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Physics

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Sunday 9 August

Solar and Stellar Astrophysics

Sun-to-Earth Coronal Mass Ejection Simulations From a Vector Magnetogram

Yifu An, Gábor Tóth and Beatrice Popescu Braileanu

We implement a novel approach to performing Sun-to-Earth coronal mass ejection (CME) simulations and test it on three geo-effective space weather events. Using a vector magnetogram observed prior to the CME as the boundary condition, we reconstruct non-linear force free field (NLFFF) solutions in solar active regions with an established magneto-frictional method. We find a pre-eruption solar corona containing the NLFFF in the AWSoM model, which then spontaneously erupts. We apply STITCH, a photospheric driving method, when needed, to increase the strength of the CME shock. The eruptions successfully produce magnetic flux ropes (MFRs) that propagate to 1 au in the full MHD simulation. The synthetic white light images of the simulated CMEs share a striking resemblance in shape to observations. The interplanetary MFRs (IMFRs) arrive at 1 au with a 1.5- to 9-hour error. A comparison of simulated solar wind plasma with in-situ measurements shows that IMFR crossing can reproduce a southward $B_z$ and often its magnitudes, which determine the geo-effectiveness of the event.
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Astrophysics of Galaxies

Exploration of UV-bright sources in Globular cluster NGC 3201 using UVIT observations

Manasi Kulkarni, Sonika Piridi, Ranjan Kumar et al. (+1 more)

We present a comprehensive study of the ultraviolet (UV)-bright stellar population in the globular cluster NGC 3201 using the Ultraviolet Imaging Telescope (UVIT) onboard AstroSat. By combining far-UV photometry of the UVIT F148W and F169M filters with Gaia and ground-based telescope optical data, we construct UV$-$optical color-magnitude diagrams (CMDs) to identify UV-bright stellar evolutionary phases. Physical parameters of all detected sources are derived by fitting stellar atmosphere models to the observed multi-wavelength spectral energy distributions (SEDs). The effective temperatures of blue horizontal branch stars (BHBs) span the range 7250$-$11250 K. We identify two extreme horizontal-branch stars (EHBs) with effective temperatures of approximately 25,000 K and 17,000 K; one lies within the cluster core radius ($r_\mathrm{c}$=1.3$'$), while the other is located outside. We also detect two candidate “gap” objects in the transitional phase between HB stars and white dwarfs, which may represent hot blue hook (BHk) stars. For the blue straggler stars (BSSs), we determine effective temperatures, radii, and luminosities through SED fittings, and estimate their masses and isochrone-equivalent ages using PARSEC isochrones. Finally, we studied the normalized cumulative radial distribution of the observed BHB stars, BSSs, MS stars, RGB stars, and variable stars along with the specific frequency of BSSs across the cluster. These results provide new insights into the late-stage stellar evolution and dynamical processes in NGC 3201.
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All authors Manasi Kulkarni, Sonika Piridi, Ranjan Kumar, Ananta C. Pradhan

Nuclear Experiment

High Precision Fundamental Physics Experiments at JLab with Spin-transparent Storage Rings of Low-energy Polarized Electron Beams

Vladimir Khachatryan, Riad Suleiman, Alberto Accardi et al. (+26 more)

A breakthrough in fundamental physics experiments measuring particle spin precession may happen if spin-transparent storage rings become adopted tools for such experiments. We present a new design of highly specialized table-sized storage rings, which use low-energy polarized electron beams and Mott polarimetry. Based on the spin transparency ansatz, the spin precession stemming from the magnetic dipole moment is canceled at any beam energy after an electron's turn along the periodic orbit in the ring. Meanwhile, a spin precession induced by the fundamental physics of interest, e.g., the electron's permanent electric dipole moment (EDM) and/or ultralight-dark-matter-mediated forces such as axions, will accumulate. However, capitalizing on such types of rings is not only desirable for measurements of EDMs and axion searches relevant to $CP$ violation and matter-antimatter asymmetry in the Universe, but may also find very promising applications in quantum computing.
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All authors Vladimir Khachatryan, Riad Suleiman, Alberto Accardi, Carlos Ayerbe Gayoso, Marco Battaglieri, Devesh Bhattarai, Silviu Covrig Dusa, Yaroslav Derbenev, Forrest Friesen, Joseph Grames, Paul Guèye, Tyler J. Hague, Ching Him Leung, Wenliang Li, Magno V.T. Machado, Preet Mann, Vasiliy Morozov, Son Nguyen, Michael Nycz, Howard Oh, Udit Raha, Mario Reig, Marco Schreck, Nathaniel Sherrill, Ye Tian, Zakia Tithi, Alexandre Vieira, Erik Wrightson, Zichen Yin

General Relativity and Quantum Cosmology

Charged Kerr–Levi-Civita geometries in Einstein–Maxwell and low-energy heterotic string theory

Haryanto M. Siahaan

We construct and compare two charged rotating extensions of the Kerr–Levi-Civita geometry. In Einstein–Maxwell theory, a fixed magnetic Kerr–Newman Ernst representative is inverted, and covariance of the coupled Ernst equations, integrability of the dragging and electric-potential quadratures, and the field equations are verified. The resulting local line element agrees with a strong-field representative obtained independently, but no global equivalence of the azimuthal quotients is assumed. In low-energy heterotic string theory, the Hassan–Sen map is instead applied after the vacuum Kerr–Levi-Civita inversion, generating Maxwell, dilaton, and Kalb–Ramond fields. Both branches possess regular local Killing horizons. For the Einstein–Maxwell branch, an exact denominator factorization proves that the subextreme exterior contains neither Ernst zeros nor azimuthal closed timelike curves. The former Kerr ring has finite curvature, although it lies inside an interior region of timelike azimuthal orbits. Its Kretschmann scalar has the form $8\mathcal P_{\rm N}/\mathcal H^6$ and approaches a parameter-independent Levi-Civita law at fixed off-axis latitude. The heterotic branch is qualitatively different: the real component connected to the horizon terminates at a finite-radius $\Lambda=0$ surface. Exact string-frame slice factorizations and independent Einstein-frame calculations show that this surface is a curvature singularity rather than a conformal-frame artifact. Both families are generically Petrov type I. The results distinguish exact local solution generation from the unresolved construction of complete global spacetimes and the identification of possible distributional sources.
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Fluid Dynamics

Data-Driven Surrogate Modeling for Micromixing of Non-Newtonian Fluids in Sinusoidal Converging-Diverging Microchannels

Kritagya Sharma and Bimalendu Mahapatra

Micromixing of non-Newtonian fluids remains challenging because laminar flow at microscales restricts transverse transport primarily to molecular diffusion. In this study, we investigate the transport mechanisms governing passive micromixing of a Carreau–Yasuda fluid in two-dimensional sinusoidal converging–diverging microchannels and develop a surrogate-assisted framework for their multi-objective design. We perform high-fidelity finite-volume simulations by systematically varying the wall-amplitude ratio, phase offset, and wave count under creeping-flow conditions. The results show that successive contraction–expansion units enhance mixing through the combined effects of interface stretching, elevated shear rates, and shear-thinning-induced viscosity reduction. These mechanisms improve scalar transport but simultaneously increase pressure drop, creating an inherent trade-off between mixing performance and hydraulic resistance. To efficiently explore the multidimensional design space, we construct surrogate models from high-fidelity numerical simulations and identify Gaussian Process Regression (GPR) as the most accurate predictor of both the mixing index and pressure drop. Coupling the validated GPR surrogate with Non-dominated Sorting Genetic Algorithm II (NSGA-II) accurately reproduces the Pareto front obtained from the high-fidelity simulations and identifies optimal microchannel geometries that balance mixing enhancement against pressure loss. The proposed machine learning framework provides a fast, accurate, and physically consistent strategy for the multi-objective design of passive micromixers for non-Newtonian fluids.
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Statistical Mechanics

Lee-Yang Theory Guided Force Field Refinement Based on Phase Diagrams

Bin Jin, Qijun Ye, Xinzheng Li et al. (+2 more)

We propose a general framework for automatic force field refinement guided by phase diagrams, grounded in Lee-Yang phase transition theory. The central idea is to directly use the partition function modulus as a phase-diagram-guided optimization target. Evaluating the modulus at points close to the real axis, where the Lee-Yang zeros are mostly associated with the phase transition, is more physically meaningful and avoids the numerical difficulty of explicitly solving for the zeros. This approach requires no system-specific order parameters or response properties for characterizing phase transition points, making it universal across various discontinuous phase transitions and material systems. We validate the method on refining parameters of a Lennard-Jones potential covering both gas-liquid and solid-liquid transitions, and a Cu embedded-atom method potential based on experimental melting curves. The refined force fields reproduce the target phase diagrams with significant improvement across all systems. For Cu, the refinement simultaneously improves predictions of enthalpy and heat capacity, which are observables beyond the optimization target. These results establish Lee-Yang theory as a practical tool for contemporary force field development.
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All authors Bin Jin, Qijun Ye, Xinzheng Li, Kuang Yu, Shenzhen Xu

Quantum Physics

Levitated Milligram-scale Ferromagnetic Magnetometer at Room Temperature

Yuanji Sheng, Kenan Tian, Rui Li et al. (+4 more)

Levitated mechanical oscillators are emerging ultrasensitive sensors with tremendous potential in both applied and fundamental physics. Levitated ferromagnets, with internal spin noises rapidly averaged, promise ultrahigh magnetic sensitivity. Here, we demonstrate a milligram-scale diamagnetically levitated ferromagnet system operating at room temperature. Through optimized geometry and multi-channel dissipation control, we achieve a magnetic sensitivity of 23~fT$/\sqrt{\text{Hz}}$ at frequency of 100-Hz level. We anticipate that a ferromagnetic magnetometer with subfemtotesla sensitivity is within reach, after modest technical improvements. This platform establishes a high-performance magnetometer for biomagnetic field detection and beyond-standard-model force searches.
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All authors Yuanji Sheng, Kenan Tian, Rui Li, Yiming Chen, Dingjiang Long, Siwen Chen, Peiran Yin

Optics

Undulating Diamond Photonic Crystal in the Royal Jewel Butterfly: Circumventing Refractive Index Limits to Defy Iridescence

Yuanbo Li, Shuo Huang, Xi Wang et al. (+9 more)

The modest refractive-indices of biomolecules place fundamental constraints on the optical performance of natural photonic organisms. To overcome this limitation, organisms reshape basic optical structures into hierarchical architectures, exhibiting performance rivals that of high-index materials. Here we show how the Royal Jewel butterfly (Hypochrysops polycletus) employs such a strategy to circumvent the low refractive-index of chitin to achieve an unusual combination of intense structural colouration and remarkably weak angular dependence. A single-diamond photonic crystal, which was hailed as the 'holy grail' and documented only in beetles and weevils, has now been discovered in the butterfly. It deforms into a hierarchically undulated superstructure guided by basal lamina and correlated with quasi-twinning boundaries with mirror symmetry. The scale surface is thus fully terminated by inclined {111} facets essential for fundamental bandgap, producing bright specular Bragg reflection at intermediate to high angles and low-angle radiation enabled by simultaneously coupling localised resonances populated through anisotropic Bloch transport, thereby transforming an otherwise strongly angle-dependent photonic crystal into a vivid, angle-robust optical structure. Following this optical concept, an artificially angle-insensitive optical prototype was fabricated through two-photon polymerisation, validating the mechanism as a transferable design principle at the intersection of fundamental nanophotonics and bio-inspired engineering.
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All authors Yuanbo Li, Shuo Huang, Xi Wang, Congcong Cui, Hao Chen, Yuqin Xiong, Wang Zhang, Matthias Saba, Xueyan Feng, Bo Chen, Yuanyuan Cao, Lu Han

Pattern Formation and Solitons · Cross-listed from math.AP

Dynamical behavior of diffusively coupled scalar differential equations as Wentzell boundary conditions

Merlin Pelz

Two identical scalar dynamical systems coupled through a scalar diffusion equation are studied herein, with respect to bifurcations from a symmetric steady-state to symmetric and asymmetric steady-states and to in-phase and anti-phase oscillations. Numerical continuations based on the developed theory show the shape of the bifurcation branches and the attracting nonlinear states far from bifurcation onset and confirm their, for the most part, derived stability. This study extends the work on the dynamical properties of a single scalar dynamical system coupled to its own delay through an adjacent diffusion field and quantifies further the delay of diffusive information transmission between two such Wentzell boundaries. The mathematical system is motivated by modeling biological membranes with yet unknown effective local fluxes that are coupled to bulk diffusion.
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Materials Science

High Thermal Conductivity of Back-End-of-Line Compatible Diamond Films

Jinwen Liu, Chufei Cheng, Feifei Tan et al. (+6 more)

Back-end-of-line (BEOL) thermal management requires electrically insulating heat-spreading dielectric that can be integrated within thermal budgets below 400 C. Here, we report polycrystalline diamond films grown directly on Si at a substrate temperature below 400C. Two films with average thickness of 760 and 1000 nm were characterized by Raman spectroscopy, scanning electron microscopy (SEM), and time-domain thermoreflectance (TDTR). Raman spectra show a sharp diamond peak with minor signatures of non-diamond carbon, while SEM reveals lateral growth and large grain size. Temperature dependent TDTR measurements were performed from room temperature to 100C. Sensitivity analysis indicates that the sensitivity of cross-plane thermal conductivity is comparative to the in-plane thermal conductivity. Accordingly, the films were analyzed using an isotropic thermal model by considering the nearly-isotropic grain structure, yielding room temperature effective thermal conductivity of 73 and 86 W m-1 K-1, respectively. These values are about two orders of magnitude higher than those of conventional dielectric materials and demonstrate the potential of diamond films grown at low temperatures as dielectric heat-spreading layers.
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All authors Jinwen Liu, Chufei Cheng, Feifei Tan, Jinquan Zhang, Di Lu, Bing Dai, Jiaqi Zhu, Runsheng Wang, Zhe Cheng

General Relativity and Quantum Cosmology

EFT Corrections to Photon Propagation and Gravitational Lensing in an Ellis-Bronnikov Wormhole

Takamasa Kanai

We investigate strong gravitational lensing by an Ellis-Bronnikov (EB) wormhole in the presence of effective field theory (EFT) corrections to photon propagation. We derive the modified photon propagation law induced by non-minimal couplings between the electromagnetic field and spacetime curvature, which leads to polarization-dependent photon trajectories in the EB wormhole spacetime. Using the strong deflection limit, we derive the corrections to the photon sphere and the logarithmically divergent part of the deflection angle. Although the EFT corrections are parametrically small, their contributions can become appreciable near the photon sphere. In particular, the $R_{\mu\nu}F^{\mu\rho}F^{\nu}{}_{\rho}$ interaction, which is nonvanishing for the EB wormhole but absent in the Schwarzschild spacetime, contributes to the strong-deflection coefficients. This may provide a distinctive lensing signature for observationally distinguishing wormholes from black holes.
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General Relativity and Quantum Cosmology

Construction of an analytic multi-component accretion environment and its application to Kerr black hole imaging

Shiyang Hu, Dan Li, Chen Deng et al. (+2 more)

The construction of accretion environments is fundamental to black hole imaging. From a purely geometric perspective, we construct a novel analytic accretion environment comprising a geometrically thick disk, ring-like bumps with a Gaussian profile, and localized compact emission regions modeled by Gaussian distributions. This environment offers high flexibility, enabling independent adjustments of disk thickness, vertical structure, and the positions and morphologies of localized spots, thereby allowing it to qualitatively mimic high-energy astrophysical phenomena. Applying this model to the Kerr spacetime, we investigate the resulting images via radiative transfer and ray-tracing simulations. The results confirm the effectiveness of the numerical implementation and reveal novel observational signatures of Kerr black holes under multi-component illumination, including multiple bright spots and arc-like structures. This work provides a convenient and fully analytic framework for modeling accretion in curved spacetimes, and offers a new perspective on inferring accretion mechanisms and transient high-energy processes from image features.
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All authors Shiyang Hu, Dan Li, Chen Deng, Kejian He, Guansheng He

High Energy Physics (Phenomenology)

Spectroscopic and Structural Properties of $B$, $B_s$, and $B_c$ Mesons within a Non-Relativistic Potential Model: A Comparative Analysis via Matrix Numerov and Variational Methods

Pritom Kumar Nath, Rishan Dev Choudhury and Jugal Lahkar

In this work, we studied the spectroscopic masses, decay constants, oscillation frequencies, and Isgur-Wise function parameters of $B$, $B_s$, and $B_c$ mesons within the framework of a non-relativistic potential model. The interaction is modelled using the Killingbeck potential, with calculations performed using two complementary approaches: the matrix Numerov method for solving the Schrödinger equation and the quantum mechanical variational method employing the Gaussian wave function. We determined the unknown parameters of the Killingbeck potential by fitting it to the Cornell potential using the ordinary least squares (OLS) method. These calibrated parameters are then used to compute the aforementioned physical observables.We obtained the masses of the heavy mesons with deviations of less than 0.5% from the highly precise experimental data. We also discussed the drawbacks and limitations of the non-relativistic model and highlighted its domain of applicability. At the end, we compare our results obtained from both methods with those from other theoretical frameworks, including QCD sum rules, lattice QCD, and alternative potential model studies.
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Mesoscale and Nanoscale Physics

Spin-Orbital Hall Nano-Oscillators using PtCr/NiFe

Utkarsh Shashank, Akash Kumar, Daegeun Jo et al. (+11 more)

The orbital Hall effect provides a promising route for generating angular-momentum currents beyond conventional spin Hall physics. PtCr alloys exhibit unusually large current-induced torques, but the contribution of orbital transport and the ability of these torques to sustain coherent nonlinear magnetization dynamics remain unresolved. Here we demonstrate spin-orbital Hall nano-oscillators by exploiting a homogeneous heavy-metal/light-metal alloy in which orbital Hall currents generated by Cr are converted by Pt into spin currents, producing giant spin-orbit torques. Using PtCr/NiFe heterostructures, the effective torque efficiency increases from ~0.14 in Pt/NiFe to ~0.40 in Pt0.38Cr0.62/NiFe despite substantial Pt dilution, enabling coherent auto-oscillations with the threshold current density reduced from ~ 1.07 x 10^12 to ~ 4.4 x 10^11 A m^-2. First-principles calculations show that Cr alloying suppresses the intrinsic spin Hall conductivity while enhancing the orbital Hall conductivity, and reproduce the observed torque enhancement only when orbital transport is included. Our combined experimental and first-principles results show that alloy engineering enables giant spin-orbit torques through an intrinsic orbital-mediated contribution, enabling coherent auto-oscillations without engineered multilayers and establishing a scalable materials platform for low-power nonlinear spintronic and orbitronic devices.
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All authors Utkarsh Shashank, Akash Kumar, Daegeun Jo, Thi Ngoc Anh Nguyen, Jong-Guk Choi, Sambit Ghosh, Michal Strach, Lunjie Zeng, Andrew B. Yankovich, Roman Khymyn, Ahmad A. Awad, Eva Olsson, Peter M. Oppeneer, Johan Åkerman

Fluid Dynamics

K41 Scaling in Bubble-Induced Turbulence Arises from Single-Bubble Wakes

Dabao Li, Zhilong Jin and Guangzhao Zhou

We use high-resolution, interface-resolved direct numerical simulations (DNS) to investigate the origin of Kolmogorov (K41) scaling in bubble-induced turbulence (BIT). Region-wise velocity structure functions show that the 2/3 scaling appears only within bubble wake regions. Comparison with matched single-bubble DNS further indicates that the K41 scaling observed in the full BIT field arises from the superposition of individual bubble wakes. On this basis, we derive a scaling for the dissipation rate in dilute BIT that is consistent with experimental results from the literature.
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Mesoscale and Nanoscale Physics

Crystalline Germanium Josephson Junctions

Frederik H. Knudsen, Axel Leblanc, Yiliu Li et al. (+8 more)

Conventional superconducting quantum electronics rely on well-established Josephson junctions made of Al/AlO$_{x}$ where the weak link AlO$_{x}$ is amorphous and is believed to host two-level systems that limit coherence. Crystalline Josephson junctions exhibit atomically ordered interface quality but remain constrained by complex fabrication and intrinsic asymmetry of epitaxial growth. Here, we demonstrate a fully epitaxial approach based on superconductivity in gallium-doped germanium, enabling the realization of Josephson junctions entirely grown in situ by molecular beam epitaxy. These devices feature atomically sharp interfaces and crystalline weak links, resulting in strong Josephson coupling in the ultra-short regime. We observe an unconventional enhancement of the switching current under applied magnetic field, which we attribute to quasiparticle-assisted thermalization processes from the Al contacts. This platform combines structural coherence, fabrication simplicity, and scalability, offering a promising route toward low-disorder, CMOS-compatible superconducting qubits in a merged element transmon architecture.
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All authors Frederik H. Knudsen, Axel Leblanc, Yiliu Li, Patrick J. Strohbeen, Jechiel van Dijk, Logan Kusher, Arunav Bordoloi, Alisa Danilenko, Xiangchao Ma, Salva Salmani-Rezaie, Javad Shabani

Superconductivity

Excitron-Induced Pair Fluctuations Reveal Superconductivity in the Electron Gas

Yasutami Takada

Understanding how superconductivity can emerge in dilute electronic systems remains a central challenge in condensed matter physics. By performing first-principles calculations of the electron self-energy \Sigma(k,iw_n) in the low-density three-dimensional electron gas, we identify a sharp divergence at r_s ~ 8 and T ~ 10^{-4}E_ F, signaling a second-order phase transition. This critical behavior originates from one-dimensional superconducting fluctuations mediated by virtual excitations of an excitron—a quasi-1D electronic composite formed by an electron and longitudinal electron-hole pairs. Although the superconducting mechanism itself is plasmon-mediated, the excitron channel provides a unique window into its fluctuation dynamics. Near the transition, we observe a pseudogap and a linear-in-T inverse electron lifetime, reminiscent of phenomena in high-T_c materials. These results reveal an unexpected route by which plasmon-driven superconductivity manifests in the dilute 3D electron gas through quasi-1D excitron dynamics.
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Chemical Physics

Bayesian Localization and Uncertainty Quantification of Trace Species in Two-Dimensional SIMS Imaging

Mengchi Wang, Binsheu Shieh, Ichiro Akai et al. (+4 more)

To enable accurate localization of trace species on material surfaces, we propose a Bayesian framework for analyzing two-dimensional (2D) secondary ion mass spectrometry (SIMS) imaging data. SIMS is widely used in semiconductor manufacturing, materials science, geology, environmental science, and life sciences because of its high sensitivity and excellent elemental and isotopic specificity. However, precise localization remains challenging because of primary ion beam broadening, overlap between neighboring ion distributions, and limited ion counts. The underlying distribution of trace species is modeled as a superposition of two-dimensional Gaussian peaks. To account for the stochastic nature of low-count measurements, the detected ion counts are assumed to follow a Poisson likelihood within a Bayesian framework. Posterior distributions of the peak parameters are estimated using replica-exchange Monte Carlo (REMC), enabling stable inference together with quantitative uncertainty estimation under low-count conditions. The proposed method is first validated using synthetic datasets with known ground truth and is then applied to SIMS measurements of semiconductor samples containing regularly arranged gold (Au) dots with diameters ranging from 0.4 to 2.0~$\mu$m, using scanning electron microscopy (SEM) images as the reference. Optimization of the measurement conditions reduced the relative localization error for 0.4~$\mu$m dots from 5.1$\%$ to 1.9$\%$. These results demonstrate accurate submicrometer localization with statistically rigorous uncertainty quantification in 2D SIMS imaging.
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All authors Mengchi Wang, Binsheu Shieh, Ichiro Akai, Masahiro Hara, Masao Yoshioka, Takeshi Hashishin, Toru Aonishi

Optics

Fundamental limits of hot-carrier and photothermal plasmonic solar chemistry

Seungwoo Lee

Plasmonic catalysts convert sunlight through direct metal–adsorbate excitation, nonequilibrium hot carriers and photothermal heating, yet these channels lack a common efficiency limit analogous to the Shockley-Queisser (SQ) limit. Here, we formulate a channel-resolved detailed-balance theory for plasmonic solar chemistry. The theory enforces exclusive partition of absorbed power, microscopic reversibility, non-negative entropy production, electromagnetic passivity and causality, and one physical nanostructure shared by all wavelengths and operating states. A reduced tightly coupled cycle obeys a chemical diode law with closed-form stall and maximum-power free energies. It recovers a 33.68% single-threshold radiative limit and the 30.58% ideal single-junction water-splitting limit at a 1.23-eV chemical load, whereas a Fowler hot-carrier kernel lowers the limit to 8.53%. Finite one-structure benchmarks show that independent wavelength optimization overestimates shared-geometry performance by 6.6-33.8%, while cross-frequency correlations tighten semidefinite upper bounds by 21-56%. An exact multi-electron network yields a universal arrival-storage criterion and the low-flux scaling J_n\sim g^n\tau^{n-1}. A source-conditioned gold/p-type gallium nitride case study and a bias- and separation-complete ledger then distinguish enhanced product formation from net solar-energy conversion. The resulting framework provides a thermodynamically closed benchmark for hot-carrier and photothermal plasmonic chemistry.
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General Relativity and Quantum Cosmology

Alternative LISA-TAIJI networks: polarization separation of the stochastic gravitational wave background

Gang Wang and Lang Liu

Stochastic gravitational-wave backgrounds (SGWBs) provide a unique opportunity to probe both unresolved astrophysical populations and fundamental physics in the early Universe. Future space-based gravitational-wave (GW) detectors, such as LISA and TAIJI, will enable cross-correlation observations that are particularly sensitive to SGWBs and their polarization content. In this work, we investigate the capabilities of two proposed LISA-TAIJI networks, LISA-TAIJIp and LISA-TAIJIm, for detecting and discriminating tensor, vector, and scalar polarization components of isotropic SGWBs. Using the cross-correlation between the two networks, we evaluate their sensitivities and signal-to-noise ratios for SGWBs containing different combinations of polarization sectors. We find that the LISA-TAIJIm configuration, which has a larger relative inclination between the two constellations, exhibits substantially weaker polarization degeneracies and significantly improved performance in separating polarization components, particularly for tensor-vector-scalar backgrounds. Fisher-matrix forecasts for power-law SGWBs show that the two configurations yield broadly comparable constraints on spectral parameters, reflecting the different roles of component separation and parameter estimation. Our results demonstrate that large-angle LISA-TAIJI networks provide a more favorable geometry for model-independent SGWB polarization measurements.
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Atomic Physics

Multiple ionization and charge equilibration in slow, multiply charged $\mathrm{Ar^{q+} + Ar}$ collision studied via L-MM Auger-Meitner electron spectroscopy

Rohit Tyagi, L. C. Tribedi, M. K. Harbola et al. (+1 more)

We report energy and angle resolved absolute cross section measurements for LMM Auger-Meitner electron emission following collisions of hundred keV protons and $\mathrm{Ar^{3+/6+}}$ ion with an atomic Ar target. The double differential cross section spectra show distinct contributions from target and projectile Auger-Meitner decay. The projectile emission exhibits the expected Doppler shift for various angles of electron emission, and the measured peak energies are in excellent agreement with kinematic calculations. The energy integrated cross sections show isotropic angular distribution for target and projectile species in their respective rest frames. The Auger-Meitner peak energy for target as well as projectile emission show significant difference in comparison to the characteristic L-MM Auger-Meitner energy peak from atomic Ar. The experimental measurements have been complimented with development of a theoretical model to calculate the transition probabilities corresponding to prominent L-MM Auger-Meitner transitions in neutral and multiply charged Ar atom. Comparison between measured and calculated spectra shows that the measured emission peak at approximately 150 eV originates from Auger-Meitner decay of $\mathrm{Ar^{4+}}$ ions. The peak energies for target and projectile emission are found to be equal, independent of the initial projectile charge state. This indicates that the decay occurs following extensive multiple ionization, charge exchange processes resulting in charge-state equilibration of the collision partners. The results demonstrate that collision-induced electronic rearrangement strongly modifies the Auger-Meitner spectra and provide evidence for an equilibrium target-projectile charge state in low-energy $\mathrm{Ar^{q+} - Ar}$ collisions.
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All authors Rohit Tyagi, L. C. Tribedi, M. K. Harbola, A. H. Kelkar

Statistical Mechanics

Nonisospectral Integrability and Exact Current Fluctuations in the Two-Dimensional SSEP

Tingfei Li

We study annealed current fluctuations in the two-dimensional symmetric simple exclusion process (SSEP) across a circular passive counting boundary. The initial average density is $\rho_1$ inside a disk of radius $R$ and $\rho_2$ outside, and the observable is the net decrease of the particle number in the disk over a finite time. Using convexity of the macroscopic fluctuation theory action and rotational averaging, we show that the minimizer of the full two-dimensional variational problem may be chosen radially symmetric. For the resulting radial problem, a suitable change of variables leads to a nonisospectral formulation on the half-line. Combining the associated scattering construction with a scalar factorization, we obtain a closed expression for the scaled cumulant generating function and hence the annealed large-deviation statistics of the current.
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Mesoscale and Nanoscale Physics

Quantum-Device Simulation of Optical Decoherence of Hole-Spin Qubits in Self-Assembled Quantum Dots

Jyun-Jie Jiang, Pericles Philippopoulos, Félix Beaudoin et al. (+1 more)

Spin-photon interfaces are essential for communications between distant spin qubits in quantum technologies, but the interband optical excitation can also damp electrically driven hole-spin Rabi oscillations in semiconductor self-assembled quantum dots (SAQDs). We report a device-level modeling workflow that integrates realistic SAQD geometry and multiband electronic-structure analysis with models of electrically driven spin control, interband optical transitions, and open-system dynamics. This workflow enables device-level estimation of Rabi-oscillation damping arising from repeated interband absorption-emission cycles. As an example, for a gated GaAs SAQD subjected to a uniform magnetic field $B_0$ along the growth direction of the SAQD, we predict the Rabi frequency of the hole spin qubit and its damping under external illumination. At $B_0=2$ T, the calculations yield a hole-spin Rabi frequency of 37.3 MHz. When the electrically driven SAQD is illuminated by a broadband LED centered at a wavelength of 790 nm, increasing the optical power from 0.3 to 1.5 mW shortens the Rabi-oscillation decay time from 90.3 to 17.5 ns. Increasing the SAQD height reduces the electron-hole overlap and thus the emission rate, but the resulting redshift moves the interband transitions into stronger spectral overlap with the LED spectrum, thereby increasing the rate of repeated absorption-emission cycles and enhancing photon-induced Rabi-oscillation damping. The results show that geometry, spin-control conditions, and illumination spectrum should be co-optimized in semiconductor spin-photon devices.
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All authors Jyun-Jie Jiang, Pericles Philippopoulos, Félix Beaudoin, Hong Guo

Materials Science

Unified open-boundary electrostatics in real-space density functional theory

Rajat Kumar, David Codony, Phanish Suryanarayana et al. (+1 more)

We present an electrostatic formulation in real-space density functional theory that provides a systematic and unified treatment of the open-boundary electrostatics of isolated and partially periodic systems, including in the presence of an applied uniform electric field along the open (finite) directions. Specifically, we formulate a local electrostatic energy functional whose stationarity yields the Poisson equation for the electrostatic potential, subject to periodic and Dirichlet boundary conditions along the periodic and open directions, respectively. Using a Green's function approach, we derive analytical expressions for the Dirichlet values arising from the total charge density of the system. We also derive the expressions for the energy, atomic forces, and stress tensor. We implement the resulting expressions within the large-scale parallel real-space SPARC electronic structure code. Using representative examples, we verify the accuracy and efficiency of the framework, demonstrating exponential convergence of the computed quantities with vacuum size and excellent agreement with established plane-wave codes while requiring significantly less vacuum at comparable accuracy. Since no existing implementation provides the stresses for such systems, we instead verify them against numerical derivatives of the energy, finding close agreement. Finally, we apply the framework to compute static polarizabilities and piezoelectric coefficients, obtaining very good agreement with values reported in the literature.
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All authors Rajat Kumar, David Codony, Phanish Suryanarayana, Abhiraj Sharma

Solar and Stellar Astrophysics

Coronal Rain Driven by Low-Frequency Impulsive Heating: Dependence of Dynamics and Morphology on Coronal Heating and Magnetic Field

Takero Yoshihisa and Takaaki Yokoyama

We performed numerical simulations to investigate how coronal heating and magnetic field strength regulate the dynamics and morphology of coronal rain in the solar corona. Coronal rain is widely interpreted as a manifestation of thermal non-equilibrium and thermal instability. Many previous studies have investigated condensation under (quasi-)steady heating scenarios, but such heating models do not fully explain the observed properties, including multiple clumps and symmetric drainage toward both loop footpoints. Condensation driven by low-frequency impulsive heating has been much less explored and may produce distinct coronal rain morphology and drainage dynamics. The role of the coronal magnetic field also remains poorly understood. We conducted 1.5-dimensional magnetohydrodynamic simulations along a single strand with self-consistent coronal heating, upon which a single impulsive heating event was imposed. Two key parameters were systematically explored: the duration of localized heating and the strength of the coronal background magnetic field. We find that condensation can be triggered even by a single impulsive heating event, provided that the injected energy is about an order of magnitude larger than that in the steady heating case. Condensation becomes more likely for longer heating durations and weaker magnetic fields. The dynamics of coronal rain depend strongly on the heating duration. When the heating duration is shorter than the radiative cooling timescale, condensations drain toward both loop footpoints. We also find that weaker magnetic fields enhance the nonlinearity of Alfvén waves, promoting fragmented condensations. These results demonstrate that the heating duration and coronal magnetic field strength play key roles in regulating coronal rain formation and dynamics.
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Quantum Physics

Effect of Strong Field Space-time Features on Vacuum Pair

B. An, N.S. Lin, C.K. Li et al. (+2 more)

The relativistic dynamics of bound states across inertial reference frames are investigated using the computational quantum field theory (CQFT). The results reveal that the spatiotemporal properties of bound states within a given potential well are strictly frame-dependent. Crucially, this spatiotemporal modulation of the external field enables a reduction in the laser intensity threshold required for vacuum electron-positron pair creation. Analytical and numerical calculations demonstrate that this threshold reduction originates from the Lorentz transformation of the four-momentum, which reshapes the vacuum excitation pathways in phase space. By developing CQFT, we establish a comprehensive framework in which relativistic effects intrinsically govern the quantum vacuum decay process
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All authors B. An, N.S. Lin, C.K. Li, M. Jiang, Y.J. Li

Optics

Simulating optical microcavities by inverting the thermal transfer function

Sudipta Nayak

I present a reduced-order approach for incorporating distributed thermal dynamics into nonlinear optical-microcavity simulations without repeatedly solving the time-dependent heat equation. A harmonic finite-element heat solve is used to obtain the thermal transfer function, which is introduced into the time domain through either a rational approximation or an impulse-response convolution. The method is validated against heat-equation-coupled finite-element simulations for prescribed TE1-mode heating and for nonlinear silicon microcavity dynamics. For the feed-forward TE1 tests up to 100 MHz and simplified cavity dynamics, the error remains below 4%. The reduced models reproduce the local self-pulsation dynamics, although long-time phase alignment is sensitive to the spatial definition of the thermal transfer function and to impulse-response truncation. These results establish a physics-based route for retaining multi-timescale thermal memory while substantially reducing the cost of coupled optical–thermal simulations.
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Statistical Mechanics

Truly Solving the Gibbs Paradox by Local Free Space and Collision Potential

Chuang Li

This paper argues that the Gibbs paradox can be resolved without using the concept of identical particles in quantum mechanics. The molecules in different regions of the gas can be distinguished, so there is no need to introduce the N! factor. For each molecule, the volume of its free movement space is local at every instant. Moreover, collisions are the primary way of interaction between gas molecules and the fundamental driving force for reaching equilibrium. The potential energy during collisions cannot be ignored. Based on the local free space assumption and collision potential energy, this paper uses the canonical ensemble method to rederive the entropy increment formula for gas mixing. It includes parameters such as molecular mass, effective radius, and collision characteristic time, which vary with the type of gas molecules. This solves the problem that the entropy increment of gas mixing is independent of gas properties, that is, it truly resolves the Gibbs paradox instead of providing a new conceptual explanation.
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Mathematical Physics · Cross-listed from math.AP

Smooth Convergence of Landau-de Gennes Minimizers in the Lyuksyutov Regime

Haotong Fu, Huaijie Wang and Wei Wang

In this paper, we analyze global minimizers of the Landau–de Gennes functional in 3-dimensional domains in the Lyuksyutov regime. We prove smooth convergence to an $\mathbb{S}^4$-valued limit and obtain an $O(\mu^{-1})$ estimate for the distance to $\mathbb{S}^4$ as $\mu \to +\infty$, thereby extending the convergence results of Dipasquale et al.[Arch. Ration. Mech. Anal. 239: 599–678, 2021].
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Mathematical Physics · Cross-listed from math.CA

Generalized Freud weight, discrete Painlevé I hierarchy and full asymptotics of Hankel determinants

Wen-Gao Long, Lin-Rong Tang and Chao Min

In this paper, we investigate the monic orthogonal polynomials $P_{n}(x;T_{m};\lambda)$ and the Hankel determinants $D_{n}(T_{m}; \lambda)$ associated with the generalized Freud weight \[w(x;T_{m};\lambda) = |x|^{2\lambda+1}\exp\biggl(-\sum_{k=1}^m t_k x^{2k}\biggr),\quad m \in \mathbb{Z}^+,\; t_{k} \in \mathbb{R} , x\in\mathbb{R}\setminus\{0\},\] where \(T_{m}=\{t_{1},t_{2},\cdots, t_{m}\}\), $t_{m}>0$ and \(\lambda>-1\).By employing ladder operators and compatibility conditions, we find that all members of the discrete Painlevé I hierarchy have a unified structure and the recurrence coefficient \(\beta_n\) of $P_{n}(x;T_{m};\lambda)$ satisfies the $m$-th member of the discrete Painlevé I hierarchy. Besides, we derive the second-order differential equation satisfied by $P_{n}(x;T_{m};\lambda)$, the partial derivatives of the recurrence coefficients \(\beta_n\) with respect to parameters \(t_1, t_2, \dots, t_{m-1}\) and the corresponding differential identities for $D_{n}(T_{m}; \lambda)$. Based on the discrete Painlevé I hierarchy and the above differential identities, we obtain new partial differential equations satisfied by $\ln\beta_n$ and $\ln D_{n}(T_{m}; \lambda)$.Using the discrete Painlevé I hierarchy and the asymptotic theory of linear difference equations, we derive the full asymptotic expansions of the recurrence coefficient $\beta_n$, the nontrivial leading coefficient $\mathrm{p}(n; T_m; \lambda)$, and the Hankel determinant $D_n(T_m; \lambda)$ as $n\to\infty$, for general $T_m$ and $\lambda>-1$. Notably, while the logarithmic term $\ln n$ appears in the leading-order contributions, it is absent from the remainder terms in these expansions.We illustrate our results under the specific decic Freud weight $w(x;t_1,t_2;\lambda)=|x|^{2\lambda+1} \exp\bigl(-x^{10}-t_2x^4-t_1x^2\bigr)$.
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