Plasma Physics
Plasma wakefield dynamics of self-generated electron bunch trains
Salome Benracassa, Sheroy Tata, Yinren shou et al. (+2 more)
Laser plasma accelerators can deliver high-energy, quasi-monoenergetic electron beams over centimeter-scale distances. In this work, we report on the generation of narrow, quasi-monoenergetic electron bunch trains with periodic energy spacing issued from downramp injection in a
laser driven wakefield accelerator. The periodicity in energy is shaped via relativistic lengthening of the wakefield during the acceleration phase, while the spatial periodicity is obtained via injection into multiple
plasma periods. At the end of the accelerator, a rotation in phase-space is performed to compress each bunch in energy, producing narrow periodic spikes in the spectrum. The experimental observations are supported by particle-in-
cell simulations, which reproduce the formation and
evolution of the periodic bunch trains, providing an insight into the underlying
plasma dynamics.
Read the full abstract ▾
All authors Salome Benracassa, Sheroy Tata, Yinren shou, Aaron Liberman, Victor Malka
Earth and Planetary Astrophysics
Peas and USPs: Can Stellar Spindown and Peas in a Pod Replicate Ultra-Short-Period Planet Characteristics?
Adam Distler and Juliette Becker
Peas-in-a-Pod (PIAP) systems have been shown to be common across
exoplanet systems, with regular
planet spacings and similar
planet sizes. In contrast, ultra-short-period
planets have displayed distinct differences from PIAP systems, including higher mutual inclinations, ages, and
planet sizes. Using Laplace-Lagrange secular theory, we investigate the ability of
stellar spindown to decouple PIAP systems. We find that strictly PIAP systems with regular spacings cannot undergo secular resonance crossings for the expected
stellar $J_2$
evolution, and that we instead require the inner
planet to migrate inward to undergo this resonance crossing. As a result, there is no inner edge to PIAP systems where systems will always cross a secular resonance and decouple the inner
planet. Using expected $J_2$
evolution tracks from
stellar evolution models, we find a diversity of expected resonance crossing times, highlighting the ability to test migration pathways and initial
stellar obliquities using this framework.
Read the full abstract ▾
Fluid Dynamics
Reward hacking in physical reinforcement learning revealed by turbulent drag reduction
Giorgio Maria Cavallazzi, Miguel Pérez-Cuadrado and Alfredo Pinelli
Reinforcement-learning controllers optimise specified rewards, but in physical systems those rewards often capture only part of the true control objective. Three mechanisms through which this mismatch can produce apparent success without physical improvement are identified: incomplete accounting that omits relevant costs, constraint enforcement outside the policy that corrupts credit assignment, and observations that fail to resolve the relevant dynamics. All three are demonstrated in active drag reduction of wall-bounded
turbulence, where the conservation constraint and full energy budget can be measured directly. A memoryless learnt policy reports drag reduction while raising total dissipation, collapsing to non-physical flow configurations. A recurrent multi-
agent controller with the zero-mean projection embedded in the actor, temporal
memory matched to the relevant timescales, and an actuation cost that bounds the wall power delivers a physically consistent control. Progress in physical reinforcement learning requires the reward, constraints, observations and evaluation metrics to represent unequivocally the physical objective.
Read the full abstract ▾
Astrophysics of Galaxies
A New Member of the Fast and Furious Family: A Relativistic and Time-Variable UV Outflow in a Luminous Quasar
Lucas M. Seaton, Patrick B. Hall, Liliana Flores et al. (+20 more)
We report the fastest
quasar outflow first detected in the ultraviolet, via variable C IV and Si IV absorption at
outflow velocities $-77,000$ km s$^{-1}$ to at least $-90,000$ km s$^{-1}$, in the
radio-quiet
quasar SDSS J231854.31+243954.2 (J2318). J2318 is a weak-lined
quasar in the rest-frame ultraviolet, but Gemini GNIRS spectroscopy reveals an H$\alpha$
redshift of $z=2.6781\pm0.0004$. A twenty-year photometric time series shows peak-to-peak variability of 0.5 mag in the $g$ band. The C IV
outflow strengthened monotonically over three epochs spanning $\sim$2.2 rest-frame years. The existence of such a high-velocity
outflow implies that models of
quasar outflows must be able to either accelerate gas to $0.3c$ while still preserving C IV and Si IV ions, or enable the formation of C IV and Si IV ions in gas which has been accelerated to $0.3c$. Virial estimates reveal a black-hole mass of $1.65\times10^9~M_\odot$, which leads to an Eddington luminosity and Eddington ratio of $2.4\times10^{47}$ erg s$^{-1}$ and $0.45$, respectively. Using very conservative assumptions, the UV-absorbing
outflow alone has an estimated mass loss of $>0.82~M_\odot~{\rm yr}^{-1}$ and a kinetic luminosity ratio $L_{kin}/L_{bol}\geq0.75$%. The lower limit is just above the threshold usually cited for significant feedback on the host
galaxy. Comparison to PDS 456, the only other known
quasar with a UV-absorbing
outflow at $0.3c$, suggests that the true $\dot{M}$ and $L_{kin}/L_{bol}$ could be up to two orders of magnitude larger.
Read the full abstract ▾
All authors Lucas M. Seaton, Patrick B. Hall, Liliana Flores, Paola Rodríguez Hidalgo, Marianna Veltri, Zezhou Zhu, Javier Serna, W. Niel Brandt, Scott Anderson, Roberto J. Assef, Eduardo Bañados, Catherine J. Grier, Yasaman Homayouni, Sean Morrison, C. Alenka Negrete, Amy L. Rankine, Jessie Runnoe, Donald P. Schneider, Yue Shen, Matthew Temple, Benny Trakhtenbrot, Jonathan R. Trump, Erik Weiss
High Energy Physics (Theory)
Chiral symmetry breaking in models with unconventional supersymmetry
Pedro D. Alvarez, Cristian Villavicencio and Jorge Zanelli
We investigate dynamical mass generation in a geometrically constructed gauge theory based on the super Lie
algebra $su(2,2|3)$, in which
gravity, Yang-Mills fields, and
fermions are unified as components of a single gauge connection. The model contains no elementary scalar fields and no ad hoc four-
fermion interactions. Instead, fermionic self-interactions arise unavoidably from the
geometric structure of the theory, through nonminimal couplings and torsion associated with the unified connection. Upon reduction to an effective low-energy description, these interactions generate a Nambu-Jona-Lasinio–type potential that triggers
chiral symmetry breaking and the formation of a
fermion mass gap. In this framework, mass generation emerges as a direct consequence of the underlying gauge-
geometric and algebraic structure, rather than as an independent dynamical assumption.
Read the full abstract ▾
Fluid Dynamics
Flapping instability of elastic disks in Stokes flows
Yijiang Yu, Hugo Perrin, Michael D. Graham et al. (+1 more)
Fluid-structure interactions at low Reynolds number can lead to a much richer phenomenology than previously expected. Here, we study the dynamics of a freely suspended, thin elastic disk in a shear flow, where the plane of the disk is initially parallel to the flow plane. Using a combination of experiments and simulations, we demonstrate that beyond a critical flow strength the disk deforms, performing flapping dynamics, in which the disk curves up and down periodically relative to the horizontal shear plane. The bifurcation diagram obtained by simulation reveals several oscillatory solutions, including a wiggling motion that is predicted by a linear stability analysis. The flapping dynamics is shown to be a subcritical instability whose key ingredient is the finite extensibility of the disk. The behavior we observe has implications for emerging investigations on the flow dynamics of sheet-like particles, such as 2D
polymers and 2D crystalline materials immersed in viscous fluids.
Read the full abstract ▾
All authors Yijiang Yu, Hugo Perrin, Michael D. Graham, Lorenzo Botto
High Energy Astrophysical Phenomena
Probing a new subclass of llGRB-SN transients: Insights from EP250304a and its associated supernova
L. Cotter, A. Martin-Carrillo, R. A. J. Eyles-Ferris et al. (+62 more)
With the advent of the Einstein Probe (EP) mission, we are entering a new era in the study of gamma-ray bursts (GRBs), enabling the detection of faint, low-luminosity transients that would previously have gone undetected. EP250304a was an event discovered by EP associated with the broad-lined type Ic
supernova (SN) SN 2025fhm located at z = 0.2. Despite no gamma-ray emission being detected at the time of the EP trigger, we identify evidence for a relativistic
outflow consistent with a GRB-like jet across multiple wavelengths. We present a detailed spectral and photometric analysis of EP250304a/SN 2025fhm, including multi-band light curve modelling performed with the Redback Python package. We find that this event closely resembles low-luminosity GRB-SNe (llGRB-SNe) such as GRB 060218/SN 2006aj, GRB 100316D/SN 2010bh, and GRB 171205A/SN 2017iuk, all of which exhibit early-time emission consistent with a thermal shocked cocoon. These similarities suggest that EP250304A/SN 2025fhm may belong to an emerging subclass of shocked cocoon-dominated llGRB-SNe, representing the low-luminosity end of a broader continuum of engine-driven GRB-SN explosions.
Read the full abstract ▾
All authors L. Cotter, A. Martin-Carrillo, R. A. J. Eyles-Ferris, L. Izzo, D. B. Malesani, Y. Julakanti, G. Corcoran, A. Saccardi, P. G. Jonker, A. J. Levan, F. Carotenuto, P. T. O'Brien, J. H. Gillanders, J. N. D. van Dalen, M. E. Ravasio, S. Schulze, N. Sarin, F. E. Bauer, M. Fraser, J. Quirola-Vasquez, A. P. C. van Hoof, S. J. Smartt, C. Gall, A. Rest, C. T. Murphey, N. Tanvir, T.-W. Chen, Q. Wu, Y. Yin, S. Campana, C. Ashall, J. P. Anderson, J. A. Chacon, F. J. Cowie, V. D'Elia, L. Galbany, C. P. Gutierrez, D. H. Hartmann, P. Jakobsson, S. Kobayashi, A. H. Kong, P. Mazalli, T. E. Muller-Bravo, M. De Pasquale, L. Rhodes, A. Rossi, J. Sanchez-Sierras, J. Sollerman, A. Andersson, A. Aryan, T. de Boer, J. S. Bright, K. C. Chambers, M. Gromadzki, M. E. Huber, C. Inserra, T. Lowe, P. Minguez, G. S. Narayan, M. Nicholl, G. S. H. Paek, A. Sedgewick, K. W. Smith, J. W. Tweddle, S. Yang
Plasma Physics
A Surrogate Model for Proton Spectrum Prediction to Map Transitions in Laser-Ion Acceleration
Chengqi-Zhang, Yang He, Mamat Ali Bake et al. (+2 more)
We present a physics-guided, decoupled dual-branch surrogate model to predict continuous
proton energy spectra from
laser-driven ion acceleration. Integrating a $\beta$-VAE for spectral feature extraction with a parallel multi-layer perceptron for scalar boundary enforcement, the framework achieves a predictive accuracy of $R^2 = 0.94$ for the maximum cutoff energy and $R^2 = 0.94$ for the total particle flux, with a median per-sample spectral $R^2 = 0.985$ (in $\log_{10}$ space) across the full 2000-bin energy distribution. The model incorporates uncertainty quantification via deep ensembles, serving as a quantitative probabilistic diagnostic tool with calibration errors below 6.2%. Within the 1D longitudinal framework, the surrogate reproduces spectral signatures consistent with the transition from Target Normal Sheath Acceleration (TNSA) to the volumetric heating dynamics of Relativistically Induced Transparency (RIT) and Breakout Afterburner (BOA) regimes, as validated against kinetic diagnostics from 1D particle-in-
cell simulations. This approach establishes a computationally efficient baseline for future multi-fidelity optimization and provides an engine for closed-loop parameter control in high-repetition-rate
laser facilities.
Read the full abstract ▾
All authors Chengqi-Zhang, Yang He, Mamat Ali Bake, Xilin-Wang, Bai-Song Xie
General Relativity and Quantum Cosmology
The first decade of gravitational-wave measurements of black hole spins
Sylvia Biscoveanu
A decade after the first direct detection of gravitational waves, the growing catalog of hundreds of confirmed events is revealing new insights into the
spins of
stellar-mass black holes.
Spin measurements have long been heralded as a promising tracer of compact-object binary formation and
evolution, as different formation channels predict distinct
spin signatures on a population level. In this review, we summarize the astrophysics, phenomenology, and current measurements of black hole
spins. We begin with an overview of the predictions for black hole
spin magnitudes and orientations from leading formation channels–isolated binary
evolution, dynamical formation in clusters, formation in AGN disks, and hierarchical triples. We then describe the imprint of
spin effects on the gravitational waveform and the measurability of
spin in individual events. Finally, we review current population-level constraints on
spin magnitudes, orientations, and effective
spin parameters, including correlations with mass and
redshift, and discuss their astrophysical implications. We conclude by highlighting open questions and future prospects, emphasizing how improved detector sensitivity will enable increasingly precise
spin measurements for both individual events and the binary black hole population as a whole.
Read the full abstract ▾
Quantum Physics
Semidefinite-programming hierarchies for classically simulable state sets
Mengyan Li, Yanning Jia, Fenzhuo Guo et al. (+3 more)
Determining whether a
quantum state set admits a classical explanation is a fundamental problem in
quantum information theory, as it reveals whether the information encoded in state preparation can be reproduced by classical means. Here we study classically simulable state sets, namely those admitting realizations using shared randomness and preparation devices that individually generate only pairwise commuting state sets. We develop a complete semidefinite programming (SDP) hierarchy to characterize the set of classically simulable state sets. The key step is a reformulation of classical simulability as a feasibility problem involving deterministic response functions and auxiliary positive-operator-valued measures (POVMs) simulable by rank-one projective measurements. We then establish a complete SDP hierarchy for rank-one projectively simulable POVMs, which in turn induces computable outer approximations converging to the set of classically simulable state sets. The corresponding dual SDP further yields affine witnesses that can be used to rule out classical simulability. Applying the hierarchy to state sets under depolarizing noise yields computable upper bounds on the critical visibility. For several highly symmetric examples, these bounds are matched by explicit classical simulations, providing evidence for the practical usefulness of the hierarchy.
Read the full abstract ▾
All authors Mengyan Li, Yanning Jia, Fenzhuo Guo, Haifeng Dong, Sujuan Qin, Fei Gao
Cosmology and Nongalactic Astrophysics · Cross-listed from cs.NE
Hub-Aware Hybrid Search: Accelerating the Locally Aligned Ant Technique
Simone Vilardi, Reynier Peletier, Felipe Contreras et al. (+1 more)
Finding
manifold structures in noisy and high-dimensional point clouds is a challenging but important problem. In astronomical observation survey and simulation data the detection of filaments, streams (1D), walls (2D) and clusters (3D) gives rise to deeper understanding of the
evolution of our universe. The Locally Aligned Ant Technique (LAAT) uses biologically inspired
agents to efficiently recover faint and multidimensional structures. However, very dense hubs (e.g. nodes or globular clusters) dominate the ants' activity, creating unnecessary computational overheads. In this paper we propose a two-stage solution. First a fast preprocessing step locates the hubs and replaces them with a tailored likelihood model. Subsequently, a mixed likelihood-pheromone strategy guides the ants to efficiently bridge the dense regions. We demonstrate improvements in detection efficiency and robustness of LAAT with synthetic and a large-scale astronomical N-body simulation of the
cosmic web.
Read the full abstract ▾
All authors Simone Vilardi, Reynier Peletier, Felipe Contreras, Kerstin Bunte
Plasma Physics
Wave drag in moving plasmas: recent developments and prospects
Renaud Gueroult, Aymeric Braud and Julien Langlois
Wave propagation in a medium differs depending on whether this medium is at rest or moving with respect to an observer. Motion can notably lead to modifications of the wave trajectory, of its polarization, or of its transverse structure. Although these effects are well documented in isotropic dielectrics, they remain largely unexplored and unaccounted for in
plasmas, despite the fact that simple models suggest they could in fact be large under certain conditions, as well as recent experimental observations. Here we first review existing models for motion effects on
plasma waves, then identify a number of basic challenges that lie in the way of using these models to quantify motion effects in realistic configurations, and finally discuss possible workarounds.
Read the full abstract ▾
Fluid Dynamics
Deep reinforcement learning with spatial and temporal awareness for active boundary control of buoyancy-driven convection
Giorgio Maria Cavallazzi, Miguel Pérez Cuadrado and Alfredo Pinelli
Deep reinforcement learning (DRL) applied to thermal convection control consistently produces degenerate actuation: wall-temperature policies whose outputs are saturated, pseudo-random, or spatially incoherent. Two compounding deficiencies are responsible: multilayer-perceptron policies that discard spatial flow structure, and memoryless policies that cannot distinguish self-induced flow changes from background
evolution. Together they degrade the actuation into forms whose relation to the convective
topology cannot be read off and which are not realisable at the actuator, even when
cell coalescence (the merging of convection rolls into fewer, larger structures), which would reduce Nu, is accessible to boundary actuation. The present framework addresses both causes through four targeted design choices: convolutional policy networks, Gated Recurrent Unit (GRU)
memory, off-policy training (TD3/MADDPG), and action-smoothness constraints. A systematic 2x2 factorial design isolates the contribution of each component. On Rayleigh-Benard convection at Ra = 10,000, all four configurations achieve
cell coalescence and reduce Nu to as low as 1.83 (26% below the uncontrolled baseline) in 350 episodes, without the full-field data augmentation required by prior work. Crucially, coalescence is achieved even by the single-
agent configuration, demonstrating that the multi-
agent formulation is not a prerequisite once the policy architecture is sufficiently expressive. Applied to double-diffusive convection in the salt-finger regime, the framework spontaneously discovers a travelling-wave actuation whose phase speed adapts to the evolving mixing state of the flow, enhancing heat transfer by 19.1% and reducing salinity variance by 21.0%.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Non-adiabatic Ehrenfest dynamics with norm-conserving and ultra-soft pseudo-potentials with nuclear velocity corrections on the atomic orbitals within the Projector Augmented Wave Method framework
Paolo Fachin, Francesco Macheda, Paolo Barone et al. (+1 more)
We derive the first-principles Ehrenfest molecular dynamics describing non-adiabatic processes with the inclusion of the
nuclear-velocity-dependent phases (also known as electron-translation factors) on the atomic-orbital basis. These phases, appearing when
nuclei are treated dynamically, affect effective
Hamiltonians constructed from localised orbitals. In this work, we focus on the effects in the first-principles pseudo-potential
Hamiltonian, both for the norm-conserving and ultra-soft cases, derived within the Projector-Augmented-Wave (PAW) method framework. Peierls-like phases depending on the
nuclear velocities appear in the non-local part of the potential, while additional
nuclear velocity and acceleration-dependent corrections appear in the ultra-soft pseudo-potential case. The use of velocity-including atomic orbital basis enables a Galilean-invariant description of the non-adiabatic Ehrenfest molecular dynamics, removing spurious non-adiabatic couplings that arise from neglecting the
nuclear velocity phases in the atomic orbitals.
Read the full abstract ▾
All authors Paolo Fachin, Francesco Macheda, Paolo Barone, Francesco Mauri
Statistical Mechanics
The mesoscopic foundations of non equilibrium thermodynamics and the arrow of time in the Dual Model of Liquids
Fabio Peluso
This manuscripts has two goals. The first goal is to show that the interaction in the Dual Model of
Liquids between the solidlike molecule aggregates and the
lattice excitations is appropriate to represent the link between the behaviour at macroscopic scale of normal
liquids and the physical processes characterizing those systems at mesoscopic scale. The second goal is to show that the duality allows identifying a time arrow on the mesoscopic scale in
liquids. The interaction of quanta of elastic energy with the molecular clusters introduces a privileged direction, which is relevant in time dependent and dissipative macroscopic processes, although the interaction remains temporally reversible
Read the full abstract ▾
High Energy Physics (Phenomenology)
Vector charmonium(-like) states in the energy range of 4.1-4.6 GeV
Xiang-Kun Dong, Vadim Baru, Leon von Detten et al. (+5 more)
The spectrum of vector charmonium(-like) states in the 4.1\dash4.6~GeV energy region exhibits a long-standing tension between inclusive and exclusive measurements. While the inclusive $R$-value indicates only conventional vector charmonia such as $\psi(4160)$ and $\psi(4415)$, exclusive $e^+e^-$ cross sections reveal additional structures whose parameters strongly depend on the observed final states when fitted with Breit–Wigner functions. This puzzling pattern suggests that coupled-channel and threshold effects play an essential role. In this work, we develop a unified coupled-channel framework for the $1^{--}$ resonances in this energy region. The framework incorporates the $S$-wave open-charm channels $D\bar{D}_1$, $D^*\bar{D}_1$, and $D^*\bar{D}_2^*$ constrained by heavy-
quark spin symmetry, optional bare poles associated with $\psi(4160)$ and $\psi(4415)$, and final-state interactions in the $Z_c$ channels. We perform simultaneous fits to the BESIII cross sections for $e^+e^-\to J/\psi\pi^+\pi^-$, $h_c\pi^+\pi^-$, $D\bar{D}^*\pi$, $D^*\bar{D}^*\pi$, $J/\psi\eta$, and $\chi_{c0}\omega$, together with invariant-mass distributions exhibiting the $Z_c(3900)$ and $Z_c(4020)$ structures. The
benchmark models differ in the number of bare seed states and the fitting strategy. We show that even the purely dynamical scheme without bare charmonia captures the gross features of the analyzed distributions. The inclusion of bare compact states improves the fit quality but does not change the conclusion that the measured line shapes can be understood in terms of strong coupled-channel effects with dynamically generated poles. We also discuss possible heavy-
quark spin partners of the exotic $1^{--}$ states.
Read the full abstract ▾
All authors Xiang-Kun Dong, Vadim Baru, Leon von Detten, Feng-Kun Guo, Christoph Hanhart, Teng Ji, Ulf-G. Meißner, Alexey Nefediev
Cosmology and Nongalactic Astrophysics
AKRA 3.0: A matrix-free Inversion Framework for Weak Lensing Mass Mapping and Its Application to DES Y3 Data
Yuan Shi, Pengjie Zhang, Li Cui et al. (+2 more)
Weak gravitational
lensing mass mapping offers a direct probe of the matter distribution. Accurate reconstruction of mass maps from masked shear catalogs remains challenging due to survey boundaries and spatially varying noise. In AKRA 2.0, we addressed the mask problem on the curved sky by constructing and inverting the normal-equation
matrix $\bf{H} \equiv \mathbf{A}^\mathrm{T}\mathbf{N}^{-1} \mathbf{A}$ explicitly, necessitating a split-scale strategy that reconstructed different angular scales independently to reach high resolution. Here we present AKRA 3.0, in which $\mathbf{H}$ is treated as a linear operator and the normal equations are solved by the conjugate gradient (CG) method. This reformulation reduces the
memory requirement from $O(N^2)$ to $O(N)$ and the inversion cost from $O(N^3)$ to $O(N_{\rm iter}N^{3/2}), N \sim \ell_{\rm{max}}^2$ for full-sky (SHT-based) operations. Such optimizations render high-resolution full-sky reconstruction tractable for Stage~III and Stage~IV surveys. Applying AKRA 3.0 to the DES Y3 METACALIBRATION catalog, we produce the highest-resolution convergence map of this
dataset to date at HEALPix $N_{\rm{nside}}= 2048$ without imposing any prior assumptions. We extract the convergence power spectrum directly from the reconstructed map and demonstrate that unbiased two-point measurements can be obtained directly from the reconstructed map. The reconstructed E-mode convergence map will be publicly released as data products to enable future studies of non-Gaussian statistics, higher-order moments, and cross-correlations with external
datasets.
Read the full abstract ▾
All authors Yuan Shi, Pengjie Zhang, Li Cui, Jian Qin, Ji Yao
Computational Physics · Cross-listed from stat.ML
Effective Dimensionality as an Operator Invariant for Physics-Preserving Constraint Adaptation in Physics-Informed Neural Networks
Cornelius Otchere and Michael Shields
Physics-Informed Neural Networks inherently suffer from task interference because they rely on a shared parameter space to satisfy both governing differential equations and boundary conditions. We analyze this structural conflict using the Fisher Information
Matrix to quantify the effective degrees of freedom ($d_{eff}$) in a physics-constrained model. Unlike the classical $d_{eff}$ which measures how many parameter directions are informed by data against a statistical prior, our $d_{eff}$ measures the dimension of the parameter directions unconstrained by the differential operator. For operators with finite-dimensional kernel, we show that $d_{eff}$ converges to the kernel dimension exactly, independent of network width, depth, or activation function, recasting it from a fit diagnostic into a structural invariant of the underlying continuous operator. For operators with infinite-dimensional kernel, $d_{eff}$ instead measures the network's finite-dimensional representational bandwidth for that kernel rather than recovering an integer invariant. Importantly, $d_{eff}$ also serves as an a priori structural diagnostic. Driving $d_{eff}$ of a well-posed problem to zero certifies that the physics and boundary constraints have absorbed the network's free directions. Building on this characterization, we introduce subspace projection strategies for boundary adaptation. Rather than retraining from scratch, we project parameter updates into the null space of the pre-trained physics operator so that new boundary conditions are satisfied without disturbing the learned physics. Gradient-based fine-tuning can match or exceed this but needs more wall-clock time and tuning, whereas subspace projection delivers near-equivalent quality in seconds to minutes. We validate on linear and nonlinear operators, demonstrating accurate adaptation to initial and boundary shifts and unencountered constraint types.
Read the full abstract ▾
Materials Science
Endowing variational phase-field fracture models with custom strength criteria
Roberto Alessi, Matteo Brunetti, Roshan Udaram Patil et al. (+1 more)
By now, several approaches have been proposed to endow phase-field fracture models with the ability to describe crack nucleation under multiaxial stress states. These include techniques for splitting the free energy, direct modifications of the phase-field driving or resisting forces that sacrifice the variational structure of the problem, and the introduction of additional internal variables, such as plastic strains or other nonlinear strains. In this paper, we propose a fundamentally different strategy for incorporating arbitrary elastic domains into phase-field fracture models, formulated within the variational framework of generalized standard materials. The proposed approach relies on letting the dissipation potential depend on the current state of the material. In this way, the variational structure of the problem is preserved, while elastic degradation and the strength criterion remain two distinct and independently controllable aspects of the material response. Simple yet representative models are presented and thoroughly discussed to demonstrate the effectiveness of the proposed methodology. The resulting
evolution of the elastic domain is investigated in both strain and stress spaces. Moreover, numerical simulations demonstrate a range of crack nucleation processes under multiaxial loading conditions for various analytical strength surfaces. This work paves the way for future developments and applications in several directions.
Read the full abstract ▾
All authors Roberto Alessi, Matteo Brunetti, Roshan Udaram Patil, Jacinto Ulloa
Computational Physics · Cross-listed from cs.LG
On the training of physics-informed neural operators for solving parametric partial differential equations
Nanxi Chen, Chuanjie Cui, Airong Chen et al. (+2 more)
Physics-informed neural operators (PINOs) aim to learn solution operators for partial differential equations by using the governing physics as supervision, rather than relying solely on paired input-output simulation data. By incorporating physical constraints into the training objective, PINOs combine the cross-instance generalization of neural operators with the data efficiency of physics-informed learning. Despite this promise, how to train PINOs efficiently and robustly remains less well-understood than the training of either data-driven neural operators or physics-informed neural networks (PINNs). To bridge this gap, we examine key components of the PINO training pipeline, including architecture design, optimizer choice, loss balancing, and collocation-point sampling strategy. We study three representative operator backbones, Deep Operator Network (DeepONet),
Fourier Neural Operator (FNO), and Continuous
Vision Transformer (CViT), across five diverse parametric PDE systems. Our results show that CViT provides consistently strong and stable performance across the considered
benchmarks. Beyond architecture, we find that several optimization pathologies previously identified in PINN training naturally arise in PINOs, including gradient conflicts and causal violation. We also find that mitigation
algorithms developed for PINNs remain effective in the PINO setting. We further compare physics-informed and data-driven training under different data regimes, revealing that a carefully designed physics-informed training pipeline can match, and in some cases, outperform purely data-driven neural operators. Taken together, these findings provide a systematic empirical understanding of the optimization challenges in PINO training and inform a practical pipeline for efficient and robust physics-informed operator learning. Code and data are available at https://github.com/NanxiiChen/PI-CViT.
Read the full abstract ▾
All authors Nanxi Chen, Chuanjie Cui, Airong Chen, Sifan Wang, Rujin Ma
Superconductivity
2.4 GHz Flip-flop Device within Nonequilibrium Superconducting Diode
Xiangyu Bi, Hongyi Li, Aoshen Yang et al. (+12 more)
Superconducting diode effect exhibits asymmetric critical supercurrent and has profound implications for condensed matter physics. The technical appeals of such superconducting diodes are their ultrahigh on-off ratio and diode efficiency for superconducting electronics owing to the dissipationless supercurrent therein. However, realizing superconducting diode operation at high working frequency, which is a key requirement for practical applications, remains elusive and challenging. Here, we demonstrate a polarity-controllable superconducting diode with non-
equilibrium Josephson junction and its edge-triggered flip-flop operation at a high frequency up to 2.4 GHz, within a van der Waals
superconductor 2M-WS$_2$. By simply tuning the thickness of superconducting 2M-WS$_2$ nanoflakes to engineer inversion asymmetry in the junction, we achieve a high diode efficiency of 67% and an on-off ratio exceeding 10$^5$. Importantly, the pulse width and duty cycle of output pulse signals in such superconducting diode flip-flop devices can be controlled in a broadband frequency range crossing 12 orders of magnitude. Theoretical analysis reveals that the non-
equilibrium dynamic nature of supercurrent in these Josephson junctions enables such a high diode operating frequency and the polarity control of supercurrent. The 2.4 GHz non-
equilibrium Josephson diode developed here provides a promising platform for advanced superconducting logic
circuits and broadband telecommunication applications.
Read the full abstract ▾
All authors Xiangyu Bi, Hongyi Li, Aoshen Yang, Yuqiang Fang, Ganyu Chen, Shichong Yang, Yicheng Shen, Qizheng Sun, Junwei Huang, Wei Jiang, Da Wang, Fuqiang Huang, Haijun Zhang, Qianghua Wang, Hongtao Yuan
Materials Science
Stacking-Dependent Magnetism and Tunable Half-Metallicity in Bilayer Janus 1T-MnSSe
Jakkapat Seeyangnok, Udomsilp Pinsook and Graeme J. Ackland
We investigate the structural, electronic, and
magnetic properties of
bilayer Janus 1T-MnSSe using first-principles calculations. Various AA- and AB-type stacking configurations are considered to examine the influence of interlayer registry on
magnetic ordering and exchange interactions. The nonmagnetic state is unstable for all stackings, confirming intrinsic magnetism. The AA2 stacking is identified as the ground state and exhibits A-type
antiferromagnetic ordering, indicating
antiferromagnetic interlayer coupling. Monte Carlo simulations based on an effective Ising model reveal enhanced
magnetic transition temperatures in the
bilayer relative to the monolayer, with Néel temperatures above 300~K for
antiferromagnetic stackings and Curie temperatures up to 250~K for
ferromagnetic phases. Several stacking configurations exhibit robust half-metallic ferromagnetism with nearly 100%
spin polarization at the
Fermi level. Moreover, the half-metallic state can be tuned and ultimately transformed into a metallic
ferromagnetic phase through carrier doping and biaxial strain. These findings establish
bilayer MnSSe as a promising platform for controllable interlayer magnetism and spintronic applications in two-dimensional materials.
Read the full abstract ▾
Strongly Correlated Electrons
Unveiling orbital landscapes in strongly correlated bulk nickelates with $s$-NIXS
Edgar Abarca Morales, Martin Sundermann, Brett Leedahl et al. (+10 more)
We leverage $s$-orbital non-resonant inelastic X-ray scattering ($s$-NIXS) to perform orbital imaging on three bulk rare-earth nickelates spanning a range of formal nickel valence (3$d$ electron filling) from Ni$^{3+}$ (3$d^7$) to Ni$^{1+}$ (3$d^9$). Our results directly reveal the ground states of these compounds all with minimal theoretical input. In particular, we demonstrate the low-
spin orbital configuration of trivalent LaNiO$_3$, the $d_{x^2-y^2}$ configuration of monovalent LaNiO$_2$, and resolve the effective $e_g$
crystal field splitting in the distorted octahedral environment of divalent La$_2$NiO$_4$. This work illustrates the potential of $s$-NIXS to study the ground state and excited states of strongly correlated materials without needing complex theoretical analysis of spectroscopic data.
Read the full abstract ▾
All authors Edgar Abarca Morales, Martin Sundermann, Brett Leedahl, Vignesh Sundaramurthy, Georg Poelchen, Ulrich Burkhardt, Raul Cardoso, Pascal Puphal, Alexander Komarek, Bernhard Keimer, Matthias Hepting, Liu Hao Tjeng, Berit H. Goodge
Solar and Stellar Astrophysics
Mass-Orbital Period Distribution of Massive White Dwarfs Formed Through Stable Mass Transfer
Rizhong Zheng, Hongwei Ge, Christopher A Tout et al. (+10 more)
White
dwarfs (WDs) in binaries can form through either the stable mass-transfer process or common envelope
evolution (CEE). Compared to CEE, the stable mass-transfer process can lead to a distinct mass$-$orbital period ($M_{ \mathrm{WD}}$-$P_{ \mathrm{orb}}$) relation. Thus, this relation of WDs contains the information about the
evolution channels. We can study the relation in WD binary systems to determine whether their progenitors undergo a CEE. We use the
stellar evolution code MESA as our primary computational tool and adopt the quasi-adiabatic criterion to ensure that our models satisfy the conditions for stable mass transfer. Our study considers different mass-transfer schemes, varying
metallicities, and the relation for both low-mass and intermediate-mass progenitors. Previous studies have focused on the relation for low-mass progenitors, which cannot explain some long-period, high-mass WD binaries. Our results show that the $M_{ \mathrm{WD}}$-$P_{ \mathrm{orb}}$ distribution for intermediate-mass progenitors whose cores remain nondegenerate prior to central helium burning can account for the formation channels of long-period and massive WD binaries.
Read the full abstract ▾
All authors Rizhong Zheng, Hongwei Ge, Christopher A Tout, Hailiang Chen, Zhenwei Li, Dengkai Jiang, Chengyuan Li, Zhijia Tian, Bo Ma, Lifu Zhang, Jian Mou, Xuefei Chen, Zhanwen Han
Quantum Gases
Charge-Conjugation Violation and Population Asymmetry in Bipartite Fermionic Lattices
Di Xiao, Xue-Ting Fang, Lushuai Cao et al. (+2 more)
Charge conjugation violation (CCV) is a central concept in particle physics and appears also for quasiparticles in
quantum many-body systems, which typically relies on an embedded external
symmetry breaking to the underlying system. An open question is how an intrinsic CCV mechanism could emerge and what its macroscopic consequences would be. We establish sublattice kinks in bipartite fermionic
lattices as a concrete setup showing intrinsic CCV. The intrinsic CCV of the sublattice kink is based on the graph-topological nature of the underlying
Hamiltonian, with no explicit
symmetry breaking taking place. It leads to a population asymmetry of different configurations and imprints a hidden leaf-like structure in the eigenenergy spectrum. The population asymmetry also leads to an imbalanced sublattice-kink production triggered by the
vacuum-instability in the quench dynamics. Our work demonstrates the graph
topology as the microscopic origin of intrinsic CCV, with the population asymmetry as the macroscopic consequence, of which the proposed setup is highly amenable to experimental implementation via cold-atom
quantum simulators.
Read the full abstract ▾
All authors Di Xiao, Xue-Ting Fang, Lushuai Cao, Zhong-Kun Hu, Peter Schmelcher
High Energy Astrophysical Phenomena
Detectability of secondary images from flares near Sgr A* with mock GRAVITY data
Fengting Xie, Qing-Hua Zhu and Xin Li
The orbital motion of near-infrared
flares reported by the
GRAVITY collaboration encodes information about both the dynamics of
accretion matter and the underlying spacetime geometry. The centroid track of these
flares, which corresponds to the flux-weighted center of light, incorporates contributions from primary, secondary and higher-order images. Thus, it potentially indicates distinctive signatures of the spacetime geometry, even when these individual multiple images remain unresolved. In this study, we explore the detectability of the secondary images from
flares orbiting Sgr A* through mock data simulating future
GRAVITY observations. Specifically, we compare the model in which the centroid coincides with the track of the primary images with another model in which the centroid incorporates flux-weighted contributions from both the primary and secondary images. Fitting these models to the mock data based on
Bayesian framework, we quantify the conditions under which the signature of secondary images can be statistically distinguishable. We demonstrate that increasing the sample size by an order of magnitude alone could not yield strong evidence for distinguishing the secondary image. Robust detectability ($|\Delta\text{BIC}| >7.9$) is achieved when both with the improved sample size and astrometric uncertainties reduced to 40% of current uncertainties of
GRAVITY astrometric data. Unlike the primary image, which is dominated by
accretion flow physics, the secondary images originate from gravitational
lensing in the strong-field regime. Their detection is an essential first step toward probing higher-order images and the
photon rings.
Read the full abstract ▾
Soft Condensed Matter
Aging Time dependent Static Friction between Soft and Hard Solid Interfaces
Vinay A. Juvekar and Arun K. Singh
Understanding of friction between sliding surfaces is critical for variety of applications. We present a friction model between soft and hard solid interfaces for studying aging time dependent static friction. The model is based on strengthening of dangling chains with the substrate during aging period. The friction model is, in turn, validated with the experimental data from literature. Friction properties are also estimated in terms of gelatin concentration to justify the results.
Read the full abstract ▾
Classical Physics
Constitutive Settings with regard to Energy- and Entropy-Balances in Non-Equilibrium Thermodynamics: the Thermodynamical Verification
Wolfgang Muschik
Constitutive equations have to be in agreement with the energy- and
entropy- balances. For achieving that, the procedure of thermodynamical verification is introduced: Because heat flux and
entropy flux as well as the time differentials of internal energy and
entropy are not independent of each other, energy- and
entropy-balances are connected with each other by so-called internal settings laying down the theoretical frame of the applied material description which is characterized by additional constitutive settings.
Read the full abstract ▾
Materials Science
Ferroelectric brightening of spin forbidden dark excitons in a WSe2/hybrid perovskite heterostructure
Xinyun Wang, Magdalena Grzeszczyk, Maxim Trushin et al. (+14 more)
Long-lived dark
excitons in monolayer WSe2 present promising candidates for carrying
spin and valley information, but their optical access and
spin manipulation have conventionally required the use of strong external
magnetic fields. Here, using a ferroelectric hybrid perovskite
heterostructure, we leverage the ferroelectric proximity effect to break the WSe2's in-plane rotational
symmetry and brighten the
spin-forbidden dark
excitons under zero
magnetic field conditions. Furthermore, we show that the twist angle between the WSe2 and perovskite
crystals controls the ferroelectric coupling strength and valley-contrasting polarization. Our proposed mechanism, supported by a four-band tight-binding model, suggests that the ferroelectric proximity effect induces an asymmetric intersublattice interaction, generating an effective in-plane
spin-orbit coupling (SOC) field that rotates
spin/valley polarization and brightens dark
excitons. Our work establishes ferroelectric proximity coupling as an electrically reconfigurable,
magnetic-field-free strategy for
spin exciton control in two-dimensional
semiconductors.
Read the full abstract ▾
All authors Xinyun Wang, Magdalena Grzeszczyk, Maxim Trushin, Ivan Verzhbitskiy, Dmitrii Litvinov, Yi Wei Ho, Yuan Chen, Zhenyue Wu, Mykola Telychko, Chuanqi Zhang, Andres Granados del Aguila, Kuan Eng Johnson Goh, Xinwei Li, Goki Eda, Shaffique Adam, Maciej Koperski, Kian Ping Loh
General Relativity and Quantum Cosmology
Two discs and a missing triangle: the maximally extended Kerr black hole revisited
Malcolm A. H. MacCallum
The region spaning the ring singularity in the Kerr black hole solution is described here as two (flat) discs rather than one. From this viewpoint it follows that the usual depiction of the worldsheet $\theta=\pi/2$, $\phi$ constant (in Boyer-Lindquist coordinates) is missing (multiple copies of) the region $r<0$, representable as a triangle in the usual conformal diagram style.
Read the full abstract ▾