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Physics

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Thursday 25 June

Statistical Mechanics

Odd transport in a two-temperature Brownian dimer

Iman Abdoli and Hartmut Löwen

We investigate a two-temperature Brownian dimer with odd mobility, characterized by antisymmetric transport coefficients, as a controlled paradigm for odd nonequilibrium dynamics. The system is made of two harmonically confined particles coupled by an elastic spring and connected to reservoirs at different temperatures. Odd mobility converts conservative forces into transverse motion, linking heat exchange to circulating probability currents without requiring external torques, spatial anisotropy, or nonconservative driving. Our exact solution shows that odd mobility creates handed correlations between the two particles while leaving the individual particle distributions isotropic. These correlations arise only when temperature imbalance, elastic coupling, and odd mobility act together, and their handedness reverses when the odd response is reversed. The steady probability current contains two distinct parts: the ordinary irreversible current of a two-temperature dimer and an additional handed contribution generated by odd mobility. When projected onto the motion of each particle, this handed contribution becomes a pair of counter-rotating circulating currents inside the traps. Based on the currents we compute the heat transfer and entropy production analytically. We show that odd mobility enhances thermal conductance between the reservoirs, while the net heat current and total dissipation remain unchanged under reversal of the odd handedness.
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High Energy Physics (Experiment)

Study of Supernova Neutrinos at ESSnuSB

ESSnuSB: J. Aguilar, M. Anastasopoulos, D. Barčot et al. (+95 more)

In this paper, we have studied the sensitivity of the ESSnuSB far detector to supernova neutrinos. ESSnuSB is a proposed long-baseline neutrino experiment in Sweden, which will use a 538 kt water Cherenkov detector to probe the leptonic phase $\delta_{\rm CP}$ by studying the second oscillation maximum. However, given the very large detector volume, it will have an excellent sensitivity to supernova neutrinos if a supernova explosion occurs during the run-time of ESSnuSB. Motivated by this, we first estimate the expected event rates at the ESSnuSB far detector for three different supernova flux models and then we probe its capability to distinguish these flux models. Additionally, we also investigate the impact of systematic errors and detector efficiency. Our results show that depending on the model of the supernova neutrinos, the expected number of events detected at Earth varies significantly. Our results also show that the ESSnuSB far detector may have excellent potential in distinguishing these flux models depending upon the distance of the supernova explosion, systematic errors and detector efficiency.
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All authors ESSnuSB: J. Aguilar, M. Anastasopoulos, D. Barčot, E. Baussan, A.K. Bhattacharyya, A. Bignami, M. Blennow, M. Bogomilov, B. Bolling, E. Bouquerel, F. Bramati, A. Branca, G. Brunetti, I. Bustinduy, C.J. Carlile, J. Cederkall, T. W. Choi, S. Choubey, P. Christiansen, E. Cristaldo Morales, P. Cupiał, D. D'Ago, H. Danared, J. P. A. M. de André, M. Dracos, I. Efthymiopoulos, T. Ekelöf, M. Eshraqi, G. Fanourakis, A. Farricker, E. Fasoula, T. Fukuda, S. Gago, N. Gazis, Th. Geralis, M. Ghosh, A. Giarnetti, G. Gokbulut, C. Hagner, L. Halić, J. Hiegel, M. Hooft, K. E. Iversen, N. Jachowicz, M. Jakkapu, M. Jensen, I. Karakoulias, E. Kasimi, A. Kayis Topaksu, B. Kliček, K. Kordas, B. Kovač, A. Leisos, A. Longhin, M. López, C. Maiano, S. Marangoni, J. G. Marcos, C. Marrelli, D. Meloni, M. Mezzetto, N. Milas, R. Mohanta, J.L. Muñoz, K. Niewczas, M. Oglakci, T. Ohlsson, M. Olvegård, P. Panda, M. Pari, D. Patrzalek, G. Petkov, Ch. Petridou, P. Poussot, A. Psallidas, F. Pupilli, D. Saiang, D. Sampsonidis, A. Scanu, C. Schwab, F. Sordo, G. Stavropoulos, M. Stipčević, R. Tarkeshian, F. Terranova, T. Tolba, M. Topp-Mugglestone, E. Trachanas, R. Tsenov, A. Tsirigotis, S. E. Tzamarias, M. Vanderpoorten, G. Vankova-Kirilova, N. Vassilopoulos, S. Vihonen, J. Wurtz, V. Zeter, O. Zormpa

High Energy Physics (Theory) · Cross-listed from math.GT

Integrality of genus-$g$ indices with adjoint Reidemeister torsions of twist knots

Ryoto Tange, Yuji Terashima and Yoshikazu Yamaguchi

We consider the sum of the adjoint Reidemeister torsions and prove the integrality for twist knots and the meridian. We also give some concrete examples of the generating functions for these sums.

Astrophysics of Galaxies

HI Galaxy Science with the SKA

Jing Wang, D.J. Pisano, Sarah Blyth et al. (+9 more)

This chapter introduces the contributions of the HI galaxy science in this volume reviewing the latest developments and urgent questions in HI galaxy science, providing guiding principles for a layered set of future key science projects. The key science will include: a complete censuses of HI morphologies and kinematics at sub-kpc and 1 km/s resolution within and around galaxies in the nearby Universe; a measurement of the cosmic HI mass density and HI mass function evolution at least up to z~1; an improved understanding of the Universe at z>1, particularly the balance between cold molecular and cool atomic gas. We also provide a view of the synergistic multi-wavelength surveys available in 2028+ in the southern hemisphere. This effort will improve our understanding of the baryon cycle across a significant fraction of the cosmic history, including the processes of gas accretion, consumption and removal as well as AGN and star formation feedback. Based on these science goals, the earlier proposed three-tiered survey strategy remains, but survey parameters and predictions are adjusted according to AA* and AA4 developments. This chapter is an update of the earlier "Advancing Astrophysics with the Square Kilometre Array" chapter 'HI Science with the SKA' by Staveley-Smith & Oosterloo.
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All authors Jing Wang, D.J. Pisano, Sarah Blyth, Neeraj Gupta, Barbara Catinella, Lister Staveley-Smith, Paolo Serra, Elizabeth A. K. Adams, W.J.G. de Blok, Martin Meyer, Lourdes Verdes-Montenegro, Tom Oosterloo

High Energy Astrophysical Phenomena

Exploring Tidal Disruption Events with SKA and VLBI: Unveiling the Mystery of Black Hole Feeding and Outflows

Xinwen Shu, Guobin Mou, Tao An et al. (+8 more)

Tidal disruption events (TDEs) probe the birth and evolution of black hole accretion flows and jets on human timescales. Radio emission traces shocks and outflows from thermal TDEs and powerful relativistic jets in the rare jetted class. SKA Mid, phased for VLBI and used together with global networks, will deliver milliarcsecond imaging, tens of microarcsecond astrometry, and microJy sensitivity, enabling: (i) proper motion measurements that discriminate off axis relativistic jets from subrelativistic winds; (ii) resolved morphologies and magnetic field diagnostics via polarimetry; and (iii) precise nuclear localization to distinguish SMBH vs. IMBH and to reveal recoiling or binary systems. SKA's wide frequency coverage (0.35 to 15.4 GHz) and 1h continuum sensitivities of 3 to 10 microJy per beam, together with multibeam tiedarray VLBI and a transient buffer for rapid triggers, are transformational. LSST, Einstein Probe, and SVOM will increase TDE alerts to hundreds per year, and late time radio flares appear common, ensuring rich SKA VLBI samples. We provide observing strategies, detection forecasts, and predictions, e.g., about 5 proper motion detections of jetted (or off axis) TDEs per year and routine core shift constraints at the microarcsecond level. This program will establish TDEs as laboratories for exploring jet launching, particle acceleration (including neutrinos), black hole accretion history and demographics, and properties of circumnuclear medium.
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All authors Xinwen Shu, Guobin Mou, Tao An, S. Komossa, Miguel Perez-Torres, Weihua Lei, Luming Sun, Ning Jiang, Tinggui Wang, Chichuan Jin, Jun Yang

Instrumentation and Methods for Astrophysics

How to access astronomical observation facilities ?

Michaël De Becker

Access to astronomical data is a central component of astrophysical research. The allocation of telescope time is organized on an international scale through a highly competitive process. Over the past decades, this framework has evolved toward an increasingly professionalized system, particularly in the context of calls for telescope time proposals issued by major agencies or organizations, where hundreds of projects may compete for selection. Preparing a telescope time proposal is a demanding task for which junior researchers are not always adequately prepared. Astrophysicists typically acquire this expertise through first-hand experience, either by submitting their first proposal or by participating as members of a proposing team. At the same time, competition for telescope time is intense, and the significant effort invested in proposal preparation is accompanied by a non-negligible risk of rejection. This paper aims to present the general framework governing telescope time applications for both ground-based and space-borne observatories, with particular emphasis on the preparation of telescope time proposals. It discusses a set of key guidelines, some mandatory and others advisory, intended to help proposers navigate the application process more effectively, avoid common pitfalls and procedural missteps, and ultimately reduce the likelihood of preventable factors leading to a substantial decrease in the probability of selection.
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Atomic Physics

Quantum statistics on atom-ion Feshbach resonances

Joachim Siemund, Fabian Thielemann, Jonathan Grieshaber et al. (+5 more)

We investigate three-body recombination in a hybrid atom-ion system consisting of a single trapped Ba$^+$ ion immersed in a two-component Fermi gas of Li atoms near an atom-ion Feshbach resonance. By tuning the spin composition at constant density and temperature, we isolate the role of quantum statistics in atom-atom-ion collisions. The measured ion loss rate exhibits a pronounced nonlinear dependence on spin polarization, revealing a reduced contribution of recombination pathways involving identical fermions already at the level of experimental observables. The observations are consistent with a two-step recombination picture and an adiabatic hyperspherical approach, where antisymmetrization restricts the available entrance channels and gives rise to interference between indistinguishable recombination pathways. Our work establishes atom-ion systems as a platform for controlling three-body collisions via quantum statistics and demonstrates that exchange-symmetry effects remain robust even under thermal averaging that obscures the underlying threshold-law behavior.
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All authors Joachim Siemund, Fabian Thielemann, Jonathan Grieshaber, Wei Wu, Patrick Mullan, Panagiotis Giannakeas, Krzysztof Jachymski, Tobias Schaetz

Mesoscale and Nanoscale Physics

Local and nonlocal STM transport signatures of spin polarization in second order topological superconductors

Paweł Szumniak, Daniel Loss and Jelena Klinovaja

We investigate numerically the spin and transport properties of two-dimensional second-order topological superconductors (2D SOTSCs) hosting a pair of Majorana corner states (MCSs). First, we show that MCSs in the considered setup are characterized by a distinct spatial distribution of electronic spin polarization in the direction perpendicular to an applied in-plane magnetic field, with opposite signs for each MCS. Such a property can be used to label MCSs in a pair by their electronic spin. We propose a comprehensive spin-resolved transport protocol for measuring such a spin texture and further detecting the braiding (exchange) of a pair of MCSs, a crucial prerequisite for topological quantum computing. To be specific, we show that the magnitude of local conductance and the sign of nonlocal conductance are precisely linked to the sign of the electronic part of the MCS spin density and the spin polarization of the probe. Moreover, we show that the proposed technique can be used to detect the spin density profile of higher-energy quasiparticle states, e.g., edge states hosted in the SOTSC. We showed that all analyzed features are highly robust to strong static disorder , which makes our findings a clear experimental pathway to verify the spin structure of MCS and other quasiparticles hosted in SOTSCs.
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Disordered Systems and Neural Networks

Physical Neural Networks Need Nonlinearity, Amplification, and Suppression for Learning

Nex Chiaki Xijana Stuhlmüller and Marjolein Dijkstra

The exponential growth in energy consumption of artificial intelligence systems has spurred interest in physical computing paradigms that exploit the relaxation of physical systems toward steady states. However, many existing physical networks are fundamentally linear and incapable of performing nonlinear operations crucial for meaningful machine learning tasks. Here we use simulations to show that nonlinearity alone is insufficient; physical learning systems must also support signal amplification and suppression to perform nontrivial computations. We present physically plausible circuit designs that incorporate these essential features, enabling effective nonlinear information processing. Our findings clarify the limitations of linear physical networks and provide guidance for developing energy-efficient physical learning architectures capable of general machine learning tasks.
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Other Condensed Matter

Electric-Field Switchable Magnetic Spin Hall Effect

Mingbo Dou, Xu Chen, Qin Zhang et al. (+4 more)

It is established that the polarity of a time-reversal-odd ($\mathcal{T}$-odd) physical quantity can be reversed under the $\mathcal{T}$ operation. Here, we use the spin-group analysis to directly demonstrate that the $\mathcal{T}$-odd magnetic spin Hall effect in ferroelectric altermagnets can be switchable by electric fields beyond the $\mathcal{T}$ operation. This arises from the ferroelectric switching of the nonrelativistic spin splitting, which swaps the roles of spin up and down channels in the reciprocal space. As a result, the $\mathcal{T}$-odd spin conductivity that are proportional to the spin-polarized conductivity difference reverses its polarity upon polarization switching. We identify spin-group operations to switch both the polarization and the magnetic spin Hall effect simultaneously for non-centrosymmetric spin point groups. Then, we exemplify those phenomena in the ferroelectric altermagnet VOI$_2$ monolayer based on density functional theory calculations and an effective Hamiltonian analysis. Our findings not only provide novel strategies to switch the magnetic spin Hall effect using the dissipation-free electric field but also open a promising avenue for electrically programmable spintronic devices.
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All authors Mingbo Dou, Xu Chen, Qin Zhang, Xianjie Wang, Xue-Zeng Lu, Jia Zhang, L. L. Tao

Fluid Dynamics

Excitation of non-modal perturbations in hypersonic boundary layers by free stream forcing. Part II: asymptotic theory and key mechanisms

Ming Dong, Mingze Sun, Qinyang Song et al. (+1 more)

Recently, Zhao & Dong (J. Fluid Mech. 2025, vol. 1013: A44) developed a high-efficiency, high-accuracy numerical framework, the shock-fitting harmonic linearised Navier-Stokes (SF-HLNS) approach, which enables a systematic study of the receptivity of non-modal perturbations in hypersonic blunt-body boundary layers over a wide parameter range. In this Part II, we employ a high-Reynolds-number asymptotic analysis to elucidate the physical mechanism of the receptivity process. A distinct slow-down convection mechanism is identified in the nose region, amplifying the perturbation streamwise vorticity from the post-shock position to the boundary layer around the stagnation point by a factor of O(\sqrt{R}), where R is the Reynolds number based on nose radius. Downstream, the lift-up mechanism further leads to a transient growth of the perturbation streamwise velocity up to an amplitude of O(R). Based on these mechanisms, a reduced model is developed to predict the downstream evolution of the non-modal perturbations initiated by receptivity, whose predictions agree well with SF-HLNS calculations. This model can also be used to investigate the effects of wall temperature and nose radius on non-modal receptivity efficiency, as will be detailed in Part III of this work series.
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All authors Ming Dong, Mingze Sun, Qinyang Song, Lei Zhao

Optics

Refractive indices of Y$_2$SiO$_5$ in the near-infrared

Shijun Zhang, Jérôme Debray, Benoît Boulanger et al. (+2 more)

Y$_2$SiO$_5$ is a reference birefringent material for optical quantum technologies. The refractive index is primarily known in the visible spectrum, whereas this crystal is also used in the near-infrared. We begin by analysing historical measurements, as well as the modelling proposed at the time. The absence of refractive index tabulated values in the near- and mid-infrared ranges motivated us to carry out independent measurements. Using interferometric techniques in the telecom wavelength range, we demonstrate the ability to determine the principal refractive indices and propose a model spanning a broad spectral range based on Sellmeier equations for which we explicitly give the coefficients and discuss the achievable accuracy. Conversely, as an illustration, white-light interference enables us to precisely determine the thickness of a Y$_2$SiO$_5$ thin film on the order of ten micrometers.
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All authors Shijun Zhang, Jérôme Debray, Benoît Boulanger, Pierre Lemonde, Thierry Chanelière

Mathematical Physics

Asymptotic solutions: glancing trajectories, Lagrangian singularities, and Bessel cylinders

Ilya Bogaevskii and Michel Rouleux

We find a normal form for the simplest Lagrangian singularity appearing as the projection onto the space-energy of a solution to the Hamilton-Jacobi equation. Using this normal form we approximate asymptotic solutions of an equation $(\widehat{H}-E_0) \, u_h = f_h$ with a semiclassical distribution $f_h$ microlocalized on a Lagrangian manifold $\Lambda_0$ when $E_0$ is a critical value of the restriction $H|_{\Lambda_0}$.
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High Energy Astrophysical Phenomena

Broad-band Spectral Modeling of Large-Scale X-ray Jets in High-Redshift Quasars: An MHD-Informed Approach

Patryk Liniewicz, Łukasz Stawarz, C. C. Cheung et al. (+2 more)

We present a systematic spectral analysis of kiloparsec-scale jets in high-redshift quasars, modeling their radio-to-X-ray emission as synchrotron radiation and inverse-comptonization of CMB by relativistic electrons. In contrast to the homogeneous one-zone approximation commonly adopted in the literature, we describe the jet as a current-carrying, axially symmetric outflow with a purely toroidal magnetic field in magnetohydrostatic equilibrium and with radial velocity shear. In this framework, the pressure, magnetic-field, and bulk-velocity profiles are linked self-consistently, capturing the radial stratification of the emitting region without introducing additional free parameters. For any individual source, the model effectively retains only a small number of free parameters, including the total jet power, $L_{\rm j}$, and the on-axis bulk Lorentz factor, $\Gamma_0$. We consider two prescriptions for the radial distribution of the radiating electrons – proportional either to the gas pressure or to the rest-frame magnetic energy density – and two toroidal-field profiles, yielding four model variants. Applying the model to a sample of ten quasar jets at $z \geq 2.5$ with X-ray features resolved by Chandra, we perform Bayesian parameter inference and model comparison. The Bayesian evidence systematically favors electron distributions that follow the gas pressure rather than the magnetic energy density, while the data discriminate only weakly between the assumed field profiles. The inferred jet powers, reaching $L_{\rm j} \sim 10^{49}\,\mathrm{erg\,s^{-1}}$, are systematically larger than those obtained from one-zone models, and the corresponding global jet magnetization parameters are low. None of the derived quantities, including $\Gamma_0 \sim \mathcal{O}(10)$, shows a significant monotonic trend with redshift.
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All authors Patryk Liniewicz, Łukasz Stawarz, C. C. Cheung, Giulia Migliori, Aneta Siemiginowska

Mathematical Physics · Cross-listed from math.PR

Spectral expansion of LQG heat trace and KPZ scaling

Nathanaël Berestycki and Jakob Klein

Let $h$ be a whole plane Gaussian free field, and let $\Omega$ be a bounded domain in two dimensions. We study the asymptotics as $t\to 0$ of the Liouville quantum gravity (LQG) heat trace, defined as the integral over $\Omega$ of the on-diagonal LQG heat kernel. Our main result is to show that the second term in the spectral expansion as $t\to 0$ of the expected heat trace is governed by a nontrivial exponent, given by the KPZ (Knizhnik–Polyakov–Zamolodchikov) relation. A similar but stronger (almost sure) result applies to the related notion of heat content. Along the way we obtain various results on the short-term behaviour of the heat kernel, notably solving a conjecture of \cite{BW} concerning its annealed asymptotics, and showing the finiteness of all moments of the properly rescaled heat kernel.
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High Energy Physics (Phenomenology)

Thermodynamical analysis of QGP using effective PNJL model with Quasiparticle approach

Yogesh Kumar, Himanshu Aggarwal, R. S. Laishram et al. (+7 more)

We study the thermodynamics of the quark-gluon plasma using an effective Two flavor Polyakov Nambu Jona Lasinio (PNJL) model extended by a quasiparticle description for quarks and gluons, incorporating temperature dependent quark masses within the PNJL framework. Two variants, Quasiparticle Model-I and Quasiparticle Model-II, are implemented to investigate bulk thermodynamic observables such as pressure, energy density, entropy density, specific heat, and the speed of sound. The combined framework yields a robust baseline for the description of hot QGP dynamics in the high temperature regime at vanishing chemical potential and zero magnetic field. Systematic comparison with lattice QCD results shows an excellent agreement and clear improvement over conventional PNJL implementations. We observe that both variants complement each other, offering mutually consistent insight into quasiparticle mass effects and medium response in the deconfined phase. This mutual consistency validates the physical foundation of the overall quasiparticle mechanism, reinforcing the credibility of the calculated Equation of State. Finally, the quasiparticle model extension improves PNJL from a descriptive tool to a more qualitative phenomenological approach, enabling an improved description of the strong interacting quark-gluon plasma.
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All authors Yogesh Kumar, Himanshu Aggarwal, R. S. Laishram, Poonam Jain, Om Prakash, Sanjay Tyagi, Pargin Bangotra, Vinod Kumar, Yagyadatta Goswami, M. K. Sahu

Fluid Dynamics

Hydrodynamic theory of premixed flames under Darcy's law: Interfacial conditions and effects of nonunity Lewis number and heat loss

Prabakaran Rajamanickam and Joel Daou

Premixed flames propagating in porous media or Hele-Shaw channels are governed by Darcy's law, which accounts for the strong frictional forces imposed by the solid matrix or confining walls. Prior theoretical studies of such flames have typically employed phenomenological Markstein-type corrections and have assumed unity Lewis numbers and adiabatic conditions. In this work, we develop a rigorous hydrodynamic theory for premixed flames under Darcy's law that incorporates nonunity Lewis numbers and heat losses. Using large activation-energy asymptotics for a one-step Arrhenius chemistry model and a systematic multiple-scale analysis, we derive the interfacial jump conditions across the flame from first principles. The conventional continuity requirements of mass flux and pressure at an interface under Darcy's law acquire corrections to the finite thickness of the flame. The adiabatic burning rate is shown to involve three distinct Markstein numbers, corresponding to curvature, tangential flow strain, and gravity-induced strain. The gravity term is unique to Darcy's law and has no counterpart in classical Navier–Stokes formulations. Moreover, the curvature Markstein number and the tangential strain Markstein number are found to be unequal, in contrast to the classical Navier–Stokes case where they coincide in the one-step chemistry model. Explicit formulas for the Markstein numbers are provided, and the resulting new dispersion relation, linking the perturbation wave number $k$ to the growth rate $s$, takes the form $s=(a|k|-bk^2-d|k|^3)/(1+c|k|)$. This relation, applicable under Darcy's law, is to be compared to the classical Clavin–Garcia dispersion relation derived from the Navier–Stokes equations. The theory provides a rigorous foundation for flame dynamics in strongly confined environments, with direct applications to porous media combustion and Hele-Shaw cell experiments.
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Quantum Physics

On the simple derivation of the Casimir effect

Hai-Chau Nguyen and Matthias Kleinmann

The Casimir effect in its simplest form describes the attraction of two parallel conducting plates at close distance due to the vacuum fluctuation of the electromagnetic field. Its derivation can be found in many introductory works on quantum optics. Here we return to the original paper by Casimir and find subtle nuances in his derivation that are worth discussing to give a complete picture of a mathematically sound derivation of the effect.
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General Relativity and Quantum Cosmology

A geometric multimessenger consistency test of radiative and near-zone gravity with LISA and SKA

Bhooshan Gadre

Compact binary pulsars observed both through precision radio timing and low-frequency gravitational waves offer a direct way to compare the same binary geometry with two independent messengers. We propose a multimessenger consistency test based on the orbital inclination, measured from the Shapiro-delay shape parameter in radio timing and from the tensor polarization amplitude ratio in the gravitational-wave signal. Defining the common-epoch residual $\eps(t_0)=s_{\rm Shapiro}(t_0)-s_{\rm GW}(t_0)$, general relativity predicts $\eps=0$, while a nonzero value would indicate either an unmodeled systematic or a mismatch between the near-zone and radiative descriptions of gravity. We estimate the attainable precision on this quantity for representative LISA–SKA compact binary pulsars using a seven-parameter timing Fisher matrix and a sky-averaged LISA sensitivity curve including the Galactic foreground. We adopt a conservative radio baseline, $\sigma_{\rm TOA}=1\,\mu{\rm s}$ and $N_{\rm eff}=10^4$, intended to summarize radiometer noise, jitter, residual dispersion-measure and scattering effects, profile evolution, and cadence losses after wideband timing. For systems at $d=5\,{\rm kpc}$ observed for four years, we find $\sigma_\eps\simeq4\times10^{-3}$ for a favorable double neutron star and $\sigma_\eps\simeq9\times10^{-4}$ for a hypothetical pulsar–black-hole system. The former is the more robust astrophysical benchmark; the latter illustrates the reach if such a high-SNR chirping source is discovered. The useful cases remain limited mainly by gravitational-wave polarimetry, while radio timing supplies the near-zone reference measurement of the inclination. These results define a quantitative target for future joint Bayesian analyses of compact binary pulsars observed in both radio and gravitational waves.
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Chemical Physics

Perturbatively Corrected Linear Response Selected Configuration Interaction

Peter Reinholdt, Erik Kjellgren and Jacob Kongsted

Selected configuration interaction (SCI) methods have emerged as powerful, lower-cost alternatives to full configuration interaction (FCI) for ground- and excited-state energies. Still, calculating molecular response properties with SCI remains a significant challenge. In this work, we introduce perturbative corrections to the linear response selected configuration interaction (LR-SCI) framework, using an order-by-order Epstein-Nesbet perturbation expansion through second order. We demonstrate that in this theoretical framework, the finite-order perturbative treatment preserves the pole structure of the parent variational LR-SCI theory, which means that although the method can be useful for static properties, it is not suitable for frequency-dependent molecular response properties. Numerical benchmarks targeting the static polarizabilities of water, ethene, boron hydride, and hydrogen chloride demonstrate systematic convergence toward the FCI limit for both ground and excited electronic states. While first-order corrections yield marginal improvements, the inclusion of second-order corrections substantially enhances accuracy over underlying variational treatments and diminishes oscillatory convergence behavior present in the parent variational LR-SCI method. Combined with extrapolation techniques, LR-SCI-PT achieves excellent agreement with high-level coupled-cluster references, establishing a powerful route toward near-FCI quality molecular properties for systems otherwise inaccessible to exact FCI treatments.
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Instrumentation and Methods for Astrophysics

VLBI with SKAMPI, the SKA-Mid MPIfR dish demonstrator

Jompoj Wongphechauxsorn, Niclas Alexander Esser, Tobias Winchen et al. (+13 more)

The SKA-MPIfR telescope (SKAMPI) is a prototype SKA-Mid antenna located at the SKA site in the Karoo Desert, South Africa. It is funded by the Max Planck Society, through the Max Planck Institute for Radio Astronomy (MPIfR), and operated in collaboration with the South African Radio Astronomy Observatory (SARAO). The first fringe-finding experiments have been conducted with the European VLBI Network and the southern hemisphere Long Baseline Array, connecting SKAMPI with Europe and Australia. Here we present early SKAMPI VLBI mode results in S-Band, including successful fringe detections and evaluating the integration and imaging performances of SKAMPI in observations with the EVN, LBA, and VLBA.
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All authors Jompoj Wongphechauxsorn, Niclas Alexander Esser, Tobias Winchen, Jan Wagner, Uwe Bach, Hans-Rainer Klöckner, Michael Kramer, Gundolf Wieching, Ewan Barr, Jonathan Quick, Roger Deane, Cormac Reynolds, Phil Edwards, Chris Phillips, Matthias Kadler, Roopesh Ojha

High Energy Astrophysical Phenomena

Unraveling the mysteries of supernovae with SKA+VLBI

Tao An, Zhengwei Liu, Ailing Wang et al. (+6 more)

Supernovae (SNe) drive cosmic chemical enrichment and shape galactic feedback, yet the link between progenitors and explosion outcomes remains poorly constrained because the earliest phases are rarely resolved. Radio emission traces synchrotron radiation where the fastest ejecta interact with the circumstellar medium (CSM), providing a uniquely penetrating probe of these phases. SKA-Mid phased into global VLBI will move from simple detections to routine interferometric imaging of nearby extragalactic SNe. Sub-$\mu$Jy sensitivity and mas-scale SKA+VLBI imaging, complemented by visibility-domain model fitting for sub-beam radius measurements at 5-15 GHz will allow us to follow the expanding shocks of stripped-envelope SNe out to $\sim$25 Mpc, measure deceleration indices ($m$) and axial ratios to $\approx 5-10\%$, and directly test jet-assisted versus neutrino-driven explosion mechanisms. For interacting SNe (Type IIn/Ibn), SKA+VLBI will resolve clumpy and toroidal CSM on progenitor scales, constraining the timing and geometry of eruptive pre-explosion mass loss. Deep limits on Type Ia SNe will tightly restrict the allowed single-degenerate parameter space, while late-time imaging will search for nascent compact remnants and pulsar wind nebulae. In synergy with optical, X-ray and gravitational wave facilities, SKA+VLBI will turn nearby SNe into laboratories for time-resolved shock physics and progenitor mapping.
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All authors Tao An, Zhengwei Liu, Ailing Wang, Miguel Pérez-Torres, Javier Moldon, Liangduan Liu, Peter Lundqvist, Xuefei Chen, Xiangcun Meng

Mathematical Physics · Cross-listed from math.DS

Onsager–Machlup functionals for McKean–Vlasov SDEs via Euler-type approximation

Ying Chao and Pingyuan Wei

The Onsager–Machlup action functional provides a variational framework for characterizing the most probable transition paths of stochastic systems and plays an important role in the study of nonequilibrium fluctuations. Its extension to McKean–Vlasov stochastic differential equations is complicated by the intrinsic distribution dependence of the coefficients. In this paper, we address this difficulty by introducing an Euler-type approximation scheme based on classical, distribution-free stochastic differential equations. Combining the classical Onsager–Machlup theory with a convergence argument for the approximation sequence, we derive an explicit expression for the Onsager–Machlup functional associated with the McKean–Vlasov SDE. The proposed approach is constructive and extends to a broad class of distribution-dependent stochastic systems.
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Nuclear Theory

Challenging chiral EFT with tritium beta decay

D.F. Ramirez Jimenez, S. Heihoff, J. Golak et al. (+6 more)

We present a detailed investigation of tritium beta decay up to third order (N2LO) in chiral effective field theory (EFT) using the LENPIC interactions. Unlike existing studies, we use nucleon-deuteron scattering observables to fix the low-energy constant D that governs the strength of the short-range contributions to the exchange axial current operator and three-nucleon forces. Surprisingly, the resulting parameter-free predictions for the tritium Gamow-Teller reduced matrix element are found to considerably overestimate its empirical value. This result remains robust against reasonable variations of the pion-nucleon coupling constants and regularization scheme. A closer look at the size of the parameter-free long-range two-body contributions to the Gamow-Teller matrix element reveals the fine-tuned nature this observable in chiral EFT, which may partially explain the observed deviation. Our results indicate a considerable N2LO truncation uncertainty for tritium beta decay and point towards large higher-order two-body corrections. More definite conclusions await a complete fourth-order analysis of nucleon-deuteron scattering observables and tritium half-life.
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All authors D.F. Ramirez Jimenez, S. Heihoff, J. Golak, E. Epelbaum, H. Krebs, P. Reinert, R. Skibinski, K. Topolnicki, H. Witala

Strongly Correlated Electrons

Coexistence of static order and spin dynamics in an S = 5/2 frustrated triangular antiferromagnet

U. Jena, B. Sana, Satish Kumar et al. (+6 more)

Frustrated triangular-lattice antiferromagnets in the classical high-spin limit provide a paradigmatic setting in which the interplay of competing exchange interactions, anisotropy, and collective degrees of freedom can lead to unconventional low-energy excitations, anomalous criticality, and persistent dynamical responses. Here, we present comprehensive thermodynamic, $\mu$SR, and neutron diffraction experiments, along with first-principles calculations, on a triangular-lattice antiferromagnet, MnSnB$_2$O$_6$, where Mn$^{2+}$ ($S=5/2$) moments form a nearly perfect 2D triangular network without any anti-site disorder. The Curie-Weiss fit to the magnetic susceptibility yields a moderate Curie-Weiss temperature of $-12$ K, indicating dominant antiferromagnetic interactions between Mn$^{2+}$ moments, which is supported by first-principles calculations. Specific-heat measurements reveal the onset of long-range magnetic order at $T_{\rm N}\approx 1$ K, which is ascribed to intraplane exchange interactions. The specific heat exhibits pronounced short-range correlations above $T_{\rm N}$ and an unconventional power-law behavior, $C\propto T^{1.37}$, deep in the ordered state, suggesting the presence of non-trivial low-energy excitations. Zero-field $\mu$SR experiments down to 50~mK confirm the presence of magnetic ordering below $T_{\rm N}$, in agreement with thermodynamic and neutron diffraction experiments. The $\mu$SR measurements detect persistent spin dynamics coexisting with static magnetic order. The temperature evolution of the order parameter down to 50~mK from neutron diffraction suggests that the ordered state is consistent with a 3D Ising-like antiferromagnet. This family of archetypal frustrated magnets offers a promising venue for the experimental realization of emergent phenomena governed by competing exchange interactions and exotic low-energy excitations.
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All authors U. Jena, B. Sana, Satish Kumar, M. Pregelj, A. Bandyopadhyay, P. Manuel, J. S. Lord, D. T. Adroja, P. Khuntia

Mathematical Physics

Wave-Particle Decomposition for Kinetic Equations I: Theory and Numerics

Chang Liu and Kun Xu

This paper presents a wave-particle decomposition (WPD) for kinetic relaxation equations, formulated around a local evolution timescale and its associated kinetic horizon. By leveraging the characteristic integral solution, we decompose the distribution function into an analytically accumulated wave component and a purely kinetic particle component. The latter is defined by the collisionless transport that survives beyond a prescribed local domain of influence, termed the horizon. This continuous formulation yields a unified wave-particle system valid across the entire Knudsen spectrum, comprising a source-free total conservation law, a wave equation, and a particle equation. The wave operator admits a Chapman–Enskog expansion, whose moments yield Euler and Navier–Stokes fluxes with horizon-dependent coefficients, while the particle equation governs the remaining non-equilibrium kinetic transport. At the algorithmic level, this system is discretized by a conservative macro-micro method. The total conservative variables are advanced by a finite-volume update using the sum of a Navier–Stokes gas-kinetic wave flux and a particle flux computed by either a deterministic discrete-ordinate $(S_N)$ method or a Monte Carlo representation. Unlike the global time-step splitting in the unified gas-kinetic wave-particle (UGKWP) method, the present partition is defined at the PDE level and governed by the local ratio of evolution timescale to relaxation time. The particle component is therefore a fractional kinetic population generated by the collisionless factor of the integral solution. Formal analysis establishes the asymptotic-preserving continuum limit, rarefied-regime consistency, and regime-adaptive scaling of active kinetic degrees of freedom. Numerical tests in one, two, and three dimensions validate the accuracy, multiscale capability, and efficiency of the framework.
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High Energy Astrophysical Phenomena

Transforming X-ray Binary Astrophysics with SKA+VLBI

Tao An, Ailing Wang, James C. A. Miller-Jones et al. (+6 more)

X-ray binaries (XRBs) are unique laboratories where accretion, jets, strong gravity and magnetic fields can be probed on humanly tractable timescales. The phased SKA-Mid operating as a single, ultra-sensitive Very Long Baseline Interferometry (VLBI) element will transform radio studies of XRBs primarily through its time-domain capabilities: substantially improved sensitivity on VLBI baselines that include SKA-Mid in Bands 2 and 5, together with connected-element SKA-Mid imaging extending down to 0.35–1 GHz (Band 1), microarcsecond-precision astrometry for bright systems, high-fidelity polarimetry for the most strongly polarized sources, and rapid target-of-opportunity response. In synergy with global VLBI networks, SKA+VLBI will track the evolution of compact ejecta and compact jets on astronomical unit (AU) scales, measure frequency-dependent core shifts to infer magnetic field strengths and gradients, resolve disk–jet coupling during state transitions in real time, and determine precise distances and natal kicks via parallaxes and proper motions. Joint campaigns with future X-ray and optical telescopes will enable strictly simultaneous, multi-band constraints on accretion–ejection physics and on jet composition. We outline a quantitative program for \aastar\ and AA4, including cadenced, multi-frequency VLBI “movies” of jets over the first days of outbursts, an XRB astrometric census, and a core-shift survey, and we provide representative detection rates, magnetic field measurements and distance accuracies. These outcomes will set the microphysical foundation for jet physics across the mass scale from stellar-mass black holes and neutron stars to active galactic nuclei, and will establish SKA+VLBI as the definitive facility for time-domain, high-resolution XRB astrophysics.
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All authors Tao An, Ailing Wang, James C. A. Miller-Jones, Valeriu Tudose, Pikky Atri, Lang Cui, Hua Feng, Benito Marcote, Sara E. Motta

Chemical Physics

A Givens-exchange ansatz for molecular variational eigensolvers

Azadeh Alavi, Fatemeh Kouchmeshki, Muhammad Usman et al. (+4 more)

Molecular ground-state energies help determine conformer rankings, reaction energetics, and electronic effects in computational drug discovery, but accurate calculations become difficult when strong correlation or large active spaces are important. Variational quantum eigensolvers estimate these energies by optimizing a parameterized quantum state, making ansatz design central to both accuracy and cost. We study a fixed-topology Givens-exchange ansatz that avoids architecture search. The circuit starts from the computational-basis state with the lowest diagonal Hamiltonian expectation and applies local RY rotations with two ordered all-pair Givens exchange blocks. Parameters are optimized using Hamiltonian expectation values, while exact diagonalization is used only after optimization to compute errors and fidelities. Across six fixed seeds, coefficient-verified LiH-6 and H2O-8 Hamiltonians, together with a BeH2-6 public-specification candidate, are chemically accurate in every run. The corresponding six-seed mean errors are 0.000000124 Hartree, equivalent to 0.000124 milli-Hartree; 0.000128558 Hartree, equivalent to 0.128558 milli-Hartree; and 0.000002152 Hartree, equivalent to 0.002152 milli-Hartree, respectively. On LiH-6 and H2O-8, these mean errors are lower than the published point errors of the compared quantum-architecture-search methods, while the ansatz uses a larger pre-compilation macro budget. The method is therefore an accurate, reproducible, and search-free reference template for molecular variational eigensolvers.
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All authors Azadeh Alavi, Fatemeh Kouchmeshki, Muhammad Usman, Yongli Ren, Ke Deng, Hossein Akhoundi, Abdolrahman Alavi

Mathematical Physics · Cross-listed from math.AP

Painlevé \uppercase\expandafter{\romannumeral34\relax} and collisionless shock in the defocusing NLS equation with step-like initial data in the transition regions

Engui Fan, Zhaoyu Wang and Yidan Zhang

We consider the Cauchy problem for the defocusing nonlinear Schrödinger (NLS) equation with step-like initial data. Using the nonlinear steepest descent method, we derive the long-time asymptotic expansion of the solution to the Cauchy problem in three distinct transition regions. In the first two transition regions, the leading-order asymptotics are characterized by Painlevé \uppercase\expandafter{\romannumeral34\relax}-type formula, while in the third one is a collisionless shock region, the leading-order asymptotics is describedin terms of Riemann theta functions. Our analysis is based on the Riemann-Hilbert formulation associated with the Cauchy problem of the defocusing NLS equation.
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Quantum Physics

An ultralow-loss integrated photonic platform for discrete-variable quantum information processing

Ruiyang Chen, Zeying Zhong, Sanli Huang et al. (+9 more)

Photonic integrated circuits offer a scalable and robust route toward quantum information technologies by consolidating photon sources and linear optical networks onto compact, wafer-manufacturable chips. Although silicon photonics has enabled diverse discrete-variable quantum breakthroughs – spanning multiphoton entanglement, quantum networking, and photonic qubit fusion for quantum computing – scaling these platforms beyond proof-of-principle demonstrations remains severely constrained by a critical system-level bottleneck. Optical loss compounds rapidly across photon generation, routing, and state analysis, causing multiphoton generation probabilities to plummet exponentially as circuit depth and complexity grow. Here we overcome this rate-loss barrier by demonstrating a monolithic, ultralow-loss silicon nitride (Si$_3$N$_4$) integrated photonic platform engineered for high-performance discrete-variable quantum information processing. Our architecture seamlessly integrates narrowband photon-pair sources with low-loss qubit-fusion circuits and reconfigurable state-analysis interferometers. The on-chip sources prepare Einstein-Podolsky-Rosen (EPR) states with a fidelity of 0.9875(3) and exhibit near-unity photon indistinguishability, yielding a heralded Hong-Ou-Mandel interference visibility of 0.990(6). By executing on-chip fusion of two EPR states, we synthesize and characterize four-photon Greenberger-Horne-Zeilinger states with a record fidelity of 0.943(8) and a fourfold count rate of 27 Hz – more than two orders of magnitude higher than previous silicon-photonic implementations. Combined with standard CMOS-compatible fabrication on 150-mm-diameter wafers, these results establish ultralow-loss Si$_3$N$_4$ integrated photonics as a definitive, manufacturable platform for deployable, large-scale quantum information processors.
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All authors Ruiyang Chen, Zeying Zhong, Sanli Huang, Sicheng Zeng, Zhenyuan Shang, Yue Hu, Zhen Chen, Yuan Chen, Shuyi Li, Xue Bai, Yi-Han Luo, Junqiu Liu