Showing 1–50 of 197 results for author: Li, J

The diverse morphology of gravitational wave signals from merging neutron-star white-dwarf binaries

Authors: Shenghua Yu, Youjun Lu, C. Simon Jeffery, Zhanwen Han, DongDong Liu, Jie Yang, Xilong Fan, Bo Peng, Jianbin Li

Abstract: In sufficiently compact neutron star-white dwarf (NSWD) binary systems, orbital decay means the white dwarf eventually fills its shrinking Roche lobe, initiating a phase of mass transfer. The exchange of angular momentum-both internal and external-plays a critical role in determining the binary's evolutionary outcome. For neutron stars with relatively low magnetic fields and spin frequencies, whet… ▽ More In sufficiently compact neutron star-white dwarf (NSWD) binary systems, orbital decay means the white dwarf eventually fills its shrinking Roche lobe, initiating a phase of mass transfer. The exchange of angular momentum-both internal and external-plays a critical role in determining the binary's evolutionary outcome. For neutron stars with relatively low magnetic fields and spin frequencies, whether the orbital separation continues to shrink depends on the interplay between gravitational wave (GW) radiation and mass transfer dynamics. We compute the orbital evolution of NSWD binaries across a broad parameter space, incorporating four key variables. Our results reveal distinct boundaries in the NS-WD mass-mass diagram: binaries with white dwarf masses above these thresholds undergo rapid orbital decay and direct coalescence. The dependence of these boundaries on system parameters indicates that Roche-lobe-filling NSWD binaries can follow multiple evolutionary pathways -- a phenomenon we refer to as branched or polymorphic evolution. NSWD binary systems emit strong and diverse GW signals, many of which would be detectable by space-based GW observatories. The morphology of the evolving GW waveform provides a direct diagnostic for the NSWD binary configuration, including any contribution from an accretion disk. Our models can provide critical waveform templates for identifying merging binary signals in real-time GW data. △ Less

Submitted 25 November, 2025; originally announced November 2025.

Comments: 13 pages, 7 figures, accepted for publication in MNRAS

Revisiting the Hubble tension problem in the framework of holographic dark energy

Authors: Jun-Xian Li, Shuang Wang

Abstract: The Hubble tension problem is one of the most significant challenges in modern cosmology. In this paper, we study the Hubble tension problem in the framework of holographic dark energy (HDE). To perform a systematic and comprehensive analysis, we select six representative theoretical models from all four categories of HDE. For the observational data, we adopt the Baryon Acoustic Oscillation (BAO)… ▽ More The Hubble tension problem is one of the most significant challenges in modern cosmology. In this paper, we study the Hubble tension problem in the framework of holographic dark energy (HDE). To perform a systematic and comprehensive analysis, we select six representative theoretical models from all four categories of HDE. For the observational data, we adopt the Baryon Acoustic Oscillation (BAO) data from the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2), a collection of alternative BAO data, the Cosmic Microwave Background (CMB) distance priors from the $Planck$ 2018, the type Ia supernovae (SN) data from the PantheonPlus, Union3, and DESY5 compilations. We find that HDE models that employ the Hubble scale or its combinations as the IR cutoff cannot alleviate the Hubble tension problem. In contrast, HDE models that employ the future event horizon as the IR cutoff can significantly alleviate the Hubble tension problem. It must be stressed that these two key conclusions hold true for cases of adopting different theoretical HDE models and different observational data. Our findings advocate for further exploration of HDE models using other types of cosmological observations. △ Less

Submitted 12 November, 2025; originally announced November 2025.

Comments: 16 pages, 10 figures, 8 tables. comments are welcome!

Interior instability of naked singularities of a scalar field

Authors: Junbin Li

Abstract: We show that the $k$-self-similar naked singularity solutions of the spherically symmetric Einstein--Scalar field system are unstable to black hole formation under perturbations that are totally supported in the interior region, in all regularities strictly below the threshold. The instability below the threshold is also established for exterior perturbations. We also show that general naked singu… ▽ More We show that the $k$-self-similar naked singularity solutions of the spherically symmetric Einstein--Scalar field system are unstable to black hole formation under perturbations that are totally supported in the interior region, in all regularities strictly below the threshold. The instability below the threshold is also established for exterior perturbations. We also show that general naked singularity solutions are unstable under interior BV perturbations, which provides a new insight into understanding the weak cosmic censorship conjecture for this model. In contrast to all previous results on the exterior instability of naked singularities (and even trapped surface formation), where only a single incoming null cone is considered, the novel approach to proving the interior instability is analyzing a family of incoming null cones becoming more and more singular. △ Less

Submitted 11 August, 2025; originally announced August 2025.

Comments: 28 pages, 5 figures

Probing globular clusters using modulated gravitational waves from binary black holes

Authors: Jie Wu, Yao Xiao, Mengfei Sun, Jin Li

Abstract: Globular clusters (GCs) are crucial for studying stellar dynamics and galactic structure, yet precise measurements of their distances and masses are often limited by uncertainties in electromagnetic (EM) observations. We present a novel method that leverages gravitational waves (GWs) from stellar-mass binary black holes (BBHs) orbiting within GCs to enhance the precision of GC parameter measuremen… ▽ More Globular clusters (GCs) are crucial for studying stellar dynamics and galactic structure, yet precise measurements of their distances and masses are often limited by uncertainties in electromagnetic (EM) observations. We present a novel method that leverages gravitational waves (GWs) from stellar-mass binary black holes (BBHs) orbiting within GCs to enhance the precision of GC parameter measurements. The BBH's orbital motion imprints characteristic modulations on the GW waveform, encoding information about the host GC. Using post-Newtonian waveforms and Lorentz transformations, we simulate modulated GW signals and evaluate the resulting parameter constraints via a Fisher information matrix analysis. Our results show that incorporating GW observations can significantly reduce the uncertainties in GC distance and mass measurements, in many cases achieving improvements by an order of magnitude. These findings demonstrate the value of BBHs as dynamical probes and highlight the power of GWs to advance GC studies beyond the limits of traditional EM methods. △ Less

Submitted 5 August, 2025; originally announced August 2025.

Comments: 10 pages, 5 figures

Effect of symmetry energy on properties of rapidly rotating neutron stars and universal relations

Authors: Pion Sudarshan Yeasin, Stefanos Tsiopelas, Armen Sedrakian, Jia-Jie Li

Abstract: We investigated universal relations for compact stars rotating at the Keplerian (mass-shedding) limit, which is highly relevant for understanding the rapidly rotating objects formed in the aftermath of a neutron star-neutron star merger. Our analysis is based on a set of nucleonic equations of state (EoSs) featuring systematic variations in the symmetry energy slope parameter $L_{\rm sym}$ and… ▽ More We investigated universal relations for compact stars rotating at the Keplerian (mass-shedding) limit, which is highly relevant for understanding the rapidly rotating objects formed in the aftermath of a neutron star-neutron star merger. Our analysis is based on a set of nucleonic equations of state (EoSs) featuring systematic variations in the symmetry energy slope parameter $L_{\rm sym}$ and the isoscalar skewness parameter $Q_{\rm sat}$, varied within ranges that are broadly consistent with current laboratory and astrophysical constraints. The global observable properties of isolated maximally rotating stars are examined, focusing on the mass-radius relation, moment of inertia, quadrupole moment, and the Keplerian (maximum) rotation frequency, as well as their variations in the $L_{\rm sym}$-$Q_{\rm sat}$ parameter space. Next, we demonstrate that, in the limit of Keplerian rotation, universal relations remain valid across the same set of EoSs characterized by varying $L_{\rm sym}$ and $\Qsat$. In particular, we present explicit results for the moment of inertia ($I$) and quadrupole moment ($Q$) as functions of compactness, as well as for the moment of inertia-quadrupole moment relation. All of these relations exhibit excellent universality, with deviations typically within a range from a few percent to 10\% across a wide range of parameters. Additionally, we verify for our set of EoSs that the universality of $I$-$Q$ holds to higher accuracy (at the level of 1\%) in the slow-rotation approximation compared with the Kepler limit, where the relative error increases up to $\lesssim 10\%$. Our findings support the applicability of $I$-Love-$Q$-type universal relations in observational modeling of maximally rotating compact stars and the gravitational wave emitted by them. △ Less

Submitted 1 September, 2025; v1 submitted 1 July, 2025; originally announced July 2025.

Comments: v2: 12 pages, 9 figures, journal version. v1: 11 pages, 8 figures

Journal ref: Phys. Rev. D 112, 063028 (2025)

Scalar perturbations to naked singularities of perfect fluid

Authors: Junbin Li, Xi-Ping Zhu

Abstract: In this paper, we study the instability of naked singularities arising in the Einstein equations coupled with isothermal perfect fluid. We show that the spherically symmetric self-similar naked singularities of this system, are unstable to trapped surface formation, under $C^{1,α}$ perturbations of an external massless scalar field. We viewed this as a toy model in studying the instability of thes… ▽ More In this paper, we study the instability of naked singularities arising in the Einstein equations coupled with isothermal perfect fluid. We show that the spherically symmetric self-similar naked singularities of this system, are unstable to trapped surface formation, under $C^{1,α}$ perturbations of an external massless scalar field. We viewed this as a toy model in studying the instability of these naked singularities under gravitational perturbations in the original Einstein--Euler system which is non-spherically symmetric. △ Less

Submitted 27 May, 2025; originally announced May 2025.

Comments: 25 pages, 2 figures

Isotropy, anisotropies and non-Gaussianity in the scalar-induced gravitational-wave background: diagrammatic approach for primordial non-Gaussianity up to arbitrary order

Authors: Jun-Peng Li, Sai Wang, Zhi-Chao Zhao, Kazunori Kohri

Abstract: Produced nonlinearly by the enhanced linear cosmological curvature perturbations, the scalar-induced gravitational waves (SIGWs) can serve as a potentially powerful probe of primordial non-Gaussianity (PNG) in the early Universe. In this work, we comprehensively investigate the imprints of local-type PNG on the SIGW background beyond the widely used quadratic and cubic approximations. We develop a… ▽ More Produced nonlinearly by the enhanced linear cosmological curvature perturbations, the scalar-induced gravitational waves (SIGWs) can serve as a potentially powerful probe of primordial non-Gaussianity (PNG) in the early Universe. In this work, we comprehensively investigate the imprints of local-type PNG on the SIGW background beyond the widely used quadratic and cubic approximations. We develop a diagrammatic approach capable of analyzing SIGWs for PNG up to arbitrary order. Following this approach, we derive semi-analytic formulas for the energy-density fraction spectrum, the angular power spectrum, and the angular bispectrum and trispectrum to describe the isotropic component, anisotropies, and non-Gaussianity of the SIGW background, respectively. Particularly, focusing on PNG up to quartic approximation (parameterized by $f_\mathrm{NL}$, $g_\mathrm{NL}$, and $h_\mathrm{NL}$), we numerically compute all contributions to these SIGW spectra. We find that PNG can significantly alter the magnitude of the SIGW energy-density spectrum, and can generate substantial anisotropies through the initial inhomogeneities in the SIGW distribution. Furthermore, we observe that the SIGW angular bispectrum and trispectrum always vanish when the primordial curvature perturbations are Gaussian; otherwise, they do not, indicating their potential utility as probes of PNG. Therefore, we anticipate that the SIGW background will provide essential information about the early Universe. △ Less

Submitted 10 September, 2025; v1 submitted 22 May, 2025; originally announced May 2025.

Comments: 107 pages, 36 figures. Version 2: Added discussions on the infrared scaling of the SIGW energy-density spectra in Section 6 and the Appendix. Corrected the calculation of PBH abundance in Section 6. Corrected some typos and included several new references

Report number: KEK-TH-2724, KEK-Cosmo-0381

The constraints on the stochastic gravitational wave background from cosmic strings by an electromagnetic resonance system

Authors: Jin Li, Meijin Li, Nan Yang, Li Wang, Hao Yu, Yingzhou Huang, Kai Lin, Zi-Chao Lin, Fangyu Li

Abstract: As one of the primary detection targets for contemporary gravitational wave (GW) observatories, the stochastic gravitational wave background (SGWB) holds significant potential for enhancing our understanding of the early universe's formation and evolution. Studies indicate that the SGWB spectrum from cosmic strings can span an extraordinarily broad frequency range, extending from extremely low fre… ▽ More As one of the primary detection targets for contemporary gravitational wave (GW) observatories, the stochastic gravitational wave background (SGWB) holds significant potential for enhancing our understanding of the early universe's formation and evolution. Studies indicate that the SGWB spectrum from cosmic strings can span an extraordinarily broad frequency range, extending from extremely low frequencies up to the microwave band. This work specifically investigates the detectability of cosmic string SGWB signals in an electromagnetic (EM) resonance system at GHz frequency. We present a systematic analysis encompassing: (1) the response of high frequency gravitational waves (HFGWs) in such EM resonance system. (2) the development and application of fundamental data processing protocols in the EM resonance system. Our results demonstrate that the EM system shows promising sensitivity to detect cosmic string SGWB signals with tension parameters $Gμ\geq 10^{-11}$ (the corresponding dimensionless amplitude $h \geq 10^{-33}$ at 1 GHz), while potentially establishing new constraints for $Gμ\leq 10^{-11}$ in the microwave band. These findings would complement existing multi-band SGWB observations and provide additional constraints on cosmic-string tension parameters in GHz frequency regimes. △ Less

Submitted 13 October, 2025; v1 submitted 19 May, 2025; originally announced May 2025.

Comments: 22 pages, 7 figures

Journal ref: Eur. Phys. J. C (2025) 85:1049

Modeling Tidal Disruptions with Dynamical Tides

Authors: Zihan Zhou, Giovanni Maria Tomaselli, Irvin Martínez-Rodríguez, Jingping Li

Abstract: Tidal disruption events (TDEs) occur when stars pass close enough to supermassive black holes to be torn apart by tidal forces. Traditionally, these events are studied with computationally intensive hydrodynamical simulations. In this paper, we present a fast, physically motivated two-stage model for TDEs. In the first stage, we model the star's tidal deformation using linear stellar perturbation… ▽ More Tidal disruption events (TDEs) occur when stars pass close enough to supermassive black holes to be torn apart by tidal forces. Traditionally, these events are studied with computationally intensive hydrodynamical simulations. In this paper, we present a fast, physically motivated two-stage model for TDEs. In the first stage, we model the star's tidal deformation using linear stellar perturbation theory, treating the star as a collection of driven harmonic oscillators. When the tidal energy exceeds a fraction $γ$ of the star's gravitational binding energy (with $γ\sim \mathcal O(1)$), we transition to the second stage, where we model the disrupted material as free particles. The parameter $γ$ is determined with a one-time calibration to the critical impact parameter obtained in hydrodynamical simulations. This method enables fast computation of the energy distribution ${\rm d} M/{\rm d}E$ and fallback rate ${\rm d} M/{\rm d} T$, while offering physical insight into the disruption process. We apply our model to MESA-generated profiles of middle-age main-sequence stars. Our code is available on GitHub. △ Less

Submitted 8 October, 2025; v1 submitted 22 April, 2025; originally announced April 2025.

Comments: 11 pages, 5 figures; v2: journal version

A unified topological classification of circular orbits for charged particles in black hole spacetimes

Authors: Yong Song, Jia Li, Yiting Cen, Kai Diao, Xiaofeng Zhao, Shunping Shi

Abstract: The study of circular orbits offers profound insights into the structure of spacetime around black holes. While the topological properties of these orbits are well-established for neutral particles, the influence of electric charge-particularly for massless particles-remains a subject of exploration. In this work, we employ a topological current $φ$-mapping approach to systematically investigate t… ▽ More The study of circular orbits offers profound insights into the structure of spacetime around black holes. While the topological properties of these orbits are well-established for neutral particles, the influence of electric charge-particularly for massless particles-remains a subject of exploration. In this work, we employ a topological current $φ$-mapping approach to systematically investigate the circular orbits of charged test particles in static, spherically symmetric black hole spacetimes with flat, anti-de Sitter (AdS), and de Sitter (dS) asymptotics. We demonstrate that the particle's charge significantly alters the topological classification of both timelike and null circular orbits. A key finding is that for multi-horizon black holes, if a circular orbit with fixed angular momentum and charge exists between two neighboring horizons, there will always be at least one unstable null and one unstable timelike circular orbit. Outside the outermost horizon, the asymptotic behavior of spacetime and the specific charge ratio crucially determine the topological charge $W$, dictating the existence and stability of orbits. Our results, validated through Reissner-Nordström (RN), RN-AdS, and RN-dS examples, extend the topological orbit classification framework and provide a foundation for potential applications in environments where effective charge dynamics may be relevant, such as magnetized plasmas around black holes. △ Less

Submitted 18 November, 2025; v1 submitted 7 April, 2025; originally announced April 2025.

Comments: 19 pages, 16 figures,2 tables, accepted version in EPJC

Journal ref: Eur. Phys. J. C 85, 1328 (2025)

Beijing Normal University 12-meter Interferometric kHz GW Detector Prototype: Design and Scientific Prospects

Authors: Mengyao Wang, Fan Zhang, Xinyao Guo, Haixing Miao, Huan Yang, Yiqiu Ma, Haoyu Wang, Teng Zhang, Mengdi Cao, Yuchao Chen, Xiaoman Huang, Junlang Li, Fangfei Liu, Jianyu Liu, Yuan Pan, Yulin Xia, Jianbo Xing, Yujie Yu, Chenjie Zhou, Zong-hong Zhu

Abstract: Current gravitational-wave detectors have achieved remarkable sensitivity around 100 Hz, enabling ground-breaking discoveries. Enhancing sensitivity at higher frequencies in the kilohertz (kHz) range promises access to rich physics, particularly the extreme conditions during the merger stage of binary neutron stars. However, the high-frequency sensitivity of Michelson-based interferometers is fund… ▽ More Current gravitational-wave detectors have achieved remarkable sensitivity around 100 Hz, enabling ground-breaking discoveries. Enhancing sensitivity at higher frequencies in the kilohertz (kHz) range promises access to rich physics, particularly the extreme conditions during the merger stage of binary neutron stars. However, the high-frequency sensitivity of Michelson-based interferometers is fundamentally limited by their linear optical cavities, which are optimized for low-frequency signal enhancement. In [Phys. Rev. X 13, 021019 (2023)], a new configuration employing an L-shaped optical resonator was proposed to overcome this limitation, offering exceptional sensitivity in the kHz band. As a pathfinder, the 12-meter prototype at Beijing Normal University is designed to demonstrate the sensing and control schemes of this new kHz detector configuration and to explore its performance in the high-power regime with suspended optics. Beyond its primary scientific goal, the prototype also offers potential sensitivity in the megahertz (MHz) range, potentially enabling constraints on exotic sources. This paper presents an overview of the prototype, including its optical design and current development status of key components. △ Less

Submitted 25 June, 2025; v1 submitted 31 March, 2025; originally announced March 2025.

Comments: 10 pages, 8 figures,2 tables

Extension principles for the Einstein Yang--Mills system

Authors: Junbin Li, Jinhua Wang

Abstract: We prove the local existence theorem and establish an extension principle for the spherically symmetric Einstein Yang--Mills system (SSEYM) with $H^1$ data. This in addition implies Cauchy stability for the system. In contrast to a massless scalar field, the purely magnetic Yang--Mills field in spherical symmetry satisfies a wave-type equation with a singular potential. As a consequence, the pro… ▽ More We prove the local existence theorem and establish an extension principle for the spherically symmetric Einstein Yang--Mills system (SSEYM) with $H^1$ data. This in addition implies Cauchy stability for the system. In contrast to a massless scalar field, the purely magnetic Yang--Mills field in spherical symmetry satisfies a wave-type equation with a singular potential. As a consequence, the proof of Christodoulou [10], based on an $L^\infty-L^\infty$ estimate, fails in the Yang--Mills context. Instead, we employ an $L^2$-based method, which is valid for both massless and massive scalar matter fields as well. △ Less

Submitted 31 August, 2025; v1 submitted 25 March, 2025; originally announced March 2025.

Comments: 32pages, comments are welcome!

Effect of kick velocity on gravitational wave detection of binary black holes with space- and ground-based detectors

Authors: Jie Wu, Mengfei Sun, Xianghe Ma, Xiaolin Liu, Jin Li, Zhoujian Cao

Abstract: During the coalescence of binary black holes (BBHs), asymmetric gravitational wave (GW) emission imparts a kick velocity to the remnant black hole, affecting observed waveforms and parameter estimation. In this study, we investigate the impact of this effect on GW observations using space- and ground-based detectors. By applying Lorentz transformations, we analyze waveform modifications due to kic… ▽ More During the coalescence of binary black holes (BBHs), asymmetric gravitational wave (GW) emission imparts a kick velocity to the remnant black hole, affecting observed waveforms and parameter estimation. In this study, we investigate the impact of this effect on GW observations using space- and ground-based detectors. By applying Lorentz transformations, we analyze waveform modifications due to kick velocities. For space-based detectors, nearly 50% of detected signals require corrections, while for ground-based detectors, this fraction is below one-third. For Q3d population model, space-based detectors could observe kick effects in over 60% of massive BBH mergers, while in pop3 model, this fraction could drop to 3$\sim$4%. Third-generation ground-based detectors may detect kick effects in up to 16% of stellar-mass BBH mergers. Our findings highlight the importance of incorporating kick velocity effects into waveform modeling, enhancing GW signal interpretation and our understanding of BBH dynamics and astrophysical implications. △ Less

Submitted 18 July, 2025; v1 submitted 19 February, 2025; originally announced February 2025.

Comments: 12 pages, 8 figures

Journal ref: Phys. Rev. D 112, 024040 (2025)

Identification of Stochastic Gravitational Wave Backgrounds from Cosmic String Using Machine Learning

Authors: Xianghe Ma, Borui Wang, Nan Yang, Jin Li, Brendan McCane, Mengfei Sun, Jie Wu, Minghui Zhang, Yan Meng

Abstract: Cosmic strings play a crucial role in enhancing our understanding of the fundamental structure and evolution of the universe, unifying our knowledge of cosmology, and potentially unveiling new physical laws and phenomena. The advent and operation of space-based detectors provide an important opportunity for detecting stochastic gravitational wave backgrounds (SGWB) generated by cosmic strings. How… ▽ More Cosmic strings play a crucial role in enhancing our understanding of the fundamental structure and evolution of the universe, unifying our knowledge of cosmology, and potentially unveiling new physical laws and phenomena. The advent and operation of space-based detectors provide an important opportunity for detecting stochastic gravitational wave backgrounds (SGWB) generated by cosmic strings. However, the intricate nature of SGWB poses a formidable challenge in distinguishing its signal from the complex noise by some traditional methods. Therefore, we attempt to identify SGWB based on machine learning. Our findings show that the joint detection of LISA and Taiji significantly outperforms individual detectors, and even in the presence of numerous low signal-to-noise ratio(SNR) signals, the identification accuracy remains exceptionally high with 95%. Although our discussion is based solely on simulated data, the relevant methods can provide data-driven analytical capabilities for future observations of SGWB. △ Less

Submitted 6 March, 2025; v1 submitted 17 February, 2025; originally announced February 2025.

Influences of accretion flow and dilaton charge on the images of Einstein-Maxwell-dilation black hole

Authors: Gang Chen, Sen Guo, Jia-Shuo Li, Yu-Xiang Huang, Li-Fang Li, Peng Xu

Abstract: The characteristics and images of Einstein-Maxwell-Dilaton (EMD) black holes are examined in this paper, focusing on their effective potential, photon trajectories, and images with thin and thick accretion disks. We found that the shadow and photon sphere radii decrease with increasing dilaton charge. As the observation inclination increases, direct and secondary images become separate, with the d… ▽ More The characteristics and images of Einstein-Maxwell-Dilaton (EMD) black holes are examined in this paper, focusing on their effective potential, photon trajectories, and images with thin and thick accretion disks. We found that the shadow and photon sphere radii decrease with increasing dilaton charge. As the observation inclination increases, direct and secondary images become separate, with the direct image appearing hat-shaped. Simulations indicate that the brightness of the shadow and photon ring is higher in static spherical accretion flows compared to infalling ones. The study also shows that in thin disk accretion flows, the direct emission predominantly influences observed luminosity, with photon ring emission being less significant. Additionally, the appearance of black hole images varies with the observer's inclination angle. △ Less

Submitted 11 February, 2025; originally announced February 2025.

Comments: 17 pages, 17 figures

Complete Hamiltonian Framework of Relativistic Hierarchical Triple Systems: Capabilities and Limitations of Secular Perturbation Theory

Authors: Kaye Jiale Li, Kinwah Wu, Ziri Younsi, Tjonnie G. F. Li

Abstract: Relativistic secular perturbation theory has ignited significant interest in uncovering intricate cross-term effects, especially the interplay between 1PN and quadrupole terms. While most existing studies rely on the Lagrangian planetary perturbation method for computing cross terms, a comprehensive Hamiltonian framework for the field has been missing. In this work, we introduce a framework based… ▽ More Relativistic secular perturbation theory has ignited significant interest in uncovering intricate cross-term effects, especially the interplay between 1PN and quadrupole terms. While most existing studies rely on the Lagrangian planetary perturbation method for computing cross terms, a comprehensive Hamiltonian framework for the field has been missing. In this work, we introduce a framework based on von Zeipel transformation, utilizing two sequential canonical transformations to systematically compute cross terms to arbitrary orders. Our results reveal secular cross terms up to quadrupole-squared order, showcasing remarkable consistency with both the Lagrangian method [1] and the effective-field-theory approach [2]. We present leading-order periodic cross terms arising from the interactions between 1PN and quadrupole, and present estimates of higher-order cross terms. It is demonstrated that this method not only accurately predicts the long-term evolution of hierarchical systems but also captures fast oscillations observed in N-body simulations. We identify and validate resonances caused by quadrupole-squared effects, highlighting both consistencies and discrepancies when compared to N-body simulations. These discrepancies underscore the importance of mean-motion resonances, a factor overlooked in current secular perturbation frameworks. Finally, we provide a comprehensive review of the subtleties and limitations inherent to secular perturbation theory, paving the way for future research and advancements in this field. △ Less

Submitted 14 January, 2025; originally announced January 2025.

Comments: 28 pages, 9 figures, comments welcome

Isotropic background and anisotropies of gravitational waves induced by cosmological soliton isocurvature perturbations

Authors: Di Luo, Yan-Heng Yu, Jun-Peng Li, Sai Wang

Abstract: Cosmological solitons are widely predicted by scenarios of the early Universe. In this work, we investigate the isotropic background and anisotropies of gravitational waves (GWs) induced by soliton isocurvature perturbations, especially considering the effects of non-Gaussianity in these perturbations. Regardless of non-Gaussianity, the energy-density fraction spectrum of isocurvature-induced GWs… ▽ More Cosmological solitons are widely predicted by scenarios of the early Universe. In this work, we investigate the isotropic background and anisotropies of gravitational waves (GWs) induced by soliton isocurvature perturbations, especially considering the effects of non-Gaussianity in these perturbations. Regardless of non-Gaussianity, the energy-density fraction spectrum of isocurvature-induced GWs approximately has a universal shape within the perturbative regime, thus serving as a distinctive signal of solitons. We derive the angular power spectrum of isocurvature-induced GWs to characterize their anisotropies. Non-Gaussianity plays a key role in generating anisotropies through the couplings between large- and small-scale isocurvature perturbations, making the angular power spectrum to be a powerful probe of non-Gaussianity. Moreover, the isocurvature-induced GWs have nearly no cross-correlations with the cosmic microwave background, providing a new observable to distinguish them from other GW sources, e.g., GWs induced by cosmological curvature perturbations enhanced at small scales. Therefore, detection of both the isotropic background and anisotropies of isocurvature-induced GWs could reveal important implications for the solitons as well as the early Universe. △ Less

Submitted 2 April, 2025; v1 submitted 6 January, 2025; originally announced January 2025.

Comments: 23 pages, 5 figures; additional references added; accepted by JCAP

A comprehensive numerical study on four categories of holographic dark energy models

Authors: Jun-Xian Li, Shuang Wang

Abstract: Holographic dark energy (HDE), which arises from a theoretical attempt to apply the holographic principle (HP) to the dark energy (DE) problem, has attracted significant attention over the past two decades. We perform a comprehensive numerical study on HDE models that can be classified into four categories: 1) HDE models with other characteristic length scale, 2) HDE models with extended Hubble sc… ▽ More Holographic dark energy (HDE), which arises from a theoretical attempt to apply the holographic principle (HP) to the dark energy (DE) problem, has attracted significant attention over the past two decades. We perform a comprehensive numerical study on HDE models that can be classified into four categories: 1) HDE models with other characteristic length scale, 2) HDE models with extended Hubble scale, 3) HDE models with dark sector interaction, 4) HDE models with modified black hole entropy. For theoretical models, we select seven representative models, including the original HDE (OHDE) model, Ricci HDE (RDE) model, generalized Ricci HDE (GRDE) model, interacting HDE (IHDE1 and IHDE2) models, Tsallis HDE (THDE) model, and Barrow HDE (BHDE) model. For cosmological data, we use the Baryon Acoustic Oscillation (BAO) data from the Dark Energy Spectroscopic Instrument (DESI) 2024 measurements, the Cosmic Microwave Background (CMB) distance priors data from the Planck 2018, and the type Ia supernovae (SNe) data from the PantheonPlus compilation. Using $χ^2$ statistic and Bayesian evidence, we compare these HDE models with current observational data. It is found that: 1) The $Λ$CDM remains the most competitive model, while the RDE model is ruled out. 2) HDE models with dark sector interaction perform the worst across the four categories, indicating that the interaction term is not favored under the framework of HDE. 3) The other three categories show comparable performance. The OHDE model performs better in the BAO+CMB dataset, and the HDE models with modified black hole entropy perform better in the BAO+CMB+SN dataset. 4) HDE models with the future event horizon exhibit significant discrepancies in parameter space across datasets. The BAO+CMB dataset favors a phantom-like HDE, whereas the BAO+CMB+SN leads to an equation of state (EoS) much closer to the cosmological constant. △ Less

Submitted 23 June, 2025; v1 submitted 12 December, 2024; originally announced December 2024.

Comments: 33 pages, 8 figures, 6 tables, comments welcome! Accepted for publication in JCAP

Journal ref: JCAP 07 (2025) 047

Study of primordial non-Gaussianity $f_{\mathrm{NL}}$ and $g_{\mathrm{NL}}$ with the cross-correlations between the scalar-induced gravitational waves and the cosmic microwave background

Authors: Zhi-Chao Zhao, Sai Wang, Jun-Peng Li, Kazunori Kohri

Abstract: The stochastic gravitational-wave background originating from cosmic sources contains vital information about the early universe. In this work, we comprehensively study the cross-correlations between the energy-density anisotropies in scalar-induced gravitational waves (SIGWs) and the temperature anisotropies and polarization in the cosmic microwave background (CMB). In our analysis of the angular… ▽ More The stochastic gravitational-wave background originating from cosmic sources contains vital information about the early universe. In this work, we comprehensively study the cross-correlations between the energy-density anisotropies in scalar-induced gravitational waves (SIGWs) and the temperature anisotropies and polarization in the cosmic microwave background (CMB). In our analysis of the angular power spectra for these cross-correlations, we consider all contributions of the local-type primordial non-Gaussianity $f_{\mathrm{NL}}$ and $g_{\mathrm{NL}}$ that can lead to large anisotropies. We show that the angular power spectra are highly sensitive to primordial non-Gaussianity. Furthermore, we project the sensitivity of future gravitational-wave detectors to detect such signals and, consequently, measure the primordial non-Gaussianity. △ Less

Submitted 24 November, 2025; v1 submitted 3 December, 2024; originally announced December 2024.

Comments: 18 pages, 5 figures, one column, version accepted by EPJC. The code is available on GitHub at https://github.com/Zhi-ChaoZhao/sigw_class

Report number: KEK-Cosmo-0364, KEK-TH-2670, KEK-QUP-2024-0025

Journal ref: Eur.Phys.J.C 85 (2025) 12, 1406

Constraining symmetron fields with a levitated optomechanical system

Authors: Jiawei Li, Ka-di Zhu

Abstract: The symmetron, one of the light scalar fields introduced by dark energy theories, is thought to modify the gravitational force when it couples to matter. However, detecting the symmetron field is challenging due to its screening behavior in the high-density environment of traditional measurements. In this paper, we propose a scheme to set constraints on the parameters of the symmetron with a levit… ▽ More The symmetron, one of the light scalar fields introduced by dark energy theories, is thought to modify the gravitational force when it couples to matter. However, detecting the symmetron field is challenging due to its screening behavior in the high-density environment of traditional measurements. In this paper, we propose a scheme to set constraints on the parameters of the symmetron with a levitated optomechanical system, in which a nanosphere serves as a testing mass coupled to an optical cavity. By measuring the frequency shift of the probe transmission spectrum, we can establish constraints for our scheme by calculating the symmetron-induced influence. These refined constraints improve by 1 to 3 orders of magnitude compared to current force-based detection methods, which offer new opportunities for the dark energy detection. △ Less

Submitted 25 November, 2024; originally announced November 2024.

Constraints and detection capabilities of GW polarizations with space-based detectors in different TDI combinations

Authors: Jie Wu, Mengfei Sun, Jin Li

Abstract: Time-delay interferometry (TDI) is essential in space-based gravitational wave (GW) detectors, effectively reducing laser noise and improving detection precision. As one of the most promising GW detectors, the space-based detectors are able to observe the effects from GW polarizations. The detection of GW additional polarizations carries significant implications, potentially revealing deviations f… ▽ More Time-delay interferometry (TDI) is essential in space-based gravitational wave (GW) detectors, effectively reducing laser noise and improving detection precision. As one of the most promising GW detectors, the space-based detectors are able to observe the effects from GW polarizations. The detection of GW additional polarizations carries significant implications, potentially revealing deviations from general relativity and opening avenues to explore alternative gravity theories. In this study, we examine the impacts of second-generation TDI combinations on GW polarization detection by simulating LISA, Taiji, and TianQin, including realistic orbital effects such as link length and angle variations. The detector performance is assessed through sensitivity curves derived from averaged response functions, as well as signal-to-noise ratio (SNR) of binary black holes (BBHs). For massive BBHs, the $\mathcal{A}$ and $\mathcal{E}$ channels typically offer the best sensitivity, while the $X$ channel in TianQin is most effective for detecting additional polarizations. For stellar-mass BBHs, the $α$ channel provides the highest SNR for vector modes in LISA and Taiji specifically for lower-mass systems, while the $\mathcal{A}$ and $\mathcal{E}$ channels are optimal for higher masses or other polarizations. TianQin consistently favors the $X$ channel for additional polarizations. Our findings emphasize the importance of selecting high-sensitivity TDI combinations to enhance detection capabilities across different polarizations, deepening our insight into GW sources and the fundamental nature of spacetime △ Less

Submitted 5 November, 2024; originally announced November 2024.

Comments: 12 pages, 12 figures

Holographic Einstein Rings of AdS Black Holes in Horndeski Theory

Authors: Zhi Luo, Ke-Jian He, Jin Li

Abstract: By utilizing the AdS/CFT correspondence and wave optics techniques, we conducted an extensive study of the imaging properties of holographic Einstein rings in the context of Anti-de Sitter (AdS) black holes (BHs) in Horndeski theory. Our results indicate that the optical characteristics of these holographic Einstein rings are significantly influenced by the observer's position, the physical parame… ▽ More By utilizing the AdS/CFT correspondence and wave optics techniques, we conducted an extensive study of the imaging properties of holographic Einstein rings in the context of Anti-de Sitter (AdS) black holes (BHs) in Horndeski theory. Our results indicate that the optical characteristics of these holographic Einstein rings are significantly influenced by the observer's position, the physical parameters of the BH, the nature of the wave source, and the configuration of the optical system. Specifically, when the observer is positioned at the north pole of the AdS boundary, the holographic image prominently displays a ring structure aligning with the BH's photon sphere. We thoroughly analyzed how various physical parameters -- including the observation position, event horizon radius, temperature, and the parameter $γ$ in Horndeski theory -- affect the holographic Einstein rings. These parameters play a crucial role in determining the rings' radius and brightness, with variations potentially causing the ring structures to deform or even transform into bright spots. Furthermore, our comparative analysis between wave optics and geometric optics reveals a strong agreement in predicting the positions and brightnesses of both the photon ring and the Einstein ring. This research offers new insights into the spacetime geometry of BHs in Horndeski theory and proposes a promising framework for exploring the gravitational duals of strongly coupled systems. △ Less

Submitted 18 September, 2024; v1 submitted 18 September, 2024; originally announced September 2024.

Comments: 21 pages, 10 figures

Prospects of constraining on the polarizations of gravitational waves from binary black holes using space- and ground-based detectors

Authors: Jie Wu, Jin Li

Abstract: The theory of general relativity (GR) predicts the existence of gravitational waves (GWs) with two tensor modes, while alternative theories propose up to six polarization modes. In this study, we investigate constraints on GW polarization using a model-independent parametrized post-Einsteinian framework and consider both space- and ground-based detectors. By evaluating the capabilities and network… ▽ More The theory of general relativity (GR) predicts the existence of gravitational waves (GWs) with two tensor modes, while alternative theories propose up to six polarization modes. In this study, we investigate constraints on GW polarization using a model-independent parametrized post-Einsteinian framework and consider both space- and ground-based detectors. By evaluating the capabilities and network performance of LISA, Taiji, TianQin, LIGO, Virgo, KAGRA, and the Einstein Telescope (ET), we analyze their respective contributions. Among space-based detectors, Taiji provides the most stringent constraints compared with LISA and TianQin.Regarding ground-based detectors, LIGO excels in vector modes while ET offers comprehensive constraints across all polarization modes. In network scenarios, LISA+TJm performs best, and ET surpasses second-generation detector combinations. Furthermore, multiband observations effectively mitigate scalar mode degeneracies thereby significantly enhancing the performance of ground-based detectors. Ultimately, combined space- and ground-based observations provide robust constraints on GW polarizations that advance tests for deviations from GR. Our findings underscore the potential of future GW missions in refining our understanding of gravitational physics through precise measurements of polarizations. △ Less

Submitted 25 October, 2024; v1 submitted 18 July, 2024; originally announced July 2024.

Comments: 17 pages, 11 figures

Journal ref: Phys.Rev.D 110 (2024) 8, 084057

Shadows, Quasinormal Modes, and Optical Appearances of Black Holes in Horndeski Theory

Authors: Zhi Luo, Jin Li, Ke-Jian He, Hao Yu

Abstract: This work describes the motion of photons in black hole (BH) spacetimes within the framework of Horndeski theory. We focus on the shadows, quasinormal modes (QNMs) and optical appearances of BHs surrounded by geometrically thin accretion disks. The QNMs of BHs are calculated by the WKB method and the eikonal limit, respectively. Using Event Horizon Telescope (EHT) observations of… ▽ More This work describes the motion of photons in black hole (BH) spacetimes within the framework of Horndeski theory. We focus on the shadows, quasinormal modes (QNMs) and optical appearances of BHs surrounded by geometrically thin accretion disks. The QNMs of BHs are calculated by the WKB method and the eikonal limit, respectively. Using Event Horizon Telescope (EHT) observations of $\mathrm{M} 87^*$ and $\mathrm{Sgr} \mathrm{A}^*$, we can constrain the parameter in Horndeski theory to a small range. Based on the constraint, we obtain the frequency ranges of the fundamental modes for $\mathrm{M} 87^*$ and $\mathrm{Sgr} \mathrm{A}^*$ in Horndeski theory. By exploring the optical appearances of BHs, we find that for the current resolution of the EHT, it primarily captures direct emission. This work advances our understanding of the observational characteristics of BHs in Horndeski theory and constrains Horndeski theory by EHT observations of $\mathrm{M} 87^*$ and $\mathrm{Sgr} \mathrm{A}^*$. △ Less

Submitted 22 July, 2024; v1 submitted 31 May, 2024; originally announced June 2024.

Energy Extraction from a Kerr Black Hole via Magnetic Reconnection within the Plunging Region

Authors: Bin Chen, Yehui Hou, Junyi Li, Ye Shen

Abstract: Magnetic reconnection within a highly magnetized plasma has been seen as a viable mechanism to extract the energy from a rotating black hole, as it can generate negative energy plasmoids in the ergoregion. For a typical accreting black hole, the ergoregion is filled with bulk plasma plunging from the innermost-stable-circular orbit (ISCO). In this study, we present an analytical study of the energ… ▽ More Magnetic reconnection within a highly magnetized plasma has been seen as a viable mechanism to extract the energy from a rotating black hole, as it can generate negative energy plasmoids in the ergoregion. For a typical accreting black hole, the ergoregion is filled with bulk plasma plunging from the innermost-stable-circular orbit (ISCO). In this study, we present an analytical study of the energy extraction via magnetic reconnection process in the plunging region. In contrast to the toroidal plasma, where the magnetic field cannot be derived from the MHD scheme, the magnetic field in the plunging plasma was determined by the ideal-MHD condition. We derive the global magnetic field structure in a fast reconnection model, and we read the expressions for the energies of plasmoids ejected from the reconnection region, for general stationary and axisymmetric spacetimes. Then, we demonstrate the behaviors of ejected energies varying with the reconnection locations in the Kerr spacetime, and identify the region where a negative-energy plasmoid can be produced. We find that for a certain magnetization there exists a critical value of the black hole spin, beyond which the energy extraction can occur, and the energy extraction is most efficient for the near-extreme black hole. Moreover, we study the conditions necessary for a plasmoid with positive energy to escape to the infinity, a crucial requirement for effective energy extractions. Considering the escaping conditions, we provide the parameter space in the radius-spin plane in which the energy extraction mechanism is effective. △ Less

Submitted 7 November, 2024; v1 submitted 19 May, 2024; originally announced May 2024.

Energy in critical collapse

Authors: Yu Hu, Jun-Qi Guo, Junbin Li, Cheng-Gang Shao, Hongsheng Zhang

Abstract: We study the energy issue in critical collapse of a spherically symmetric scalar field. It is found that in critical collapse, the contribution from the material energy is greater than that from the gravitational energy. The quantity $m/r$ plays an important role in identifying the formation of apparent horizon in gravitational collapse, where $m$ is the Misner-Sharp mass and $r$ the areal radius.… ▽ More We study the energy issue in critical collapse of a spherically symmetric scalar field. It is found that in critical collapse, the contribution from the material energy is greater than that from the gravitational energy. The quantity $m/r$ plays an important role in identifying the formation of apparent horizon in gravitational collapse, where $m$ is the Misner-Sharp mass and $r$ the areal radius. We observe that in critical collapse, the maximum value of $m/r$ fluctuates between $2/15$ and $4/15$. This denotes a large gap between critical collapse and black hole formation for which the criterion is $m/r=1/2$. △ Less

Submitted 10 May, 2024; originally announced May 2024.

Comments: 8 pages, 7 figures

Journal ref: Commun.Theor.Phys. 75, 125402 (2023)

Does anti-Unruh effect assist quantum entanglement and coherence?

Authors: Shu-Min Wu, Xiao-Wei Teng, Jin-Xuan Li, Hao-Sheng Zeng, Tonghua Liu

Abstract: In this paper, we use the concepts of quantum entanglement and coherence to analyze the Unruh and anti-Unruh effects based on the model of Unruh-DeWitt detector. For the first time, we find that (i) the Unruh effect reduces quantum entanglement but enhances quantum coherence; (ii) the anti-Unruh effect enhances quantum entanglement but reduces quantum coherence. This surprising result refutes the… ▽ More In this paper, we use the concepts of quantum entanglement and coherence to analyze the Unruh and anti-Unruh effects based on the model of Unruh-DeWitt detector. For the first time, we find that (i) the Unruh effect reduces quantum entanglement but enhances quantum coherence; (ii) the anti-Unruh effect enhances quantum entanglement but reduces quantum coherence. This surprising result refutes the notion that the Unruh effect can only destroy quantum entanglement and coherence simultaneously, and that the anti-Unruh can only protect quantum resources. Consequently, it opens up a new source for discovering experimental evidence supporting the existence of the Unruh and anti-Unruh effects. △ Less

Submitted 23 April, 2024; originally announced April 2024.

Comments: 12 pages, 2 figures

Journal ref: New J. Phys. 26 (2024) 043016

VLBI with SKA: Possible Arrays and Astrometric Science

Authors: Yingjie Li, Ye Xu, Jingjing Li, Shuaibo Bian, Zehao Lin, Chaojie Hao, Dejian Liu

Abstract: The next generation of very long baseline interferometry (VLBI) is stepping into the era of microarcsecond ($μ$as) astronomy, and pushing astronomy, especially astrometry, to new heights. VLBI with the Square Kilometre Array (SKA), SKA-VLBI, will increase current sensitivity by an order of magnitude, and reach astrometric precision routinely below 10 $μ$as, even challenging 1 $μ$as. This advanceme… ▽ More The next generation of very long baseline interferometry (VLBI) is stepping into the era of microarcsecond ($μ$as) astronomy, and pushing astronomy, especially astrometry, to new heights. VLBI with the Square Kilometre Array (SKA), SKA-VLBI, will increase current sensitivity by an order of magnitude, and reach astrometric precision routinely below 10 $μ$as, even challenging 1 $μ$as. This advancement allows precise parallax and proper motion measurements of various celestial objects. Such improvements can be used to study objects (including isolated objects, and binary or multiple systems) in different stellar stages (such as star formation, main-sequence stars, asymptotic giant branch stars, pulsars, black holes, white dwarfs, etc.), unveil the structure and evolution of complex systems (such as the Milky Way), benchmark the international celestial reference frame, and reveal cosmic expansion. Furthermore, the theory of general relativity can also be tested with SKA-VLBI using precise measurements of light deflection under the gravitational fields of different solar system objects and the perihelion precession of solar system objects. △ Less

Submitted 22 April, 2024; originally announced April 2024.

Comments: 41 pages, 12 figures, 4 tables. Accepted to RAA (Review)

Generic gravito-magnetic clock effects

Authors: Kaye Jiale Li, Kinwah Wu, Ziri Younsi, Joana Teixeira, Dinesh Singh

Abstract: General relativity predicts that two counter-orbiting clocks around a spinning mass differ in the time required to complete the same orbit. The difference in these two values for the orbital period is generally referred to as the gravito-magnetic (GM) clock effect. It has been proposed to measure the GM clock effect using atomic clocks carried by satellites in prograde and retrograde orbits around… ▽ More General relativity predicts that two counter-orbiting clocks around a spinning mass differ in the time required to complete the same orbit. The difference in these two values for the orbital period is generally referred to as the gravito-magnetic (GM) clock effect. It has been proposed to measure the GM clock effect using atomic clocks carried by satellites in prograde and retrograde orbits around the Earth. The precision and stability required for satellites to accurately perform this measurement remains a challenge for current instrumentation. One of the most accurate clocks in the Universe is a millisecond pulsar, which emits periodic radio pulses with high stability. Timing of the pulsed signals from millisecond pulsars has proven to be very successful in testing predictions of general relativity and the GM clock effect is potentially measurable in binary systems. In this work we derive the generic GM clock effect by considering a slowly-spinning binary system on an elliptical orbit, with both arbitrary mass ratio and arbitrary spin orientations. The spin-orbit interaction introduces a perturbation to the orbit, causing the orbital plane to precess and nutate. We identify several different contributions to the clock effects: the choice of spin supplementary condition and the observer-dependent definition of a full revolution and "nearly-identical" orbits. We discuss the impact of these subtle definitions on the formula for GM clock effects and show that most of the existing formulae in the literature can be recovered under appropriate assumptions. △ Less

Submitted 25 March, 2024; originally announced March 2024.

Comments: 11 pages

Holographic entropy bound and a special class of spherical systems in cosmology

Authors: Hao Yu, Zi-Chao Lin, Jin Li

Abstract: The holographic entropy bound is discussed in cosmology. Inspired by the work of Fischler and Susskind [hep-th/9806039], we aim to define a special class of spherical systems in cosmology, within which the entropy of matter remains compliant with the holographic entropy bound throughout the evolution of the universe, irrespective of the universe's components. It is found that if the entropy of mat… ▽ More The holographic entropy bound is discussed in cosmology. Inspired by the work of Fischler and Susskind [hep-th/9806039], we aim to define a special class of spherical systems in cosmology, within which the entropy of matter remains compliant with the holographic entropy bound throughout the evolution of the universe, irrespective of the universe's components. It is found that if the entropy of matter per unit co-moving volume is bounded from above, such a special class of spherical systems indeed exists. Moreover, the matter contained within a unit co-moving volume can be replaced by a black hole of the same mass-energy. Provided that the entropy of the black hole consistently exceeds that of the matter it replaces, there is also a unified definition for these special spherical systems. △ Less

Submitted 14 October, 2025; v1 submitted 4 March, 2024; originally announced March 2024.

Comments: 13 pages (improved analysis); comments are welcome

Angular bispectrum and trispectrum of scalar-induced gravitational waves: all contributions from primordial non-Gaussianity $f_\mathrm{NL}$ and $g_\mathrm{NL}$

Authors: Jun-Peng Li, Sai Wang, Zhi-Chao Zhao, Kazunori Kohri

Abstract: Studying the primordial non-Gaussianity of inflationary perturbations is crucial for testing the inflation paradigm of the early universe. In this work, we conduct a comprehensive analysis of the angular bispectrum and trispectrum of scalar-induced gravitational waves (SIGWs) in the presence of local-type primordial non-Gaussianity parameterized by $f_\mathrm{NL}$ and $g_\mathrm{NL}$, deriving the… ▽ More Studying the primordial non-Gaussianity of inflationary perturbations is crucial for testing the inflation paradigm of the early universe. In this work, we conduct a comprehensive analysis of the angular bispectrum and trispectrum of scalar-induced gravitational waves (SIGWs) in the presence of local-type primordial non-Gaussianity parameterized by $f_\mathrm{NL}$ and $g_\mathrm{NL}$, deriving their semi-analytical formulae for the first time. Our findings indicate that it is the presence of primordial non-Gaussianity that leads to a non-Gaussian SIGW background, suggesting that the angular bispectrum and trispectrum of SIGWs could serve as probes of the primordial non-Gaussianity. Our numerical results further illustrate that $f_\mathrm{NL}$ and $g_\mathrm{NL}$ exert significant impacts on the spectral amplitudes, potentially reaching up to $10^{-5}$ for the former and $10^{-8}$ for the latter. In particular, we demonstrate that the angular bispectrum and trispectrum exhibit characteristic dependence on the angular multipoles and frequency bands. They hold potentials to be measured by gravitational-wave detectors that may advance our understanding of the origin of the universe. △ Less

Submitted 7 May, 2024; v1 submitted 29 February, 2024; originally announced March 2024.

Comments: Minor revision, version accepted for publication in JCAP

Report number: KEK-TH-2606, KEK-Cosmo-0340, KEK-QUP-2024-0004

Journal ref: JCAP05(2024)109

The Bondi-Sachs formalism for the Einstein scalar field equations with the zero cosmological constant

Authors: Jialue Li, Xiao Zhang

Abstract: Inspired by interaction of gravitational waves and dark matters, we study the Bondi-Sachs formalism for Einstein massless scalar field with zero cosmological constant. We provide asymptotic expansions for the Bondi-Sachs metrics as well as the scalar fields and prove the peeling property. We also prove the positivity of the Bondi energy-momentum under condition $c=d=0$ at some retarded time $u_0$.… ▽ More Inspired by interaction of gravitational waves and dark matters, we study the Bondi-Sachs formalism for Einstein massless scalar field with zero cosmological constant. We provide asymptotic expansions for the Bondi-Sachs metrics as well as the scalar fields and prove the peeling property. We also prove the positivity of the Bondi energy-momentum under condition $c=d=0$ at some retarded time $u_0$. This condition ensures that asymptotically null hypersurfaces near $u=u_0$ are asymptotically null initial data sets of order 2 and the positive energy theorem for null infinity can be applied. △ Less

Submitted 27 October, 2024; v1 submitted 6 February, 2024; originally announced February 2024.

Comments: 32 pages, revised version, to appear in Peking Mathematical Journal

Probing the speed of scalar-induced gravitational waves with pulsar timing arrays

Authors: Zu-Cheng Chen, Jun Li, Lang Liu, Zhu Yi

Abstract: Recently, several regional pulsar timing array collaborations, including CPTA, EPTA, PPTA, and NANOGrav, have individually reported compelling evidence for a stochastic signal at nanohertz frequencies. This signal originates potentially from scalar-induced gravitational waves associated with significant primordial curvature perturbations on small scales. In this letter, we employ data from the EPT… ▽ More Recently, several regional pulsar timing array collaborations, including CPTA, EPTA, PPTA, and NANOGrav, have individually reported compelling evidence for a stochastic signal at nanohertz frequencies. This signal originates potentially from scalar-induced gravitational waves associated with significant primordial curvature perturbations on small scales. In this letter, we employ data from the EPTA DR2, PPTA DR3, and NANOGrav 15-year data set, to explore the speed of scalar-induced gravitational waves using a comprehensive Bayesian analysis. Our results suggest that, to be consistent with pulsar timing array observations, the speed of scalar-induced gravitational waves should be $c_g \gtrsim 0.61$ at a $95\%$ credible interval for a lognormal power spectrum of curvature perturbations. Additionally, this constraint aligns with the prediction of general relativity that $c_g=1$ within a $90\%$ credible interval. Our findings underscore the capacity of pulsar timing arrays as a powerful tool for probing the speed of scalar-induced gravitational waves. △ Less

Submitted 10 May, 2024; v1 submitted 18 January, 2024; originally announced January 2024.

Comments: 8 pages, 2 figures

Journal ref: Phys. Rev. D 109, L101302 (2024)

Comparison and application of different post-Newtonian models for inspiralling stellar-mass binary black holes with space-based GW detectors

Authors: Jie Wu, Jin Li, Xiaolin Liu, Zhoujian Cao

Abstract: Space-based gravitational wave (GW) detectors are expected to detect the stellar-mass binary black holes (SBBHs) inspiralling in the low-frequency band, which exist in several years before the merger. Accurate GW waveforms in the inspiral phase are crucial for the detection and analysis of those SBBHs. In our study, based on post-Newtonian (PN) models, we investigate the differences in the detecti… ▽ More Space-based gravitational wave (GW) detectors are expected to detect the stellar-mass binary black holes (SBBHs) inspiralling in the low-frequency band, which exist in several years before the merger. Accurate GW waveforms in the inspiral phase are crucial for the detection and analysis of those SBBHs. In our study, based on post-Newtonian (PN) models, we investigate the differences in the detection, accuracy requirement, and parameter estimation of SBBHs in the cases of LISA, Taiji, and their joint detection. We find that low-order PN models are sufficient for simulating low-mass ($\le 50\ \mathrm{M}_\odot$) SBBHs population. Moreover, for detectable SBBHs in space-based GW detectors, over 90% of the GW signals from low-order PN models meet accuracy requirement. Additionally, different PN models do not exhibit significant differences in Bayesian inference. Our research provides a comprehensive reference for balancing computational resources and the desired accuracy of GW waveform generation. It highlights the suitability of low-order PN models for simulating SBBHs and emphasizes their potential in the detection and parameter estimation of SBBHs. △ Less

Submitted 7 May, 2024; v1 submitted 5 January, 2024; originally announced January 2024.

Comments: 16 pages, 11 figures

Journal ref: Phys.Rev.D 109 (2024) 10, 104014

Parameter Estimation for Intermediate-Mass Binary Black Holes through Gravitational Waves Observed by DECIGO

Authors: Mengfei Sun, Jin Li

Abstract: With the anticipated launch of space-based gravitational wave detectors, including LISA, TaiJi, TianQin, and DECIGO, expected around 2030, the detection of gravitational waves generated by intermediate-mass black hole binaries (IMBBHs) becomes a tangible prospect. However, due to the detector's reception of a substantial amount of non-Gaussian, non-stationary data, employing traditional Bayesian i… ▽ More With the anticipated launch of space-based gravitational wave detectors, including LISA, TaiJi, TianQin, and DECIGO, expected around 2030, the detection of gravitational waves generated by intermediate-mass black hole binaries (IMBBHs) becomes a tangible prospect. However, due to the detector's reception of a substantial amount of non-Gaussian, non-stationary data, employing traditional Bayesian inference methods for parameter estimation would result in significant resource demands and limitations in the waveform template library. Therefore, in this paper, we simulated foreground noise induced by stellar-origin binary black holes (SOBBHs), which is non-Gaussian and non-stationary, and we explore the use of Gaussian process regression (GPR) and deep learning for parameter estimation of Intermediate Mass Binary Black Holes (IMBBHs) in the presence of such non-Gaussian, non-stationary background noise. By comparing these results from deep learning and GPR, we demonstrate that deep learning can offer improved precision in parameter estimation compared to traditional GPR. Furthermore, compared to GPR, deep learning can provide posterior distributions of the sample parameters faster. △ Less

Submitted 12 December, 2023; originally announced December 2023.

Observational appearance and additional photon rings of the asymmetric thin-shell wormhole in Horndeski theory

Authors: Zhi Luo, Hao Yu, Jin Li

Abstract: In this paper, we study the observational appearance of the asymmetric thin-shell wormhole (ATW) in Horndeski theory by employing the ray-tracing method. We first calculate the effective potential and null geodesic of the ATW, and then we obtain the deflection angle of the photon in the ATW spacetime. Based on the impact parameter of the photon, the trajectory of the photon can be classified into… ▽ More In this paper, we study the observational appearance of the asymmetric thin-shell wormhole (ATW) in Horndeski theory by employing the ray-tracing method. We first calculate the effective potential and null geodesic of the ATW, and then we obtain the deflection angle of the photon in the ATW spacetime. Based on the impact parameter of the photon, the trajectory of the photon can be classified into three cases. Two typical emission models of the thin accretion disk are considered to analyze the observational appearance of the ATW. By comparing the observational appearances of the ATW and a black hole with the same mass parameter, we find additional features in the observational appearance of the ATW, such as the ``lensing band" and ``photon ring group". △ Less

Submitted 16 January, 2024; v1 submitted 12 December, 2023; originally announced December 2023.

Comments: 17 pages, 7 figures

Measuring the speed of scalar induced gravitational waves from observations

Authors: Jun Li, Guang-Hai Guo

Abstract: We investigate the scalar induced gravitational waves which propagate with a speed different from the speed of light. First, we analytically calculate the expression of the power spectrum of the scalar induced gravitational waves which is based on the speed and the spectrum of the primordial curvature perturbations. Then, we discuss several scalar power spectra and obtain corresponding fractional… ▽ More We investigate the scalar induced gravitational waves which propagate with a speed different from the speed of light. First, we analytically calculate the expression of the power spectrum of the scalar induced gravitational waves which is based on the speed and the spectrum of the primordial curvature perturbations. Then, we discuss several scalar power spectra and obtain corresponding fractional energy density, such as the monochromatic power spectrum, the scale invariant power spectrum and the power-law power spectrum. Finally, we constrain the scalar induced gravitational waves and evaluate the signatures of the speed from the combination of CMB+BAO and gravitational waves observations. The numerical results are obvious to reveal the influence of speed of scalar induced gravitational waves. △ Less

Submitted 5 December, 2023; originally announced December 2023.

Comments: arXiv admin note: text overlap with arXiv:2204.09237

Genuinely accessible and inaccessible entanglement in Schwarzschild black hole

Authors: Shu-Min Wu, Xiao-Wei Teng, Jin-Xuan Li, Si-Han Li, Tong-Hua Liu, Jie-Ci Wang

Abstract: The genuine entanglement of Dirac fields for an N-partite system is investigated in Schwarzschild spacetime and the analysis is carried out using the single-mode approximation. Due to the Hawking effect, quantum entanglement is divided into two parts physically accessible and inaccessible entanglement. We obtain a general analytic expression of genuine N-partite entanglement that includes all acce… ▽ More The genuine entanglement of Dirac fields for an N-partite system is investigated in Schwarzschild spacetime and the analysis is carried out using the single-mode approximation. Due to the Hawking effect, quantum entanglement is divided into two parts physically accessible and inaccessible entanglement. We obtain a general analytic expression of genuine N-partite entanglement that includes all accessible and inaccessible entanglement in a Schwarzschild black hole. Unlike bosonic entanglement, the accessible N-partite entanglement of Dirac fields monotonically decreases to a nonzero value with the Hawking temperature. Interestingly, the inaccessible N-partite entanglement is a monotonic or non-monotonic function of the Hawking temperature, depending on the ratio between accessible and inaccessible modes, in contrast to bipartite or tripartite entanglement that is only a monotonic function of the Hawking temperature. Finally, we obtain two restrictive relationships for the quantum information of the black hole. This conclusion provides a new understanding of Hawking effect of the black hole. △ Less

Submitted 21 November, 2023; originally announced November 2023.

Comments: 14 pages, 1 figure

Journal ref: Phys. Lett. B 848 (2024) 138334

Fermionic steering is not nonlocal in the background of dilaton black hole

Authors: Shu-Min Wu, Jin-Xuan Li, Xiao-Ying Jiang, Xiao-Wei Teng, Xiao-Li Huang, Jianbo Lu

Abstract: We study the redistribution of the fermionic steering and the relation among fermionic Bell nonlocality, steering, and entanglement in the background of the Garfinkle-Horowitz-Strominger dilaton black hole. We analyze the meaning of the fermionic steering in terms of the Bell inequality in curved spacetime. We find that the fermionic steering, which is previously found to survive in the extreme di… ▽ More We study the redistribution of the fermionic steering and the relation among fermionic Bell nonlocality, steering, and entanglement in the background of the Garfinkle-Horowitz-Strominger dilaton black hole. We analyze the meaning of the fermionic steering in terms of the Bell inequality in curved spacetime. We find that the fermionic steering, which is previously found to survive in the extreme dilaton black hole, cannot be considered to be nonlocal. We also find that the dilaton gravity can redistribute the fermionic steering, but cannot redistribute Bell nonlocality, which means that the physically inaccessible steering is also not nonlocal. Unlike the inaccessible entanglement, the inaccessible steering may increase non-monotonically with the dilaton. Furthermore, we obtain some monogamy relations between the fermionic steering and entanglement in dilaton spacetime. In addition, we show the difference between the fermionic and bosonic steering in curved spacetime. △ Less

Submitted 16 February, 2024; v1 submitted 15 November, 2023; originally announced November 2023.

Comments: 21 pages, 4 figures

Journal ref: Eur. Phys. J. C (2024) 84:161

The ability of Lisa, Taiji, and their networks to detect the stochastic gravitational wave background generated by Cosmic Strings

Authors: Bo-Rui Wang, Jin Li

Abstract: The cosmic string contributes to our understanding and revelation of the fundamental structure and evolutionary patterns of the universe, unifying our knowledge of the cosmos and unveiling new physical laws and phenomena. Therefore, we anticipate the detection of Stochastic Gravitational Wave Background (SGWB) signals generated by cosmic strings in space-based detectors. We have analyzed the detec… ▽ More The cosmic string contributes to our understanding and revelation of the fundamental structure and evolutionary patterns of the universe, unifying our knowledge of the cosmos and unveiling new physical laws and phenomena. Therefore, we anticipate the detection of Stochastic Gravitational Wave Background (SGWB) signals generated by cosmic strings in space-based detectors. We have analyzed the detection capabilities of individual space-based detectors, Lisa and Taiji, as well as the joint space-based detector network, Lisa-Taiji, for SGWB signals produced by cosmic strings, taking into account other astronomical noise sources. The results indicate that the Lisa-Taiji network exhibits superior capabilities in detecting SGWB signals generated by cosmic strings and can provide strong evidence. The Lisa-Taiji network can achieve an uncertainty estimation of $ΔGμ/Gμ<0.5$ for cosmic string tension $Gμ\sim4\times10^{-17}$, and can provide evidence for the presence of SGWB signals generated by cosmic strings at $Gμ\sim10^{-17}$, and strong evidence at $Gμ\sim10^{-16}$. Even in the presence of only SGWB signals, it can achieve a relative uncertainty of $ΔGμ/Gμ<0.5$ for cosmic string tension $Gμ<10^{-18}$, and provide strong evidence at $Gμ\sim10^{-17}$. △ Less

Submitted 13 November, 2023; originally announced November 2023.

Complete analysis of the background and anisotropies of scalar-induced gravitational waves: primordial non-Gaussianity $f_{\mathrm{NL}}$ and $g_{\mathrm{NL}}$ considered

Authors: Jun-Peng Li, Sai Wang, Zhi-Chao Zhao, Kazunori Kohri

Abstract: Investigation of primordial non-Gaussianity holds immense importance in testing the inflation paradigm and shedding light on the physics of the early Universe. In this study, we conduct the complete analysis of scalar-induced gravitational waves (SIGWs) by incorporating the local-type non-Gaussianity $f_{\mathrm{NL}}$ and $g_{\mathrm{NL}}$. We develop Feynman-like diagrammatic technique and derive… ▽ More Investigation of primordial non-Gaussianity holds immense importance in testing the inflation paradigm and shedding light on the physics of the early Universe. In this study, we conduct the complete analysis of scalar-induced gravitational waves (SIGWs) by incorporating the local-type non-Gaussianity $f_{\mathrm{NL}}$ and $g_{\mathrm{NL}}$. We develop Feynman-like diagrammatic technique and derive semi-analytic formulas for both the energy-density fraction spectrum and the angular power spectrum. For the energy-density fraction spectrum, we analyze all the relevant Feynman-like diagrams, determining their contributions to the spectrum in an order-by-order fashion. As for the angular power spectrum, our focus lies on the initial inhomogeneities, giving rise to anisotropies in SIGWs, that arise from the coupling between short- and long-wavelength modes due to primordial non-Gaussianity. Our analysis reveals that this spectrum exhibits a typical multipole dependence, characterized by $\tilde{C}_{\ell}\propto[\ell(\ell+1)]^{-1}$, which plays a crucial role in distinguishing between different sources of gravitational waves. Depending on model parameters, significant anisotropies can be achieved. We also show that the degeneracies in model parameters can be broken. The findings of our study underscore the angular power spectrum as a robust probe for investigating primordial non-Gaussianity and the physics of the early Universe. Moreover, our theoretical predictions can be tested using space-borne gravitational-wave detectors and pulsar timing arrays. △ Less

Submitted 29 May, 2024; v1 submitted 14 September, 2023; originally announced September 2023.

Comments: 49 pages, 18 figures, 3 appendices, Version accepted for publication in JCAP

Report number: KEK-Cosmo-0326, KEK-TH-2556, KEK-QUP-2023-0024, https://github.com/Zhi-ChaoZhao/sigw_class

Journal ref: JCAP06(2024)039

Corrections to the thermodynamic quantities of Bose system by the generalized uncertainty principle

Authors: Jun-Xian Li, Jing-Yi Zhang

Abstract: This paper investigated the Bose system in a spherical shell close to the black hole horizon. Several thermodynamic quantities of the Bose system are derived, which are different from those in the flat spacetime, by introducing the generalized uncertainty principle (GUP) into the grand partition function of statistical mechanics. The internal energy and the pressure of the Bose system appear to ha… ▽ More This paper investigated the Bose system in a spherical shell close to the black hole horizon. Several thermodynamic quantities of the Bose system are derived, which are different from those in the flat spacetime, by introducing the generalized uncertainty principle (GUP) into the grand partition function of statistical mechanics. The internal energy and the pressure of the Bose system appear to have a correction term of $T^6$, while the entropy has a $T^5$ correction term where both the coefficients are functions of the spacetime component $g_{00}$ and the brick-wall model parameter $ε$. Taking the Schwarzschild black hole as an example, the physical quantities of the shell such as temperature, pressure and entropy are calculated for the final stage of black hole radiation. △ Less

Submitted 3 August, 2023; originally announced August 2023.

Journal ref: EPL 139 69003 (2022)

Subtraction of the confusion foreground and parameter uncertainty of resolvable galactic binaries on the networks of space-based gravitational-wave detectors

Authors: Jie Wu, Jin Li

Abstract: There are tens of millions of compact binary systems in the Milky Way, called galactic binaries (GBs), most of which are unresolved, and the Gravitational waves (GWs) emitted overlap to form foreground confusion. By simulating such foreground confusion, we have studied how LISA, Taiji and TianQin, including their alternative orbital configurations, subtract resolvable GBs when they combine as some… ▽ More There are tens of millions of compact binary systems in the Milky Way, called galactic binaries (GBs), most of which are unresolved, and the Gravitational waves (GWs) emitted overlap to form foreground confusion. By simulating such foreground confusion, we have studied how LISA, Taiji and TianQin, including their alternative orbital configurations, subtract resolvable GBs when they combine as some networks. The results of our research indicate that the order of detected number for a single detector from high to low is: Taiji-m, Taiji-p (c), LISA, TianQin I, TianQin II. For detector combinations on the network, the foreground confusion is effectively reduced as the number of detectors grows, and the optimal combinations with different numbers are: Taiji-m, LISA+Taiji-m, LISA+Taiji-m+TianQin I, and LISA+Taiji-m+TianQin I+II. The sensitivity curve is optimized as the number of detectors increases, which renders it possible to detect other gravitational wave sources more precisely and decrease the resolvable GBs parameter uncertainty. Based on this, we discuss the parameter uncertainty of resolvable GBs detected by the combinations above and find that GW detection can promote electromagnetic (EM) detection. On the contrary, we discovered that by utilizing EM detection, determining the inclination angle can reduce the uncertainty of GW strain amplitude by $\sim$93%, and determining the sky position can reduce the uncertainty of the phase by $\sim$30%, further strengthening the connection between GW detection and EM detection, and contributing to the research of Multi-messenger astronomy. △ Less

Submitted 20 December, 2023; v1 submitted 9 July, 2023; originally announced July 2023.

Comments: 13 pages, 8 figures

Journal ref: Phys. Rev. D 108, 124047 (2023) [gr-qc]

Curvature-enhanced multipartite coherence in the multiverse

Authors: Shu-Min Wu, Chun-Xu Wang, Rui-Di Wang, Jin-Xuan Li, Xiao-Li Huang, Hao-Sheng Zeng

Abstract: Here, we study quantum coherence of N-partite GHZ (Greenberger-Horne-Zeilinger) and W states in the multiverse consisting of N causally disconnected de Sitter spaces. Interestingly, N-partite coherence increases monotonically as the curvature increases, while the Unruh effect destroys multipartite coherence in Rindler spacetime. Conversely, the curvature effect destroys quantum entanglement and di… ▽ More Here, we study quantum coherence of N-partite GHZ (Greenberger-Horne-Zeilinger) and W states in the multiverse consisting of N causally disconnected de Sitter spaces. Interestingly, N-partite coherence increases monotonically as the curvature increases, while the Unruh effect destroys multipartite coherence in Rindler spacetime. Conversely, the curvature effect destroys quantum entanglement and discord, meaning that the curvature effect is beneficial to quantum coherence and harmful to quantum correlations in the multiverse. We find that, with the increase of n expanding de Sitter spaces, N-partite coherence of GHZ state increases monotonically for any curvature, while quantum coherence of the W state decreases or increases monotonically depending on the curvature. We find a distribution relationship, which indicates that the correlated coherence of N-partite W state is equal to the sum of all bipartite correlated coherence in the multiverse. Multipartite coherence exhibits unique properties in the multiverse, which argues that it may provide some evidence for the existence of the multiverse. △ Less

Submitted 20 June, 2024; v1 submitted 2 July, 2023; originally announced July 2023.

Comments: 26 pages, 8 figures

Journal ref: Chin. Phys. C 48, 075107 (2024)

Implications of Pulsar Timing Array Data for Scalar-Induced Gravitational Waves and Primordial Black Holes: Primordial Non-Gaussianity $f_{\mathrm{NL}}$ Considered

Authors: Sai Wang, Zhi-Chao Zhao, Jun-Peng Li, Qing-Hua Zhu

Abstract: Multiple pulsar-timing-array collaborations have reported strong evidence for the existence of a gravitational-wave background. We study physical implications of this signal for cosmology, assuming that it is attributed to scalar-induced gravitational waves. By incorporating primordial non-Gaussianity $f_{\mathrm{NL}}$, we specifically examine the nature of primordial curvature perturbations and p… ▽ More Multiple pulsar-timing-array collaborations have reported strong evidence for the existence of a gravitational-wave background. We study physical implications of this signal for cosmology, assuming that it is attributed to scalar-induced gravitational waves. By incorporating primordial non-Gaussianity $f_{\mathrm{NL}}$, we specifically examine the nature of primordial curvature perturbations and primordial black holes. We find that the signal allows for a primordial non-Gaussianity $f_{\mathrm{NL}}$ in the range of $-4.1\lesssim f_{\mathrm{NL}} \lesssim 4.1$ (68\% confidence intervals) and a mass range for primordial black holes $m_{\mathrm{pbh}}$ spanning from $\sim10^{-5}M_{\odot}$ to $\sim10^{-2}M_{\odot}$. Furthermore, we find that the signal favors a negative non-Gaussianity, which can suppress the abundance of primordial black holes. We also demonstrate that the anisotropies of scalar-induced gravitational waves serve as a powerful tool to probe the non-Gaussianity $f_{\mathrm{NL}}$. We conduct a comprehensive analysis of the angular power spectrum within the nano-Hertz band. Looking ahead, we anticipate that future projects, such as the Square Kilometre Array, will have the potential to measure these anisotropies and provide further insights into the primordial universe. △ Less

Submitted 27 September, 2023; v1 submitted 2 July, 2023; originally announced July 2023.

Comments: Major revisions, 2 columns, 8 pages, 4 figures, 1 appendix

Report number: version-01, https://github.com/Zhi-ChaoZhao/sigw_class

Journal ref: Phys. Rev. Research 6, L012060 (2024)

The Joule--Thomson and Joule--Thomson-like effects of the black holes in a cavity

Authors: Nan Li, Jin-Yu Li, Bing-Yu Su

Abstract: When a black hole is enclosed in a cavity in asymptotically flat space, an effective volume can be introduced, and an effective pressure can be further defined as its conjugate variable. By this means, an extended phase space is constructed in a cavity, which resembles that in the anti-de Sitter (AdS) space in many aspects. However, there are still some notable dissimilarities simultaneously. In t… ▽ More When a black hole is enclosed in a cavity in asymptotically flat space, an effective volume can be introduced, and an effective pressure can be further defined as its conjugate variable. By this means, an extended phase space is constructed in a cavity, which resembles that in the anti-de Sitter (AdS) space in many aspects. However, there are still some notable dissimilarities simultaneously. In this work, the Joule--Thomson (JT) effect of the black holes, widely discussed in the AdS space as an isenthalpic (constant-mass) process, is shown to only have cooling region in a cavity. On the contrary, in a constant-thermal-energy process (the JT-like effect), there is only heating region in a cavity. Altogether, different from the AdS case, there is no inversion temperature or inversion curve in a cavity. Our work reveals the subtle discrepancy between the two different extended phase spaces that is sensitive to the specific boundary conditions. △ Less

Submitted 2 July, 2023; v1 submitted 28 June, 2023; originally announced June 2023.

Comments: 19 pages, 2 figures

Journal ref: Fortsch. Phys. 71 (2023), 2200166

Primordial Non-Gaussianity $f_{\mathrm{NL}}$ and Anisotropies in Scalar-Induced Gravitational Waves

Authors: Jun-Peng Li, Sai Wang, Zhi-Chao Zhao, Kazunori Kohri

Abstract: Primordial non-Gaussianity encodes vital information of the physics of the early universe, particularly during the inflationary epoch. To explore the local-type primordial non-Gaussianity $f_{\mathrm{NL}}$, we study the anisotropies in gravitational wave background induced by the linear cosmological scalar perturbations during radiation domination in the early universe. We provide the first comple… ▽ More Primordial non-Gaussianity encodes vital information of the physics of the early universe, particularly during the inflationary epoch. To explore the local-type primordial non-Gaussianity $f_{\mathrm{NL}}$, we study the anisotropies in gravitational wave background induced by the linear cosmological scalar perturbations during radiation domination in the early universe. We provide the first complete analysis to the angular power spectrum of such scalar-induced gravitational waves. The spectrum is expressed in terms of the initial inhomogeneities, the Sachs-Wolfe effect, and their crossing. It is anticipated to have frequency dependence and multipole dependence, i.e., $C_\ell(ν)\propto [\ell(\ell+1)]^{-1}$ with $ν$ being a frequency and $\ell$ referring to the $\ell$-th spherical harmonic multipole. In particular, the initial inhomogeneites in this background depend on gravitational-wave frequency. These properties are potentially useful for the component separation, foreground removal, and breaking degeneracies in model parameters, making the non-Gaussian parameter $f_{\mathrm{NL}}$ measurable. Further, theoretical expectations may be tested by space-borne gravitational-wave detectors in future. △ Less

Submitted 7 October, 2023; v1 submitted 31 May, 2023; originally announced May 2023.

Comments: Extended version, 40 pages, 16 figures, matched with acceptance by JCAP

Report number: KEK-Cosmo-0315, KEK-TH-2531, KEK-QUP-2023-0012, https://github.com/Zhi-ChaoZhao/sigw_class

Journal ref: JCAP10(2023)056

Massive white dwarfs in Rastall-Rainbow gravity

Authors: Jie Li, Bo Yang, Wenbin Lin

Abstract: We investigate the hydrostatic equilibrium of white dwarfs within the framework of Rastall-Rainbow gravity, aiming to explore the effects of this modified gravitational theory on their properties. By employing the Chandrasekhar equation of state in conjunction with the modified Tolman-Oppenheimer-Volkoff equation, we derive the mass-radius relations for white dwarfs. Our results show that the maxi… ▽ More We investigate the hydrostatic equilibrium of white dwarfs within the framework of Rastall-Rainbow gravity, aiming to explore the effects of this modified gravitational theory on their properties. By employing the Chandrasekhar equation of state in conjunction with the modified Tolman-Oppenheimer-Volkoff equation, we derive the mass-radius relations for white dwarfs. Our results show that the maximum mass of white dwarfs deviates significantly from the predictions of general relativity, potentially exceeding the Chandrasekhar limit. Furthermore, we discuss other properties of white dwarfs, such as the gravitational redshift, compactness and dynamical stability, shedding light on their behavior within the context of this modified gravitational framework. △ Less

Submitted 28 May, 2023; originally announced May 2023.

Comments: 13 pages,5 figures

Electromagnetic counterparts of high-frequency gravitational waves in a rotating laboratory frame system and their detection

Authors: Fang-Yu Li, Hao Yu, Jin Li, Lian-Fu Wei, Qing-Quan Jiang

Abstract: We consider the perturbative photon flows (PPFs, i.e., electromagnetic (EM) counterparts) generated by the EM resonance response to high-frequency gravitational waves (HFGWs) with additional polarization states in a rotating laboratory frame system. It is found that when the propagating direction of HFGWs and the symmetrical axis of the laboratory frame system are the same, the PPFs have the maxim… ▽ More We consider the perturbative photon flows (PPFs, i.e., electromagnetic (EM) counterparts) generated by the EM resonance response to high-frequency gravitational waves (HFGWs) with additional polarization states in a rotating laboratory frame system. It is found that when the propagating direction of HFGWs and the symmetrical axis of the laboratory frame system are the same, the PPFs have the maximum value. In this case, using the rotation (the rotation of the azimuth $φ$) of the EM detection system, all six possible polarization states of HFGWs can be separated and displayed. For the current experimental conditions, it is quite prospective to detect the PPFs generated by the HFGWs predicted in the braneworld models, the primordial black hole theories, the interaction mechanism between astrophysical plasma and intense EM radiation, etc., due to the large amplitudes (or high spectral densities) and spectral characteristics of these HFGWs. Detecting the primordial HFGWs from inflation faces great challenges at present, but it is not impossible. △ Less

Submitted 24 October, 2023; v1 submitted 7 March, 2023; originally announced March 2023.

Comments: 31 pages, 8 figures, 1 table; minor change according to the published version

Journal ref: Phys.Rev.D 108 (2023) 6, 065014

Shadow thermodynamics of the Hayward-AdS black hole

Authors: Zhi Luo, Hao Yu, Shuo Cao, Jin Li

Abstract: In this paper, the phase structure of the Hayward-AdS black hole (BH) is studied using shadow formalism. It has been found that the shadow radius is a monotonic function of the horizon radius and can therefore play an equivalent role to the horizon radius in characterizing the thermodynamics of Hayward-AdS BH. The thermodynamic phase transition (PT) of the Hayward-AdS BH is investigated with the s… ▽ More In this paper, the phase structure of the Hayward-AdS black hole (BH) is studied using shadow formalism. It has been found that the shadow radius is a monotonic function of the horizon radius and can therefore play an equivalent role to the horizon radius in characterizing the thermodynamics of Hayward-AdS BH. The thermodynamic phase transition (PT) of the Hayward-AdS BH is investigated with the shadow radius. It is shown that as the magnetic charge increases, the shadow radius becomes larger, while the coexistence temperature becomes lower. The thermal profile of the Hayward-AdS BH is established by combining the temperature diagram and the shadow cast diagram, which shows that for a fixed magnetic charge, the temperature of the Hayward-AdS BH increases with the pressure while the region of the thermal profile decreases with the pressure. In particular, the temperature of the Hayward-AdS BH follows an N-type change trend when it is smaller than the critical temperature. This imply that the BH shadow may be used to investigate the thermodynamics of the Hayward-AdS BH. △ Less

Submitted 15 January, 2023; originally announced January 2023.

Comments: 14 pages, 6 figures