Showing 1–50 of 72 results for author: Neto, A

Position measurement of a levitated particle with vectorial light

Authors: Daniel Tandeitnik, Lucas Bianchi, Sebastian Gutierrez-Bernal, Joanna A. Zielińska, Paulo A. Maia Neto, Thiago Guerreiro

Abstract: We develop a fully vectorial, semiclassical scattering formalism for optically levitated dipolar scatterers, expressed within the angular spectrum representation and applicable to arbitrary trapping-field configurations as well as to high--numerical-aperture focusing. Within this framework, we introduce the information radiation pattern to characterize the angular distribution of position-dependen… ▽ More We develop a fully vectorial, semiclassical scattering formalism for optically levitated dipolar scatterers, expressed within the angular spectrum representation and applicable to arbitrary trapping-field configurations as well as to high--numerical-aperture focusing. Within this framework, we introduce the information radiation pattern to characterize the angular distribution of position-dependent information and use a Richards--Wolf projection of the scattered field onto the local-oscillator mode to quantify the resulting mode-matching efficiency, yielding experimentally realistic forward- and backward-detection efficiencies. As a worked example, we apply the formalism to a radially polarized trapping beam and confirm that the axial recoil heating rate is reduced relative to a conventional linearly polarized Gaussian tweezer. The theoretical framework is implemented in LevitationToolbox, an open-source Python package intended to support the design and optimization of near-Heisenberg-limited levitated optomechanical experiments. △ Less

Submitted 26 July, 2026; originally announced July 2026.

Enantioselective optical trapping and characterization of all dielectric disorder-enabled chiral particles

Authors: Guilherme T. Moura, Tanja Schoger, Kainã G. Diniz, Marcel A. B. Morte, Diney S. Ether Jr, Leonardo de S. Menezes, Yicui Kang, Emiliano Cortés, Cyriaque Genet, Nathan B. Viana, Felipe A. Pinheiro, Paulo A. Maia Neto

Abstract: We trap submicroscopic silica spheres coated with randomly distributed titanium dioxide nanoparticles in optical tweezers with Laguerre-Gaussian modes and observe orbital dynamics that differ from those of achiral silica spheres. We show that the disordered nanoparticle coating generates an effective chiral geometry, giving rise to enhanced enantioselective chiral optical forces and a measurable m… ▽ More We trap submicroscopic silica spheres coated with randomly distributed titanium dioxide nanoparticles in optical tweezers with Laguerre-Gaussian modes and observe orbital dynamics that differ from those of achiral silica spheres. We show that the disordered nanoparticle coating generates an effective chiral geometry, giving rise to enhanced enantioselective chiral optical forces and a measurable modification of the orbital period. A theoretical model based on the Mie-Debye formalism, including optical aberrations, not only quantitatively explains the experimental results but also allows to characterize the Pasteur parameter quantifying the chiroptical response of individual composite particles. These findings constitute direct experimental evidence of chiral optical forces exerted by structured light beams on individual chiral particles and identify disorder-enabled, all-dielectric particles as a versatile material platform to tailor chiral optical forces at the nanoscale. △ Less

Submitted 21 July, 2026; originally announced July 2026.

Electron Paramagnetic Resonance Study of Radical Species on NaNbO3@CeO2-Modified Carbon Vulcan XC72 Gas Diffusion Electrode for Electrochemical Degradation of Paracetamol via Electro-Fenton

Authors: Caio Machado Fernandes, Joao Paulo C. Moura, Aline B. Trench, Rafael Sotana, Ana Maria P. Neto, Willy G. Santos, Mauro C. Santos

Abstract: While electrochemical oxidation is a promising technology for water treatment, a fundamental understanding of the specific radical mechanisms involved in pharmaceutical degradation has remained limited. This study addresses this gap by employing Electron Paramagnetic Resonance (EPR) spectroscopy to directly quantify the radical species generated during the degradation of paracetamol using a novel… ▽ More While electrochemical oxidation is a promising technology for water treatment, a fundamental understanding of the specific radical mechanisms involved in pharmaceutical degradation has remained limited. This study addresses this gap by employing Electron Paramagnetic Resonance (EPR) spectroscopy to directly quantify the radical species generated during the degradation of paracetamol using a novel gas diffusion electrode (GDE) modified with NaNbO3 nanocubes and CeO2 nanorods. This approach provides a critical advancement beyond prior literature by moving from indirect inference to direct, quantitative analysis of reactive species. Results demonstrated that a boron-doped diamond (BDD) anode (65% OH radical, 35% aryl radicals) drastically outperformed a Platinum (Pt) anode (74% OH radical, 26% aryl radicals), achieving complete degradation in 15 minutes versus 45 minutes and 81.6% versus 67.8% mineralization. Consequently, this work provides a foundational mechanistic framework that fundamentally advances the field, offering not just a more effective material system (BDD/NaNbO3@CeO2-GDE) but also a validated methodology for rationally designing and optimizing electrochemical water treatment processes based on quantifiable radical pathways. △ Less

Submitted 8 June, 2026; originally announced June 2026.

Deep brain microelectrode signal: $q$-statistical approach

Authors: Ana Luiza Souza Tavares, Henrique Santos Lima, Artur Pedro Martins Neto, Bruno Duarte Gomes, Constantino Tsallis

Abstract: We characterize the amplitude statistics of intraoperative microelectrode recordings (MERs) obtained during deep brain stimulation (DBS) surgery in 46 patients with Parkinson's disease, using 184 recordings equally balanced between inside and outside the subthalamic nucleus (STN). The probability density of every recording is quantitatively well described by a $q$-Gaussian (grounded on a nonadditi… ▽ More We characterize the amplitude statistics of intraoperative microelectrode recordings (MERs) obtained during deep brain stimulation (DBS) surgery in 46 patients with Parkinson's disease, using 184 recordings equally balanced between inside and outside the subthalamic nucleus (STN). The probability density of every recording is quantitatively well described by a $q$-Gaussian (grounded on a nonadditive entropic functional), $ρ(x) \propto [1 + β(q-1) x^2]^{-1/(q-1)}$, with $q > 1$ in all cases, reflecting persistent long-range temporal correlations inconsistent with Gaussian dynamics. Within the superstatistics framework, the slowly fluctuating local variance visible in the raw MER signals is a physical mechanism that directly generates the $q > 1$ form. Beyond individual fits, $q$ and $β$ collapse across all 184 recordings onto the single functional constraint $q = 3 - 1.85\,β^{-0.33}$ ($R \approx -0.91$), a reduction to one effective degree of freedom that is the quantitative hallmark of near-critical dynamics, previously identified in scale-free network growth and in acoustic precursors of material fracture. The index $q$ is statistically indistinguishable across the STN boundary ($\langle\bar{q}_\text{out}/\bar{q}_\text{in} \rangle = 1.03$), while the inverse-widthparameter shows a modest systematic difference ($\langle\barβ_\text{out}/\barβ_\text{in} \rangle = 1.18$). Since $q > 1$ is expected for any brain structure exhibiting long-range correlations, healthy or pathological, it is the tight $q(β)$ coupling, not $q > 1$ per se, that constitutes the candidate near-criticality signature of the parkinsonian cortico-basal-ganglia-thalamocortical loop. △ Less

Submitted 28 March, 2026; originally announced March 2026.

Comments: 13 pages and 4 figures

Intermediate Thermal Equilibrium Stages in Molecular Dynamics Simulations of two Bodies in Contact

Authors: Jonathas N. da Silva, Octavio D. Rodriguez Salmon, Minos A. Neto

Abstract: The Zeroth Law of Thermodynamics states that if two systems are in thermal equilibrium with a third one, then they are also in equilibrium with each other. This study explores not only the final state of thermal equilibrium between ideal gases separated by heat-conducting walls, but also the intermediate stages leading up to equilibrium, using classical molecular dynamics simulations. Two- and thr… ▽ More The Zeroth Law of Thermodynamics states that if two systems are in thermal equilibrium with a third one, then they are also in equilibrium with each other. This study explores not only the final state of thermal equilibrium between ideal gases separated by heat-conducting walls, but also the intermediate stages leading up to equilibrium, using classical molecular dynamics simulations. Two- and three-region models with argon atoms are analyzed. Fluctuations, correlations, and temperature distributions are observed, highlighting how heat conduction between regions influences the time to reach equilibrium. This work is distinguished by its detailed analysis of the intermediate stages that occur until the system reaches thermal equilibrium, in accordance with the Zeroth Law of Thermodynamics. △ Less

Submitted 11 February, 2026; originally announced February 2026.

Comments: 15 pages, 12 figures

Casimir effect with dielectric matter in salted water and implications at the cell scale

Authors: Larissa Inácio, Felipe S. S. Rosa, Astrid Lambrecht, Paulo A. Maia Neto, Serge Reynaud

Abstract: The Casimir interaction in salted water contains a universal contribution of electromagnetic fluctuations that makes it of a longer range than previously thought. The universal contribution dominates non universal ones at the distances relevant for actin fibers inside the cell. We discuss universal and non-universal contributions with a model mimicking biological matter. We also show that the univ… ▽ More The Casimir interaction in salted water contains a universal contribution of electromagnetic fluctuations that makes it of a longer range than previously thought. The universal contribution dominates non universal ones at the distances relevant for actin fibers inside the cell. We discuss universal and non-universal contributions with a model mimicking biological matter. We also show that the universal Casimir effect should have important implications at the cell scale. △ Less

Submitted 11 March, 2026; v1 submitted 13 January, 2026; originally announced January 2026.

Comments: 13 pages, 9 figures

Journal ref: Physics 2026, 8, 40

Evolving spatiotemporal patterns and urban scaling of deaths from external causes

Authors: Cesar I. N. Sampaio Filho, Humberto A. Carmona, Antonio S. Lima Neto, Monica V. Prates, Haroldo V. Ribeiro, Marcia C. Castro, Jose S. Andrade Jr

Abstract: Urban scaling theory posits that urban indicators follow power-law relations with population, yet the evolution of these patterns - and the role of regional differences in settings marked by social inequalities and unplanned urbanization - remains poorly understood. Here, we analyze nearly three decades of mortality data from Brazilian cities to investigate the scaling of external causes of death:… ▽ More Urban scaling theory posits that urban indicators follow power-law relations with population, yet the evolution of these patterns - and the role of regional differences in settings marked by social inequalities and unplanned urbanization - remains poorly understood. Here, we analyze nearly three decades of mortality data from Brazilian cities to investigate the scaling of external causes of death: homicides, suicides, and accidents. Using a hierarchical Bayesian framework and spatial correlation analysis, we find that these mortality indicators exhibit distinct, regionally heterogeneous scaling trajectories. Homicide mortality has significantly attenuated its typical superlinear scaling with increased spatial clustering, suggesting a redistribution of violence to smaller cities and intensified intercity interactions, possibly linked to the consolidation of organized crime. Suicide mortality, usually sublinear, has trended upward, implying a weakening of urban agglomerations' protective effect. Accident mortality remains superlinear, with transport fatalities scaling nearly proportionally, and non-transport accidents becoming superlinear. The scaling changes for suicides and accidents coincide with less correlated and stable spatial patterns, suggesting that the underlying processes predominantly operate within city boundaries. Finally, while scaling exponents have evolved more homogeneously across Brazilian states, scale-adjusted mortality remains highly heterogeneous, indicating that fundamental processes govern scaling laws, whereas state-specific factors drive scale-adjusted metrics. △ Less

Submitted 13 January, 2026; originally announced January 2026.

Comments: 16 pages, 8 figures, supplementary information; accepted for publication in Scientific Reports

Circular Dichroism without absorption in isolated chiral dielectric Mie particles

Authors: Rafael S. Dutra, Felipe A. Pinheiro, Diney S. Ether Jr, Cyriaque Genet, Nathan B. Viana, Paulo A. Maia Neto

Abstract: We demonstrate that an effect phenomenologically analogous to circular dichroism can arise even for dielectric and isotropic chiral spherical particles. By analyzing the polarimetry of light scattered from a chiral, lossless microsphere illuminated with linearly polarized light, we show that the scattered light becomes nearly circularly polarized, exhibiting large, nonresonant values of the Stokes… ▽ More We demonstrate that an effect phenomenologically analogous to circular dichroism can arise even for dielectric and isotropic chiral spherical particles. By analyzing the polarimetry of light scattered from a chiral, lossless microsphere illuminated with linearly polarized light, we show that the scattered light becomes nearly circularly polarized, exhibiting large, nonresonant values of the Stokes parameter $S_3$ for a broad range of visible frequencies. This phenomenon occurs only in the Mie regime, with the microsphere radius comparable to the wavelength, and provided that the scattered light is collected by a high-NA objective lens, including non-paraxial Fourier components. Altogether, our findings offer a theoretical framework and motivation for an experimental demonstration of a novel chiroptical effect with isolated dielectric particles, with potential applications in enantioselection and characterization of single microparticles, each and every one with its own chiral response. △ Less

Submitted 9 October, 2025; originally announced October 2025.

Comments: 22 pages, 5 figures

Journal ref: ACS Photonics 13(4), 949-957 (2026)

Teaching materials aligned or unaligned with the principles of the Cognitive Theory of Multimedia Learning: the choices made by Physics teachers and students

Authors: Aline N. Braga, Antonio A. M. Neto, Alessandra N. Braga, Silvio C. F. Pereira Filho, Nelson P. C. de Souza, Danilo T. Alves

Abstract: In a recent study [Rev. Bras. Ens. Fís. vol. 45, 2023], the absence of the Cognitive Theory of Multimedia Learning (CTML) in the curricula of Physics teacher education programs at Brazilian public universities was highlighted. Considering this gap, the present study investigates whether, even without any formal prior knowledge of CTML principles (Coherence, Signaling, Spatial Contiguity, Segmentat… ▽ More In a recent study [Rev. Bras. Ens. Fís. vol. 45, 2023], the absence of the Cognitive Theory of Multimedia Learning (CTML) in the curricula of Physics teacher education programs at Brazilian public universities was highlighted. Considering this gap, the present study investigates whether, even without any formal prior knowledge of CTML principles (Coherence, Signaling, Spatial Contiguity, Segmentation, Multimedia, and Personalization), Physics teacher trainees and educators tend to choose, among two formats of multimedia materials - one aligned with a given CTML principle and the other not - the materials aligned with these principles. The findings of this case study revealed that, although most participants generally selected materials aligned with the mentioned principles, a significant portion did not. These results underscore the importance of Brazilian universities considering the inclusion of CTML in Physics teacher education curricula. △ Less

Submitted 27 December, 2024; originally announced December 2024.

Comments: 24 pages, 7 figures

Diagonalization without Diagonalization: A Direct Optimization Approach for Solid-State Density Functional Theory

Authors: Tianbo Li, Min Lin, Stephen Dale, Zekun Shi, A. H. Castro Neto, Kostya S. Novoselov, Giovanni Vignale

Abstract: We present a novel approach to address the challenges of variable occupation numbers in direct optimization of density functional theory (DFT). By parameterizing both the eigenfunctions and the occupation matrix, our method minimizes the free energy with respect to these parameters. As the stationary conditions require the occupation matrix and the Kohn-Sham Hamiltonian to be simultaneously diagon… ▽ More We present a novel approach to address the challenges of variable occupation numbers in direct optimization of density functional theory (DFT). By parameterizing both the eigenfunctions and the occupation matrix, our method minimizes the free energy with respect to these parameters. As the stationary conditions require the occupation matrix and the Kohn-Sham Hamiltonian to be simultaneously diagonalizable, this leads to the concept of ``self-diagonalization,'' where, by assuming a diagonal occupation matrix without loss of generality, the Hamiltonian matrix naturally becomes diagonal at stationary points. Our method incorporates physical constraints on both the eigenfunctions and the occupations into the parameterization, transforming the constrained optimization into an fully differentiable unconstrained problem, which is solvable via gradient descent. Implemented in JAX, our method was tested on aluminum and silicon, confirming that it achieves efficient self-diagonalization, produces the correct Fermi-Dirac distribution of the occupation numbers and yields band structures consistent with those obtained with SCF methods in Quantum Espresso. △ Less

Submitted 6 November, 2024; originally announced November 2024.

Probing the chirality of a single microsphere trapped by a focused vortex beam through their orbital period

Authors: Kainã Diniz, Tanja Schoger, Arthur L. Fonseca, Rafael S. Dutra, Diney S. Ether Jr, Gert-Ludwig Ingold, Felipe A. Pinheiro, Nathan B. Viana, Paulo A. Maia Neto

Abstract: When microspheres are illuminated by tightly focused vortex beams, they can be trapped in a non-equilibrium steady state where they orbit around the optical axis. By using the Mie-Debye theory for optical tweezers, we demonstrate that the orbital period strongly depends on the particle's chirality index. Taking advantage of such sensitivity, we put forth a method to experimentally characterize wit… ▽ More When microspheres are illuminated by tightly focused vortex beams, they can be trapped in a non-equilibrium steady state where they orbit around the optical axis. By using the Mie-Debye theory for optical tweezers, we demonstrate that the orbital period strongly depends on the particle's chirality index. Taking advantage of such sensitivity, we put forth a method to experimentally characterize with high precision the chiroptical response of individual optically trapped particles. The method allows for an enhanced precision at least one order of magnitude larger than that of similar existing enantioselective approaches. It is particularly suited to probe the chiroptical response of individual particles, for which light-chiral matter interactions are typically weak. △ Less

Submitted 5 September, 2024; originally announced September 2024.

Search for reactor-produced millicharged particles with Skipper-CCDs at the CONNIE and Atucha-II experiments

Authors: Alexis A. Aguilar-Arevalo, Nicolas Avalos, Pablo Bellino, Xavier Bertou, Carla Bonifazi, Ana Botti, Mariano Cababié, Gustavo Cancelo, Brenda A. Cervantes-Vergara, Claudio Chavez, Fernando Chierchie, David Delgado, Eliana Depaoli, Juan Carlos D'Olivo, João dos Anjos, Juan Estrada, Guillermo Fernandez Moroni, Aldo R. Fernandes Neto, Richard Ford, Ben Kilminster, Kevin Kuk, Andrew Lathrop, Patrick Lemos, Herman P. Lima Jr., Martin Makler , et al. (15 additional authors not shown)

Abstract: Millicharged particles, proposed by various extensions of the standard model, can be created in pairs by high-energy photons within nuclear reactors and can interact electromagnetically with electrons in matter. Recently, the existence of a plasmon peak in the interaction cross-section with silicon in the eV range was highlighted as a promising approach to enhance low-energy sensitivities. The CON… ▽ More Millicharged particles, proposed by various extensions of the standard model, can be created in pairs by high-energy photons within nuclear reactors and can interact electromagnetically with electrons in matter. Recently, the existence of a plasmon peak in the interaction cross-section with silicon in the eV range was highlighted as a promising approach to enhance low-energy sensitivities. The CONNIE and Atucha-II reactor neutrino experiments utilize Skipper-CCD sensors, which enable the detection of interactions in the eV range. We present world-leading limits on the charge of millicharged particles within a mass range spanning six orders of magnitude, derived through a comprehensive analysis and the combination of data from both experiments. △ Less

Submitted 5 November, 2024; v1 submitted 25 May, 2024; originally announced May 2024.

Comments: 10 pages, 3 figures

Searches for CEνNS and Physics beyond the Standard Model using Skipper-CCDs at CONNIE

Authors: Alexis A. Aguilar-Arevalo, Nicolas Avalos, Xavier Bertou, Carla Bonifazi, Gustavo Cancelo, Brenda A. Cervantes-Vergara, Claudio Chavez, Fernando Chierchie, Gustavo Coelho Corrêa, Juan Carlos D'Olivo, João dos Anjos, Juan Estrada, Guillermo Fernandez Moroni, Aldo R. Fernandes Neto, Richard Ford, Ben Kilminster, Kevin Kuk, Andrew Lathrop, Patrick Lemos, Herman P. Lima Jr., Martin Makler, Katherine Maslova, Franciole Marinho, Jorge Molina, Irina Nasteva , et al. (9 additional authors not shown)

Abstract: The Coherent Neutrino-Nucleus Interaction Experiment (CONNIE) aims to detect the coherent scattering (CE$ν$NS) of reactor antineutrinos off silicon nuclei using thick fully-depleted high-resistivity silicon CCDs. Two Skipper-CCD sensors with sub-electron readout noise capability were installed at the experiment next to the Angra-2 reactor in 2021, making CONNIE the first experiment to employ Skipp… ▽ More The Coherent Neutrino-Nucleus Interaction Experiment (CONNIE) aims to detect the coherent scattering (CE$ν$NS) of reactor antineutrinos off silicon nuclei using thick fully-depleted high-resistivity silicon CCDs. Two Skipper-CCD sensors with sub-electron readout noise capability were installed at the experiment next to the Angra-2 reactor in 2021, making CONNIE the first experiment to employ Skipper-CCDs for reactor neutrino detection. We report on the performance of the Skipper-CCDs, the new data processing and data quality selection techniques and the event selection for CE$ν$NS interactions, which enable CONNIE to reach a record low detection threshold of 15 eV. The data were collected over 300 days in 2021-2022 and correspond to exposures of 14.9 g-days with the reactor-on and 3.5 g-days with the reactor-off. The difference between the reactor-on and off event rates shows no excess and yields upper limits at 95% confidence level for the neutrino interaction rates comparable with previous CONNIE limits from standard CCDs and higher exposures. Searches for new neutrino interactions beyond the Standard Model were performed, yielding an improvement on the previous CONNIE limit on a simplified model with light vector mediators. A first dark matter (DM) search by diurnal modulation was performed by CONNIE and the results represent the best limits on the DM-electron scattering cross-section, obtained by a surface-level experiment. These promising results, obtained using a very small-mass sensor, illustrate the potential of Skipper-CCDs to probe rare neutrino interactions and motivate the plans to increase the detector mass in the near future. △ Less

Submitted 27 April, 2026; v1 submitted 23 March, 2024; originally announced March 2024.

Precise in situ radius measurement of individual optically trapped microspheres using negative optical torque exerted by focused vortex beams

Authors: Kainã Diniz, Tanja Schoger, Guilherme T. Moura, Arthur L. Fonseca, Diney S. Ether Jr, Rafael S. Dutra, Gert-Ludwig Ingold, Nathan B. Viana, Paulo A. Maia Neto

Abstract: We demonstrate a new method for determining the radius of micron-sized particles trapped by a vortex laser beam. The technique is based on measuring the rotation experienced by the center of mass of a microsphere that is laterally displaced by a Stokes drag force to an off-axis equilibrium position. The rotation results from an optical torque pointing along the direction opposite to the vortex bea… ▽ More We demonstrate a new method for determining the radius of micron-sized particles trapped by a vortex laser beam. The technique is based on measuring the rotation experienced by the center of mass of a microsphere that is laterally displaced by a Stokes drag force to an off-axis equilibrium position. The rotation results from an optical torque pointing along the direction opposite to the vortex beam angular momentum. We fit the rotation angle data for different Laguerre-Gaussian modes taking the radius as a fitting parameter in the Mie-Debye theory of optical tweezers. We also discuss how micron-sized beads can be used as probes for optical aberrations introduced by the experimental setup. △ Less

Submitted 28 December, 2023; originally announced December 2023.

Comments: 11 pages, 5 figures

Journal ref: Phys. Rev. A 110, 013513 (2024)

Tailoring bistability in optical tweezers with vortex beams and spherical aberration

Authors: Arthur Luna da Fonseca, Kainã Diniz, Paula Borges Monteiro, Luís Barbosa Pires, Guilherme Tenório Moura, Mateus Borges, Rafael de Sousa Dutra, Diney Soares Ether Jr, Nathan Bessa Viana, Paulo Américo Maia Neto

Abstract: We demonstrate a bistable optical trap by tightly focusing a vortex laser beam. The optical potential has the form of a Mexican hat with an additional minimum at the center. The bistable trapping corresponds to a non-equilibrium steady state (NESS), where the microsphere continually hops, due to thermal activation, between an axial equilibrium state and an orbital state driven by the optical torqu… ▽ More We demonstrate a bistable optical trap by tightly focusing a vortex laser beam. The optical potential has the form of a Mexican hat with an additional minimum at the center. The bistable trapping corresponds to a non-equilibrium steady state (NESS), where the microsphere continually hops, due to thermal activation, between an axial equilibrium state and an orbital state driven by the optical torque. We develop a theoretical model for the optical force field, based entirely on experimentally accessible parameters, combining a Debye-type non-paraxial description of the focused vortex beam with Mie scattering by the microsphere. The theoretical prediction that the microsphere and the annular laser focal spot should have comparable sizes is confirmed experimentally by taking different values for the topological charge of the vortex beam. Spherical aberration introduced by refraction at the interface between the glass slide and the sample is taken into account and allows to fine tune between axial, bistable and orbital states as the sample is shifted with respect to the objective focal plane. We find an overall agreement between theory and experiment for a rather broad range of topological charges. Our results open the way for applications in stochastic thermodynamics as it establishes a new control parameter, the height of the objective focal plane with respect to the glass slide, that allows to shape the optical force field in real time and in a controllable way. △ Less

Submitted 8 November, 2023; originally announced November 2023.

Theory of defect-mediated ionic transport in Li, Na and K beta and beta prime prime aluminas

Authors: Suchit Negi, Alexandra Carvalho, A. H. Castro Neto

Abstract: Alkali metal $β$/$β^{\prime\prime}$ aluminas are among the fastest ionic conductors, yet little is understood about the role of defects in the ion transport mechanism. Here, we use density functional theory (DFT) to investigate the crystal structures of $β$ and $β^{\prime\prime}$ phases, and vacancy and interstitial defects in these materials. We find that charge transport is likely to be dominate… ▽ More Alkali metal $β$/$β^{\prime\prime}$ aluminas are among the fastest ionic conductors, yet little is understood about the role of defects in the ion transport mechanism. Here, we use density functional theory (DFT) to investigate the crystal structures of $β$ and $β^{\prime\prime}$ phases, and vacancy and interstitial defects in these materials. We find that charge transport is likely to be dominated by alkali metal interstitials in $β$-aluminas and by vacancies in $β^{\prime\prime}$ aluminas. Lower bounds for the activation energy for diffusion are found by determining the minimum energy paths for defect migration. The resulting migration barriers are lower than the experimental activation energies for conduction in Na $β$ and $β^{\prime\prime}$ aluminas, suggesting a latent potential for optimization. The lowest activation energy of about 20 meV is predicted for correlated vacancy migration in K $β^{\prime\prime}$ alumina. △ Less

Submitted 5 October, 2023; v1 submitted 26 September, 2023; originally announced September 2023.

Universal Casimir attraction between filaments at the cell scale

Authors: Benjamin Spreng, Hélène Berthoumieux, Astrid Lambrecht, Anne-Florence Bitbol, Paulo A. Maia Neto, Serge Reynaud

Abstract: The electromagnetic Casimir interaction between dielectric objects immersed in salted water includes a universal contribution that is not screened by the solvent and therefore long-ranged. Here, we study the geometry of two parallel dielectric cylinders. We derive the Casimir free energy by using the scattering method. We show that its magnitude largely exceeds the thermal energy scale for a large… ▽ More The electromagnetic Casimir interaction between dielectric objects immersed in salted water includes a universal contribution that is not screened by the solvent and therefore long-ranged. Here, we study the geometry of two parallel dielectric cylinders. We derive the Casimir free energy by using the scattering method. We show that its magnitude largely exceeds the thermal energy scale for a large parameter range. This includes length scales relevant for actin filaments and microtubules in cells. We show that the Casimir free energy is a universal function of the geometry, independent of the dielectric response functions of the cylinders, at all distances of biological interest. While multiple interactions exist between filaments in cells, this universal attractive interaction should have an important role in the cohesion of bundles of parallel filaments. △ Less

Submitted 25 December, 2023; v1 submitted 24 June, 2023; originally announced June 2023.

Comments: 15 pages, 9 figures. This paper extends the unpublished short report arXiv:2304.06006

Journal ref: 2024 New J. Phys. 26 013009

A universal attractive interaction between filaments at the cell scale

Authors: Anne-Florence Bitbol, Hélène Berthoumieux, Benjamin Spreng, Paulo A. Maia Neto, Serge Reynaud

Abstract: Actin filaments and microtubules both often form bundles of parallel filaments within cells. Here, we shed light on a universal attractive interaction between two such parallel filaments. Indeed, the electrodynamic Casimir interaction between dielectric objects immersed in salted water at room or body temperature includes a universal contribution that is unscreened by the solvent and therefore lon… ▽ More Actin filaments and microtubules both often form bundles of parallel filaments within cells. Here, we shed light on a universal attractive interaction between two such parallel filaments. Indeed, the electrodynamic Casimir interaction between dielectric objects immersed in salted water at room or body temperature includes a universal contribution that is unscreened by the solvent and therefore long-ranged. We study this interaction between two parallel cylinders immersed in salted water with strong Debye screening. We show that its magnitude can largely exceed the energy scale of thermal fluctuations in the case of actin filaments and microtubules in cells. While multiple interactions exist between filaments in cells, this universal attractive interaction should thus have an important role, e.g. in bundle formation and cohesion. △ Less

Submitted 22 December, 2023; v1 submitted 12 April, 2023; originally announced April 2023.

Comments: 18 pages, 5 figures. No change. This short report has been expanded into a longer paper arXiv:2306.14059

3D WC-MPS coupled with geometrically nonlinear shell for hydro-elastic free-surface flows

Authors: Rubens Augusto Amaro Junior, Alfredo Gay Neto, Liang-Yee Cheng

Abstract: A 3D fluid-structure interaction solver based on an improved weakly-compressible moving particle simulation (WC-MPS) method and a geometrically nonlinear shell structural model is developed and applied to hydro-elastic free-surface flows. The fluid-structure coupling is performed by a polygon wall boundary model that can handle particles and finite elements of distinct sizes. In WC-MPS, a tuning-f… ▽ More A 3D fluid-structure interaction solver based on an improved weakly-compressible moving particle simulation (WC-MPS) method and a geometrically nonlinear shell structural model is developed and applied to hydro-elastic free-surface flows. The fluid-structure coupling is performed by a polygon wall boundary model that can handle particles and finite elements of distinct sizes. In WC-MPS, a tuning-free diffusive term is introduced to the continuity equation to mitigate non-physical pressure oscillations. Discrete divergence operators are derived and applied to the polygon wall boundary, of which the numerical stability is enhanced by a repulsive Lennard-Jones force. Additionally, an efficient technique to deal with the interaction between fluid particles placed at opposite sides of zero-thickness walls is proposed. The geometrically nonlinear shell is modeled by an unstructured mesh of six-node triangular elements. Finite rotations are considered with Rodrigues parameters and a hyperelastic constitutive model is adopted. Benchmark examples involving free-surface flows and thin-walled structures demonstrate that the proposed model is robust, numerically stable and offers more efficient computation by allowing mesh size larger than that of fluid particles. △ Less

Submitted 3 April, 2023; originally announced April 2023.

Comments: 48 pages, 19 figures

Journal ref: International Journal for Numerical Methods in Fluids 94 (2022) 1048-1081

Enhancing Oceanic Variables Forecast in the Santos Channel by Estimating Model Error with Random Forests

Authors: Felipe M. Moreno, Caio F. D. Netto, Marcel R. de Barros, Jefferson F. Coelho, Lucas P. de Freitas, Marlon S. Mathias, Luiz A. Schiaveto Neto, Marcelo Dottori, Fabio G. Cozman, Anna H. R. Costa, Edson S. Gomi, Eduardo A. Tannuri

Abstract: In this work we improve forecasting of Sea Surface Height (SSH) and current velocity (speed and direction) in oceanic scenarios. We do so by resorting to Random Forests so as to predict the error of a numerical forecasting system developed for the Santos Channel in Brazil. We have used the Santos Operational Forecasting System (SOFS) and data collected in situ between the years of 2019 and 2021. I… ▽ More In this work we improve forecasting of Sea Surface Height (SSH) and current velocity (speed and direction) in oceanic scenarios. We do so by resorting to Random Forests so as to predict the error of a numerical forecasting system developed for the Santos Channel in Brazil. We have used the Santos Operational Forecasting System (SOFS) and data collected in situ between the years of 2019 and 2021. In previous studies we have applied similar methods for current velocity in the channel entrance, in this work we expand the application to improve the SHH forecast and include four other stations in the channel. We have obtained an average reduction of 11.9% in forecasting Root-Mean Square Error (RMSE) and 38.7% in bias with our approach. We also obtained an increase of Agreement (IOA) in 10 of the 14 combinations of forecasted variables and stations. △ Less

Submitted 22 July, 2022; originally announced August 2022.

Solving partial differential equations on near-term quantum computers

Authors: Anton Simen Albino, Lucas Correia Jardim, Diego Campos Knupp, Antonio Jose Silva Neto, Otto Menegasso Pires, Erick Giovani Sperandio Nascimento

Abstract: In this work, we obtain the numerical temperature field to a thermally developing fluid flow inside parallel plates problem with a quantum computing method. The physical problem deals with the heat transfer of a steady state, hydrodinamically developed and thermally developing fluid flow inside two parallel plates channel subjected to a prescribed constant heat flux. Its solution is formulated num… ▽ More In this work, we obtain the numerical temperature field to a thermally developing fluid flow inside parallel plates problem with a quantum computing method. The physical problem deals with the heat transfer of a steady state, hydrodinamically developed and thermally developing fluid flow inside two parallel plates channel subjected to a prescribed constant heat flux. Its solution is formulated numerically with Finite Differences method, where a sequence of linear systems must be solved in order to determine the complete temperature field. Such linear systems are written as discrete unconstrained optimization problems with floating points being approximated using binary variables and solved using near-term quantum heuristics. Due to the exponential cost of simulating quantum algorithms, a reduced number of qubits had to be used in the simulations, causing a loss of precision in the results. However, this work advances the state of the art of solutions of differential equations with noisy quantum devices and could be used for useful applications when quantum computers with thousands of qubits become available. △ Less

Submitted 11 August, 2022; originally announced August 2022.

Two-dimensional non-linear hydrodynamics and nanofluidics

Authors: Maxim Trushin, Alexandra Carvalho, A. H. Castro Neto

Abstract: A water monolayer squeezed between two solid planes experiences strong out-of-plane confinement effects while expanding freely within the plane. As a consequence, the transport of such two-dimensional water combines hydrodynamic and nanofluidic features, intimately linked with each other. In this paper, we propose and explicitly solve a non-linear hydrodynamic equation describing two-dimensional w… ▽ More A water monolayer squeezed between two solid planes experiences strong out-of-plane confinement effects while expanding freely within the plane. As a consequence, the transport of such two-dimensional water combines hydrodynamic and nanofluidic features, intimately linked with each other. In this paper, we propose and explicitly solve a non-linear hydrodynamic equation describing two-dimensional water flow with viscosity parameters deduced from molecular dynamic simulations. We demonstrate that the very ability of two-dimensional water to flow in short channels is governed by the second (dilatational) viscosity coefficient, leading to flow compression and velocity saturation in the high-pressure limit. The viscosity parameter values depend strongly on whether graphene or hexoganal boron nitride layers are used to confine 2D water that offers an interesting opportunity to obtain various nanofluids out of the same water molecules just by using alternate materials to fabricate the 2D channels. △ Less

Submitted 5 July, 2023; v1 submitted 6 July, 2022; originally announced July 2022.

Comments: 10+ pages, 6 figures. The supplementary information and multimedia files are available via doi link to the Springer Nature publisher

Journal ref: Commun Phys 6, 162 (2023)

Dynamical Casimir effects with atoms: from the emission of photon pairs to geometric phases

Authors: François Impens, Reinaldo de Melo e Souza, Guilherme C. Matos, Paulo A. Maia Neto

Abstract: The coupling between a moving ground-state atom and the quantum electromagnetic field is at the origin of several intriguing phenomena ranging from the dynamical Casimir emission of photons to Sagnac-like geometric phase shifts in atom interferometers. Recent progress in this emerging field reveals unprecedented connections between non-trivial aspects of modern physics such as electrodynamic retar… ▽ More The coupling between a moving ground-state atom and the quantum electromagnetic field is at the origin of several intriguing phenomena ranging from the dynamical Casimir emission of photons to Sagnac-like geometric phase shifts in atom interferometers. Recent progress in this emerging field reveals unprecedented connections between non-trivial aspects of modern physics such as electrodynamic retardation, non-unitary evolution in open quantum systems, geometric phases, non-locality and inertia. △ Less

Submitted 30 March, 2022; originally announced March 2022.

Journal ref: EPL 138, 30001 (2022)

Quantum Vacuum Sagnac Effect

Authors: Guilherme C. Matos, Reinaldo de Melo e Souza, Paulo A. Maia Neto, François Impens

Abstract: We report on the quantum electrodynamical analogue of a Sagnac phase induced by the fast rotation of a neutral nanoparticle onto atomic waves propagating in its vicinity. The quantum vacuum Sagnac phase is a geometric Berry phase proportional to the angular velocity of rotation. The persistence of a noninertial effect into the inertial frame is also analogous to the Aharonov-Bohm effect. Here, a r… ▽ More We report on the quantum electrodynamical analogue of a Sagnac phase induced by the fast rotation of a neutral nanoparticle onto atomic waves propagating in its vicinity. The quantum vacuum Sagnac phase is a geometric Berry phase proportional to the angular velocity of rotation. The persistence of a noninertial effect into the inertial frame is also analogous to the Aharonov-Bohm effect. Here, a rotation confined to a restricted domain of space gives rise to an atomic phase even though the interferometer is at rest with respect to an inertial frame. By taking advantage of a plasmon resonance, we show that the magnitude of the induced phase can be close to the sensitivity limit of state of the art interferometers. The quantum vacuum Sagnac atomic phase is a geometric footprint of a dynamical Casimir-like effect △ Less

Submitted 6 January, 2022; v1 submitted 3 December, 2021; originally announced December 2021.

Comments: Typos corrected

Journal ref: Phys. Rev. Lett. 127, 270401 (2021)

Search for coherent elastic neutrino-nucleus scattering at a nuclear reactor with CONNIE 2019 data

Authors: CONNIE collaboration, Alexis Aguilar-Arevalo, Javier Bernal, Xavier Bertou, Carla Bonifazi, Gustavo Cancelo, Victor G. P. B. de Carvalho, Brenda A. Cervantes-Vergara, Claudio Chavez, Gustavo Coelho Corrêa, Juan C. D'Olivo, João C. dos Anjos, Juan Estrada, Aldo R. Fernandes Neto, Guillermo Fernandez Moroni, Ana Foguel, Richard Ford, Julián Gasanego Barbuscio, Juan Gonzalez Cuevas, Susana Hernandez, Federico Izraelevitch, Ben Kilminster, Kevin Kuk, Herman P. Lima Jr, Martin Makler , et al. (11 additional authors not shown)

Abstract: The Coherent Neutrino-Nucleus Interaction Experiment (CONNIE) is taking data at the Angra 2 nuclear reactor with the aim of detecting the coherent elastic scattering of reactor antineutrinos with silicon nuclei using charge-coupled devices (CCDs). In 2019 the experiment operated with a hardware binning applied to the readout stage, leading to lower levels of readout noise and improving the detecti… ▽ More The Coherent Neutrino-Nucleus Interaction Experiment (CONNIE) is taking data at the Angra 2 nuclear reactor with the aim of detecting the coherent elastic scattering of reactor antineutrinos with silicon nuclei using charge-coupled devices (CCDs). In 2019 the experiment operated with a hardware binning applied to the readout stage, leading to lower levels of readout noise and improving the detection threshold down to 50 eV. The results of the analysis of 2019 data are reported here, corresponding to the detector array of 8 CCDs with a fiducial mass of 36.2 g and a total exposure of 2.2 kg-days. The difference between the reactor-on and reactor-off spectra shows no excess at low energies and yields upper limits at 95% confidence level for the neutrino interaction rates. In the lowest-energy range, 50-180 eV, the expected limit stands at 34 (39) times the standard model prediction, while the observed limit is 66 (75) times the standard model prediction with Sarkis (Chavarria) quenching factors. △ Less

Submitted 6 April, 2022; v1 submitted 25 October, 2021; originally announced October 2021.

Comments: 23 pages, 14 figures

Journal ref: J. High Energ. Phys. 2022, 17 (2022)

Gain-assisted optical tweezing of plasmonic and large refractive index microspheres

Authors: R. Ali, R. S. Dutra, F. A. Pinheiro, P. A. Maia Neto

Abstract: We have theoretically investigated optical tweezing of gain-functionalized microspheres using a highly focused single beam in the nonparaxial regime. We employ the Mie-Debye theory of optical tweezers to calculate the optical force acting on homogeneous and core-shell Mie microspheres with gain. We demonstrate that the optical gain plays a crucial role in optical manipulation, especially to optimi… ▽ More We have theoretically investigated optical tweezing of gain-functionalized microspheres using a highly focused single beam in the nonparaxial regime. We employ the Mie-Debye theory of optical tweezers to calculate the optical force acting on homogeneous and core-shell Mie microspheres with gain. We demonstrate that the optical gain plays a crucial role in optical manipulation, especially to optimize the restoring force and thus allowing for trapping of large refractive index and plasmonic particles. Indeed we demonstrate that one can trap such particles, which is usually not possible in the case of passive media, by functionalizing them with an optical gain material. We show that by varying the value of the gain, which can be realized by changing the pump power, one can not only achieve trapping but also manipulate the equilibrium position of the tweezed particle. Altogether our findings open new venues for gain-assisted optomechanics, where gain functionalized systems could facilitate optical trapping and manipulation of plasmonic nanoparticles in particular, with potential applications in self-assembling of nanoparticle suspensions and on a chip. △ Less

Submitted 23 July, 2021; originally announced July 2021.

Comments: This paper is submitted to Journal of Optics

Tracing contacts to evaluate the transmission of COVID-19 from highly exposed individuals in public transportation

Authors: Caio Ponte, Humberto A. Carmona, Erneson A. Oliveira, Carlos Caminha, Antonio S. Lima Neto, José S. Andrade Jr., Vasco Furtado

Abstract: We investigate, through a data-driven contact tracing model, the transmission of COVID-19 inside buses during distinct phases of the pandemic in a large Brazilian city. From this microscopic approach, we recover the networks of close contacts within consecutive time windows. A longitudinal comparison is then performed by upscaling the traced contacts with the transmission computed from a mean-fiel… ▽ More We investigate, through a data-driven contact tracing model, the transmission of COVID-19 inside buses during distinct phases of the pandemic in a large Brazilian city. From this microscopic approach, we recover the networks of close contacts within consecutive time windows. A longitudinal comparison is then performed by upscaling the traced contacts with the transmission computed from a mean-field compartmental model for the entire city. Our results show that the effective reproduction numbers inside the buses, $Re^{bus}$, and in the city, $Re^{city}$, followed a compatible behavior during the first wave of the local outbreak. Moreover, by distinguishing the close contacts of healthcare workers in the buses, we discovered that their transmission, $Re^{health}$, during the same period, was systematically higher than $Re^{bus}$. This result reinforces the need for special public transportation policies for highly exposed groups of people. △ Less

Submitted 9 June, 2021; originally announced June 2021.

Superspreading k-cores at the center of COVID-19 pandemic persistence

Authors: Matteo Serafino, Higor S. Monteiro, Shaojun Luo, Saulo D. S. Reis, Carles Igual, Antonio S. Lima Neto, Matias Travizano, José S. Andrade, Jr., Hernán A. Makse

Abstract: The spread of COVID-19 caused by the recently discovered SARS-CoV-2 virus has become a worldwide problem with devastating consequences. To slow down the spread of the pandemic, mass quarantines have been implemented globally, provoking further social and economic disruptions. Here, we implement a comprehensive contact tracing network analysis to find an optimized quarantine protocol to dismantle t… ▽ More The spread of COVID-19 caused by the recently discovered SARS-CoV-2 virus has become a worldwide problem with devastating consequences. To slow down the spread of the pandemic, mass quarantines have been implemented globally, provoking further social and economic disruptions. Here, we implement a comprehensive contact tracing network analysis to find an optimized quarantine protocol to dismantle the chain of transmission of coronavirus with minimal disruptions to society. We track billions of anonymized GPS human mobility datapoints from a compilation of hundreds of mobile apps deployed in Latin America to monitor the evolution of the contact network of disease transmission before and after the confinements. As a consequence of the lockdowns, people's mobility across the region decreases by $\sim$53\%, which results in a drastic disintegration of the transmission network by $\sim$90\%. However, this disintegration did not halt the spreading of the disease. Our analysis indicates that superspreading k-core structures persist in the transmission network to prolong the pandemic. Once the k-cores are identified, an optimized strategy to break the chain of transmission is to quarantine a minimal number of 'weak links' with high betweenness centrality connecting the large k-cores. As countries built contact tracing apps to fight the pandemic, our results could turn into a valuable resource to help deploy quarantine protocols with minimized disruptions. △ Less

Submitted 15 March, 2021; originally announced March 2021.

Comments: 7 pages, 4 figures

Journal ref: PLoS Comput Biol 18(4): e1009865 (2022)

Enantioselection and chiral sorting of single microspheres using optical pulling forces

Authors: R. Ali, R. S. Dutra, F. A. Pinheiro, P. A. Maia Neto

Abstract: We put forward a novel, twofold scheme that enables at the same time all-optical enantioselection and sorting of single multipolar chiral microspheres based on optical pulling forces exerted by two non-collinear, nonstructured, circularly-polarized light sources. Our chiral resolution method can be externally controlled by varying the angle between their incident wavevectors, allowing for a fine-t… ▽ More We put forward a novel, twofold scheme that enables at the same time all-optical enantioselection and sorting of single multipolar chiral microspheres based on optical pulling forces exerted by two non-collinear, nonstructured, circularly-polarized light sources. Our chiral resolution method can be externally controlled by varying the angle between their incident wavevectors, allowing for a fine-tuning of the range of chiral indices for enantioselection. Enantioselectivity is achieved by choosing angles such that only particles with the same handedness of the light sources are pulled. This proposal allows one to achieve all-optical sorting of chiral microspheres with arbitrarily small chiral parameters, thus outperforming current optical methods. △ Less

Submitted 2 March, 2021; originally announced March 2021.

Comments: 4 pages 4 Figures

Effect of carbon nanotube on ballistic conduction through single-quantum-dot

Authors: Thiago Lobo, Minos A. Neto, Marcio G. da Silva, Octavio D. R. Salmon

Abstract: We will study the competitive effect between the transport of a quantum dot adsorbed to a ballistic channel and laterally coupled to a single-walled carbon nanotube (SWNT). We will use the tight-binding approach to analytically write the SWNT Green function and the quantum dot will be solved by the atomic method for U very large. We will present curves of the electronic density of states for some… ▽ More We will study the competitive effect between the transport of a quantum dot adsorbed to a ballistic channel and laterally coupled to a single-walled carbon nanotube (SWNT). We will use the tight-binding approach to analytically write the SWNT Green function and the quantum dot will be solved by the atomic method for U very large. We will present curves of the electronic density of states for some different sizes of nanotubes. The results for the conductance curves will be presented as a function of Ef and for different values of n and hopping between the nanotube and the quantum dot. △ Less

Submitted 22 October, 2020; originally announced October 2020.

Comments: 7 pages and 7 figures

Theory of optical tweezing of dielectric microspheres in chiral host media and its applications

Authors: Rfaqat Ali, R. S. Dutra, F. A. Pinheiro, F. S. S. Rosa, P. A. Maia Neto

Abstract: We report for the first time the theory of optical tweezers of spherical dielectric particles embedded in a chiral medium. We develop a partial-wave (Mie) expansion to calculate the optical force acting on a dielectric microsphere illuminated by a circularly-polarized, highly focused laser beam. When choosing a polarization with the same handedness of the medium, the axial trap stability is improv… ▽ More We report for the first time the theory of optical tweezers of spherical dielectric particles embedded in a chiral medium. We develop a partial-wave (Mie) expansion to calculate the optical force acting on a dielectric microsphere illuminated by a circularly-polarized, highly focused laser beam. When choosing a polarization with the same handedness of the medium, the axial trap stability is improved, thus allowing for tweezing of high-refractive-index particles. When the particle is displaced off-axis by an external force, its equilibrium position is rotated around the optical axis by the mechanical effect of an optical torque. Both the optical torque and the angle of rotation are greatly enhanced in the presence of a chiral host medium when considering radii a few times larger than the wavelength. In this range, the angle of rotation depends strongly on the microsphere radius and the chirality parameter of the host medium, opening the way for a quantitative characterization of both parameters. Measurable angles are predicted even in the case of naturally occurring chiral solutes, allowing for a novel all-optical method to locally probe the chiral response at the nanoscale. △ Less

Submitted 24 September, 2020; v1 submitted 7 July, 2020; originally announced July 2020.

Comments: This work is published in Scientific Reports

Tailoring optical pulling forces with composite microspheres

Authors: R. Ali, F. A. Pinheiro, R. S. Dutra, P. A. Maia Neto

Abstract: Optical pulling forces or tractor beams can pull particles against light propagation by redirecting the incident photons forward. This is typically achieved using Bessel beams with very small half-cone angles, which considerably limits its applicability. One can circumvent such issue by using a superposition of plane waves. In order to investigate optical pulling forces exerted by a pair of non-co… ▽ More Optical pulling forces or tractor beams can pull particles against light propagation by redirecting the incident photons forward. This is typically achieved using Bessel beams with very small half-cone angles, which considerably limits its applicability. One can circumvent such issue by using a superposition of plane waves. In order to investigate optical pulling forces exerted by a pair of non-colinear plane waves, we develop a theoretical framework based on Mie theory, Debye potentials and Wigner rotation matrices. We apply this framework to calculate the optical pulling force on metallo-dielectric composite particles, which we put forward as an alternative material platform to optimize and tailor tractor beams. Indeed we demonstrate that by adding a few plasmonic inclusions to low-refractive index dielectric particles of arbitrary sizes, we are able to produce polarization dependent optical pulling forces that cannot occur in the corresponding homogeneous particles. Altogether our findings not only provide innovative theoretical methods to compute optical pulling forces, but also provide new strategies to tailor and optimize them, paving the way to increase their applicability. △ Less

Submitted 16 June, 2020; originally announced June 2020.

Comments: 8 pages 4 figures

Journal ref: Phys. Rev. A 102, 023514 (2020)

Probing the optical chiral response of single nanoparticles with optical tweezers

Authors: R. Ali, F. A. Pinheiro, R. S. Dutra, F. S. S. Rosa, P. A. Maia Neto

Abstract: We propose an enantioselective scheme to sort homogeneous chiral particles using optical tweezers. For a certain range of material parameters, we show that a highly focused circularly-polarized laser beam traps particles of a specific chirality selected by the handedness of the trapping beam. Furthermore, by applying a transverse Stokes drag force that displaces the trapped particle off-axis, we a… ▽ More We propose an enantioselective scheme to sort homogeneous chiral particles using optical tweezers. For a certain range of material parameters, we show that a highly focused circularly-polarized laser beam traps particles of a specific chirality selected by the handedness of the trapping beam. Furthermore, by applying a transverse Stokes drag force that displaces the trapped particle off-axis, we allow for the rotation of the particle center-of-mass around the trapping beam axis. The rotation angle is highly dependent on the handedness of the trapped particle and is easily measurable with standard video-microscopy techniques, allowing for an alternative mechanism for chiral resolution. Our platform not only allows for enantioselection of particles dispersed in solution but also paves the way to the characterization of the chiral parameter of individual, homogeneous chiral microspheres using optical tweezing. △ Less

Submitted 6 June, 2020; originally announced June 2020.

Comments: 9 pages, 5 figures

Spatio-temporal characteristics of dengue outbreaks

Authors: Saulo D. S. Reis, Lucas Böttcher, João P. da C. Nogueira, Geziel S. Sousa, Antonio S. Lima Neto, Hans J. Herrmann, José S. Andrade Jr

Abstract: After their re-emergence in the last decades, dengue fever and other vector-borne diseases are a potential threat to the lives of millions of people. Based on a data set of dengue cases in the Brazilian city of Fortaleza, collected from 2011 to 2016, we study the spatio-temporal characteristics of dengue outbreaks to characterize epidemic and non-epidemic years. First, we identify regions that sho… ▽ More After their re-emergence in the last decades, dengue fever and other vector-borne diseases are a potential threat to the lives of millions of people. Based on a data set of dengue cases in the Brazilian city of Fortaleza, collected from 2011 to 2016, we study the spatio-temporal characteristics of dengue outbreaks to characterize epidemic and non-epidemic years. First, we identify regions that show a high prevalence of dengue cases and mosquito larvae in different years and also analyze their corresponding correlations. Our results show that the characteristic correlation length of the epidemic is of the order of the system size, suggesting that factors such as citizen mobility may play a major role as a drive for spatial spreading of vector-borne diseases. Inspired by this observation, we perform a mean-field estimation of the basic reproduction number and find that our estimated values agree well with the values reported for other regions, pointing towards similar underlying spreading mechanisms. These findings provide insights into the spreading characteristics of dengue in densely populated areas and should be of relevance for the design of improved disease containment strategies. △ Less

Submitted 4 June, 2020; originally announced June 2020.

Comments: 25 pages, 8 figures

Reversible Single Spin Control of Individual Magnetic Molecule by Hydrogen Atom Adsorption

Authors: Liwei Liu, Kai Yang, Yuhang Jiang, Boqun Song, Wende Xiao, Linfei Li, Haitao Zhou, Yeliang Wang, Shixuan Du, Min Ouyang, Werner A. Hofer, Antonio H. Castro Neto, Hong-Jun Gao

Abstract: The reversible control of a single spin of an atom or a molecule is of great interest in Kondo physics and a potential application in spin based electronics.Here we demonstrate that the Kondo resonance of manganese phthalocyanine molecules on an Au(111) substrate have been reversibly switched off and on via a robust route through attachment and detachment of single hydrogen atom to the magnetic co… ▽ More The reversible control of a single spin of an atom or a molecule is of great interest in Kondo physics and a potential application in spin based electronics.Here we demonstrate that the Kondo resonance of manganese phthalocyanine molecules on an Au(111) substrate have been reversibly switched off and on via a robust route through attachment and detachment of single hydrogen atom to the magnetic core of the molecule. As further revealed by density functional theory calculations, even though the total number of electrons of the Mn ion remains almost the same in the process, gaining one single hydrogen atom leads to redistribution of charges within 3d orbitals with a reduction of the molecular spin state from S = 3/2 to S = 1 that directly contributes to the Kondo resonance disappearance. This process is reversed by a local voltage pulse or thermal annealing to desorb the hydrogen atom. △ Less

Submitted 6 April, 2020; originally announced April 2020.

Journal ref: SCIENTIFIC REPORTS | 3 : 1210 (2013)

An Ultra-Wideband Leaky Lens Antenna for Broadband Spectroscopic Imaging Applications

Authors: Sebastian Hähnle, Ozan Yurduseven, Sven van Berkel, Nuria Llombart, Juan Bueno, Stephen J. C. Yates, Vignesh Murugesan, David J. Thoen, Andrea Neto, Jochem J. A. Baselmans

Abstract: We present the design, fabrication and characterisation of a broadband leaky lens antenna for broadband, spectroscopic imaging applications. The antenna is designed for operation in the 300-900 GHz band. We integrate the antenna directly into an Al-NbTiN hybrid MKID to measure the beam pattern and absolute coupling efficiency at three frequency bands centred around 350, 650 and 850 GHz, covering t… ▽ More We present the design, fabrication and characterisation of a broadband leaky lens antenna for broadband, spectroscopic imaging applications. The antenna is designed for operation in the 300-900 GHz band. We integrate the antenna directly into an Al-NbTiN hybrid MKID to measure the beam pattern and absolute coupling efficiency at three frequency bands centred around 350, 650 and 850 GHz, covering the full antenna band. We find an aperture efficiency $η_{ap} \approx 0.4$ over the whole frequency band, limited by lens reflections. We find a good match with simulations for both the patterns and efficiency, demonstrating a 1:3 bandwidth in the sub-mm wavelength range for future on-chip spectrometers. △ Less

Submitted 16 December, 2019; originally announced December 2019.

Comments: Accepted for Publication at IEEE Transactions on Antennas and Propagation

Discontinuous transitions can survive to quenched disorder in a 2-dimensional nonequilibrium system

Authors: Minos A. Neto, E. Brigatti

Abstract: We explore the effects that quenched disorder has on discontinuous nonequilibrium phase transitions into absorbing states. We focus our analysis on the Naming Game model, a nonequilibrium low-dimensional system with different absorbing states. The results obtained by means of the finite-size scaling analysis and from the study of the temporal dynamics of the density of active sites near the transi… ▽ More We explore the effects that quenched disorder has on discontinuous nonequilibrium phase transitions into absorbing states. We focus our analysis on the Naming Game model, a nonequilibrium low-dimensional system with different absorbing states. The results obtained by means of the finite-size scaling analysis and from the study of the temporal dynamics of the density of active sites near the transition point evidence that the spatial quenched disorder does not destroy the discontinuous transition. △ Less

Submitted 17 February, 2020; v1 submitted 12 November, 2019; originally announced November 2019.

Comments: 5 pages, 4 figures. arXiv admin note: text overlap with arXiv:1609.02869

Journal ref: Phys. Rev. E 101, 022112 (2020)

Search for light mediators in the low-energy data of the CONNIE reactor neutrino experiment

Authors: Alexis Aguilar-Arevalo, Xavier Bertou, Carla Bonifazi, Gustavo Cancelo, Brenda A. Cervantes-Vergara, Claudio Chavez, Juan C. D'Olivo, João C. dos Anjos, Juan Estrada, Aldo R. Fernandes Neto, Guillermo Fernandez-Moroni, Ana Foguel, Richard Ford, Federico Izraelevitch, Ben Kilminster, H. P. Lima Jr, Martin Makler, Jorge Molina, Philipe Mota, Irina Nasteva, Eduardo Paolini, Carlos Romero, Youssef Sarkis, Miguel Sofo-Haro, Javier Tiffenberg , et al. (1 additional authors not shown)

Abstract: The CONNIE experiment is located at a distance of 30 m from the core of a commercial nuclear reactor, and has collected a 3.7 kg-day exposure using a CCD detector array sensitive to an $\sim$1 keV threshold for the study of coherent neutrino-nucleus elastic scattering. Here we demonstrate the potential of this low-energy neutrino experiment as a probe for physics Beyond the Standard Model, by usin… ▽ More The CONNIE experiment is located at a distance of 30 m from the core of a commercial nuclear reactor, and has collected a 3.7 kg-day exposure using a CCD detector array sensitive to an $\sim$1 keV threshold for the study of coherent neutrino-nucleus elastic scattering. Here we demonstrate the potential of this low-energy neutrino experiment as a probe for physics Beyond the Standard Model, by using the recently published results to constrain two simplified extensions of the Standard Model with light mediators. We compare the new limits with those obtained for the same models using neutrinos from the Spallation Neutron Source. Our new constraints represent the best limits for these simplified models among the experiments searching for CE$ν$NS for a light vector mediator with mass $M_{Z^{\prime}}<$ 10 MeV, and for a light scalar mediator with mass $M_φ<$ 30 MeV. These results constitute the first use of the CONNIE data as a probe for physics Beyond the Standard Model. △ Less

Submitted 29 March, 2020; v1 submitted 10 October, 2019; originally announced October 2019.

Comments: Accepted for publication in JHEP

Journal ref: J. High Energ. Phys. 2020, 54 (2020)

Magnetic, Structural and cation distribution studies on $FeO \cdot Fe_{(2-x)}Nd_{x}O_{3}$ ($x=0.00, 0.02, 0.04, 0.06 \text{ and } 0.1$) nanoparticles

Authors: W. W. R. Araujo, J. F. D. F. Araujo, C. L. P. Oliveira, G. E. S. Brito, A. M. Figueiredo Neto

Abstract: We synthesized and characterized the colloidal suspensions of $FeO \cdot Fe_{(2-x)}Nd_{x}O_{3}$ nanoparticles with $x=0.00, 0.02, 0.04, 0.06 \text{ and }0.1.$ The effect of the $Fe^{3+}$ ion replacement by $Nd^{3+}$ on the crystal structure is in-depth studied, through X-ray diffraction (XRD) and the obtained cation distribution. The magnetic properties of the synthesized… ▽ More We synthesized and characterized the colloidal suspensions of $FeO \cdot Fe_{(2-x)}Nd_{x}O_{3}$ nanoparticles with $x=0.00, 0.02, 0.04, 0.06 \text{ and }0.1.$ The effect of the $Fe^{3+}$ ion replacement by $Nd^{3+}$ on the crystal structure is in-depth studied, through X-ray diffraction (XRD) and the obtained cation distribution. The magnetic properties of the synthesized $FeO \cdot Fe_{(2-x)}Nd_{x}O_{3}$ nanoparticles also were investigated and corroborated by other physical methods. A remarkable saturation magnetization of 105 $Am^{2}/kg$ was achieved for $x=0.06$. △ Less

Submitted 16 July, 2019; originally announced July 2019.

Comments: 28 pages, 8 figures, 9 tables, Last submission to Physical Review E

Enantioselective manipulation of chiral nanoparticles using optical tweezers

Authors: R. Ali, F. A. Pinheiro, F. S. S. Rosa, R. S. Dutra, P. A. Maia Neto

Abstract: We put forward an enantioselective method for chiral nanoparticles using optical tweezers. We demonstrate that the optical trapping force in a typical, realistic optical tweezing setup with circularly-polarized trapping beams is sensitive to the chirality of core-shell nanoparticles, allowing for efficient enantioselection. It turns out that the handedness of the trapped particles can be selected… ▽ More We put forward an enantioselective method for chiral nanoparticles using optical tweezers. We demonstrate that the optical trapping force in a typical, realistic optical tweezing setup with circularly-polarized trapping beams is sensitive to the chirality of core-shell nanoparticles, allowing for efficient enantioselection. It turns out that the handedness of the trapped particles can be selected by choosing the appropriate circular polarization of the trapping beam. The chirality of each individual trapped nanoparticle can be characterized by measuring the rotation of the equilibrium position under the effect of a transverse Stokes drag force. We show that the chirality of the shell gives rise to an additional twist, leading to a strong enhancement of the optical torque driving the rotation. Both methods are shown to be robust against variations of size and material parameters, demonstrating that they are particularly useful in (but not restricted to) several situations of practical interest in chiral plasmonics, where enantioselection and characterization of single chiral nanoparticles, each and every with its unique handedness and optical properties, are in order. In particular, our method could be employed to unveil the chiral response arising from disorder in individual plasmonic raspberries, synthesized by close-packing a large number of metallic nanospheres around a dielectric core. △ Less

Submitted 5 November, 2019; v1 submitted 6 June, 2019; originally announced June 2019.

Comments: 10 pages, 4 figures

Exploring low-energy neutrino physics with the Coherent Neutrino Nucleus Interaction Experiment (CONNIE)

Authors: Alexis Aguilar-Arevalo, Xavier Bertou, Carla Bonifazi, Gustavo Cancelo, Alejandro Castañeda, Brenda Cervantes Vergara, Claudio Chavez, Juan C. D'Olivo, João C. dos Anjos, Juan Estrada, Aldo R. Fernandes Neto, Guillermo Fernandez Moroni, Ana Foguel, Richard Ford, Juan Gonzalez Cuevas, Pamela Hernández, Susana Hernandez, Federico Izraelevitch, Alexander R. Kavner, Ben Kilminster, Kevin Kuk, H. P. Lima Jr, Martin Makler, Jorge Molina, Philipe Mota , et al. (8 additional authors not shown)

Abstract: The Coherent Neutrino-Nucleus Interaction Experiment (CONNIE) uses low-noise fully depleted charge-coupled devices (CCDs) with the goal of measuring low-energy recoils from coherent elastic scattering (CE$ν$NS) of reactor antineutrinos with silicon nuclei and testing nonstandard neutrino interactions (NSI). We report here the first results of the detector array deployed in 2016, considering an act… ▽ More The Coherent Neutrino-Nucleus Interaction Experiment (CONNIE) uses low-noise fully depleted charge-coupled devices (CCDs) with the goal of measuring low-energy recoils from coherent elastic scattering (CE$ν$NS) of reactor antineutrinos with silicon nuclei and testing nonstandard neutrino interactions (NSI). We report here the first results of the detector array deployed in 2016, considering an active mass 47.6 g (8 CCDs), which is operating at a distance of 30 m from the core of the Angra 2 nuclear reactor, with a thermal power of 3.8 GW. A search for neutrino events is performed by comparing data collected with reactor on (2.1 kg-day) and reactor off (1.6 kg-day). The results show no excess in the reactor-on data, reaching the world record sensitivity down to recoil energies of about 1 keV (0.1 keV electron-equivalent). A 95% confidence level limit for new physics is established at an event rate of 40 times the one expected from the standard model at this energy scale. The results presented here provide a new window to low-energy neutrino physics, allowing one to explore for the first time the energies accessible through the low threshold of CCDs. They will lead to new constrains on NSI from the CE$ν$NS of antineutrinos from nuclear reactors. △ Less

Submitted 10 October, 2019; v1 submitted 5 June, 2019; originally announced June 2019.

Comments: Updated to match the version accepted for publication in Physical Review D

Journal ref: Phys. Rev. D 100, 092005 (2019)

Negative optical torque on a microsphere in optical tweezers

Authors: K. Diniz, R. S. Dutra, L. B. Pires, N. B. Viana, H. M. Nussenzveig, P. A. Maia Neto

Abstract: We show that the optical force field in optical tweezers with elliptically polarized beams has the opposite handedness for a wide range of particle sizes and for the most common configurations. Our method is based on the direct observation of the particle equilibrium position under the effect of a transverse Stokes drag force, and its rotation around the optical axis by the mechanical effect of th… ▽ More We show that the optical force field in optical tweezers with elliptically polarized beams has the opposite handedness for a wide range of particle sizes and for the most common configurations. Our method is based on the direct observation of the particle equilibrium position under the effect of a transverse Stokes drag force, and its rotation around the optical axis by the mechanical effect of the optical torque. We find overall agreement with theory, with no fitting, provided that astigmatism, which is characterized separately, is included in the theoretical description. Our work opens the way for characterization of the trapping parameters, such as the microsphere complex refractive index and the astigmatism of the optical system, from measurements of the microsphere rotation angle. △ Less

Submitted 27 January, 2019; originally announced January 2019.

Comments: 10 pages, 5 figures

Non-Gaussian thermostatistical considerations upon the Saha equation

Authors: Bráulio B. Soares, Edésio M. Barboza Jr., Everton M. C. Abreu, Jorge Ananias Neto

Abstract: The Saha equation provides the relation between two consecutive ionization state populations, like the Maxwell-Boltzmann velocity distribution of the atoms in a gas ensemble. Saha equation can also consider the partitions functions for both states and its main application is in stellar astrophysics population statistics. This paper presents two non-Gaussian thermostatistical generalizations for th… ▽ More The Saha equation provides the relation between two consecutive ionization state populations, like the Maxwell-Boltzmann velocity distribution of the atoms in a gas ensemble. Saha equation can also consider the partitions functions for both states and its main application is in stellar astrophysics population statistics. This paper presents two non-Gaussian thermostatistical generalizations for the Saha equation: the first one towards the Tsallis nonextensive $q$-entropy and the other one is based upon Kaniadakis $κ$-statistics. Both thermostatistical formalisms are very successful when used in several complex astrophysical statistical systems and we have demonstrated here that they work also in Saha's ionization distribution. We have obtained new chemical $q$-potentials and their respective graphical regions with a well defined boundary that separated the two symmetric intervals for the $q$-potentials. The asymptotic behavior of the $q$-potential was also discussed. Besides the proton-electron, we have also investigated the complex atoms and pair production ionization reactions. △ Less

Submitted 27 December, 2018; originally announced January 2019.

Comments: 15 pages. Preprint format

Variational Procedure for Higher-Derivative Mechanical Models in a Fractional Integral Framework

Authors: C. F. L. Godinho, Nelson Panza, J. A. Helayël Neto

Abstract: We present both the Lagrangian and Hamiltonian procedures for treating higher-order equations of motion for mechanical models by adopting the Riemann-Liouville Fractional integral to describe their action. We point out and discuss its efficacy and difficulties. We also present the physical and geometric interpretations for the approach we pursue and present the details of a higher-order harmonic o… ▽ More We present both the Lagrangian and Hamiltonian procedures for treating higher-order equations of motion for mechanical models by adopting the Riemann-Liouville Fractional integral to describe their action. We point out and discuss its efficacy and difficulties. We also present the physical and geometric interpretations for the approach we pursue and present the details of a higher-order harmonic oscillator. △ Less

Submitted 18 August, 2018; originally announced August 2018.

Comments: 12 pages, 5 figures. arXiv admin note: text overlap with arXiv:1102.4532

Optimizing optical tweezing with directional scattering in composite microspheres

Authors: R. Ali, F. A. Pinheiro, F. S. S. Rosa, R. S. Dutra, P. A. Maia Neto

Abstract: Trapping of microspheres with a single focused laser beam is usually limited to materials with relative refractive indexes slightly larger than one. We show that directional light scattering can be employed to optically trap high-index materials. For this purpose, we propose a material platform to achieve zero backward scattering (ZBS), also known as the first Kerker condition, in a composite medi… ▽ More Trapping of microspheres with a single focused laser beam is usually limited to materials with relative refractive indexes slightly larger than one. We show that directional light scattering can be employed to optically trap high-index materials. For this purpose, we propose a material platform to achieve zero backward scattering (ZBS), also known as the first Kerker condition, in a composite media containing spherical inclusions of silica embedded in a SiC microsphere. By tuning the volume filling fraction of inclusions and the microsphere radius, stable trapping can be achieved, provided that ZBS is combined with the condition for destructive interference between the fields reflected at the external and internal interfaces of the microsphere when located at the focal point. We show that our proposal also holds even in the presence of a significant amount of spherical aberration, which is a common condition in most optical tweezers setups. In this case, achieving ZBS is essential for trapping high-index materials. △ Less

Submitted 18 June, 2018; originally announced June 2018.

Comments: 8 pages,6 figures

Journal ref: Phys. Rev. A 98, 053804 (2018)

Microscopic dynamical Casimir effect

Authors: Reinaldo de Melo e Souza, François Impens, Paulo A. Maia Neto

Abstract: We consider an atom in its ground state undergoing a non-relativistic oscillation in free space. The interaction with the electromagnetic quantum vacuum leads to two effects to leading order in perturbation theory. When the mechanical frequency is larger than the atomic transition frequency, the dominant effect is the motion-induced transition to an excited state with the emission of a photon carr… ▽ More We consider an atom in its ground state undergoing a non-relativistic oscillation in free space. The interaction with the electromagnetic quantum vacuum leads to two effects to leading order in perturbation theory. When the mechanical frequency is larger than the atomic transition frequency, the dominant effect is the motion-induced transition to an excited state with the emission of a photon carrying the excess energy. We compute the angular distribution of emitted photons and the excitation rate. On the other hand, when the mechanical frequency is smaller than the transition frequency, the leading-order effect is the parametric emission of photon pairs, which constitutes the microscopic counterpart of the dynamical Casimir effect. We discuss the properties of the microscopic dynamical Casimir effect and build a connection with the photon production by an oscillating macroscopic metallic mirror. △ Less

Submitted 6 March, 2018; originally announced March 2018.

Helicity and Vortex generation

Authors: Albert C. R. Mendes, Flavio Takakura, Everton M. C. Abreu, Patrick Paolo Silva, João Vitor Frossad, Jorge Ananias Neto

Abstract: In this paper we have continued the calculations made recently concerning he generalization of the minimal coupling prescription. We have obtained the Navier-Stokes equation for the charged fluid embedded into an electromagnetic field. We have analyzed the wave feature of the fields. Wave equations for velocity and vorticity were obtained and gauge choices were discussed. In this paper we have stu… ▽ More In this paper we have continued the calculations made recently concerning he generalization of the minimal coupling prescription. We have obtained the Navier-Stokes equation for the charged fluid embedded into an electromagnetic field. We have analyzed the wave feature of the fields. Wave equations for velocity and vorticity were obtained and gauge choices were discussed. In this paper we have studied the evolution of helicity and circulation from the Maxwell type formulation to the equations of a compressible fluid, charged in interaction with an electromagnetic field. We see that for both helicity and circulation there are terms that, in principle, can be considered as source terms or creation of circulation in the dynamics of fluids △ Less

Submitted 14 December, 2017; originally announced December 2017.

Comments: 9 pages. Preprint format. arXiv admin note: text overlap with arXiv:1609.06238

Double-layer force suppression between charged microspheres

Authors: D. S. Ether, F. S. S. Rosa, D. M. Tibaduiza, L. B. Pires, R. S. Decca, P. A. Maia Neto

Abstract: In this paper we propose a protocol to suppress double-layer forces between two microspheres immersed in a dielectric medium, being one microsphere metallic at a controlled potential ψM and the other a charged one either metallic or dielectric. The approach is valid for a wide range of distances between them. We show that, for a given distance between the two microspheres, the double-layer force c… ▽ More In this paper we propose a protocol to suppress double-layer forces between two microspheres immersed in a dielectric medium, being one microsphere metallic at a controlled potential ψM and the other a charged one either metallic or dielectric. The approach is valid for a wide range of distances between them. We show that, for a given distance between the two microspheres, the double-layer force can be totally suppressed by simply tuning ψM up to values dictated by the linearized Poisson-Boltzmann equation. Our key finding is that such values can be substantially different from the ones predicted by the commonly used proximity force approximation (PFA), also known as Derjaguin approximation, even in situations where the latter is expected to be accurate. The proposed procedure can be used to suppress the double-layer interaction in force spectroscopy experiments, thus paving the way for measurements of other surface interactions, such as Casimir dispersion forces. △ Less

Submitted 30 November, 2017; originally announced December 2017.

Journal ref: Phys. Rev. E 97, 022611 (2018)

Accelerated cosmos in a non-extensive setup

Authors: H. Moradpour, Alexander Bonilla, Everton M. C. Abreu, Jorge Ananias Neto

Abstract: Here, we consider a flat FRW universe whose its horizon entropy meets the Rényi entropy of non-extensive systems. In our model, the ordinary energy-momentum conservation law is not always valid. By applying the Clausius relation as well as the Cai-Kim temperature to the apparent horizon of a flat FRW universe, we obtain modified Friedmann equations. Fitting the model to the observational data on c… ▽ More Here, we consider a flat FRW universe whose its horizon entropy meets the Rényi entropy of non-extensive systems. In our model, the ordinary energy-momentum conservation law is not always valid. By applying the Clausius relation as well as the Cai-Kim temperature to the apparent horizon of a flat FRW universe, we obtain modified Friedmann equations. Fitting the model to the observational data on current accelerated universe, some values for the model parameters are also addressed. Our study shows that the current accelerating phase of universe expansion may be described by a geometrical fluid, originated from the non-extensive aspects of geometry, which models a varying dark energy source interacting with matter field in the Rastall way. Moreover, our results indicate that the probable non-extensive features of spacetime may also be used to model a varying dark energy source which does not interact with matter field, and is compatible with the current accelerated phase of universe. △ Less

Submitted 18 November, 2017; originally announced November 2017.

Comments: Accepted by Phys. Rev. D

Faddeev-Jackiw approach of the noncommutative spacetime Podolsky electromagnetic theory

Authors: Everton M. C. Abreu, Rafael L. Fernandes, Albert C. R. Mendes, Jorge Ananias Neto

Abstract: The interest in higher derivatives field theories has its origin mainly in their influence concerning the renormalization properties of physical models and to remove ultraviolet divergences. The noncommutative Podolsky theory is a constrained system that cannot by directly quantized by the canonical way. In this work we have used the Faddeev-Jackiw method in order to obtain the Dirac brackets of t… ▽ More The interest in higher derivatives field theories has its origin mainly in their influence concerning the renormalization properties of physical models and to remove ultraviolet divergences. The noncommutative Podolsky theory is a constrained system that cannot by directly quantized by the canonical way. In this work we have used the Faddeev-Jackiw method in order to obtain the Dirac brackets of the NC Podolsky theory. △ Less

Submitted 4 May, 2017; originally announced May 2017.

Comments: 17 pages, preprint format