arXiv subjects

S. Roy

Publications and source records attributed to S. Roy.

At least 19 recordsLinked to original sources

arXiv2026

X-ray Fractional Orbital Angular Momentum from Coherent Magnetic Scattering

Artificial spin ice (ASI) based on a square lattice with a topological defect are known to generate orbital angular momentum (OAM) in diffracted X-ray beams. A previous investigation of ASI with even-charge topological defects showed both charge and magnetic X-ray scattering yield photon OAM, but these were confined to integer OAM values. However, the period of the square ASI's antiferromagnetic ground state is twice the period of the structural ground state, which should lead to fractional OAM from magnetic scattering when the topological defect has odd-charge. We employed photoemission electron microscopy to confirm that these ASIs order into antiferromagnetic ground states with protected superdomain walls that provide the phase discontinuity required for fractional OAM. Resonant, coherent X-ray scattering from ASIs with topological defects of charge 1 yields integer-valued X-ray OAM at structural charge peaks and fractional X-ray OAM at magnetic peaks. For thermally active ASIs, the fractional OAM beam exhibits fluctuations in the position of the phase discontinuity and thus dynamic rotation of the beam.

physics.optics↗

arXiv2026

Chaos in the dynamics of electromagnetic solitons in relativistic degenerate plasmas

We propose a coupled system for the nonlinear interaction between high-frequency, circularly polarized, intense electromagnetic (EM) waves and low-frequency electron-density perturbations, driven by the EM-wave ponderomotive force, in an unmagnetized plasma composed of fully degenerate relativistic electrons and stationary positive ions, including a higher-order correction to the nonlocal nonlinearity. We show that the modulational instability (MI) growth rate associated with the generation of EM envelope solitons gets significantly reduced with a slight increase in either the nonlocal nonlinear correction or the degeneracy parameter. Furthermore, a three-wave temporal model predicts the existence of quasiperiodic and chaotic states of EM solitons while interacting with longitudinal electron density perturbations. We show that the greater the degeneracy (or the higher the contribution from the nonlocal correction), the smaller the instability domain of modulation wave numbers; thus, degeneracy favors the stability of EM soliton evolution. The existence of temporal chaos in a low-dimensional model could be a signature of the development of spatiotemporal chaos in the complete nonlinear model, in which many electromagnetic solitons can be excited and saturated as they interact with electron plasma waves.

physics.plasm-ph↗

arXiv2025

Isoscalar Giant Resonances in Highly-Deformed $^{172}$Yb

To study the isoscalar giant resonances in a deformed case, background-free $\alpha$-particle inelastic scattering measurements using a 386 MeV $\alpha$ beam were performed on the highly-deformed $^{172}$Yb nucleus using the Grand Raiden spectrometer at the Research Center for Nuclear Physics (RCNP) at very forward angles, including $0^\circ$. The strength distributions for the isoscalar giant resonances up to $L \leq 3$ were obtained using multipole decomposition analysis. The isoscalar giant monopole resonance (ISGMR) strength exhibits a splitting into two components, interpreted as the coupling of the ISGMR with the $K=0$ component of the isoscalar giant quadrupole resonance (ISGQR). A \textit{bimodal} structure is observed in the strength distribution of the isoscalar giant dipole resonance. The ISGQR strength shows an enhancement near 25 MeV, attributed to the excitation of an overtone mode, while the broadening of the main-tone peak is associated with nuclear deformation. The experimental results are well reproduced by theoretical strength distributions calculated using the quasiparticle finite amplitude method for $L \leq 3$.

nucl-ex↗

arXiv2025

Hadron Physics Opportunities at FAIR

This White Paper outlines a coordinated, decade-spanning programme of hadron and QCD studies anchored at the GSI/FAIR accelerator complex. Profiting from intense deuteron, proton and pion beams coupled with high-rate capable detectors and an international theory effort, the initiative addresses fundamental questions related to the strong interaction featuring confinement and dynamical mass generation. This includes our understanding of hadron-hadron interactions and the composition of hadrons through mapping the baryon and meson spectra, including exotic states, and quantifying hadron structure. This interdisciplinary research connects topics in the fields of nuclear, heavy-ion, and (nuclear) astro (particle) physics, linking, for example, terrestrial data to constraints on neutron star structure. A phased roadmap with SIS100 accelerator start-up and envisaged detector upgrades will yield precision cross sections, transition form factors, in-medium spectral functions, and validated theory inputs. Synergies with external programmes at international accelerator facilities worldwide are anticipated. The programme is expected to deliver decisive advances in our understanding of non-perturbative (strong) QCD and astrophysics, and high-rate detector and data-science technology.

hep-ex↗

arXiv2025

Factors Controlling the Statistics of Magnetic Reconnection in MHD Turbulence

We study the statistics of dynamical quantities associated with magnetic reconnection events embedded in a sea of strong background magnetohydrodynamic (MHD) turbulence using direct numerical simulations. We focus on the relationship of the reconnection properties to the statistics of global turbulent fields. For the first time, we show that the distribution in turbulence of reconnection rates (determined by upstream fields) is strongly correlated with the magnitude of the global turbulent magnetic field at the correlation scale. The average reconnection rates, and associated dissipation rates, during turbulence are thus much larger than predicted by using turbulent magnetic field fluctuation amplitudes at the dissipation or kinetic scales. Magnetic reconnection may therefore be playing a major role in energy dissipation in astrophysical and heliospheric turbulence.

physics.plasm-ph↗

arXiv2025

Magnetically modified double slit based x-ray interferometry

We demonstrate an experimental approach to determine magneto-optical effects which combines x-ray magnetic circular dichroism (XMCD) with x-ray interferometry, based on the concepts of Young's canonical double slit. By covering one of two slits with a magnetic thin film and employing XMCD, we show that it is possible to determine both the real and the imaginary parts of the complex refractive index by measuring the fringe shifts that occur due to a change in the sample magnetization. Our hybrid spectroscopic-interferometric methodology provides a means to probe changes in the magnetic refractive index in terms of the electron spin moment.

cond-mat.mtrl-sci↗

arXiv2025

Anomaly resolution by non-invertible symmetries

In this paper we generalize previous results on anomaly resolution to noninvertible symmetries. Briefly, given a global symmetry G of some theory with a 't Hooft anomaly rendering it ungaugeable, the idea of anomaly resolution is to extend G to a larger anomaly-free symmetry of the same theory with a trivially-acting kernel. In previous work, several of the coauthors demonstrated that in two-dimensional theories, by virtue of decomposition, gauging the larger symmetry is equivalent to a disjoint union of theories in which a nonanomalous subgroup of G is gauged. In this paper, we consider examples in which the larger symmetry is not a group, but instead a noninvertible symmetry defined by some fusion category. In principle the same ideas apply to the case that G itself is noninvertible. We discuss the construction of larger symmetries using both SymTFT methods as well as algebraically via (quasi-)Hopf algebras.

hep-th↗

arXiv2025

Investigation of Direct Nuclear Reactions in a Storage Ring Using In-Ring Detection

\textbf{Background:} Experiments involving nuclear reactions in a storage ring offer exceptional possibilities for precise measurements in inverse kinematics. These experiments provide excellent angular and energy resolution by particle spectroscopy, in addition to high luminosities. However, the extremely low-pressure environment maintained in the storage rings poses significant difficulties for experiments employing detectors or any outgassing material in the ring. \textbf{Purpose:} To investigate nuclear reactions in inverse kinematics using the storage-ring technique. The reactions were induced by scattering of a ${}^{20}\mathrm{Ne}$ beam off a hydrogen target at an energy of 50~MeV/u. \textbf{Method:} A beam of fully stripped ${}^{20}$Ne ions was injected into the ESR storage ring at an energy of 50 MeV/u. The beam interacted with an internal hydrogen gas-jet target. An ultra-high vacuum compatible detector setup was installed around the gas jet inside the ring to measure the recoiling particles generated by nuclear reactions. \textbf{Results:} Multiple reaction channels were observed during the experiment. In particular, we present the results from studies on elastic and inelastic scattering, as well as the neutron transfer reaction ${}^{20}\mathrm{Ne}(p,d){}^{19}\mathrm{Ne}^*$. The experimental data were compared to calculations that took into account the most significant excited states, using a coupled-reaction channel approach. A very good agreement with the experimental data was achieved. \textbf{Conclusions:} The present results are the first demonstration of the investigation transfer reactions using detectors directly installed in the ring. This provides an important proof-of-principle for prospective studies with far-from-stability radioactive beams in the future.

nucl-ex↗

arXiv2024

Effect of ground-state deformation on the Isoscalar Giant Monopole Resonance and the first observation of overtones of the Isoscalar Giant Quadrupole Resonance in rare-earth Nd isotopes

The strength distributions of the Isoscalar Giant Monopole Resonance (ISGMR) and Isoscalar Giant Quadrupole Resonance (ISGQR) in 142,146-150Nd have been determined via inelastic alpha-particle scattering with the Grand Raiden (GR) Spectrometer at the Research Center for Nuclear Physics (RCNP), Japan. In the deformed nuclei 146-150Nd, the ISGMR strength distributions exhibit a splitting into two components, while the nearly spherical nucleus 142Nd displays a single peak in the ISGMR strength distribution. A noteworthy achievement in this study is the first-time detection of overtones in the Isoscalar Giant Quadrupole Resonance (ISGQR) strength distributions within Nd isotopes at an excitation energy around 25 MeV obtained through Multipole Decomposition Analysis (MDA).

nucl-ex↗

arXiv2024

Nematicity of a Magnetic Helix

A system that possesses translational symmetry but breaks orientational symmetry is known as a nematic phase. While there are many examples of nematic phases in a wide range of contexts, such as in liquid crystals, complex oxides, and superconductors, of particular interest is the magnetic analogue, where the spin, charge, and orbital degrees of freedom of the electron are intertwined. The difficulty of spin nematics is the unambiguous realization and characterization of the phase. Here we present an entirely new type of magnetic nematic phase, which replaces the basis of individual spins with magnetic helices. The helical basis allows for the direct measurement of the order parameters with soft X-ray scattering and a thorough characterization of the nematic phase and its thermodynamic transitions. We discover two distinct nematic phases with unique spatio-temporal correlation signatures. Using coherent X-ray methods, we find that near the phase boundary between the two nematic phases, fluctuations coexist on the timescale of both seconds and sub-nanoseconds. Additionally, we have determined that the fluctuations occur simultaneously with a reorientation of the magnetic helices, indicating that there is spontaneous symmetry breaking and new degrees of freedom become available. Our results provide a novel framework for characterizing exotic phases and the phenomena presented can be mapped onto a broad class of physical systems.

cond-mat.mtrl-sci↗

arXiv2024

First (calibration) experiment using proton beam from FRENA at SINP

This work presents the first calibration experiment of a 3 MV Tandetron accelerator, FRENA, performed in May 2022. The $^7$Li(p,n) reaction threshold was measured to calibrate the terminal voltage measuring device. A LiF target of thickness 175 $\mu$g/cm$^2$ was used in the experiment. The measured threshold was 1872$\pm$2.7 keV, indicating 6$-$10 keV energy shift.

physics.ins-det↗

arXiv2023

GMRT observations of the radio trail from CXOU J163802.6-471358

The X-ray source CXOU J163802.6-471358is thought to be a pulsar wind nebula (PWN), as it shows an extended, $\approx 40$ arcsec trail from a compact source. Here we present GMRT observations of this source at 330 and 1390 MHz, which reveal a remarkable linear radio trail $\approx 90$ arcsec in extent. Although the radio trail points back to the supernova remnant (SNR) G338.1+0.4, $\approx 50$ arcmin from ,CXOU J163802.6-471358 associating it with this remnant would require a very large velocity for the pulsar. There are no known galactic SNRs close to the PWN and radio trail. No pulsar has yet been identified in CXOU J163802.6-471358, but if one could be found, this would allow more quantitative studies of the PWN and radio trail to be made.

astro-ph.GA↗

arXiv2023

Electronic Transport and Fermi Surface Topology of Zintl Phase Compound SrZn2Ge2

We report a comprehensive study on the electronic transport properties of SrZn2Ge2 single crystals. The electrical resistivity of the compound exhibits metallic behavior, following a T^2 dependence below 35 K, consistent with the Fermi liquid behavior. However, a notable deviation is observed from this behavior at lower temperatures as a pronounced resistivity plateau emerges below 10 K. This plateau is remarkably robust, and persists under the magnetic fields of up to 10 T. Both the transverse and longitudinal magnetoresistance exhibit a crossover at critical field B* from weak-field quadratic-like to high-field unsaturated linear field dependence at low temperatures (T \leq 50 K). Possible sources of linear magnetoresistance are discussed based on the Fermi surface topology, classical and quantum transport models. The Hall resistivity data establish SrZn2Ge2 as a multiband system with contributions from both the electrons and holes. The Hall coefficient is observed to decrease with increasing temperature and magnetic field, changing its sign from positive to negative. The negative Hall coefficient observed at low temperatures in high fields and at high temperatures over the entire field range suggests that the highly mobile electron charge carriers dominate the electronic transport. Our first-principles calculations show that nontrivial topological surface states exist in SrZn2Ge2 within the bulk gap along the Gamma-M path. Notably, these surface states extend from the valence to conduction band with their number varying based on the Sr and Ge termination plane. The Fermi surface of the compound exhibits a distinct tetragonal petal-like structure, with one open and several closed surfaces. Overall, these findings offer crucial insights into the mechanisms underlying the electronic transport of the compound.

cond-mat.str-el↗

arXiv2023

Ultrafast Raman thermometry in driven YBa$_2$Cu$_3$O$_{6.48}$

Signatures of photo-induced superconductivity have been reported in cuprate materials subjected to a coherent phonon drive. A 'cold' superfluid was extracted from the transient Terahertz conductivity and was seen to coexist with 'hot' uncondensed quasi-particles, a hallmark of a driven-dissipative system of which the interplay between coherent and incoherent responses are not well understood. Here, time resolved spontaneous Raman scattering was used to probe the lattice temperature in the photo-induced superconducting state of YBa2Cu3O6.48. An increase in lattice temperature of approximately 80 K was observed by measuring the time dependent Raman scattering intensity of an undriven 'spectator' phonon mode. This is to be compared with an estimated increase in quasi-particle temperatures of nearly 200 K. These temperature changes provide quantitative information on the nature of the driven state and its decay, and may provide a strategy to optimize this effect.

cond-mat.supr-con↗

arXiv2023

A hybrid quantum-classical fusion neural network to improve protein-ligand binding affinity predictions for drug discovery

The field of drug discovery hinges on the accurate prediction of binding affinity between prospective drug molecules and target proteins, especially when such proteins directly influence disease progression. However, estimating binding affinity demands significant financial and computational resources. While state-of-the-art methodologies employ classical machine learning (ML) techniques, emerging hybrid quantum machine learning (QML) models have shown promise for enhanced performance, owing to their inherent parallelism and capacity to manage exponential increases in data dimensionality. Despite these advances, existing models encounter issues related to convergence stability and prediction accuracy. This paper introduces a novel hybrid quantum-classical deep learning model tailored for binding affinity prediction in drug discovery. Specifically, the proposed model synergistically integrates 3D and spatial graph convolutional neural networks within an optimized quantum architecture. Simulation results demonstrate a 6% improvement in prediction accuracy relative to existing classical models, as well as a significantly more stable convergence performance compared to previous classical approaches.

quant-ph↗

arXiv2023

Modulation of electromagnetic waves in a relativistic degenerate plasma at finite temperature

We study the modulational instability (MI) of a linearly polarized electromagnetic (EM) wave envelope in an intermediate regime of relativistic degenerate plasmas at a finite temperature $(T\neq0)$ where the thermal energy $(K_BT)$ and the rest-mass energy $(m_ec^2)$ of electrons do not differ significantly, i.e., $\beta_e\equiv K_{B}T/m_{e}c^2\lesssim~(\rm{or}~\gtrsim) 1$, but, the Fermi energy $(K_BT_F)$ and the chemical potential energy $(\mu_e)$ of electrons are still a bit higher than the thermal energy, i.e., $T_F>T$ and $\xi_{e}=\mu_e/K_{B}T\gtrsim1$. Starting from a set of relativistic fluid equations for degenerate electrons at finite temperature, coupled to the EM wave equation and using the multiple scale perturbation expansion scheme, a one-dimensional nonlinear Sch{\"o}dinger (NLS) equation is derived, which describes the evolution of slowly varying amplitudes of EM wave envelopes. Then we study the MI of the latter in two different regimes, namely $\beta_e<1$ and $\beta_e>1$. Like unmagnetized classical cold plasmas, the modulated EM envelope is always unstable in the region $\beta_e>4$. However, for $\beta_e\lesssim1$ and $1<\beta_e<4$, the wave can be stable or unstable depending on the values of the EM wave frequency, $\omega$ and the parameter $\xi_e$. We also obtain the instability growth rate for the modulated wave and find a significant reduction by increasing the values of either $\beta_e$ or $\xi_e$. Finally, we present the profiles of the traveling EM waves in the form of bright (envelope pulses) and dark (voids) solitons, as well as the profiles (other than traveling waves) of the Kuznetsov-Ma breather, the Akhmediev breather, and the Peregrine solitons as EM rogue (freak) waves, and discuss their characteristics in the regimes of $\beta_e\lesssim1$ and $\beta_e>1$.

physics.plasm-ph↗

arXiv2022

Chaos and complexity in the dynamics of nonlinear Alfv\'en waves in a magnetoplasma

The nonlinear dynamics of circularly polarized dispersive Alfv{\'e}n wave (AW) envelopes coupled to the driven ion sound waves of plasma slow response is studied in a uniform magnetoplasma. By restricting the wave dynamics to a few number of harmonic modes, a low-dimensional dynamical model is proposed to describe the nonlinear wave-wave interactions. It is found that two subintervals of the wave number of modulation $k$ of AW envelope exists, namely $(3/4)k_c<k<k_c$ and $0<k<(3/4)k_c$, where $k_c$ is the critical value of $k$ below which the modulational instability (MI) occurs. In the former, where the MI growth rate is low, the periodic and/or quasi-periodic states are shown to occur, whereas the latter, where the MI growth is high, brings about the chaotic states. The existence of these states is established by the analyses of Lyapunov exponent spectra together with the bifurcation diagram and phase-space portraits of dynamical variables. Furthermore, the complexities of chaotic phase spaces in the nonlinear motion are measured by the estimations of the correlation dimension (CD) as well as the approximate entropy (ApEn), and compared with those for the known H{\'e}non map and the Lorenz system in which a good qualitative agreement is noted. The chaotic motion thus predicted in a low-dimensional model can be a prerequisite for the onset of Alfv{\'e}nic wave turbulence to be observed in a higher dimensional model that and is relevant in the Earth's ionosphere and magnetosphere.

physics.plasm-ph↗

arXiv2022

White Paper on Light Sterile Neutrino Searches and Related Phenomenology

This white paper provides a comprehensive review of our present understanding of experimental neutrino anomalies that remain unresolved, charting the progress achieved over the last decade at the experimental and phenomenological level, and sets the stage for future programmatic prospects in addressing those anomalies. It is purposed to serve as a guiding and motivational "encyclopedic" reference, with emphasis on needs and options for future exploration that may lead to the ultimate resolution of the anomalies. We see the main experimental, analysis, and theory-driven thrusts that will be essential to achieving this goal being: 1) Cover all anomaly sectors -- given the unresolved nature of all four canonical anomalies, it is imperative to support all pillars of a diverse experimental portfolio, source, reactor, decay-at-rest, decay-in-flight, and other methods/sources, to provide complementary probes of and increased precision for new physics explanations; 2) Pursue diverse signatures -- it is imperative that experiments make design and analysis choices that maximize sensitivity to as broad an array of these potential new physics signatures as possible; 3) Deepen theoretical engagement -- priority in the theory community should be placed on development of standard and beyond standard models relevant to all four short-baseline anomalies and the development of tools for efficient tests of these models with existing and future experimental datasets; 4) Openly share data -- Fluid communication between the experimental and theory communities will be required, which implies that both experimental data releases and theoretical calculations should be publicly available; and 5) Apply robust analysis techniques -- Appropriate statistical treatment is crucial to assess the compatibility of data sets within the context of any given model.

hep-ex↗