Quantum Physics
Measuring correlations in quantum and statistical systems
V.I. Yukalov and E.P. Yukalova
The survey discusses the problem of measuring correlations in composite
quantum and statistical systems. After briefly recalling the standard methods of describing correlations, the emphasis is on the method of correlation indices. The latter method for quantifying the strength of correlations in composite physical systems is sufficiently general allowing for measuring in a unique way the correlation strength in both
quantum and statistical systems, for static as well as for dynamic processes. The correlation indices, can be defined for correlation operators, reduced density
matrices, and other operators containing information on correlations in the studied composite systems. The correlation indices measure all types of correlations,
quantum correlations, such as
entanglement, as well as classical correlations. They are applicable for characterizing static as well as dynamical processes. Examples are given of correlation indices for several
quantum states and for
spin and pseudospin systems. The quantification of correlations in a nonequilibrium system is exemplified by calculating the correlation index for a trapped Bose-Einstein condensate subject to the action of an alternating field.
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High Energy Physics (Theory)
Differential equations for Dotsenko–Fateev integrals: the case of degenerate fields $\Phi_{n,1}$
Aleksandra Ivanova
We study higher-order differential equations corresponding to integrals of the Dotsenko–Fateev type and associated with four-point correlation functions with degenerate fields $\Phi_{n,1}$. We determine the general structure and coefficients of the equations in terms of the integral parameters $ \{ A,B,C,g \} $. In particular, special cases of these equations in CFT are used for verification. In addition, the relationship between higher-order differential equations and hypergeometric operators is established.
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Quantum Physics
Benchmarking indirect quantum control schemes via higher-order quantum operations
Simon Vedl, Varun Srivastava, Riddhi Ghosh et al. (+1 more)
Indirect
quantum control aims to manipulate a target system through interventions on an auxiliary controller with which it interacts. We formulate finite-step indirect-control protocols using the
language of higher-order
quantum operations, representing admissible controller manipulations as deterministic superinstruments. This representation separates the uncontrolled but fixed dynamics from the controllable operations and allows the optimal control problem to be written as a semidefinite program for a chosen figure of merit. The resulting optimum gives an operational
benchmark by providing the best performance achievable by a finite sequence of control operations, including protocols with classical or
quantum feed-forward. More restricted and experimentally motivated control classes, such as independent
unitary controls or memoryless
quantum channels, can then be compared against this
benchmark. We illustrate the framework with a two-step
qubit-purification task, in which an initially mixed target
qubit is steered toward a pure state through a fixed interaction with a controller
qubit. The example shows regimes where simple
unitary strategies saturate the higher-order
benchmark, as well as regimes where they are provably suboptimal. This approach provides a systematic way to study the value of control resources in indirect
quantum-control schemes.
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All authors Simon Vedl, Varun Srivastava, Riddhi Ghosh, Alexei Gilchrist
Astrophysics of Galaxies
Low Star Formation Efficiency in M31: Evidence for a Deficit of Bound Gas
Fangyuan Deng, Sihan Jiao, Hauyu Baobab Liu et al. (+14 more)
The Andromeda
galaxy (M31) exhibits a systematically low
star formation efficiency (SFE) compared to other
star-forming
galaxies.
Star formation is thought to be regulated by the mass of gravitationally bound gas. To investigate whether the low SFE in M31 originates from a scarcity of such bound gas, we analyze the dynamical state of its
giant molecular cloud (GMC) population by estimating their virial parameters ($\alpha_{\rm vir}$). Using a JCMT-SCUBA2 850 micron
dust-continuum GMC catalog as the parent sample, we combine it with IRAM 30 m CO(1-0) data to define a working sample of 173 GMCs and derive their kinematic properties. Most analyzed GMCs exhibit high $\alpha_{\rm vir}$, indicating that they are predominantly gravitationally unbound at the approximately 86 pc resolution of our observations. While no statistically significant global correlation is found between SFE and $\alpha_{\rm vir}$ for the full cloud sample, the upper
quantiles of the SFE distribution show progressively stronger negative trends with increasing $\alpha_{\rm vir}$. This upper-tail trend may arise from the combined effects of the virial parameter limiting the upper range of SFE values accessible to the GMC population and feedback-driven disruption reducing the number of high-SFE, high-$\alpha_{\rm vir}$ CO-bright clouds in the observed sample. The substantial scatter in the SFE-$\alpha_{\rm vir}$ plane likely reflects the diverse evolutionary stages of GMCs, the temporal mismatch between gas and
star formation tracers, and the limitations of a cloud-averaged virial parameter as a tracer of internal dynamical structure, making a simple one-to-one correspondence between $\alpha_{\rm vir}$ and instantaneous SFE difficult to recover for individual GMCs.
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All authors Fangyuan Deng, Sihan Jiao, Hauyu Baobab Liu, Jingwen Wu, Henrik Beuther, Fanyi Meng, Caroline Gieser, Yuxin Lin, Di Li, Chao-Wei Tsai, Junzhi Wang, Zhi-Yu Zhang, Fengwei Xu, Jakob den Brok, Linjing Feng, Zongnan Li, Yuxiang Liu
Pattern Formation and Solitons · Cross-listed from math.NA
Constrained weak identification of Allen–Cahn free energies with surface-tension calibration
Soobeen Jung and Hyunju Kim
Phase-field trajectories governed by the Allen–Cahn equation determine the effective force $G=F'/\eps^2$, but not the free-energy potential $F$ and interfacial scale $\eps$ separately. We introduce surface-tension-calibrated Allen–Cahn identification (STAC), a two-step method that resolves this ambiguity using an independently supplied surface tension. First, space–time weak moments produce a linear inverse problem without differentiating the measured field. A Bernstein representation with positive coefficients enforces two stable pure phases and a single central energy maximum. Second, the surface tension fixes the remaining scale algebraically. We prove scale equivalence of the forward model, uniqueness of the calibrated pair within this class, and finite perturbation bounds that remain valid when the potential vanishes at the pure phases. Experiments with resolved synthetic phase fields separate the effects of the structural constraint, ridge regularization, and constitutive approximation error. Across 80 shared noisy records, unconstrained degree-five regression produces six potentials with an incorrect well structure. Positivity combined with ridge regularization eliminates these violations and reduces the mean force error from 8.70% to 5.66%. Lower-degree models are nevertheless more accurate in some tests, and an admissible law outside the positive Bernstein family shows how the constraint can introduce approximation bias. STAC thus recovers a structurally admissible, physically scaled potential while making explicit which information comes from the observed dynamics and which comes from the independent surface-tension datum.
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Mesoscale and Nanoscale Physics
Fröhlich Bipolarons in Two-Dimensional Materials
A. Kudlis, V. Shahnazaryan, I. Iorsh et al. (+2 more)
Motivated by the progress in the physics of two-dimensional materials and the recent two-dimensional generalization of the Fröhlich model, we study the formation of bipolarons in polar monolayers. Because of very special nonlocal dielectric screening in two dimensions, this setting differs qualitatively from the conventional Fröhlich model. In monolayers, (i) long wavelength LO
phonons acquire a nontrivial dispersion; (ii) the Fröhlich electron-
phonon vertex becomes momentum-dependent and regular at small momenta; and (iii) direct repulsion between charge carriers takes the Keldysh-Rytova form. Using the Feynman path-integral variational approach, we show that the region in the parameter space where stable bipolarons exist is strongly modified compared to the usual quasi-two-dimensional model with dispersionless
phonons. Specifically, in the most favorable limit, when the ratio $\sigma_0$ of the static polarizability to the high-frequency polarizability tends to infinity, the lower critical coupling, sufficient for the formation of bipolarons, can be made arbitrarily small. More surprisingly, we demonstrate that no stable bipolarons can exist in the strong coupling limit: in the isolated monolayer the stability region is always confined to a finite range of coupling constants. In general, the stability region is strongly shifted toward large values of the polarizability ratio $\sigma_0$, well beyond the parameter regimes in representative
crystals, which indicates that polar monolayers do not favor bipolarons.
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All authors A. Kudlis, V. Shahnazaryan, I. Iorsh, I. A. Shelykh, I. V. Tokatly
Fluid Dynamics
Vertical transport and confinement of weakly buoyant particles in a convective ocean mixed-layer model
Luz Andrea Silva-Torres, Enrico Calzavarini and Stefano Berti
Understanding how particles such as microplastics and plankton spread, or accumulate in localized regions below the ocean surface is crucial both for the development of sea pollutant control strategies and for marine ecology. Yet the role of vertically inhomogeneous
turbulence, due to the vertical structure of density stratification in the ocean, remains poorly understood. We study, by means of direct numerical simulations, the dynamics of weakly inertial, quasi-neutrally buoyant particles in an idealized two-layer fluid model aimed to represent the ocean convective mixed layer and the more stably stratified upper thermocline beneath. We find that particles eventually rise at the surface if their density matches the mean value of the fluid at a selected depth within the mixed layer. Interestingly, however, for all other values of density, they accumulate around their neutral-buoyancy depth within the thermocline, where stratification hinders vertical transport. Our analysis shows that the thickness of the accumulation layer results from the competition between buoyancy-driven confinement, internal-wave motions, and turbulent fluctuations penetrating from the mixed layer. Smaller particles, which respond more rapidly to flow fluctuations, form broader layers; layers also broaden as their
equilibrium depth approaches the mixed layer. We then derive a reduced
stochastic model that explains the dependence on particle inertia and reference depth of such spreading around the
equilibrium position. These results show how the coupled action of stratification and decaying mixed-layer
turbulence controls subsurface particle-layer formation, which may be relevant to ocean-biology oriented studies and to improve the sampling of plastic pollution in the sea.
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Mesoscale and Nanoscale Physics
Altermagnetic Magnons in Dipolar Nanomagnet Arrays
Rhea Hoyer, Ephraim Spindler, Lukas Körber et al. (+3 more)
Altermagnetism is conventionally understood in a
spin-conserving framework, where
symmetry-enforced momentum-dependent
spin splitting emerges in collinear magnets with vanishing net magnetization. Here, we show that its defining signatures persist in nanomagnet arrays coupled exclusively by dipolar interactions, despite the intrinsic breaking of
spin conservation. Using a macrospin theory of dipolar-coupled
ferromagnetic nanoislands, corroborated by micromagnetic simulations, we demonstrate that arrays engineered with altermagnetic
symmetries exhibit
spin-split
magnon bands whose eigenstates can partially remain strongly
spin polarized. The resulting
spin expectation value displays the characteristic $d$-wave pattern throughout the Brillouin zone, establishing a mesoscopic realization of altermagnetic
magnons beyond the conventional
spin-conserving paradigm. As a consequence,
spin-wave propagation becomes strongly direction dependent, providing a highly tunable platform for anisotropic
magnon transport and synthetic altermagnetic functionality.
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All authors Rhea Hoyer, Ephraim Spindler, Lukas Körber, Tobias Wagner, Mathias Weiler, Alexander Mook
Computational Physics
Moment-informed force rescaling for random-batch Langevin dynamics
Xingguo Wu, Yangshuai Wang and Zhenli Xu
Random-batch methods accelerate molecular dynamics by replacing full interaction sums with
stochastic force
estimators. In Langevin simulations, however, random-batch force errors can cause artificial heating and distort
equilibrium and dynamical observables, especially for small batch sizes or under weak thermostat coupling. Moreover, the magnitude of these errors can vary across particles. We introduce moment-informed force rescaling for random-batch list (Mi-RBL) and random-batch Ewald (Mi-RBE) methods. A lagged average of each particle's sampled-force intensity sets an isotropic gain before the current batch is sampled, changing the random-batch force magnitude without changing its direction. The formal finite-time analysis quantifies the bias–variance tradeoff, and an estimate of the steady-state kinetic-temperature error predicts the scaling of the kinetic error with time step and thermostat friction. In the coexistence, binary-mixture, and electrolyte tests, Mi-RBL and Mi-RBE reduce kinetic errors and more closely reproduce the mean-square displacement, radial distribution function, and charge density profiles of the reference solutions. Mi-RBE also reduces the growth rate of the kinetic error with the time step by more than half and retains the predicted dependence on thermostat friction. The tested rescaling strength decreases with increasing batch size, and the particlewise update retains $O(N)$ complexity for fixed batch size.
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Quantum Gases
Geometry-Driven Suppression of Fermionic Pairing on a Spherical Surface
Lorenzo Frigato, Andrea Tononi and Luca Salasnich
We investigate the ground-state properties of a two-component attractive
Fermi gas confined to a spherical surface, demonstrating how
curvature and finite-size effects lead to qualitatively different behavior compared to the planar limit. In the strongly attractive regime, the system forms a Bose-Einstein condensate (BEC) of tightly bound dimers, yielding a gap and chemical potential that approach flat-space results with leading-order
geometric corrections. However, as the attraction decreases, the system crosses over into a Bardeen-Cooper-Schrieffer (BCS) regime where the Cooper pair size becomes constrained by the sphere radius, producing pronounced deviations from flat-space behavior. We identify strong shell effects at magic particle numbers set by the single-particle spectrum, revealing the geometry-driven suppression of fermionic pairing at weak interactions. Our results highlight a fundamental interplay among geometry,
quantum statistics, and interactions, motivating future experiments with shell-trapped ultracold
fermions and inspiring geometry-controlled condensed matter devices.
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Instrumentation and Detectors
On the importance of cosmic-ray background in the Atomki anomaly
Hicham Benmansour, Gianluigi Boca, Gianluca Cavoto et al. (+8 more)
We report Geant4-based simulations of
cosmic-ray
muon backgrounds in models reproducing the geometries of the five-arm and six-arm e+e- pair spectrometers operated by the Atomki group at Debrecen. Full detector geometries are implemented for both setups, including position-sensitive detectors and plastic scintillators. In both configurations,
cosmic muons generating two-arm coincidences produce statistically significant excesses in the opening-angle distribution whose positions are determined by the discrete azimuthal arrangement of detector arms and the plastic scintillators dimensions: in the six-arm spectrometer a peak appears near 140 degrees when the scintillator energy sum is selected in the 8Be transition window (16-20 MeV) and is suppressed for energy-asymmetric pairs, while a distinct peak near 120 degrees emerges in the 4He window (18-22 MeV), with no comparable enhancement in the respective background energy region. These angles, asymmetry dependences, and background characteristics show behaviours similar to those reported by the Atomki group as evidence for a 17 MeV
boson. For the five-arm setup, a 140-degree excess is also reproduced at 8Be energies, and normalizing internal pair conversion events and
cosmic coincidences to typical Atomki running conditions yields a
cosmic-to-IPC ratio above unity in the signal window, indicating that the
cosmic background is a leading contribution to the event rate at the energies and angles of interest. While they do not settle the question of the origin of the Atomki excesses, these results highlight the critical importance of a robust
cosmic-ray treatment in this type of measurements, and call for a detailed description of the beam-off studies supporting the search for anomalies in the opening-angle vs. energy-sum distribution around the signal region.
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All authors Hicham Benmansour, Gianluigi Boca, Gianluca Cavoto, Marco Chiappini, Elia G. Grandoni, Luca Galli, Giovanni Gallucci, Angela Papa, Francesco Renga, Antoine Venturini, Cecilia Voena
Atmospheric and Oceanic Physics · Cross-listed from cs.LG
Every Fixed Metric Has a Blind Spot: A Learned Atmospheric Critic for Scoring Forecast Realism
Younes Elberkennou, Dmitri Demler, Thierry Meier et al. (+3 more)
Despite their high accuracy on point-wise metrics, machine learning weather
forecasting models can exhibit different failure modes such as blurring, periodic irregularities, and other unphysical spatial artifacts. This has motivated a variety of metrics to detect known failure cases. Existing metrics fix a representation or transformation in advance, and that choice limits the artifacts they can detect. We propose to train a discriminator for separating reference data from the model's output, and using its output logit to obtain a divergence-like realism score. The discriminator learns whatever separates the model's fields from real weather, adapting to whichever failure mode that model exhibits. We compare our learned atmospheric critic to existing metrics using various synthetic corruptions applied to ERA5 reanalysis data. Our method successfully identifies the corruptions and ranks their severity, while existing metrics fail on at least one corruption. Additionally, we evaluate forecasts from real weather models, and find that the realism score degrades with longer lead times and the metric generally assigns higher realism to numerical models than to machine learning models.
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All authors Younes Elberkennou, Dmitri Demler, Thierry Meier, Luca Rispoli, Fanny Lehmann, Joel Oskarsson
General Relativity and Quantum Cosmology
Causal structure and optical signatures of rotating power law Kalb-Ramond geometry
Hassan Hassanabadi and Orlando Luongo
We investigate a stationary and axisymmetric power law Kalb-Ramond geometry, obtained as a rotating extension of the asymptotically flat static solution. We reconstruct the exact inverse Einstein source supporting the geometry and determine its energy conditions and
curvature properties. We characterize the horizon and stationary limit configurations and quantify the outer ergoregion through its angular dependent radial thickness plus its coordinate and proper spatial volumes. We derive the unstable spherical
photon region and show that the Kalb-Ramond deformation shifts the prograde
photon orbit into the ergoregion at lower
spin, while the retrograde region remains outside throughout the entire domain. From the unstable
photon region, we construct the exact
vacuum critical curve and analyze its area equivalent diameter and displacement, including comparisons with M87$^\ast$ and Sgr~A$^\ast$ within the asymptotically admissible domain. We further examine the fixed-$J$
geometric behavior and rotational energy extraction, with emphasis to rotating weak deflection and two dimensional weak
lensing, commenting the physical consequences of our solution in terms of observable outcomes.
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Optics
Multi-contrast wide-field mid-infrared photothermal imaging
Anooj Thayyil Raveendran, Cornelia Reuter, Samir F. El-Mashtoly et al. (+2 more)
Wide-field mid-infrared photothermal (MIP) imaging enables high-speed, chemically specific imaging at sub-micrometer spatial resolution through several possible contrast mechanisms, including scattering change, fluorescence modulation, and phase change. Each mechanism offers distinct advantages, yet existing wide-field MIP instruments have typically been limited to a single contrast mechanism so far, requiring a dedicated instrument for each. Here, we introduce a switchable multi-contrast wide-field MIP microscope that allows the photothermal readout mechanism (based on scattering-, fluorescence-, or quantitative phase imaging (QPI)) to be matched to the sample and imaging conditions. We characterize the spectral fidelity and signal-to-noise (SNR) ratio of each mechanism using 5 \mu m polystyrene (PS) beads, and the effective spatial resolution using 300 nm PS beads. Scattering- and fluorescence-based detection achieved a sub-500 nm measured point spread function full width at half maximum, while QPI-based detection reached approximately 900 nm but provided up to 26-fold higher SNR than scattering. We further demonstrate imaging across a range of samples, including A549
cells in buffer, mouse lung tissue section, bacteria, and SU8
polymer at 1.4 and 5 \mu m thickness, with a field of view exceeding 200 \mu m. Comparison across these samples shows that each contrast mechanism offers distinct trade-offs in resolution, sensitivity, and applicability, guiding readout-strategy selection by sample type. These results establish a flexible, switchable multi-contrast platform for wide-field MIP imaging, with broad applicability across
polymer and biological samples.
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All authors Anooj Thayyil Raveendran, Cornelia Reuter, Samir F. El-Mashtoly, Jürgen Popp, Christoph Kraft
Materials Science
Electronic Origins of Elastic Behavior in Rocksalt, Zinc-Blende and Wurtzite 3d Transition-Metal Nitrides
Jesus Cañas and Oliver Ambacher
We present a comprehensive ab-initio study of the elastic properties of the IV-period transition metal nitrides, highlighting the correlation between their mechanical behavior and electronic structure. By analyzing the electronic density of states, we reveal how the occupation of bonding or antibonding orbitals determines the
evolution of elastic properties along the period. Furthermore, we examine trends across different
crystal structures, specifically comparing rocksalt, zincblende and wurtzite phases, to uncover how variations in
crystal symmetry and atomic coordination influence their elastic properties.
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Applied Physics
A Scaling Framework for Mechanical Memristance: Dimensionless Metrics and Material Design Maps
Abdulla Alhembar, Fabrizio Scarpa, Chrystel D. L. Remillat et al. (+6 more)
Mechanical memristors are systems whose dissipative response depends on the history of previous loading through an evolving internal state. History-dependent forces and dissipation occur in a wide range of materials and devices, including viscoelastic
polymers, shape-
memory materials, piezoelectrics, granular media and field-responsive fluids. Determining which of these responses admits a mechanical-memristor representation requires a constitutive test, as well as a comparison of scales. In this work, a fractional-order mechanical memristor model is developed and cast into a nondimensional form to identify the governing parameters controlling
memory-dependent dissipation. The formulation leads to a set of dimensionless groups that characterise dissipation magnitude,
memory-state scale and
memory transfer. These quantities are combined into an effective mechanical memristance screening index \(\Mh = \beta\gamma |\mathcal H_\alpha(\Omega)|\), which provides a conditional measure of local damping modulation at matched response amplitude, constitutive slope and reference scales. Illustrative parameter scenarios are then constructed for material classes including shape-
memory polymers, shape-
memory alloys, hydrogels, nanocellulose, lignin-rich materials, natural fibres, piezoelectric
polymers, piezoelectric ceramics, electrorheological fluids, magnetorheological fluids and granular dampers. The framework establishes a common basis for comparing
memory-dependent damping within the adopted constitutive description and identifies the calibration required for its application to candidate materials and devices
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All authors Abdulla Alhembar, Fabrizio Scarpa, Chrystel D. L. Remillat, Rodrigo J. da Silva, Ross Anderson, Ludovico Cademartiri, Abderrezak Bezazi, James P. K. Armstrong, Adam W. Perriman
Optics
Topological photonic cavities based on dissimilar Bragg gratings
Alejandro Sánchez-Sánchez, José Manuel Luque-González, Gauthier Krizman et al. (+12 more)
Topological photonic cavities offer a powerful route to robust optical confinement and enhanced light-matter interactions. Interface states that emerge at the boundary between one-dimensional periodic structures with distinct topological phases, enable cavities with ultra-small mode volumes and intrinsic protection against disorder. Existing implementations typically create the trivial and topological phases by redefining the unit
cell on either side of the cavity, so that both periodic structures share the same band structure. This constraint limits design flexibility and the range of accessible devices. Here we introduce a fundamentally different strategy for realizing topological cavities based on combining periodic waveguides with distinct band structures. By exploiting bandgap closing and band inversion in Bragg gratings, we independently control the topological phase and bandgap width of each structure. We experimentally realize silicon topological cavities formed by two different Bragg gratings without period shifting, and observe topological modes despite significant differences between the two gratings. Our results establish a new route to topological photonic cavity design, demonstrating that band inversion between dissimilar Bragg gratings enables cavity formation beyond symmetric constraints and provides a mechanism to engineer optical confinement via mirror asymmetry.
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All authors Alejandro Sánchez-Sánchez, José Manuel Luque-González, Gauthier Krizman, Dorian Oser, Paula Nuño Ruano, David González-Andrade, David Medina Quiroz, Samson Edmond, Alejandro Ortega-Moñux, Jens H. Schmid, Pavel Cheben, Laurent Vivien, Iñigo Molina-Fernández, J. Gonzalo Wangüemert-Pérez, Carlos Alonso-Ramos
Mathematical Physics
Pathology-Free Real-Space Renormalization Group Theory on an Inverse Limit Space
Fabio Arz
It has been over fifty years since Kenneth Wilson had his Nobel-prize-winning ideas on the renormalization group. In this time frame, despite many attempts, no mathematical results have implemented Wilson's
vision to a satisfactory degree. Although a number of predictions stemming from the renormalization group framework have been proven to date, these proofs usually rely on alternative ideas and do not cover the full predictive power of Wilson's renormalization group. The discovery of pathologies within rigorous implementations of renormalization group transformations have further reduced the enthusiasm of the mathematics community for this subject. This paper presents a novel framework to implement Wilson's original idea in a rigorous manner based on inverse limits of finite systems. Doing so, one avoids these pathologies and hence obtains a mathematically sound framework for Wilson's renormalization group. This opens up a completely new path to tackle some of the existing problems in rigorous renormalization group theory like the existence of non-trivial fixed points.
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Materials Science
Complex magnetic properties of EuAgAs single crystals
Karolina Kowalczyk, Kamila Komędera, Janusz Przewoźnik et al. (+6 more)
EuAgAs is an
antiferromagnetic topological material exhibiting intriguing
magnetic behavior. We investigate its structural,
magnetic, and local electronic properties using X ray diffraction, Mössbauer spectroscopy, dc magnetization, ac susceptibility, and heat capacity measurements. The results confirm
antiferromagnetic ordering below $T_\text{N}$ and reveal pronounced
magnetic anisotropy and several field induced metamagnetic transitions. We construct the
magnetic phase diagram of EuAgAs, identifying several distinct
magnetic regions. The field and temperature dependent behavior observed suggests a noncollinear
magnetic structure in the low field regime. The sequence of field induced transitions resembles that observed in centrosymmetric rare earth compounds hosting skyrmion phases, suggesting that competing
magnetic interactions may play an important role in stabilizing the observed
magnetic states.
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All authors Karolina Kowalczyk, Kamila Komędera, Janusz Przewoźnik, Łukasz Gondek, Czesław Kapusta, Wojciech Tabiś, Michał Babij, Lan Maria Tran, Damian Rybicki
High Energy Astrophysical Phenomena
The unidentified PeV source LHAASO J2108+5157: A microquasar remnant?
Josep Martí, Pedro L. Luque-Escamilla, Leandro Abaroa et al. (+4 more)
Context. LHAASO~J2108+5157 is one of the most intriguing
Galactic ultra-high-energy $\gamma$-ray sources. It is detected up to hundreds of TeV but lacks a clear counterpart at lower frequencies.
Fermi-LAT observations have revealed a compact GeV source spatially coincident with the PeV emission, while VERITAS and LST-1 impose stringent upper limits in the intermediate TeV band, producing a pronounced spectral suppression between the GeV and TeV domains. Aims. We investigate a time-dependent hadronic scenario in which a past episode of microquasar jet activity injected relativistic
protons that are now observed in a relic phase. Methods. Energy-dependent
diffusion naturally segregates the particle population: Lower-energy
protons remain confined near dense molecular gas and account for the GeV emission, whereas higher-energy particles reach more distant material, producing the hard TeV–PeV component. Results. For representative interstellar conditions, the model is simultaneously consistent with the broadband spectral energy distribution, the spatial compact–extended dichotomy, and the lack of detectable
radio or X-ray counterparts. Conclusions. The observed bimodal $\gamma$-ray phenomenology thus emerges as a transport effect of a single injected
proton population, supporting the interpretation of LHAASO~J2108+5157 as a fossil microquasar remnant observed at an intermediate evolutionary stage and highlighting relic jet systems as a viable class of
Galactic PeVatrons.
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All authors Josep Martí, Pedro L. Luque-Escamilla, Leandro Abaroa, Gustavo E. Romero, Valentí Bosch-Ramon, Josep M. Paredes, Cintia S. Peri
Quantum Physics
Signatures of Chaos in a Quasiperiodically Driven Quantum Impact Oscillator
Deepshikha Singh, Titir Mukherjee and Soumitro Banerjee
We demonstrate the emergence of
quantum-chaotic dynamics in a quasiperiodically driven impact oscillator near the grazing condition. While previous studies of the
quantum impact oscillator under periodic driving reported strange nonchaotic dynamics, we show that quasiperiodic driving produces robust signatures of chaos. The corresponding classical system undergoes a sharp grazing-induced transition from quasiperiodic motion to chaos, as established by bifurcation analysis, Lyapunov exponents,
Fourier spectra, and the 0-1 test. In the
quantum system, Shannon-
entropy time series exhibit broadband spectra, 0-1 test values close to unity, and predominantly positive finite-time Lyapunov exponents for both rational and irrational driving-frequency ratios. Independent
quantum diagnostics reinforce this result: the out-of-time-order correlator (OTOC) displays early-time exponential growth with nearly identical rates, while the golden-ratio drive leads to a substantially faster saturation of the OTOC. Fidelity exhibits an exponential decay regime that is approximately independent of perturbation strength. These results establish quasiperiodic driving near grazing as a mechanism for generating
quantum-chaotic behavior and reveal that, although the initial onset of scrambling is largely insensitive to frequency-ratio rationality, the subsequent development of global scrambling is strongly influenced by the degree of irrationality of the drive.
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Quantum Physics
Optical Quantum Computing
Hamza Hasnaoui, Leonardo Limongi, Taira Giordani et al. (+5 more)
Under the label of optical
quantum computing, there are a variety of protocols and experiments that use the
quantum properties of light to achieve a computational advantage over classical computing machines. In this review, we describe some of the main implementations, which differ in the type of encoding and in how the computation is performed, whether using gates or cluster states. For each protocol, we describe advantages and challenges with an overview of the experimental results obtained, summarized in tables. Because of the great relevance achieved in this field, there is a section dedicated to non-universal
quantum computation with
photons, where
boson sampling, variational
quantum eigensolvers, and
quantum machine learning applications are described. The aim is to give the reader the broadest overview of the applications where
photons and their
quantum properties play a key role in computation.
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All authors Hamza Hasnaoui, Leonardo Limongi, Taira Giordani, Beatrice Polacchi, Alberto Quaranta, Martino Bernard, Fabio Sciarrino, Mirko Lobino
Astrophysics of Galaxies
Self-interacting dark matter delays bar growth in an isolated gas-rich galactic disk: torque-resolved numerical evidence
Dong-Biao kang
We investigate how a dynamically responsive gas disk changes the influence of self-interacting dark matter (SIDM) on
stellar-bar formation. In an isolated Milky-Way-mass
galaxy with fixed total baryonic mass, the gas-rich collisionless (CDM) model develops a persistent bar at $1.96\,\Gyr$, whereas the matched SIDM model with $\sigmam=1\,\mathrm{cm^2\,g^{-1}}$ does so at $2.69\,\Gyr$. The final
stellar $m=2$ amplitude is 0.437 in CDM and 0.340 in SIDM, a 22 per cent suppression; the corresponding gas-free controls remain weak over the same interval. An independently sampled gas-rich pair preserves the direction of both differences. Direct component-force measurements show that the SIDM
stellar disk loses $2.82\times10^{11}\,\Msun\,\kpc\,\kms$ less angular momentum than its CDM counterpart. The integrated torque contrast is dominated by the dark
halo (approximately 74 per cent), with a substantial gas contribution (26 per cent), and is redistributed in radius and time rather than being a uniform reduction of
halo coupling. Conservation, force-accuracy, aperture, threshold, and independent-sampling checks support the ordering as a dynamical effect within this model. The result demonstrates that a live gas component can change both the sign and timing of the early SIDM impact inferred from collisionless disks, providing a mechanism-based constraint for future hydrodynamic SIDM studies.
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Mesoscale and Nanoscale Physics
Tuneable terahertz transitions in zigzag graphene nanoribbons
R. R. Hartmann and M. E. Portnoi
We show that a transverse electric field applied to a zigzag
graphene nanoribbon opens a band gap whose energy can be tuned through the terahertz (THz) range. The field breaks the reflection
symmetry of the ribbon, allowing optical transitions that are forbidden in its absence. The relative strengths of transitions polarized parallel and transverse to the ribbon depend strongly on excitation frequency and become equal at a particular frequency. At this frequency, each helicity selectively excites carriers in only one of the two field-induced edge-state valleys, with the selected valley reversed for the opposite helicity. Since this excitation occurs away from the valley minima, the photoexcited carriers have finite group velocity, giving rise to a circular photogalvanic response. Van Hove singularities enhance radiative recombination at the band edge, providing a route towards compact, tunable THz emitters.
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General Relativity and Quantum Cosmology
Searching for gravitational wave echo with group equivariant neural posterior estimation
Jian-Wei Luo and Yun-Song Piao
Current methods for the gravitational-wave (GW) echo searches generally require substantial computational time and resources. Recent advances in group equivariant neural posterior estimation (GNPE) have demonstrated the potential to substantially accelerate posterior inference. In this work, we adopt this framework and train a GNPE model to perform echo searches, significantly improving computational efficiency while maintaining comparable inference accuracy. We apply it to the O4a events and find no significant evidence for the GW echo.
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Earth and Planetary Astrophysics
Bridging magnetothermal winds and photoevaporation to model discs dispersal
Giovanni Picogna and Barbara Ercolano
Protoplanetary disc dispersal is driven by two processes usually modelled separately: photoevaporative and magnetohydrodynamic (MHD) disc winds. Global simulations indicate that in the inner disc these are not distinct
outflows but a single magnetothermal wind. We assemble a closed-form, two-phase model that respects it. A single-field-line wind, whose base is fixed by the irradiated temperature and penetration column, supplies the launch and feeds a secular
evolution, with photoevaporation convolved on as a sink. The flux closure $B_z\propto\Sigma^q$ is self-limiting: for $q\le1/2$ depletion alone cannot demagnetise the disc, so dispersal requires independent flux loss, parameterised by the
magnetic Reynolds number $\mathcal{R}_m$. Integrating the coupled system yields two regimes. Efficient flux loss ($\mathcal{R}_m\lesssim1$) lets the magnetisation front recede by over an order of magnitude and opens a photoevaporative gap. Flux retention ($\mathcal{R}_m\gg1$) drives the front outward, sustains
accretion, and defers dispersal by $\approx2.7$~Myr. Deriving the base from
stellar irradiation instead of prescribing it, we find that the cold-launch approximation is valid during the early stages of disc
evolution: anchoring the base at
plasma equipartition ($\beta_{\rm base} \sim 1$) confines irradiation's influence on the
magnetic lever arm to the magnetothermal annulus, decoupling the peak
accretion rate from the incident flux. Both regimes clear the disc inside-out, through either a photoevaporatively amplified cavity wall or an expanding magnetothermal front.
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Materials Science
Direct observation of phonon mode with an antisymmetric Raman tensor
Shangfei Wu, Shang Ren, Kai Du et al. (+4 more)
Phonon angular momentum, characterized by circular or elliptical motion of atoms, plays a decisive role in diverse phenomena, ranging from the
phonon Hall effect,
phonon magnetic moment, Einstein-de Haas effect, Weyl
phonons, and driven
chiral phonons. The
phonon modes with an antisymmetric Raman tensor, which carry an intrinsic
phonon angular momentum in a pseudovector
symmetry channel, have been overlooked in the past in the
chiral phonon community. Here, we report the detection of this type of
phonon mode using polarization-resolved Raman spectroscopy. We observe a
phonon at 266cm$^{-1}$ in the
antiferromagnetic chiral phase of Cr$_2$O$_3$ in the $A_2$-pseudovector
symmetry channel. This $A_2$ mode's frequency and the elliptical motion are captured by first-principles
phonon calculations, which treat both
lattice and
spins on an equal footing as 'slow' degrees of freedom. This mode gets Raman activity due to the presence of Cr vacancies in Cr$_2$O$_3$ that locally break the twofold rotational
symmetry perpendicular to the threefold axis. Our results provide a new way to detect the novel
symmetry-forbidden $A_2$
phonon modes with an antisymmetric Raman tensor in a pseudovector
symmetry channel.
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All authors Shangfei Wu, Shang Ren, Kai Du, Xianghan Xu, Sang-Wook Cheong, David Vanderbilt, Girsh Blumberg
Materials Science
Quantum electrodynamics of equilibrium systems: A rigorous Maxwell-regularized functional-theoretic formulation
Markus Penz, Christian Jöns, Michael Ruggenthaler et al. (+1 more)
A framework for
quantum electrodynamics of
equilibrium systems is proposed that takes the Maxwell equations as foundational and links them to the structure of density-functional theory for the
quantum system. By switching from purely internal observables like the one-particle density to combined internal and external quantities, the external sources and their energy are taken into account. A fully regularized functional theory emerges that avoids the usual representability problems. With the Kohn-Sham construction that links to an auxiliary uncoupled system, the ultra-violet cutoff can be removed and one arrives at a fully renormalized and non-perturbative light-matter description. Regularized forms of density-functional theory with and without
magnetic fields appear as boundary cases, while the emergent physical picture reproduces the macroscopic Maxwell equations.
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All authors Markus Penz, Christian Jöns, Michael Ruggenthaler, Angel Rubio
Astrophysics of Galaxies
The Delegate Survey: KOALA/AAOmega-IFU spectroscopy of three nearby dwarf galaxies
Kyungdo Ko, Helmut Jerjen, Sarah M. Sweet et al. (+6 more)
Assessing the cosmological typicality of the Local Group is crucial for establishing whether its
dwarf galaxy population is representative. To this end, the Delegate Survey targets
dwarf galaxies in Local Group analogues for systematic comparison. As a pilot study for the Delegate Survey, we obtained integral-field spectra of three
dwarf galaxies, GAMA 79098, GAMA 569709, and HIPASS J1159-19 S2, in two nearby
galaxy groups using the KOALA instrument on the AAT. The
galaxies were mapped at a spatial sampling of 1.25 arcsec per spaxel, providing two-dimensional spectral coverage of both the
stellar and ionised gas components. Using continuum and emission-line maps, we investigate the ionisation structure,
star-forming properties,
metallicity,
star formation histories, and velocity fields of each system. GAMA 79098 exhibits properties closely analogous to the SMC, with ongoing
star formation superimposed on an old
stellar population and moderate rotational support. GAMA 569709 resembles transition-type Local Group (LG)
dwarfs such as NGC 147 and NGC 185, showing predominantly an old
stellar population. HIPASS J1159-19 S2 is dominated by young
stars and intense
star-forming complexes, consistent with a dynamically young, gas-rich
galaxy group environment. The two GAMA
dwarfs follow the LG
stellar mass-
metallicity relation within uncertainties, while HIPASS J1159-19 S2 appears approximately 0.5 dex more metal-rich for its
stellar mass. Overall, the structural, chemical, and kinematic properties of these
dwarfs overlap substantially with analogous LG
dwarfs.
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All authors Kyungdo Ko, Helmut Jerjen, Sarah M. Sweet, Ángel R. López-Sánchez, Simon Deeley, Caroline Foster, Holger Baumgardt, Pratyush Kumar Das, Adebusola Alabi
Instrumentation and Methods for Astrophysics
cosmokdtree: a flexible OpenMP-parallelized k-d tree for computational astrophysics applications
Óscar Monllor-Berbegal, David Vallés-Pérez, Susana Planelles et al. (+1 more)
Modern numerical astrophysics applications present a common demand for efficient spatial querying techniques, such as neighbor searches or density estimations over billions of resolution elements. To address the growing need for fast and versatile tools tailored to these tasks, we present cosmokdtree, a fast and flexible multi-purpose k-d tree implementation in Fortran, parallelized with OpenMP directives. Our library supports arbitrary dimensionality and spatial distributions, and is designed for efficient tree construction and fast query performance for moderate-scale applications (performance tested up to 10^9 points). Python bindings coupled to the module are also provided. All these ingredients yield a k-d tree package suitable for analysis purposes. We
benchmark cosmokdtree across a variety of scenarios, including different point distributions, dimensionality, and parallel scaling. We also compare its performance against the widely used scipy implementation and other efficient alternatives such as coretran's and a GPU-based version, showing that cosmokdtree consistently achieves lower construction and query times than CPU alternatives while keeping a reasonable
memory usage. Our tree-building phase implementation, executed on a mid-range workstation-class CPU, approaches the performance of GPU-based implementations when run on high-end consumer graphic cards, although data-center GPUs, out of the scope for our comparison, could still deliver substantially higher performance and a broader conclusion cannot be extracted. We further present some applications tackling common problems in astrophysics, namely, the friends-of-friends clustering
algorithm and the particle-to-mesh assignment process. The code is publicly released and intended to serve as a flexible multi-purpose tool for computational applications in a wide range of scenarios, particularly in astrophysics.
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All authors Óscar Monllor-Berbegal, David Vallés-Pérez, Susana Planelles, Vicent Quilis