemma of Altermagnetism (FLAM) deriving the exact conditions required for the existence of altermagnetic phase in a magnetic material on the basis of site-symmetry groups and halving subgroups for a given crystallographic space group. The spin group formalism further clubs ferrimagnetism with ferromagnetism since the same-spin and opposite-spin sublattices lose their meaning in the presence of multiple magnetic species. As a consequence of FLAM, we further propose a class of fully compensated ferrimagnets, termed as Alterferrimagnets (AFiMs), which can show alternating momentum-dependent spin-polarized non-relativistic electronic bands within the first Brillouin zone. We show that alterferrimagnetism is a generalization of traditional collinear altermagnetism where multiple magnetic species are allowed to coexist forming fully compensated magnetic-sublattices, each with individual up-spin and down-spin sublattices. △ Less

Submitted 29 December, 2025; originally announced December 2025.

Comments: Chanchal K. Barman and Bishal Das contributed equally to this work. 38 pages (27 pages main, 11 pages supplement), 17 figures (11 figures main, 6 figures supplement), 2 tables (all in main)

Superradiant and dynamical spin-down of neutron stars with gravitational wave implications

Authors: Indra Kumar Banerjee, Sandeep Chatterjee, Biswarup Das, Ujjal Kumar Dey

Abstract: Neutron stars such as pulsars and magnetars lose angular momentum primarily through electromagnetic dipole radiation, gravitational waves, $r$-mode oscillation, and also affected by fallback accretion processes. However, anomalous spin variations, particularly sudden enhanced spin-down rates, indicate additional spin-down mechanisms. We propose superradiant spin-down as a potential explanation for… ▽ More Neutron stars such as pulsars and magnetars lose angular momentum primarily through electromagnetic dipole radiation, gravitational waves, $r$-mode oscillation, and also affected by fallback accretion processes. However, anomalous spin variations, particularly sudden enhanced spin-down rates, indicate additional spin-down mechanisms. We propose superradiant spin-down as a potential explanation for these events. By modelling the interplay between conventional and superradiant spin-down channels, we evaluate their impact on neutron star rotational evolution. We also discuss gravitational-wave emission produced by quadrupole deformation, $r$-mode oscillations, and axion-induced bosonic clouds around an isolated neutron star, highlighting their potential as distinct multimessenger probes in upcoming detectors. △ Less

Submitted 26 December, 2025; originally announced December 2025.

Comments: 17 pages, 9 figures

Sculpting ultrafast mid-infrared light for solid-state high harmonic generation

Authors: Camilo Granados, Bálint Kiss, Eric Cormier, Bikash Kumar Das, Debobrata Rajak, Carmelo Rosales-Guzman, Rajaram Shrestha, Qiwen Zhan, Wenlong Gao

Abstract: The ability to sculpt light in space, time, and polarization has revolutionized studies of light-matter interaction and enabled breakthroughs in optical communication, imaging, and ultrafast science. Among the many degrees of freedom of light, orbital angular momentum (OAM) further expands these capabilities by unlocking new regimes of control in information encoding, particle manipulation, and sy… ▽ More The ability to sculpt light in space, time, and polarization has revolutionized studies of light-matter interaction and enabled breakthroughs in optical communication, imaging, and ultrafast science. Among the many degrees of freedom of light, orbital angular momentum (OAM) further expands these capabilities by unlocking new regimes of control in information encoding, particle manipulation, and symmetry-driven selection rules. However, exploiting OAM to drive nonlinear, non-perturbative effects in solids remains challenging, especially in the mid-infrared (MIR) spectral regime, a key region for accessing these effects in ambient air, where spatial light modulators do not operate. Here, we circumvent this limitation by generating femtosecond, few-cycle MIR Bessel-Gauss vortex (BGV) and Perfect optical vortices (POVs), using a robust, static spatial-shaping strategy. Using those beams to drive the high-harmonic generation (HHG) process in solids, we show that the resulting harmonic beams faithfully inherit the structural properties of the drivers: the constant-intensity ring of the POV is preserved across harmonic orders, while the harmonic BGVs retain their intrinsic TC-dependent profiles. Furthermore, by verifying the OAM up-scaling law, we confirm OAM conservation during HHG in solids. These results establish strong-field HHG in solids as a robust platform for synthesizing ultrafast structured harmonic light with controllable, high-value OAM. △ Less

Submitted 22 December, 2025; originally announced December 2025.

Expanding stellar horizons with polarized light

Authors: J. Vandersnickt, R. Ochoa Armenta, V. Vanlaer, A. David-Uraz, C. Aerts, S. B. Das, J. -C. Bouret, D. M. Bowman, L. Bugnet, V. Khalack, J. Labadie-Bartz, S. Mathis, Y. Nazé, C. Neiner, P. Petit, V. Petit, K. Thomson-Paressant, T. Van Doorsselaere, M. Vanrespaille

Abstract: The polarization of light is a critically under-utilized, rich source of information in astronomy. For stars in particular, surface magnetism polarization that can be detected and measured with spectro-polarimetry. Many questions about these surface fields remain unanswered due to a lack of dedicated instruments capable of probing weak and strong surface magnetic fields for the entire mass range o… ▽ More The polarization of light is a critically under-utilized, rich source of information in astronomy. For stars in particular, surface magnetism polarization that can be detected and measured with spectro-polarimetry. Many questions about these surface fields remain unanswered due to a lack of dedicated instruments capable of probing weak and strong surface magnetic fields for the entire mass range of stars, from M-dwarfs (and even substellar objects) to massive O-type stars at different evolutionary stages and metallicities. These questions range from the origin of these fields to their true incidence rate throughout the stellar population and the dependence on metallicity. Magnetic fields, although currently often excluded from stellar evolution models, play an important role in stellar evolution. Connecting the surface fields to internal fields through asteroseismology will instigate a new era of understanding stellar evolution and the transport of angular momentum and chemical elements throughout stellar interiors, also impacting our understanding of star-planet interactions and stellar remnants. Polarimetry is also an under-utilized tool to observationally constrain the mode identification of nonradial oscillations, which lies at the basis of accurate asteroseismic parameter estimation at percentage-level for stellar radii, masses, ages, internal rotation, and magnetic field strengths. Combining strong constraints on mode identification and surface magnetic properties through the acquisition of time-resolved, high-resolution and high-signal-to-noise (S/N) spectro-polarimetry and spectroscopy promises to bring leaps forward in our understanding of stellar structure, particularly when combined with long-term space photometric data from past, current, and future missions. △ Less

Submitted 17 December, 2025; originally announced December 2025.

Comments: White paper in response to ESO call Expanding Horizons (4 pages)

Optimal non-adaptive algorithm for edge estimation

Authors: Arijit Bishnu, Debarshi Chanda, Buddha Dev Das, Arijit Ghosh, Gopinath Mishra

Abstract: We present a simple nonadaptive randomized algorithm that estimates the number of edges in a simple, unweighted, undirected graph, possibly containing isolated vertices, using only degree and random edge queries. For an $n$-vertex graph, our method requires only $\widetilde{O}(\sqrt{n})$ queries, achieving sublinear query complexity. The algorithm independently samples a set of vertices and querie… ▽ More We present a simple nonadaptive randomized algorithm that estimates the number of edges in a simple, unweighted, undirected graph, possibly containing isolated vertices, using only degree and random edge queries. For an $n$-vertex graph, our method requires only $\widetilde{O}(\sqrt{n})$ queries, achieving sublinear query complexity. The algorithm independently samples a set of vertices and queries their degrees, and also independently samples a set of edges, using the answers to these queries to estimate the total number of edges in the graph. We further prove a matching lower bound, establishing the optimality of our algorithm and resolving the non-adaptive query complexity of this problem with respect to degree and random-edge queries. △ Less

Submitted 12 December, 2025; originally announced December 2025.

Comments: 15 pages

MSC Class: 68W20; 68Q25; 60C05 ACM Class: F.2.2

Smart Timing for Mining: A Deep Learning Framework for Bitcoin Hardware ROI Prediction

Authors: Sithumi Wickramasinghe, Bikramjit Das, Dorien Herremans

Abstract: Bitcoin mining hardware acquisition requires strategic timing due to volatile markets, rapid technological obsolescence, and protocol-driven revenue cycles. Despite mining's evolution into a capital-intensive industry, there is little guidance on when to purchase new Application-Specific Integrated Circuit (ASIC) hardware, and no prior computational frameworks address this decision problem. We add… ▽ More Bitcoin mining hardware acquisition requires strategic timing due to volatile markets, rapid technological obsolescence, and protocol-driven revenue cycles. Despite mining's evolution into a capital-intensive industry, there is little guidance on when to purchase new Application-Specific Integrated Circuit (ASIC) hardware, and no prior computational frameworks address this decision problem. We address this gap by formulating hardware acquisition as a time series classification task, predicting whether purchasing ASIC machines yields profitable (Return on Investment (ROI) >= 1), marginal (0 < ROI < 1), or unprofitable (ROI <= 0) returns within one year. We propose MineROI-Net, an open source Transformer-based architecture designed to capture multi-scale temporal patterns in mining profitability. Evaluated on data from 20 ASIC miners released between 2015 and 2024 across diverse market regimes, MineROI-Net outperforms LSTM-based and TSLANet baselines, achieving 83.7% accuracy and 83.1% macro F1-score. The model demonstrates strong economic relevance, achieving 93.6% precision in detecting unprofitable periods and 98.5% precision for profitable ones, while avoiding misclassification of profitable scenarios as unprofitable and vice versa. These results indicate that MineROI-Net offers a practical, data-driven tool for timing mining hardware acquisitions, potentially reducing financial risk in capital-intensive mining operations. The model is available through: https://github.com/AMAAI-Lab/MineROI-Net. △ Less

Submitted 4 December, 2025; originally announced December 2025.

Spherical accretion onto higher-dimensional Reissner-Nordström Black Hole

Authors: Bibhash Das, Anirban Chanda, Bikash Chandra Paul

Abstract: We obtain relativistic solutions of spherically symmetric accretion by a dynamical analysis of a generalised Hamiltonian for higher-dimensional Reissner-Nordström (RN) Black Hole (BH). We consider two different fluids namely, an isotropic fluid and a non-linear polytropic fluid to analyse the critical points in a higher-dimensional RN BH. The flow dynamics of the fluids are studied in different sp… ▽ More We obtain relativistic solutions of spherically symmetric accretion by a dynamical analysis of a generalised Hamiltonian for higher-dimensional Reissner-Nordström (RN) Black Hole (BH). We consider two different fluids namely, an isotropic fluid and a non-linear polytropic fluid to analyse the critical points in a higher-dimensional RN BH. The flow dynamics of the fluids are studied in different spacetime dimensions in the framework of Hamiltonian formalism. The isotropic fluid is found to have both transonic and non-transonic flow behaviour, but in the case of polytropic fluid, the flow behaviour is found to exhibit only non-transonic flow, determined by a critical point that is related to the local sound speed. The critical radius is found to change with the spacetime dimensions. Starting from the usual four dimensions it is noted that as the dimension increases the critical radius decreases, attains a minimum at a specific dimension ($D>4$) and thereafter increases again. The mass accretion rate for isotropic fluid is determined using Hamiltonian formalism. The maximum mass accretion rate for RN BH with different equations of state parameters is studied in addition to spacetime dimensions. The flow behaviour and mass accretion rate for a change in BH charge is also studied analytically. It is noted that the maximum mass accretion rate in a higher-dimensional Schwarzschild BH is the lowest, which however, increases with the increase in charge parameter in a higher-dimensional RN BH. △ Less

Submitted 3 December, 2025; originally announced December 2025.

Comments: This is the Accepted Manuscript version of an article accepted for publication in Classical and Quantum Gravity. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-6382/ad87a2

Journal ref: Bibhash Das et al 2024 Class. Quantum Grav. 41 235004

Velocity-space turbulent cascade in the near-Sun solar wind: first insights from the Parker Solar Probe mission

Authors: A. Larosa, O. Pezzi, T. Bowen, L. Sorriso-Valvo, N. Sioulas, F. Pucci, D. Trotta, J. L. Verniero, R. Livi, S. Bharati Das, A. Chasapis, D. Perrone, F. Valentini, S. Servidio

Abstract: In space plasmas, the rarity of collisions leads to complex structures in the velocity space where a turbulent cascade of the velocity distribution function fluctuations is thought to occur. Previous studies have explored this phenomenon using the Hermite decomposition of the ion velocity distribution function (VDF) in both magnetosheath data and numerical simulations. In this work, we investigate… ▽ More In space plasmas, the rarity of collisions leads to complex structures in the velocity space where a turbulent cascade of the velocity distribution function fluctuations is thought to occur. Previous studies have explored this phenomenon using the Hermite decomposition of the ion velocity distribution function (VDF) in both magnetosheath data and numerical simulations. In this work, we investigate the Hermite spectrum of the ion VDFs measured by Parker Solar Probe in the inner heliosphere. We analyze a superalfvénic stream at a radial distances of $R \approx 28 R_{sun}$ and a subalfvénic at $R \approx 11 R_{sun}$, the former characterized by a prevalence of VDFs with suprathermal beams (also known as hammerhead). The Hermite analysis is also compared with various proxies of energization and dissipation, in order to establish a connection between turbulent cascades in real space and those in the velocity space. A qualitative agreement between the energization proxies and the Hermite analysis is observed. The results are suggestive of the presence of a dual cascade in real and velocity space. △ Less

Submitted 1 December, 2025; originally announced December 2025.

DS-Span: Single-Phase Discriminative Subgraph Mining for Efficient Graph Embeddings

Authors: Yeamin Kaiser, Muhammed Tasnim Bin Anwar, Bholanath Das

Abstract: Graph representation learning seeks to transform complex, high-dimensional graph structures into compact vector spaces that preserve both topology and semantics. Among the various strategies, subgraph-based methods provide an interpretable bridge between symbolic pattern discovery and continuous embedding learning. Yet, existing frequent or discriminative subgraph mining approaches often suffer fr… ▽ More Graph representation learning seeks to transform complex, high-dimensional graph structures into compact vector spaces that preserve both topology and semantics. Among the various strategies, subgraph-based methods provide an interpretable bridge between symbolic pattern discovery and continuous embedding learning. Yet, existing frequent or discriminative subgraph mining approaches often suffer from redundant multi-phase pipelines, high computational cost, and weak coupling between mined structures and their discriminative relevance. We propose DS-Span, a single-phase discriminative subgraph mining framework that unifies pattern growth, pruning, and supervision-driven scoring within one traversal of the search space. DS-Span introduces a coverage-capped eligibility mechanism that dynamically limits exploration once a graph is sufficiently represented, and an information-gain-guided selection that promotes subgraphs with strong class-separating ability while minimizing redundancy. The resulting subgraph set serves as an efficient, interpretable basis for downstream graph embedding and classification. Extensive experiments across benchmarks demonstrate that DS-Span generates more compact and discriminative subgraph features than prior multi-stage methods, achieving higher or comparable accuracy with significantly reduced runtime. These results highlight the potential of unified, single-phase discriminative mining as a foundation for scalable and interpretable graph representation learning. △ Less

Submitted 3 December, 2025; v1 submitted 21 November, 2025; originally announced November 2025.

Jailbreaking Large Vision Language Models in Intelligent Transportation Systems

Authors: Badhan Chandra Das, Md Tasnim Jawad, Md Jueal Mia, M. Hadi Amini, Yanzhao Wu

Abstract: Large Vision Language Models (LVLMs) demonstrate strong capabilities in multimodal reasoning and many real-world applications, such as visual question answering. However, LVLMs are highly vulnerable to jailbreaking attacks. This paper systematically analyzes the vulnerabilities of LVLMs integrated in Intelligent Transportation Systems (ITS) under carefully crafted jailbreaking attacks. First, we c… ▽ More Large Vision Language Models (LVLMs) demonstrate strong capabilities in multimodal reasoning and many real-world applications, such as visual question answering. However, LVLMs are highly vulnerable to jailbreaking attacks. This paper systematically analyzes the vulnerabilities of LVLMs integrated in Intelligent Transportation Systems (ITS) under carefully crafted jailbreaking attacks. First, we carefully construct a dataset with harmful queries relevant to transportation, following OpenAI's prohibited categories to which the LVLMs should not respond. Second, we introduce a novel jailbreaking attack that exploits the vulnerabilities of LVLMs through image typography manipulation and multi-turn prompting. Third, we propose a multi-layered response filtering defense technique to prevent the model from generating inappropriate responses. We perform extensive experiments with the proposed attack and defense on the state-of-the-art LVLMs (both open-source and closed-source). To evaluate the attack method and defense technique, we use GPT-4's judgment to determine the toxicity score of the generated responses, as well as manual verification. Further, we compare our proposed jailbreaking method with existing jailbreaking techniques and highlight severe security risks involved with jailbreaking attacks with image typography manipulation and multi-turn prompting in the LVLMs integrated in ITS. △ Less

Submitted 17 November, 2025; originally announced November 2025.

Searching for Long-Period Radio Transients in ASKAP EMU Data with 10-Second Imaging

Authors: Yu Wing Joshua Lee, Yuanming Wang, Manisha Caleb, Tara Murphy, Tao An, Barnali Das, Dougal Dobie, Laura N. Driessen, David L. Kaplan, Emil Lenc, Joshua Pritchard, Zorawar Wadiasingh, Zhijun Xu

Abstract: Long-period radio transients (LPTs) are a recently identified phenomenon that challenge our current understanding of compact objects and coherent radio emission mechanisms. These objects emit radio pulses similar to those of pulsars, but at much longer periods -- on the order of minutes to hours. With duty cycles of only a few percent, individual pulses have been observed to last between 10 and 10… ▽ More Long-period radio transients (LPTs) are a recently identified phenomenon that challenge our current understanding of compact objects and coherent radio emission mechanisms. These objects emit radio pulses similar to those of pulsars, but at much longer periods -- on the order of minutes to hours. With duty cycles of only a few percent, individual pulses have been observed to last between 10 and 1000 seconds. This places LPTs in a timescale gap between the two main techniques used in transient radio searches: time-series analysis at millisecond to second timescales, and image-plane searches sensitive to variability on the scale of days. As a result, LPTs remained undetected until recently, and only a handful are currently known. To increase the sample of known LPTs, we conducted a dedicated search using 200 hours of archival data from the ASKAP Evolutionary Map of the Universe survey, covering 750 deg$^2$ of sky at the shortest possible imaging time step of 10-seconds. This represents the first large-scale search using ASKAP data at second-scale resolution. Although no LPTs were detected, we identified flares from six stars, at least one had never been detected in the radio regime before. We placed a lower limit on the transient surface density of $2.21\times10^{-6}$ deg$^{-2}$ at a 10-second timescale, with a sensitivity of 16.9 mJy. Our findings evaluate the feasibility of detecting radio transients using 10-second imaging with ASKAP and provide insights into improving detection pipelines and observation strategies for LPTs. △ Less

Submitted 12 November, 2025; originally announced November 2025.

Comments: 19 pages, 14 figures, 5 tables

Is a 1D perturbative method sufficient for asteroseismic modelling of $β$ Cephei pulsators? Implications for measurements of rotation and internal magnetic fields

Authors: J. S. G. Mombarg, V. Vanlaer, S. B. Das, M. Rieutord, C. Aerts, L. Bugnet, S. Mathis, D. R. Reese, J. Ballot

Abstract: Asymmetries in the observed rotational splittings of a multiplet contain information about the star's rotation profile and internal magnetic field. However, to exploit this information, highly accurate theoretical predictions are needed. We aim to quantify the difference in the predicted mode asymmetries between a 1D perturbative method, and a 2D method that includes a 2D stellar structure model,… ▽ More Asymmetries in the observed rotational splittings of a multiplet contain information about the star's rotation profile and internal magnetic field. However, to exploit this information, highly accurate theoretical predictions are needed. We aim to quantify the difference in the predicted mode asymmetries between a 1D perturbative method, and a 2D method that includes a 2D stellar structure model, which takes rotation into account. We then put these differences in the context of asteroseismic measurements of internal magnetic fields. We couple the 1D pulsation codes GYRE and StORM to the 2D stellar structure code ESTER and compare the oscillation predictions with the results from the 2D TOP pulsation code. We focus on ZAMS models representative of rotating $β$~Cephei pulsators, going up to 20% of the critical rotation rate. We find a generally good agreement between the oscillation frequencies resulting from the 1D and 2D pulsation codes. Since the magnetic asymmetries are small compared to the differences in the rotational asymmetries resulting from the 1D and 2D predictions, accurate measurements of the magnetic field are in most cases challenging. Differences in the predicted mode asymmetries between 1D perturbative methods and 2D non-perturbative methods can greatly hinder accurate measurements of internal magnetic fields in main-sequence pulsators with low-order modes. Nevertheless, reasonably accurate measurements could be possible with $n_{pg} \ge 2$ modes if the internal rotation is roughly below 10% of the critical rotation frequency for (aligned) magnetic fields on the order of a few hundred kG. While the differences between the 1D and 2D predictions are mostly too large for internal magnetic field detections, the rotational asymmetries predicted by StORM are in general accurate enough for asteroseismic modelling of the stellar rotation in main-sequence stars. △ Less

Submitted 12 November, 2025; originally announced November 2025.

Comments: Accepted for publication in Astronomy & Astrophysics, 8 pages. Abstract shortened to meet arXiv requirements

Recovering Ion Distribution Functions: II. Gyrotropic Slepian Reconstruction of Solar Wind Electrostatic Analyzer Measurements

Authors: Srijan Bharati Das, Michael Terres

Abstract: Velocity distribution functions (VDF) are an essential observable for studying kinetic and wave-particle processes in solar wind plasmas. To experimentally distinguish modes of heating, acceleration, and turbulence in the solar wind, precise representations of particle phase space VDFs are needed. In the first paper of this series, we developed the Slepian Basis Reconstruction (SBR) method to appr… ▽ More Velocity distribution functions (VDF) are an essential observable for studying kinetic and wave-particle processes in solar wind plasmas. To experimentally distinguish modes of heating, acceleration, and turbulence in the solar wind, precise representations of particle phase space VDFs are needed. In the first paper of this series, we developed the Slepian Basis Reconstruction (SBR) method to approximate fully agyrotropic continuous distributions from discrete measurements of electrostatic analyzers (ESAs). The method enables accurate determination of plasma moments, preserves kinetic features, and prescribes smooth gradients in phase space. In this paper, we extend the SBR method by imposing gyrotropic symmetry (g-SBR). Incorporating this symmetry enables high-fidelity reconstruction of VDFs that are partially measured, as from an ESA with a limited field-of-view (FOV). We introduce three frameworks for g-SBR, the gyrotropic Slepian Basis Reconstruction: (A) 1D angular Slepian functions on a polar-cap, (B) 2D Slepian functions in a Cartesian plane, and (C) a hybrid method. We employ model distributions representing multiple anisotropic ion populations in the solar wind to benchmark these methods, and we show that the g-SBR method produces a reconstruction that preserves kinetic structures and plasma moments, even with a strongly limited FOV. For our choice of model distribution, g-SBR can recover $\geq90\%$ of the density when only $20\%$ is measured. We provide the package \texttt{gdf} for open-source use and contribution by the heliophysics community. This work establishes direct pathways to bridge particle observations with kinetic theory and simulations, facilitating the investigation of gyrotropic plasma heating phenomena across the heliosphere. △ Less

Submitted 7 November, 2025; originally announced November 2025.

Comments: 22 pages, 10 figures, Accepted for publication in ApJ. Publicly available package (gdf) with documentation provided with the paper. Interested parties are encouraged to get in touch with authors with feedback or request to contribute to package

A scaling relationship for non-thermal radio emission from ordered magnetospheres - II. Investigating the efficiency of relativistic electron production in magnetospheres of BA-type stars

Authors: P. Leto, S. Owocki, C. Trigilio, F. Cavallaro, B. Das, M. E. Shultz, C. S. Buemi, G. Umana, L. Fossati, R. Ignace, J. Krticka, L. M. Oskinova, I. Pillitteri, C. Bordiu, F. Bufano, L. Cerrigone, A. Ingallinera, S. Loru, S. Riggi, A. C. Ruggeri, A. ud-Doula, F. Leone

Abstract: Magnetic BA stars host dipole-like magnetospheres. When detected as radio sources, their luminosities correlate with the magnetic field and rotation. Rotation is crucial because the mechanism undergirding the relativistic electron production is powered by centrifugal breakouts. CBOs occur wherever magnetic tension does not balance centrifugal force; the resulting magnetic reconnection provides par… ▽ More Magnetic BA stars host dipole-like magnetospheres. When detected as radio sources, their luminosities correlate with the magnetic field and rotation. Rotation is crucial because the mechanism undergirding the relativistic electron production is powered by centrifugal breakouts. CBOs occur wherever magnetic tension does not balance centrifugal force; the resulting magnetic reconnection provides particle acceleration. To investigate how physical conditions at the site of the CBOs affect the efficiency of the acceleration mechanism, we broadly explore the parameter space governing radio emission by increasing the sample of radio-loud magnetic stars. High-sensitivity VLA observations of 32 stars were performed in the hope of identifying new centrifugal magnetospheres and associated CBOs. We calculated gyro-synchrotron spectra using 3D modeling of a dipole-shaped magnetosphere. We evaluated combinations of parameters. The number of relativistic electrons was constrained by the need to produce the emission level predicted by the scaling relationship for the radio emission from magnetic BA stars. About half of the observed stars were detected, with luminosities in agreement with the expected values, reinforcing the robust nature of the scaling relationship for CBO-powered radio emission. Comparing the competing centrifugal and magnetic effects on plasma locked in a rigidly rotating magnetosphere, we located the site of CBOs and inferred the local plasma density. We then estimated the efficiency of the acceleration mechanism needed to produce enough non-thermal electrons to support the radio emission level. Given a constant acceleration efficiency, relativistic electrons represent a fixed fraction of the local thermal plasma. Thus, dense magnetospheres host more energetic particles than less dense ones; consequently, with other parameters similar, they are intrinsically brighter radio sources. △ Less

Submitted 7 November, 2025; originally announced November 2025.

Comments: Under review for publication in A&A

Optical Vortices: Revolutionizing the field of linear and nonlinear optics

Authors: Bikash K. Das, Camilo Granados, Marcelo F. Ciappina

Abstract: Light is the fundamental medium through which we perceive the world around us. In the modern era, light can not only be used in its raw form but can also be used as a versatile tool. Generally, light fields carry energy and momentum (both linear and angular). Due to the transfer of linear momentum from light to matter, the radiation pressure is exerted, whereas, the intrinsic spin angular momentum… ▽ More Light is the fundamental medium through which we perceive the world around us. In the modern era, light can not only be used in its raw form but can also be used as a versatile tool. Generally, light fields carry energy and momentum (both linear and angular). Due to the transfer of linear momentum from light to matter, the radiation pressure is exerted, whereas, the intrinsic spin angular momentum (SAM) is associated with the polarization states of light. Light fields embedded with optical orbital angular momentum (OAM) -- also known as optical vortices or phase singular beams -- have truly revolutionized the field of optics and extended our basic understanding of the light-matter interaction process across various scales. Optical vortices -- spatially characterized by the presence of twisted phase fronts and a central intensity null -- have found a myriad of applications starting from microparticle trapping and manipulation to microscopy, optical communication, and quantum information science, among others. Here, we revisit some of the fundamental concepts on optical vortices and discuss extensively on how this new dimension of light i.e., the OAM, has been exploited in both linear and nonlinear optical regimes. We discuss the different types of vortex beams, the techniques used to generate and detect their OAM, and their propagation. Particularly, we put a special emphasis on the utilization of vortex beams in nonlinear regimes to explain different optical phenomena such as the second harmonic generation, parametric down-conversion, and high-order harmonic generation. The generation of vortex beams in the UV to XUV regimes, encoded with higher OAM values, could potentially extend their application range to areas such as high-capacity data transmission, stimulated emission depletion microscopy, phase-contrast imaging, and particle trapping in optical tweezers, among others. △ Less

Submitted 17 December, 2025; v1 submitted 31 October, 2025; originally announced October 2025.

Comments: Invited Review (Adv. Phys.: X); 104 pages; 38 figures

Learning Product Graphs from Two-dimensional Stationary Signals

Authors: Andrei Buciulea, Bishwadeep Das, Elvin Isufi, Antonio G. Marques

Abstract: Graph learning aims to infer a network structure directly from observed data, enabling the analysis of complex dependencies in irregular domains. Traditional methods focus on scalar signals at each node, ignoring dependencies along additional dimensions such as time, configurations of the observation device, or populations. In this work, we propose a graph signal processing framework for learning… ▽ More Graph learning aims to infer a network structure directly from observed data, enabling the analysis of complex dependencies in irregular domains. Traditional methods focus on scalar signals at each node, ignoring dependencies along additional dimensions such as time, configurations of the observation device, or populations. In this work, we propose a graph signal processing framework for learning graphs from two-dimensional signals, modeled as matrix graph signals generated by joint filtering along both dimensions. This formulation leverages the concept of graph stationarity across the two dimensions and leverages product graph representations to capture structured dependencies. Based on this model, we design an optimization problem that can be solved efficiently and provably recovers the optimal underlying Kronecker/Cartesian/strong product graphs. Experiments on synthetic data demonstrate that our approach achieves higher estimation accuracy and reduced computational cost compared to existing methods. △ Less

Submitted 10 October, 2025; originally announced October 2025.

Absence of quantum Darwinism as a resource in secure quantum communication and computation

Authors: Bishal Kumar Das, Sourav Manna, Vaibhav Madhok

Abstract: The emergence of classical world from underlying quantum mechanics is characterized by not only vanishing quantum correlations but also an unfolding of objectivity also known as quantum Darwinism. We show that the absence of this objectivity has a quantum advantage in cryptography and also provides the crucial missing link in efficient classical simulation of quantum circuits with zero discord. Fo… ▽ More The emergence of classical world from underlying quantum mechanics is characterized by not only vanishing quantum correlations but also an unfolding of objectivity also known as quantum Darwinism. We show that the absence of this objectivity has a quantum advantage in cryptography and also provides the crucial missing link in efficient classical simulation of quantum circuits with zero discord. For this purpose, we consider a model of mixed state quantum computation where one is promised concordant states at all stages of the quantum circuit. A concordant quantum state has zero discord with respect to any part and there exists a basis made up of a tensor product of orthonormal local subsystem basis in which the density matrix is diagonal. Efficient classical simulation of concordant computation has surprisingly been an outstanding question in quantum information theory. We argue that a key ingredient of an efficient classical simulation algorithm, a knowledge of the local basis in which the multi-party state is diagonal, is made available by quantum Darwinism. Concordant states in the absence of quantum Darwinism cannot be efficiently simulated by existing methods and give a cryptographic advantage in communication. We show this by giving a protocol for secure quantum communication that exploits this insight. Our work also has implications for the quantum-classical border and we discuss how objectivity emerging out of Darwinism demarcates this border in three ways - empirical based on our observations and experience of objectivity, information theoretic due to the absence of any quantum correlations and lastly computational in the sense discussed above. Lastly, we show that the quantum-classical boundary as drawn by quantum Darwinism as well by what can be simulated efficiently in a mixed state quantum computation aligns with the boundary given by Hardy △ Less

Submitted 3 October, 2025; originally announced October 2025.

Comments: 14 pages (main text + references), 18 pages total including appendix; 3 figures

Quantum sensing with discrete time crystals in the Lipkin-Meshkov-Glick Model

Authors: Rahul Ghosh, Bandita Das, Victor Mukherjee

Abstract: Quantum phase transitions have been shown to be highly beneficial for quantum sensing, owing to diverging quantum Fisher information close to criticality. In this work we consider a periodically modulated Lipkin-Meshkov-Glick model to show that discrete time crystal (DTC) phase transition in this setup can enable us to achieve quantum-enhanced high-precision sensing of field strength. We employ a… ▽ More Quantum phase transitions have been shown to be highly beneficial for quantum sensing, owing to diverging quantum Fisher information close to criticality. In this work we consider a periodically modulated Lipkin-Meshkov-Glick model to show that discrete time crystal (DTC) phase transition in this setup can enable us to achieve quantum-enhanced high-precision sensing of field strength. We employ a detailed finite-size scaling analysis and a time-averaged Inverse Participation Ratio analysis to determine the critical properties of this second-order phase transition. Our studies provide a comprehensive understanding of how quantum criticality in DTCs involving long-range interactions can be harnessed for advanced quantum sensing applications. △ Less

Submitted 3 October, 2025; originally announced October 2025.

Comments: 10 pages, 6 figures

Design and Evaluation of CZT-based Micro-activity Dose Calibrator for TAT Application using Monte Carlo Simulation

Authors: Seoyun Jang, Robin Peter, Biswajit Das, Youngho Seo, Gyuseong Cho

Abstract: A novel CZT-based micro-activity dose calibrator has been designed via Monte Carlo simulation (GATE) to accurately measure low-level activity 225Ac for targeted alpha therapy (TAT) application. Because even small overdoses in TAT can induce severe local toxicity, activities in the microcurie down to nanocurie regime are often required, and accurate activity measurement by dose calibrators is a pri… ▽ More A novel CZT-based micro-activity dose calibrator has been designed via Monte Carlo simulation (GATE) to accurately measure low-level activity 225Ac for targeted alpha therapy (TAT) application. Because even small overdoses in TAT can induce severe local toxicity, activities in the microcurie down to nanocurie regime are often required, and accurate activity measurement by dose calibrators is a priori to safe and effective treatment. Standard dose calibrators, or high-pressurized gas-filled ionization chambers, are not suitable in this range due to limited sensitivity and lack of energy discrimination. To address this, we designed a CZT-based micro-activity calibrator that (i) adopts a box-shaped well geometry to obtain higher solid-angle coverage and (ii) applies time-coincident pixel-level clustering to recover full-energy-peak net counts otherwise lost to multi-site Compton scattering. Using GATE, serial dilutions from 1.0 uCi down to 1e-6 uCi were simulated, activities were reconstructed from the 218 and 440 keV gamma peaks and performance was compared against a NaI(Tl) well counter, which serves as an alternative to standard dose calibrator. Across six orders of magnitude, the CZT-based micro-activity dose calibrator exhibited near-unity linearity (slope m=0.9934) with percent-level bias, whereas the NaI(Tl) counter showed systematic under-response under identical conditions. These results indicate that a CZT-based approach can provide accurate low-activity quantification for TAT, motivating forthcoming hardware validation. △ Less

Submitted 30 September, 2025; originally announced September 2025.

Tuning Magnetic and Electronic Properties of Double Perovskite La$_2$CoIr$_{1-x}$Ti$_x$O$_6$

Authors: Sromona Nandi, Vineeta Yadav, Sheetal, C. S. Yadav, Bikash Das, Subhadeep Datta, Kapildeb Dolui, Rudra Sekhar Manna

Abstract: The La$_2$CoIr$_{1-x}$Ti$_x$O$_6$ double perovskite series serves as an effective platform for investigating the evolution of magnetic and electronic properties as a function of chemical pressure (doping) or hydrostatic pressure due to the interplay between the electrons correlation and spin-orbit coupling. In this study, the substitution of nonmagnetic Ti$^{4+}$ at the magnetic Ir$^{4+}$-site lea… ▽ More The La$_2$CoIr$_{1-x}$Ti$_x$O$_6$ double perovskite series serves as an effective platform for investigating the evolution of magnetic and electronic properties as a function of chemical pressure (doping) or hydrostatic pressure due to the interplay between the electrons correlation and spin-orbit coupling. In this study, the substitution of nonmagnetic Ti$^{4+}$ at the magnetic Ir$^{4+}$-site leads to a systematic decrease in unit cell volume keeping the monoclinic symmetry throughout, reflecting the effect of chemical pressure along with a gradual suppression of magnetic interactions. The parent compound ($x =$ 0) exhibits a ferromagnetic-like state with a Curie temperature of 92 K, which continuously evolves into an antiferromagnetic ground state upon full Ti substitution ($x =$ 1) with a Neel temperature of 14.6 K. Isothermal magnetization measurements reveal a hysteresis behavior with step-like feature at zero field, indicative of a noncollinear magnetic ordering. Additionally, the enhancement of magnetization under hydrostatic pressure on La$_2$CoIrO$_6$ suggests the presence of piezomagnetic behavior. Thermal expansion measurements on La$_2$CoIrO$_6$ highlight a coupling between spin and lattice degrees of freedom. The pressure dependence of the transition temperature in the zero-pressure limit, calculated using Ehrenfest's relation, shows good agreement with magnetization data under applied pressure. First-principles density functional theory (DFT) calculations preformed for $x =$ 0, 0.5 and 1, further reveal that strong SOC associated with Ir plays a decisive role in shaping the electronic band structure, with the insulating gap progressively widening as Ti content increases from 0.28 eV ($x =$ 0), 0.44 eV ($x =$ 0.5), and 1.01 eV ($x =$ 1). The magnetic moment decreased more than 50\% for $x =$ 0.5, showing the decrease in magnetic exchange pathways. △ Less

Submitted 20 October, 2025; v1 submitted 22 September, 2025; originally announced September 2025.

Comments: 11 pages, 8 figures

Journal ref: Phys. Rev. B 112, 155144 (2025)

Radiation damage study of Belle II silicon strip sensors with 90 MeV electron irradiation

Authors: K. Adamczyk, H. Aihara, K. Amos, S. Bacher, S. Bahinipati, J. Baudot, P. K. Behera, S. Bettarini, L. Bosisio, A. Bozek, F. Buchsteiner, G. Casarosa, C. Cheshta, L. Corona, S. B. Das, G. Dujany, C. Finck, F. Forti, M. Friedl, A. Gabrielli, V. Gautam, B. Gobbo, K. Hara, T. Higuchi, C. Irmler , et al. (36 additional authors not shown)

Abstract: The silicon strip sensors of the Belle II silicon vertex detector were irradiated with 90 MeV electron beams up to an equivalent 1-MeV-neutron fluence of $3.0\times 10^{13}~{\rm n}_{\rm eq}/{\rm cm^2}$. We measure changes in sensor properties induced by radiation damage in the semiconductor bulk. Electrons around this energy are a major source of beam-induced background during Belle II operation.… ▽ More The silicon strip sensors of the Belle II silicon vertex detector were irradiated with 90 MeV electron beams up to an equivalent 1-MeV-neutron fluence of $3.0\times 10^{13}~{\rm n}_{\rm eq}/{\rm cm^2}$. We measure changes in sensor properties induced by radiation damage in the semiconductor bulk. Electrons around this energy are a major source of beam-induced background during Belle II operation. We discuss observed changes in full depletion voltage, sensor leakage current, noise, and charge collection. The sensor bulk type inverts at an equivalent 1-MeV-neutron fluence of $6.0\times 10^{12}~{\rm n}_{\rm eq}/{\rm cm^2}$. The leakage current increases proportionally to the radiation dose. We determine a damage constant of $3.9 \times 10^{-17}$ A/cm at 17 C$^\circ$ immediately after irradiation, which drops significantly to approximately 40% of the initial value in 200 hours, then stabilizes to approximately 30% of the initial value in 1000 hours. We measure sensor noise and signal charge for a sensor irradiated with the equivalent 1-MeV-neutron fluence of $3.0\times 10^{13}~{\rm n}_{\rm eq}/{\rm cm^2}$. Noise increases by approximately 44% after irradiation, while signal charge does not change significantly when a sufficiently high bias voltage is applied. △ Less

Submitted 22 September, 2025; originally announced September 2025.

Comments: 23 pages, 15 figures

A stochastic heat engine driven using a nonlinear protocol

Authors: Amrutayani Panda, Biswajit Das, Shuvojit Paul, Arnab Saha, Ayan Banerjee

Abstract: A colloidal particle confined in a time-dependent optical trap can function as a microscopic heat engine, with optimization strategies playing a crucial role in enhancing its performance. In this study, we numerically investigate a Stirling heat engine operating in both passive and active environments using a protocol inspired by the Engineered Swift Equilibration (ESE) method. This approach diffe… ▽ More A colloidal particle confined in a time-dependent optical trap can function as a microscopic heat engine, with optimization strategies playing a crucial role in enhancing its performance. In this study, we numerically investigate a Stirling heat engine operating in both passive and active environments using a protocol inspired by the Engineered Swift Equilibration (ESE) method. This approach differs from the standard process and focuses on enhancing engine efficiency, particularly at short time scales. We analyze various fluctuating parameters throughout the cycle to validate the robustness of the engine, and demonstrate a significant enhancement in performance compared to conventional Stirling engines. Most crucially, we observe that the nonlinear protocol can even transform a heat-pump-like operation into a genuine heat engine under strong activity, thereby surpassing bounds imposed on efficiency by high-temperature and quasi-static conditions. Finally, the proposed protocol is designed with experimental feasibility in mind, making it a promising framework for the practical realization of efficient microscopic heat engines. △ Less

Submitted 19 September, 2025; originally announced September 2025.

Comments: 8 pages, 8 figures, comments are welcome

Intrinsic Berry Curvature Driven Anomalous Hall and Nernst Effect in Co$_2$MnSn

Authors: Bishal Das, Arnab Bhattacharya, Amit Chanda, Chanchal K. Barman, Jadupati Nag, Hariharan Srikanth, Aftab Alam, I. Das

Abstract: Magnetic topological semimetals often exhibit unusual electronic and thermal transport due to nontrivial bulk band crossings, enabling simultaneous realization of large anomalous Hall and Nernst conductivities ($σ_{xy}$ and $α_{xy}$). Here, a comprehensive experimental and theoretical study of the anomalous transport properties of ferromagnetic Co$_2$MnSn is reported. First-principles calculations… ▽ More Magnetic topological semimetals often exhibit unusual electronic and thermal transport due to nontrivial bulk band crossings, enabling simultaneous realization of large anomalous Hall and Nernst conductivities ($σ_{xy}$ and $α_{xy}$). Here, a comprehensive experimental and theoretical study of the anomalous transport properties of ferromagnetic Co$_2$MnSn is reported. First-principles calculations reveal topological Weyl points producing significant Berry curvature, driving dominant intrinsic anomalous Hall/Nernst effects. Electronic and thermal transport measurements demonstrate robust anomalous transport with substantial conductivity values that persist at room temperature ($σ_{xy}\sim$ 500 S/cm, $α_{xy}\sim$ 1.3 A/m/K). We also show how the chemical substitution (via tuning Fermi level) can boost these effects (up to $σ_{xy}\sim$ 1376 S/cm, $α_{xy}\sim$ 1.49 A/m/K at 150 K). These findings position Co$_2$MnSn as a compelling platform for exploring topological transport phenomena and advancing next-generation thermoelectric and spintronic technologies. △ Less

Submitted 19 September, 2025; originally announced September 2025.

Comments: Bishal Das and Arnab Bhattacharya contributed equally to this work. 17 pages (11 pages main, 6 pages supplement), 11 figures (4 figures main, 7 figures supplement)

The effect of collisional cooling of energetic electrons on radio emission from the centrifugal magnetospheres of magnetic hot stars

Authors: B. Das, S. P. Owocki

Abstract: This paper extends our previous study of gyro-emission by energetic electrons in the magnetospheres of rapidly rotating, magnetic massive stars, through a quantitative analysis of the role of Coulomb collisions with thermal electrons from stellar wind material trapped within the centrifugal magnetosphere (CM). For a dipolar field with aligned magnetic and rotational axes, we show that both gyro-co… ▽ More This paper extends our previous study of gyro-emission by energetic electrons in the magnetospheres of rapidly rotating, magnetic massive stars, through a quantitative analysis of the role of Coulomb collisions with thermal electrons from stellar wind material trapped within the centrifugal magnetosphere (CM). For a dipolar field with aligned magnetic and rotational axes, we show that both gyro-cooling along magnetic loops and Coulomb cooling in the CM layer have nearly the same dependence on the magnitude and radial variation of magnetic field, implying that their ratio is a global parameter that is largely independent of the field. Analytic analysis shows that, for electrons introduced near the CM layer around a magnetic loop apex, collisional cooling is more important for electrons with high pitch angle, while more field-aligned electrons cool by gyro-emission near their mirror point close to the loop base. Numerical models that assume a gyrotropic initial deposition with a gaussian distribution in both radius and loop co-latitude show the residual gyro-emission is generally strongest near the loop base, with highly relativistic electrons suffering much lower collisional losses than lower-energy electrons that are only mildly relativistic. Finally, we briefly discuss the potential applicability of this formalism to magnetic ultracool dwarfs, for which VLBI observations indicate incoherent radio emission to be concentrated around the magnetic equator, in contrast to our predictions here for magnetic hot stars. We suggest that this difference could be attributed to either a lower ambient density of thermal electrons, or more highly relativistic non-thermal electrons, both of which would reduce the relative importance of the collisional cooling explored here. △ Less

Submitted 17 September, 2025; originally announced September 2025.

Comments: 11 pages, 11 Figures, accepted for publication in PASA

A study of the pulsar EXO 1745-248 in $f(Q)$ gravity with pseudo-spheroidal geometry

Authors: Bibhash Das, Bikash Chandra Paul

Abstract: We present a singularity-free relativistic interior solution for constructing stable quark stellar models in the framework of a linear $f(Q)$ gravity ($f(Q) = αQ + φ$) satisfying the pseudo-spheroidal geometry. The physical features and the stability of the stellar model is explored with strange star (SS) candidate EXO 1745-248 ($M = 1.7\, M_{\odot}$ and $R = 9\, km$). The Durgapal-Banerjee transf… ▽ More We present a singularity-free relativistic interior solution for constructing stable quark stellar models in the framework of a linear $f(Q)$ gravity ($f(Q) = αQ + φ$) satisfying the pseudo-spheroidal geometry. The physical features and the stability of the stellar model is explored with strange star (SS) candidate EXO 1745-248 ($M = 1.7\, M_{\odot}$ and $R = 9\, km$). The Durgapal-Banerjee transformation is employed to obtain the relativistic interior solution using the MIT Bag model equation of state (EoS): $P = \frac{1}{3}(ρ- 4 B_{g})$. For a linear form of $f(Q)$ gravity, we obtain the exterior vacuum solution, which reduces to the Schwarzschild-de Sitter (SdS) solution with the cosmological constant term, $Λ= \fracφ{2α}$. The stellar model is analyzed for the different values of the spheroidicity parameter ($μ$). The value of $α$ is constrained using a viable physical limit on the Bag parameter ($B_{g} \in [57.55,95.11]\,MeV\,fm^{-3}$). The constraints on Mass-Radius relation indicates that physically acceptable SS models are permitted for $μ\geq 7$. The contribution of $μ$ to the energy density, pressure profiles, and other physical features is studied for the SS candidate EXO 1745-248. The stability of the stellar model obtained here is also analyzed through causality condition, adiabatic index and other stability criteria. We also investigate the stellar model for other SS candidates to test its viability. The relativistic interior solution obtained here can be used to construct viable and physically acceptable strange star models with very high compactness ratio in the framework of linear $f(Q)$ gravity. △ Less

Submitted 15 September, 2025; originally announced September 2025.

Anomalous vortex beam driven harmonic generation

Authors: B. Kumar Das, M. Ciappina, W. Gao, C. Granados

Abstract: The generation and control of the properties of light beams carrying orbital angular momentum is fundamental to extend our understanding on the light-matter interaction process. In this letter, we investigate the use of anomalous and modified anomalous vortex beams for the generation of high-order harmonics (HHG) of the fundamental field. We demonstrate that by controlling the order and topologica… ▽ More The generation and control of the properties of light beams carrying orbital angular momentum is fundamental to extend our understanding on the light-matter interaction process. In this letter, we investigate the use of anomalous and modified anomalous vortex beams for the generation of high-order harmonics (HHG) of the fundamental field. We demonstrate that by controlling the order and topological charge (TC) of the driving field, one can control the vortex beam size of the generated harmonics. A key outcome of this control is the ability to drive the HHG process with fundamental beams of higher TCs and consequently generating harmonics with higher TCs ($\approx 100$) while maintaining a compact beam size and nearly uniform divergence in the far-field across a wide range of harmonic orders. △ Less

Submitted 10 September, 2025; originally announced September 2025.

Perfect spatiotemporal optical vortex driven high harmonic generation

Authors: C. Granados, B. Kumar Das, W. Gao

Abstract: The generation of high-order harmonic beams carrying orbital angular momentum (OAM) promises application in diverse research fields. Recently, the perfect spatiotemporal optical vortex (PSTOV) beam has garnered much attention due to its topological charge (TC)-independent ring size and intensity distribution in the spatiotemporal plane. Here, we theoretically investigate the harmonic generation pr… ▽ More The generation of high-order harmonic beams carrying orbital angular momentum (OAM) promises application in diverse research fields. Recently, the perfect spatiotemporal optical vortex (PSTOV) beam has garnered much attention due to its topological charge (TC)-independent ring size and intensity distribution in the spatiotemporal plane. Here, we theoretically investigate the harmonic generation process in atomic gases driven PSTOV beams carrying transverse OAM. The unique spatiotemporal characteristics of the PSTOV beam make it an excellent candidate to generate harmonic beams with high TC values. We demonstrate that the conservation of transverse OAM is strictly followed when the harmonic generation is driven by the PSTOV beam. Additionally, in the near-field, the intensity distributions of harmonics show tilted lobed structures, which encapsulate information about the TC. By solving the Fraunhofer diffraction integral, we demonstrate that the generated harmonic vortices exhibit similar divergence properties at the far-field. Our research provides a unique route to create Bessel-Gauss spatiotemporal optical vortex beams with high TC in the extreme-ultraviolet (XUV) spectral regime. △ Less

Submitted 8 September, 2025; originally announced September 2025.

Physics-Informed Neural Networks for Nonlocal Beam Eigenvalue Problems

Authors: Baidehi Das, Raffaele Barretta, Marko Čanađija

Abstract: The present study investigates the dynamics of nonlocal beams by establishing a consistent stress-driven integral elastic using the Physics-Informed Neural Network (PINN) approach. Specifically, a PINN is developed to compute the first eigenfunction and eigenvalue arising from the underlying sixth-order ordinary differential equation. The PINN is based on a feedforward neural network, with a loss… ▽ More The present study investigates the dynamics of nonlocal beams by establishing a consistent stress-driven integral elastic using the Physics-Informed Neural Network (PINN) approach. Specifically, a PINN is developed to compute the first eigenfunction and eigenvalue arising from the underlying sixth-order ordinary differential equation. The PINN is based on a feedforward neural network, with a loss function composed of terms from the differential equation, the normalization condition, and both boundary and constitutive boundary conditions. Relevant eigenvalues are treated as separate trainable variables. The results demonstrate that the proposed method is a powerful and robust tool for addressing the complexity of the problem. Once trained, the neural network is less computationally intensive than analytical methods. The obtained results are compared with benchmark analytical solutions and show strong agreement. △ Less

Submitted 4 September, 2025; originally announced September 2025.

Representation number of word-representable co-bipartite graph

Authors: Biswajit Das, Ramesh Hariharasubramanian

Abstract: A graph $G = (V, E)$ is said to be word-representable if there exists a word $w$ over the alphabet $V$ such that, for any two distinct letters $x, y \in V$, the letters $x$ and $y$ alternate in $w$ if and only if $xy \in E$. A graph is co-bipartite if its complement is bipartite. Therefore, the vertex set of a co-bipartite graph can be partitioned into two disjoint subsets $X$ and $Y$ such that th… ▽ More A graph $G = (V, E)$ is said to be word-representable if there exists a word $w$ over the alphabet $V$ such that, for any two distinct letters $x, y \in V$, the letters $x$ and $y$ alternate in $w$ if and only if $xy \in E$. A graph is co-bipartite if its complement is bipartite. Therefore, the vertex set of a co-bipartite graph can be partitioned into two disjoint subsets $X$ and $Y$ such that the subgraphs induced by $X$ and $Y$ are cliques. The concept of word-representability for graph classes has gained significant attention in recent years. The book Words and Graphs by Sergey Kitaev and Vadim Lozin presents examples of co-bipartite graphs that are not word-representable. It is known that a graph is word-representable if and only if it admits a semi-transitive orientation. Although the necessary and sufficient conditions for the existence of a semi-transitive orientation in co-bipartite graphs have been established, the characterization based on vertex ordering remains open. In this paper, we present necessary and sufficient conditions for a co-bipartite graph to be word-representable in terms of its vertex ordering. Furthermore, based on this vertex ordering, we provide an algorithm to construct a $3$-uniform word-representation for any word-representable co-bipartite graph. Using this result, we prove that except for the permutation graphs, the representation number of all other word-representable co-bipartite graphs is $3$. △ Less

Submitted 3 September, 2025; originally announced September 2025.

Dimension Agnostic Testing of Survey Data Credibility through the Lens of Regression

Authors: Debabrota Basu, Sourav Chakraborty, Debarshi Chanda, Buddha Dev Das, Arijit Ghosh, Arnab Ray

Abstract: Assessing whether a sample survey credibly represents the population is a critical question for ensuring the validity of downstream research. Generally, this problem reduces to estimating the distance between two high-dimensional distributions, which typically requires a number of samples that grows exponentially with the dimension. However, depending on the model used for data analysis, the concl… ▽ More Assessing whether a sample survey credibly represents the population is a critical question for ensuring the validity of downstream research. Generally, this problem reduces to estimating the distance between two high-dimensional distributions, which typically requires a number of samples that grows exponentially with the dimension. However, depending on the model used for data analysis, the conclusions drawn from the data may remain consistent across different underlying distributions. In this context, we propose a task-based approach to assess the credibility of sampled surveys. Specifically, we introduce a model-specific distance metric to quantify this notion of credibility. We also design an algorithm to verify the credibility of survey data in the context of regression models. Notably, the sample complexity of our algorithm is independent of the data dimension. This efficiency stems from the fact that the algorithm focuses on verifying the credibility of the survey data rather than reconstructing the underlying regression model. Furthermore, we show that if one attempts to verify credibility by reconstructing the regression model, the sample complexity scales linearly with the dimensionality of the data. We prove the theoretical correctness of our algorithm and numerically demonstrate our algorithm's performance. △ Less

Submitted 28 August, 2025; originally announced August 2025.

Comments: 30 pages, 8 figures, 6 Tables

Rethinking Federated Learning Over the Air: The Blessing of Scaling Up

Authors: Jiaqi Zhu, Bikramjit Das, Yong Xie, Nikolaos Pappas, Howard H. Yang

Abstract: Federated learning facilitates collaborative model training across multiple clients while preserving data privacy. However, its performance is often constrained by limited communication resources, particularly in systems supporting a large number of clients. To address this challenge, integrating over-the-air computations into the training process has emerged as a promising solution to alleviate c… ▽ More Federated learning facilitates collaborative model training across multiple clients while preserving data privacy. However, its performance is often constrained by limited communication resources, particularly in systems supporting a large number of clients. To address this challenge, integrating over-the-air computations into the training process has emerged as a promising solution to alleviate communication bottlenecks. The system significantly increases the number of clients it can support in each communication round by transmitting intermediate parameters via analog signals rather than digital ones. This improvement, however, comes at the cost of channel-induced distortions, such as fading and noise, which affect the aggregated global parameters. To elucidate these effects, this paper develops a theoretical framework to analyze the performance of over-the-air federated learning in large-scale client scenarios. Our analysis reveals three key advantages of scaling up the number of participating clients: (1) Enhanced Privacy: The mutual information between a client's local gradient and the server's aggregated gradient diminishes, effectively reducing privacy leakage. (2) Mitigation of Channel Fading: The channel hardening effect eliminates the impact of small-scale fading in the noisy global gradient. (3) Improved Convergence: Reduced thermal noise and gradient estimation errors benefit the convergence rate. These findings solidify over-the-air model training as a viable approach for federated learning in networks with a large number of clients. The theoretical insights are further substantiated through extensive experimental evaluations. △ Less

Submitted 25 August, 2025; originally announced August 2025.

Quickly Tuning Foundation Models for Image Segmentation

Authors: Breenda Das, Lennart Purucker, Timur Carstensen, Frank Hutter

Abstract: Foundation models like SAM (Segment Anything Model) exhibit strong zero-shot image segmentation performance, but often fall short on domain-specific tasks. Fine-tuning these models typically requires significant manual effort and domain expertise. In this work, we introduce QTT-SEG, a meta-learning-driven approach for automating and accelerating the fine-tuning of SAM for image segmentation. Built… ▽ More Foundation models like SAM (Segment Anything Model) exhibit strong zero-shot image segmentation performance, but often fall short on domain-specific tasks. Fine-tuning these models typically requires significant manual effort and domain expertise. In this work, we introduce QTT-SEG, a meta-learning-driven approach for automating and accelerating the fine-tuning of SAM for image segmentation. Built on the Quick-Tune hyperparameter optimization framework, QTT-SEG predicts high-performing configurations using meta-learned cost and performance models, efficiently navigating a search space of over 200 million possibilities. We evaluate QTT-SEG on eight binary and five multiclass segmentation datasets under tight time constraints. Our results show that QTT-SEG consistently improves upon SAM's zero-shot performance and surpasses AutoGluon Multimodal, a strong AutoML baseline, on most binary tasks within three minutes. On multiclass datasets, QTT-SEG delivers consistent gains as well. These findings highlight the promise of meta-learning in automating model adaptation for specialized segmentation tasks. Code available at: https://github.com/ds-brx/QTT-SEG/ △ Less

Submitted 24 August, 2025; originally announced August 2025.

Comments: Accepted as a short paper at the non-archival content track of AutoML 2025

An Arithmetic Characterization of 2-Generated Numbers

Authors: Bireswar Das, Kavita Samant, Dhara Thakkar

Abstract: A group $G$ is said to be $k$-generated if it has a generating set with $k$ elements. A positive integer $n$ is called a \emph{2-generated number} if every group of order $n$ is 2-generated. In this article, we establish an arithmetic characterization of 2-generated numbers expressed in terms of the prime factorization of $n$. A group $G$ is said to be $k$-generated if it has a generating set with $k$ elements. A positive integer $n$ is called a \emph{2-generated number} if every group of order $n$ is 2-generated. In this article, we establish an arithmetic characterization of 2-generated numbers expressed in terms of the prime factorization of $n$. △ Less

Submitted 22 August, 2025; originally announced August 2025.

Comments: 15 pages

MSC Class: 20D60; 20F05; 05C25

Spike Agreement Dependent Plasticity: A scalable Bio-Inspired learning paradigm for Spiking Neural Networks

Authors: Saptarshi Bej, Muhammed Sahad E, Gouri Lakshmi, Harshit Kumar, Pritam Kar, Bikas C Das

Abstract: We introduce Spike Agreement Dependent Plasticity (SADP), a biologically inspired synaptic learning rule for Spiking Neural Networks (SNNs) that relies on the agreement between pre- and post-synaptic spike trains rather than precise spike-pair timing. SADP generalizes classical Spike-Timing-Dependent Plasticity (STDP) by replacing pairwise temporal updates with population-level correlation metrics… ▽ More We introduce Spike Agreement Dependent Plasticity (SADP), a biologically inspired synaptic learning rule for Spiking Neural Networks (SNNs) that relies on the agreement between pre- and post-synaptic spike trains rather than precise spike-pair timing. SADP generalizes classical Spike-Timing-Dependent Plasticity (STDP) by replacing pairwise temporal updates with population-level correlation metrics such as Cohen's kappa. The SADP update rule admits linear-time complexity and supports efficient hardware implementation via bitwise logic. Empirical results on MNIST and Fashion-MNIST show that SADP, especially when equipped with spline-based kernels derived from our experimental iontronic organic memtransistor device data, outperforms classical STDP in both accuracy and runtime. Our framework bridges the gap between biological plausibility and computational scalability, offering a viable learning mechanism for neuromorphic systems. △ Less

Submitted 22 August, 2025; originally announced August 2025.

Application of Quantum Annealing to Computation of Molecular Properties

Authors: Pradyot Pritam Sahoo, V. S. Prasannaa, B. P. Das

Abstract: We present the results of our quantum annealing computations of the permanent electric dipole moments of several molecules. By applying an electric field as a perturbation and measuring the corresponding energy responses, the molecular electric dipole moments are obtained numerically through the finite field method. The ground-state electronic wavefunctions and energies are obtained using… ▽ More We present the results of our quantum annealing computations of the permanent electric dipole moments of several molecules. By applying an electric field as a perturbation and measuring the corresponding energy responses, the molecular electric dipole moments are obtained numerically through the finite field method. The ground-state electronic wavefunctions and energies are obtained using the quantum annealer eignsolver algorithm. This work provides a pathway for the computation of molecular properties in the quantum annealing paradigm. △ Less

Submitted 5 December, 2025; v1 submitted 18 August, 2025; originally announced August 2025.

Comments: 8 pages, 1+1 figures, comments are welcome

Efficient Quantum Information-Inspired Ansatz for Variational Quantum Eigensolver Algorithm: Applications to Atomic Systems

Authors: Abdul Kalam, Prasenjit Deb, Akitada Sakurai, B. K. Sahoo, V. S. Prasannaa, B. P. Das

Abstract: We present a quantum information-inspired ansatz for the variational quantum eigensolver (VQE) and demonstrate its efficacy in calculating ground-state energies of atomic systems. Instead of adopting a heuristic approach, we start with an approximate multi-qubit target state and utilize two quantum information-theoretic quantities, i.e., von Neumann entropy and quantum mutual information, to const… ▽ More We present a quantum information-inspired ansatz for the variational quantum eigensolver (VQE) and demonstrate its efficacy in calculating ground-state energies of atomic systems. Instead of adopting a heuristic approach, we start with an approximate multi-qubit target state and utilize two quantum information-theoretic quantities, i.e., von Neumann entropy and quantum mutual information, to construct our ansatz. The quantum information encoded in the target state helps us to design unique blocks and identify qubit pairs that share maximum quantum correlations among them in the multi-qubit system, thereby enabling us to deterministically place two-qubit entanglers in the suitably constructed parametrized quantum circuit. We find that our approach has the advantage of reduced circuit depth compared to the unitary coupled-cluster (UCC) ansatz (the gold standard for VQE), and yet yields accurate results. To test the performance of our ansatz, we apply it to compute ground-state energies of atomic systems. We find that for up to 12 qubits (or 12 spin orbitals) noiseless calculation, the proposed ansatz yields energies with 99.99% accuracy relative to the complete active space configuration interaction values, while utilizing only two blocks, which contain at most 99% fewer 2-qubit gates than the UCC ansatz. △ Less

Submitted 14 August, 2025; originally announced August 2025.

Comments: 6+6 pages, 5 figures, comments are welcome

Stabilizing boundary time crystals through Non-markovian dynamics

Authors: Bandita Das, Rahul Ghosh, Victor Mukherjee

Abstract: We study Boundary time crystals (BTCs) in the presence of non-Markovian dynamics. In contrast to BTCs observed in earlier works in the Markovian regime, we show that non-Markovian dynamics can be highly beneficial for stabilizing BTCs over a wide range of parameter values, even in the presence of intermediate rates of dissipation. We analyze the effect of non-Markovian dynamics on BTCs using quant… ▽ More We study Boundary time crystals (BTCs) in the presence of non-Markovian dynamics. In contrast to BTCs observed in earlier works in the Markovian regime, we show that non-Markovian dynamics can be highly beneficial for stabilizing BTCs over a wide range of parameter values, even in the presence of intermediate rates of dissipation. We analyze the effect of non-Markovian dynamics on BTCs using quantum Fisher information, order parameter, a measure of non-Markovianity, and a dynamical phase diagram, all of which show complex behaviours with changing non-Markovianity parameters. Our studies can pave the way for stabilizing time crystals in dissipative systems, as well as lead to studies on varied dissipative dynamics on time translational symmetry breaking. △ Less

Submitted 13 August, 2025; originally announced August 2025.

Comments: 6 pages, 5 figures

Chiral enhancement in soft-photon bremsstrahlung and charge asymmetry in low-energy lepton-proton scattering

Authors: Bhoomika Das, Rakshanda Goswami, Pulak Talukdar, Udit Raha, Fred Myhrer

Abstract: We carry out a Lorentz gauge evaluation of the single-soft photon bremsstrahlung radiative corrections to the unpolarized elastic lepton-proton scattering cross section at low energies using the framework of heavy baryon chiral effective field theory (HB$χ$PT). We systematically incorporate all next-to-leading order [i.e., ${\mathcal O}(α^3/M)$] contributions to the cross section arising from radi… ▽ More We carry out a Lorentz gauge evaluation of the single-soft photon bremsstrahlung radiative corrections to the unpolarized elastic lepton-proton scattering cross section at low energies using the framework of heavy baryon chiral effective field theory (HB$χ$PT). We systematically incorporate all next-to-leading order [i.e., ${\mathcal O}(α^3/M)$] contributions to the cross section arising from radiative and proton's low-energy recoil effects. An important component of the soft-photon bremsstrahlung corrections arises from the interference between lepton and proton bremsstrahlung processes, which are characterized as charge-odd. We identify a class of Feynman diagrams involving the final-state radiating proton that induces a chiral enhancement, thereby modifying the naive amplitude hierarchy based on the standard chiral power-counting scheme. The recently derived HB$χ$PT result for the analytically computed exact two-photon exchange (TPE) counterpart at NLO is combined with our charge-odd soft-photon bremsstrahlung contribution to yield the complete charge-odd radiative correction. By incorporating the leading hadronic correction to the leading order Born one-photon exchange (OPE) process within the charge-even radiative correction, we obtain a prediction for the charge asymmetry observable, which can be compared with forthcoming MUSE data on elastic lepton-anti-lepton scattering off the proton. In all our calculations, we use finite lepton masses. △ Less

Submitted 11 August, 2025; originally announced August 2025.

Comments: 47 pages with 15 figures

Trustworthy Medical Imaging with Large Language Models: A Study of Hallucinations Across Modalities

Authors: Anindya Bijoy Das, Shahnewaz Karim Sakib, Shibbir Ahmed

Abstract: Large Language Models (LLMs) are increasingly applied to medical imaging tasks, including image interpretation and synthetic image generation. However, these models often produce hallucinations, which are confident but incorrect outputs that can mislead clinical decisions. This study examines hallucinations in two directions: image to text, where LLMs generate reports from X-ray, CT, or MRI scans,… ▽ More Large Language Models (LLMs) are increasingly applied to medical imaging tasks, including image interpretation and synthetic image generation. However, these models often produce hallucinations, which are confident but incorrect outputs that can mislead clinical decisions. This study examines hallucinations in two directions: image to text, where LLMs generate reports from X-ray, CT, or MRI scans, and text to image, where models create medical images from clinical prompts. We analyze errors such as factual inconsistencies and anatomical inaccuracies, evaluating outputs using expert informed criteria across imaging modalities. Our findings reveal common patterns of hallucination in both interpretive and generative tasks, with implications for clinical reliability. We also discuss factors contributing to these failures, including model architecture and training data. By systematically studying both image understanding and generation, this work provides insights into improving the safety and trustworthiness of LLM driven medical imaging systems. △ Less

Submitted 9 August, 2025; originally announced August 2025.

AI-Driven Cybersecurity Threat Detection: Building Resilient Defense Systems Using Predictive Analytics

Authors: Biswajit Chandra Das, M Saif Sartaz, Syed Ali Reza, Arat Hossain, Md Nasiruddin, Kanchon Kumar Bishnu, Kazi Sharmin Sultana, Sadia Sharmeen Shatyi, MD Azam Khan, Joynal Abed

Abstract: This study examines how Artificial Intelligence can aid in identifying and mitigating cyber threats in the U.S. across four key areas: intrusion detection, malware classification, phishing detection, and insider threat analysis. Each of these problems has its quirks, meaning there needs to be different approaches to each, so we matched the models to the shape of the problem. For intrusion detectio… ▽ More This study examines how Artificial Intelligence can aid in identifying and mitigating cyber threats in the U.S. across four key areas: intrusion detection, malware classification, phishing detection, and insider threat analysis. Each of these problems has its quirks, meaning there needs to be different approaches to each, so we matched the models to the shape of the problem. For intrusion detection, catching things like unauthorized access, we tested unsupervised anomaly detection methods. Isolation forests and deep autoencoders both gave us useful signals by picking up odd patterns in network traffic. When it came to malware detection, we leaned on ensemble models like Random Forest and XGBoost, trained on features pulled from files and traffic logs. Phishing was more straightforward. We fed standard classifiers (logistic regression, Random Forest, XGBoost) a mix of email and web-based features. These models handled the task surprisingly well. Phishing turned out to be the easiest problem to crack, at least with the data we had. There was a different story. We utilized an LSTM autoencoder to identify behavioral anomalies in user activity logs. It caught every suspicious behavior but flagged a lot of harmless ones too. That kind of model makes sense when the cost of missing a threat is high and you are willing to sift through some noise. What we saw across the board is that performance was not about stacking the most complex model. What mattered was how well the models structure matched the way the data behaved. When signals were strong and obvious, simple models worked fine. But for messier, more subtle threats, we needed something more adaptive, sequence models and anomaly detectors, though they brought their trade offs. The takeaway here is clear in cybersecurity, context drives the solution. △ Less

Submitted 2 August, 2025; originally announced August 2025.

An improved Copson inequality

Authors: Bikram Das, Atanu Manna

Abstract: In this paper, we prove that the discrete Copson inequality (E.T. Copson, \emph{Notes on a series of positive terms}, J. London Math. Soc., 2 (1927), 49-51) of one-dimension in general cases admits an improvement. In fact we study the improvement of the following Copson's inequality \begin{align*} &\displaystyle\sum_{n=1}^{\infty}\frac{Q_{n}^α|A_n-A_{n-1}|^{2}}{q_{n}}\geq\frac{(α-1)^2}{4}\displays… ▽ More In this paper, we prove that the discrete Copson inequality (E.T. Copson, \emph{Notes on a series of positive terms}, J. London Math. Soc., 2 (1927), 49-51) of one-dimension in general cases admits an improvement. In fact we study the improvement of the following Copson's inequality \begin{align*} &\displaystyle\sum_{n=1}^{\infty}\frac{Q_{n}^α|A_n-A_{n-1}|^{2}}{q_{n}}\geq\frac{(α-1)^2}{4}\displaystyle\sum_{n=1}^{\infty} \frac{q_{n}}{Q_{n}^{2-α}}|A_{n}|^{2}, \end{align*}where $α\in[0,1)$, $A_{n}=q_{1}a_{1}+ q_{2}a_{2}+ \ldots +q_{n}a_{n}$, $Q_{n}=q_1+q_2+\ldots+q_{n}$ for $n\in \mathbb{N}$, $\{q_n\}$ is a positive real sequence and $\{a_n\}$ is a sequence of complex numbers. We show that if $\{q_n\}$ is decreasing then the above inequality has an improvement for $α\in [1/3, 1)$. We also prove that for some increasing sequences $\{q_n\}$ the above inequality can also be improved. Indeed, we prove that for $q_{n}=n$ and $q_n=n^3$, $n\in \mathbb{N}$ the corresponding Copson inequalities admit an improvement for $α\in[\frac{17}{50}, 1)$ and $α\in[0, \frac{1}{2}]$, respectively. Further, we show that in case of $q_{n}=1$, $n\in \mathbb{N}$ the reduced Copson inequality (known as Hardy's inequality with power weights) has achieved an improvement for $α\in[0, 1)$. △ Less

Submitted 1 August, 2025; originally announced August 2025.

Comments: 16 pages

MSC Class: 26D15; 26D10

Multiplier varieties and multiplier algebras of CNP Dirichlet series kernels

Authors: Hamidul Ahmed, B. Krishna Das, Chaman Kumar Sahu

Abstract: We investigate isometric and algebraic isomorphism problems for multiplier algebras associated with Hilbert spaces of Dirichlet series whose kernels possess the complete Nevanlinna-Pick (CNP) property. We begin by providing a complete characterization of the set of all normalized CNP Dirichlet series kernels by their weight and frequency data. A central aspect of our work is the explicit determina… ▽ More We investigate isometric and algebraic isomorphism problems for multiplier algebras associated with Hilbert spaces of Dirichlet series whose kernels possess the complete Nevanlinna-Pick (CNP) property. We begin by providing a complete characterization of the set of all normalized CNP Dirichlet series kernels by their weight and frequency data. A central aspect of our work is the explicit determination of the multiplier variety associated with each CNP Dirichlet series kernel. We show that these varieties are defined by polynomial equations derived from the arithmetic structure of the weight and frequency data associated with the kernel. This description of multiplier varieties enables us to classify when the multiplier algebras of a significant class of CNP Dirichlet series kernels are isomorphic, or isometrically isomorphic. Surprisingly, in this setting, every algebraic isomorphism between multiplier algebras is automatically isometric, revealing a striking rigidity phenomenon whereby the structure of the multiplier algebra uniquely determines the kernel up to a natural equivalence of the underlying weight and frequency data. As an application, we resolve an open problem posed by McCarthy and Shalit ([19]). △ Less

Submitted 13 November, 2025; v1 submitted 29 July, 2025; originally announced July 2025.

Comments: 35 pages. In section 6, Proposition 6.1 and Theorem 6.2 have been improved. Any suggestions or comments are most welcome

MSC Class: 14M10; 11M41; 47L15; 47A57; 46E22

Towards Benchmarking Foundation Models for Tabular Data With Text

Authors: Martin Mráz, Breenda Das, Anshul Gupta, Lennart Purucker, Frank Hutter

Abstract: Foundation models for tabular data are rapidly evolving, with increasing interest in extending them to support additional modalities such as free-text features. However, existing benchmarks for tabular data rarely include textual columns, and identifying real-world tabular datasets with semantically rich text features is non-trivial. We propose a series of simple yet effective ablation-style strat… ▽ More Foundation models for tabular data are rapidly evolving, with increasing interest in extending them to support additional modalities such as free-text features. However, existing benchmarks for tabular data rarely include textual columns, and identifying real-world tabular datasets with semantically rich text features is non-trivial. We propose a series of simple yet effective ablation-style strategies for incorporating text into conventional tabular pipelines. Moreover, we benchmark how state-of-the-art tabular foundation models can handle textual data by manually curating a collection of real-world tabular datasets with meaningful textual features. Our study is an important step towards improving benchmarking of foundation models for tabular data with text. △ Less

Submitted 10 July, 2025; originally announced July 2025.

Comments: Accepted at Foundation Models for Structured Data workshop at ICML 2025

On the Complexity of Problems on Graphs Defined on Groups

Authors: Bireswar Das, Dipan Dey, Jinia Ghosh

Abstract: We study the complexity of graph problems on graphs defined on groups, especially power graphs. We observe that an isomorphism invariant problem, such as Hamiltonian Path, Partition into Cliques, Feedback Vertex Set, Subgraph Isomorphism, cannot be NP-complete for power graphs, commuting graphs, enhanced power graphs, directed power graphs, and bounded-degree Cayley graphs, assuming the Exponentia… ▽ More We study the complexity of graph problems on graphs defined on groups, especially power graphs. We observe that an isomorphism invariant problem, such as Hamiltonian Path, Partition into Cliques, Feedback Vertex Set, Subgraph Isomorphism, cannot be NP-complete for power graphs, commuting graphs, enhanced power graphs, directed power graphs, and bounded-degree Cayley graphs, assuming the Exponential Time Hypothesis (ETH). An analogous result holds for isomorphism invariant group problems: no such problem can be NP-complete unless ETH is false. We show that the Weighted Max-Cut problem is NP-complete in power graphs. We also show that, unless ETH is false, the Graph Motif problem cannot be solved in quasipolynomial time on power graphs, even for power graphs of cyclic groups. We study the recognition problem of power graphs when the adjacency matrix or list is given as input and show that for abelian groups and some classes of nilpotent groups, it is solvable in polynomial time. △ Less

Submitted 8 July, 2025; originally announced July 2025.

Comments: 22 pages, this is the full version of the corresponding paper accepted at the 25th International Symposium on Fundamentals of Computation Theory (FCT 2025)

ACM Class: F.1.3; G.2.2

Discoveries of fine structures and secondary pulses in coherent radio emission from a magnetic massive star

Authors: Barnali Das, Poonam Chandra, William Cotton, Véronique Petit

Abstract: In this paper, we report auroral radio emission from a magnetic B star HD 142990 using the MeerKAT radio telescope at $900-1670$ MHz. The star is known to produce such emission (observed as periodic radio pulses) via electron cyclotron maser emission (ECME). However, past studies on ECME from this star were confined to observations at specific rotational phase ranges where one expects to see such… ▽ More In this paper, we report auroral radio emission from a magnetic B star HD 142990 using the MeerKAT radio telescope at $900-1670$ MHz. The star is known to produce such emission (observed as periodic radio pulses) via electron cyclotron maser emission (ECME). However, past studies on ECME from this star were confined to observations at specific rotational phase ranges where one expects to see such pulses. We, for the first time, observed the star for its one complete rotation cycle and discovered that the star also produces 'off-pulse' emission, which we term as secondary enhancements. Two such enhancements were observed, one of which is left circularly polarized (LCP) and the other is right circularly polarized (RCP), the latter is confirmed to be persistent. Using simulation, we infer that such pulses are likely related to the large misalignment between the stellar rotation and magnetic dipole axes ($>80^\circ$), leading to the formation of highly complex magnetospheric plasma distribution. In addition, by extracting dynamic spectra for the primary pulses, we discovered prominent fine structures in one of the LCP pulses, with timescales as small as the instrumental time resolution (8 seconds). This is the first time that such structures are seen from a magnetic hot star, and has the potential to reveal detailed information about how the emission is driven, and the nature of the elementary sources of radiation. To pinpoint the origin of these fine structures and their significance, higher time and spectral resolution observations should be conducted in the future. △ Less

Submitted 4 July, 2025; originally announced July 2025.

Comments: 19 pages, 11 figures; accepted for publication in ApJ

Effect of phase-lag on synchronization in adaptive multilayer networks with higher-order interactions

Authors: Anath Bandhu Das, Sangita Dutta, Pinaki Pal

Abstract: We investigate the transition to synchronization in adaptive multilayer networks with higher-order interactions both analytically and numerically in the presence of phase frustration ($β$). The higher order topology consists of pairwise and triadic couplings. The analytical framework for the investigation is based on the Ott-Antonsen ansatz which leads to a convenient low-dimensional model. Extens… ▽ More We investigate the transition to synchronization in adaptive multilayer networks with higher-order interactions both analytically and numerically in the presence of phase frustration ($β$). The higher order topology consists of pairwise and triadic couplings. The analytical framework for the investigation is based on the Ott-Antonsen ansatz which leads to a convenient low-dimensional model. Extensive bifurcation analysis of the low-dimensional model and the numerical simulation of the full networks are performed to explore the paths to synchronization. The combined analysis shows a complex dependence of the transition to synchronization on adaptation exponents, coupling strengths, phase lag parameter, and multilayer configuration. Various types of transitions to synchronization, namely continuous, tiered, and explosive, are exhibited by the system in different regions of the parameter space. In all the cases, a satisfactory match between the low-dimensional model and the numerical simulation results is observed. The origin of different transitions to synchronization is clearly understood using the low-dimensional model. Exploration of a wide region of the parameter space suggests that the phase frustration parameter inhibits tired as well as explosive synchronization transitions for fixed triadic coupling strength ($K_2$). On the other hand, discontinuous transition is promoted by the phase frustration parameter for fixed pairwise coupling strength ($K_1$). Moreover, the exponent of the adaptation function with the pairwise coupling decreases the width of the hysteresis, despite the dominance of the higher-order coupling for fixed $β$ and $K_2$. While, the exponent of the function adapted with higher-order coupling shows the opposite effect, it promotes bistability in spite of dominance of pairwise coupling strength for fixed $β$, and $K_1$. △ Less

Submitted 2 July, 2025; originally announced July 2025.

Comments: 14 pages, 14 figures

Effect of anomalous $HHH$ coupling on the decay $H\rightarrow Z\,Z^*\rightarrow$ 4 charged leptons

Authors: Pankaj Agrawal, Biswajit Das

Abstract: We have computed the electroweak corrections to $H\rightarrow Z\,Z^*\rightarrow$ 4 charged leptons, including the effect of anomalous $HHH$ coupling in the $κ$-framework. The results of this scaling are gauge invariant. We have computed the results for $ H \to e^+ e^- μ^+ μ^-$ and $ H \to e^+ e^- e^+ e^-$ processes. The corrections for the both processes depend on the input parameter scheme. In th… ▽ More We have computed the electroweak corrections to $H\rightarrow Z\,Z^*\rightarrow$ 4 charged leptons, including the effect of anomalous $HHH$ coupling in the $κ$-framework. The results of this scaling are gauge invariant. We have computed the results for $ H \to e^+ e^- μ^+ μ^-$ and $ H \to e^+ e^- e^+ e^-$ processes. The corrections for the both processes depend on the input parameter scheme. In the $G_F$ scheme, the electroweak corrections are about $1.26\%$ for the $ H \to e^+ e^- μ^+ μ^-$ and about $0.25\%$ for the $ H \to e^+ e^- e^+ e^-$ process. However changing the $κ$ from $4$ to $-4$, the corrections vary from less than $1\%$ to about $-6\%$. We have plotted a number of kinematic distributions. The corrections over most of the phase space regions are similar. These large corrections can be used to put a bound on the $HHH$ coupling. This can help in determining the structure of the Higgs potential. △ Less

Submitted 30 June, 2025; originally announced June 2025.

Comments: 18 pages, 11 figures, 4 tables

NLO QCD effects on angular observables in $e^-p \to e^-(ν_e)Hj$ in presence of non-standard $HVV$ couplings

Authors: Biswajit Das, Pramod Sharma, Ambresh Shivaji

Abstract: The single Higgs production in neutral-current (NC) and charged-current (CC) processes at an electron-proton ($ep$) collider is a useful channel to probe new physics effects in the Higgs coupling to vector boson ($HVV$). In this context, observables sensitive to non-standard couplings previously studied at leading order require improved theoretical precision through the inclusion of radiative corr… ▽ More The single Higgs production in neutral-current (NC) and charged-current (CC) processes at an electron-proton ($ep$) collider is a useful channel to probe new physics effects in the Higgs coupling to vector boson ($HVV$). In this context, observables sensitive to non-standard couplings previously studied at leading order require improved theoretical precision through the inclusion of radiative corrections. In this work, we present a fully differential Higgs plus one jet production at next-to-leading-order (NLO) accuracy in QCD for both the NC and CC processes. For the proposed Large Hadron electron Collider (LHeC) configuration, with a 60~GeV electron beam and a 7~TeV proton beam, the total cross sections receive modest corrections with significantly reduced scale uncertainties. We find that in several kinematic distributions which are relevant to the analysis of $HVV$ couplings, the NLO K-factors are not flat. Within the Standard Model, the polar angle of the electron (for NC) and the azimuthal angular correlation (for both NC and CC processes) receive maximum corrections in the range of 8-10\% in certain bins. We also compute NLO QCD corrections in the presence of non-standard $HVV$ interactions. The corrections in the azimuthal angular correlations are similar to the standard model predictions. For the polar angle of the electron, the corrections are sensitive to the nature of the $HVV$ coupling. △ Less

Submitted 15 September, 2025; v1 submitted 26 June, 2025; originally announced June 2025.

Comments: 22 pages, 11 figures, 2 tables, Code corrected for real and dipole terms, total NLO cross sections changed by ~1%

Interior rotation modelling of the $β$ Cep pulsator HD 192575 including multiplet asymmetries

Authors: V. Vanlaer, D. M. Bowman, S. Burssens, S. Bharati Das, L. Bugnet, S. Mathis, C. Aerts

Abstract: Rotation plays an important role in stellar evolution. However, the mechanisms behind the transport of angular momentum in stars at various stages of their evolution are not well understood. To improve our understanding of these processes, it is necessary to measure and validate the internal rotation profiles of stars across different stages of evolution and mass regimes. Our aim is to constrain t… ▽ More Rotation plays an important role in stellar evolution. However, the mechanisms behind the transport of angular momentum in stars at various stages of their evolution are not well understood. To improve our understanding of these processes, it is necessary to measure and validate the internal rotation profiles of stars across different stages of evolution and mass regimes. Our aim is to constrain the internal rotation profile of the 12Msun $β$ Cep pulsator HD 192575 from the observed pulsational multiplets and the asymmetries of their component frequencies. We update the forward asteroseismic modelling of HD 192575 based on new TESS observations. We invert for the rotation profile from the symmetric part of the splittings, and compute the multiplet asymmetries due to the Coriolis force and stellar deformation treated perturbatively. We compare the computed asymmetries with the observed asymmetries. Our new forward asteroseismic modelling is in agreement with previous results, but with increased uncertainties, partially due to increased frequency precision, requiring us to relax certain constraints. Ambiguity in the mode identification is the main source of the uncertainty, which also affects the inferred rotation profiles. Almost all acceptable rotation profiles occur in the regime below 0.4/d and favour weak radial differential rotation, with a ratio of core and envelope rotation below two. We find that the quality of the match between the observed and theoretically predicted mode asymmetries is strongly dependent on the mode identification and the internal structure of the star. Our results offer the first detailed rotation inversion for a $β$ Cep pulsator. They show that the rotation profile and the mode asymmetries provide a valuable tool to further constrain the evolutionary properties of HD 192575, and in particular the details of angular momentum transport in massive stars. △ Less

Submitted 24 June, 2025; originally announced June 2025.

Comments: 14 pages, 24 figures, submitted to A&A, second revised revision

Journal ref: A&A 701, A5 (2025)

Charge Ordering in out-of-plane Boron Doped Reduced Graphene Oxide

Authors: Saikat Sarkar, Rajarshi Roy, Bikram Kumar Das, Suman Chatterjee, Kalyan Kumar Chattopadhyay

Abstract: Symmetry-breaking phase transitions analogous to superconductivity (SC), charge ordering (CO) etc. in metal-intercalated graphene are favorable resulting from modified electronic and phonon band structures. Strong carrier-lattice interaction evolved from the out-of-plane soft vibrations with accumulation of charges at the out-of-plane region, can set a favorable environment for CO in graphene syst… ▽ More Symmetry-breaking phase transitions analogous to superconductivity (SC), charge ordering (CO) etc. in metal-intercalated graphene are favorable resulting from modified electronic and phonon band structures. Strong carrier-lattice interaction evolved from the out-of-plane soft vibrations with accumulation of charges at the out-of-plane region, can set a favorable environment for CO in graphene system. Here, we employ boron-doped reduced graphene oxide (BG) to acquire charge-ordered state above a transition temperature, T1~97.5 K. Signatures of this state are identified using ab-initio simulations and low temperature electrical transport measurements. The out-of-plane boron groups play a crucial role in reinforcing the electron-phonon coupling (EPC) allowing an ordered-state transition. Temperature-dependent Raman spectroscopy further supports the emergence of ordering. Key characterization techniques (X-ray diffraction, Raman spectra etc.) are used to quantify the EPC interaction and associated factors like tensile strain, boundary defects, etc. affecting charge ordering with doping. Additionally, we find interesting electric field dependency on the CO in this non-metallic, light-atom-doped chemically derived graphene. △ Less

Submitted 11 June, 2025; originally announced June 2025.