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Wednesday 22 July

Statistical Mechanics

Derivation of the Boltzmann equation with no "molecular chaos"-type approximation

Victor F. Los

The paper resolves the problem of the derivation of a completely closed evolution equation for $s$-particle distribution function $F_s(t)$ ($s \le N$) from the Liouville equation for $N \gg 1$-particle distribution function $F_N(t)$ with arbitrary initial condition $F_N(0)$ and without any use of the "molecular chaos" type approximation. The initial correlations are accounted for in this equation in the kernel governing the evolution of $F_s(t)$ via the special projection operator which exactly transforms the inhomogeneous Nakajima-Zwanzig Generalized Master Equation (GME) with an irrelevant initial condition term into the homogenous one. This equation is further simplified by presenting its kernel in the linear in the particles' density $n$ approximation. In this approximation the equations for one-particle $F_1(t)$ and two-particle $F_2(t)$ distribution functions are derived. It is shown that the terms describing the influence of initial correlations in the equation for $F_1(t)$ disappear at the large timescale $t \sim t_{\text{rel}} \gg t_{\text{cor}}$ ($t_{\text{cor}}$ is a short correlation time as compared to a relaxation time $t_{\text{rel}}$ of $F_1(t)$) resulting in the linear Boltzmann equation. This equation can be presented as the nonlinear Boltzmann equation in the time interval $t_{\text{cor}} \ll t \ll t_{\text{rel}}$. At $t_{\text{rel}} \to \infty$ (mean free path $l \to \infty$) the Boltzmann equation holds for all finite times $t \gg t_{\text{cor}}$.
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Quantum Physics · Cross-listed from cs.IT

Learning to Decode Quantum LDPC Codes via Cluster-Based Sequential Belief Propagation

Mohsen Moradi, Taejoon Kim, Rémi A. Chou et al. (+1 more)

Belief-propagation (BP) decoding for quantum low-density parity-check (QLDPC) codes is attractive due to its low complexity, but its performance is often limited by short cycles, degeneracy, and convergence failures. Recently, reinforcement-learning-based sequential variable-node (VN) scheduling (RL-S) was shown to improve BP decoding by learning state-dependent update orders. However, the VN-by-VN nature of that approach offers limited within-iteration parallelism, since only one VN is updated at a time. In this paper, we propose a cluster-based extension of RL-S for QLDPC codes. The VNs are partitioned into fixed clusters, and at each scheduling step the RL agent selects one cluster to update, after which all VNs in that cluster are updated in parallel using the same pre-update incoming messages. To keep the tabular state space practical for large cluster sizes, we introduce a permutation-invariant cluster state based on a normalized histogram of local mismatch weights, followed by quantization. This representation makes the number of cluster states depend on the quantization resolution rather than the cluster size. We also develop the corresponding cluster-level Markov decision process, reward function, and Q-learning update. Numerical results on representative QLDPC codes show that the proposed clustered learned scheduling preserves most of the error-rate benefit of VN-level learned sequential scheduling while substantially reducing the number of scheduling decisions per BP iteration, thereby providing an attractive latency-parallelism tradeoff.
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All authors Mohsen Moradi, Taejoon Kim, Rémi A. Chou, David G. M. Mitchell

Earth and Planetary Astrophysics

Predicting Atmospheric Re-entries Using Segmented M/A Calibration of Public TLE Data

Joseph Remis

We present a reproducible method for predicting atmospheric re-entries using only publicly available Two-Line Elements (TLEs). The approach is based on a segmented calibration of the effective mass-to-area ratio (M/A), adjusted independently over intervals of at least 12 hours to suppress short-period catalogue noise. Longer segments provide a stable dynamical signal from which the effective drag behaviour can be retrieved. Applied to recent natural re-entries of rocket bodies, debris, and non-manoeuvring satellites, the method consistently identifies the final orbital revolution and reproduces published Tracking and Impact Prediction (TIP) times with an accuracy of approximately +/- 1 hour in the terminal phase. The limiting factor is the intrinsic noise and cadence of the TLE catalogue rather than atmospheric or solar-flux modelling. Within these constraints, segmented M/A calibration offers a transparent, lightweight, and operationally robust alternative for re-entry analysis when only public data are available.
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Instrumentation and Methods for Astrophysics

Skipper CCD readout time optimization for astronomical applications

Johannes Wüthrich, Andrin Fazan, Sean MacBride et al. (+1 more)

Skipper CCDs enable the reduction of CCD readout noise by non-destructively measuring the individual pixel charge packets multiple times. This readout noise reduction has attracted considerable interest in the astronomical community, particularly in spectroscopic surveys targeting faint objects at high redshifts. However, noise reduction via repetitive sampling leads to an unavoidable increase in readout time, often to prohibitive levels. To enable their use in astronomical applications, the optimal operation regime of Skipper CCDs must be determined, balancing noise improvement and readout time. Traditionally, such optimization has been carried out empirically for each CCD architecture. We present a general optimization scheme derived from first principles and experimentally verified in the laboratory using a Skipper CCD as used by the Oscura experiment. While the existence of an optimal combination of correlated double-sampling integration time and number of Skipper samples for reaching a given readout noise level at minimal readout time has previously been observed empirically, we model this trade-off analytically based on the intrinsic noise power spectral density of the sensor, allowing the optimal operating point to be predicted rather than determined experimentally for each architecture. We further show that the location of this optimum is governed by the per-sample charge-transfer time, whose minimization is therefore key to achieving fast Skipper CCD readout.
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All authors Johannes Wüthrich, Andrin Fazan, Sean MacBride, Marcelle Soares-Santos

Cosmology and Nongalactic Astrophysics

Modeling the HI-Halo Connection: Evolution, Scatter, and a Halo-based Prescription for 21-cm Mock Catalogs

Mohd Kamran, Gabriella De Lucia, Marta Spinelli et al. (+3 more)

The redshifted 21-cm line of neutral hydrogen (HI) is a powerful tracer of large-scale structure, and post-reionization HI intensity mapping is emerging as a competitive cosmological probe whose interpretation requires a description of how HI populates galaxies and dark matter halos. We characterize the HI–halo mass relation, its redshift evolution, and its intrinsic scatter, identifying its secondary dependences. We use the updated GAlaxy Evolution and Assembly (GAEA) semi-analytic model, applied to the Millennium-I and Millennium-II simulations, to predict the HI mass function (HIMF) and the HI–halo mass relation from the present day to redshift $z\simeq5$. At $z=0$, the model reproduces the observed HIMF and its decomposition by host-halo mass. The median HI–halo mass relation rises with halo mass, peaks near $10^{11.7}\,M_\odot$, declines as central galaxies are quenched by feedback from active galactic nuclei, and rises again where satellites dominate, approaching a single power law at high redshift. We show that the substantial scatter, of about 0.5 dex, is not random but is governed by halo assembly: at fixed mass, higher-spin, later-forming, and less-concentrated halos are systematically HI-richer, with spin together with either concentration or formation time accounting for part of this scatter and leaving an intrinsic dispersion of about 0.3 dex. We encode the median relation, these secondary trends, and the intrinsic scatter in a compact, physically motivated prescription expressed entirely in terms of quantities available in dark-matter halo catalogs. This prescription reproduces the full scatter and enables the construction of large-volume 21-cm mock catalogs for interpreting ongoing intensity-mapping measurements with SKA precursor facilities, such as MeerKAT, and for preparing for forthcoming surveys with the SKA.
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All authors Mohd Kamran, Gabriella De Lucia, Marta Spinelli, Lizhi Xie, Fabio Fontanot, Michaela Hirschmann

Soft Condensed Matter

Let's Stalk About Membranes: Committor-Based Enhanced Sampling of Stalk Formation

Giorgia Rossi, Enrico Trizio, Davide Bochicchio et al. (+2 more)

Membrane fusion is essential for cellular communication and function, and understanding how two lipid bilayers merge is key to informing therapeutic strategies. Functionalized nanoparticles have recently emerged as synthetic fusogens, but the molecular mechanisms driving this process remain unclear, partly because fusion involves transitions over high free-energy barriers, difficult to capture in molecular simulations. While enhanced sampling methods can address this problem, they also rely on the definition of collective variables, which are especially hard to define for fusion, as it arises from the collective rearrangement of many molecules and cannot be easily reduced to a simple intuitive coordinate. Here, we study stalk formation, the first step of fusion, mediated by an amphiphilic gold nanoparticle, by employing an enhanced sampling strategy based on the committor function, machine-learned through a self-consistent procedure. This method requires minimal prior knowledge of the system and leverages the learned committor function as an effective collective variable, enabling uniform sampling of the entire pathway. From the resulting reactive trajectories and extensive transition region sampling, we obtain converged free-energy estimates and mechanistic insight into stalk formation.
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All authors Giorgia Rossi, Enrico Trizio, Davide Bochicchio, Giulia Rossi, Michele Parrinello

Fluid Dynamics

Theoretical development of an operational wave-induced ice erosion model through laboratory experiments

Wenjun Lu, Behnam Ghadimi, Dominique Mouaze et al. (+6 more)

Wave-induced melting of vertical ice fronts is represented in several operational iceberg and coastal-erosion models by the rough-wall parameterization of White (1980), whose closure chain is incompletely documented and whose commonly used compact expression is stated at the waterline. We reconstruct the formulation, specify the rough-turbulent wave-friction closure using Jonsson's implicit relation and its Lambert-W solution, and extend the model to a depth-resolved melt-rate profile under linear wave kinematics. Because the horizontal and vertical orbital-velocity components are linked, we use the horizontal component as a convenient representative scale and introduce a dimensionless coefficient alpha for the remaining closure uncertainty. The reconstruction gives a waterline coefficient of 3.0 x 10^-4 with White's resultant-velocity definition and 2.09 x 10^-4 for the reference choice alpha = 1; neither reproduces White's published 1.46 x 10^-4 directly. Two monochromatic wave-flume experiments with freshwater ice are then used to calibrate alpha from profiles below the wave trough. The full Lambert-W friction coefficient is used in this calibration. Best-fit values are 0.684 and 0.612 for periods of 1.54 and 0.87 s, respectively, a relative difference of approximately 11%. Their corresponding effective waterline coefficients, 1.43 x 10^-4 and 1.28 x 10^-4, are close to White's published value but do not constitute an independent validation. The fitted profiles reproduce the observed depth dependence below the trough, while deviations near the surface expose unresolved effects of intermittent submergence, local wave impact, and uncertain thermal forcing.
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All authors Wenjun Lu, Behnam Ghadimi, Dominique Mouaze, Marianne Font, Rémi Lambert, Harvey Goodwin, Widar Weizhi Wang, Raed Lubbad, Sveinung Løset

Mesoscale and Nanoscale Physics

Frequency-dependent electron-phonon coupling and vibrational responses in tight-binding and continuous Dirac models with nuclear velocity correction

Paolo Fachin, Francesco Macheda, Paolo Barone et al. (+1 more)

The nuclear motion induces in the electronic atomic orbitals a nuclear-velocity-dependent phase (also known as electron-translation factor), which modifies the effective Hamiltonians constructed from localised atomic orbitals. In this work, using an Ehrenfest Lagrangian approach for the localised atomic orbitals (LCAO) and tight-binding methods, we determine, at any order in the nuclear velocity, the equations of motion and the vibrational responses within a linear response formalism, focusing on the tight-binding assessment of the Born effective charges and the force-constant matrix. The appearance of nuclear-velocity-dependent Peierls-like phases in the non-local part of the interactions restores the all-electron sum rules for frequency-dependent vibrational responses. In tight-binding models these corrections crucially modify the vibrational response from a qualitative point of view, also yielding contributions required to capture phenomena such as vibrational circular dichroism. We test these corrections in the tight-binding model for metallic gapped graphene - finding excellent agreement with ab initio calculations - and for the topological time-reversal symmetry breaking Haldane model.
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All authors Paolo Fachin, Francesco Macheda, Paolo Barone, Francesco Mauri

General Relativity and Quantum Cosmology

Cosmological horizon thermodynamics in Gauss-Bonnet quasi-dilaton Massive Gravity

Sobhan Kazempour, Orlando Luongo, Sabahat et al. (+2 more)

We investigate the thermodynamic properties of the cosmological apparent horizon in Gauss-Bonnet quasi-dilaton massive gravity. We derive the modified Friedmann equations and reformulate them in standard form, thereby allowing us to study the first and second laws of thermodynamics for the apparent horizon. Both equilibrium and non-equilibrium states are considered. In the equilibrium description, the first law retains the conventional form with the Bekenstein-Hawking area law for the horizon entropy, and we show that the generalized second law is satisfied under the null energy condition. In the non-equilibrium description, the Wald entropy receives a correction from the Gauss-Bonnet coupling, and the first law acquires an additional term associated with using the Wald entropy representation of the Gauss-Bonnet sector. We demonstrate that the total entropy change is non-negative provided the null energy condition, the positive horizon temperature condition, and the Gauss-Bonnet positivity constraints $\xi(\sigma)\ge0$ are simultaneously satisfied. Furthermore, we investigate the holographic entropy bound $S_{\text{inside}} \le S_{\text{horizon}}$. We demonstrate that while the idealized local thermal equilibrium assumption leads to a formal saturation or apparent breakdown during dust-dominated eras, the bound is robustly preserved across all cosmological epochs when utilizing realistic physical fluid temperatures. The condition $\xi(\sigma)\ge0$ is shown to be compatible with the stability constraints derived from tensor perturbations in our previous work. Our results establish that Gauss-Bonnet quasi-dilaton massive gravity is a consistent modified gravity theory from the perspective of horizon thermodynamics and the holographic principle.
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All authors Sobhan Kazempour, Orlando Luongo, Sabahat, Sichun Sun, Chengye Yu

Exactly Solvable and Integrable Systems

Combinatorial geometry of the 2D Toda lattice and Davey Stewartson equation

Rodrigo Navarro Betancourt, Marvin Anas Hahn, Vera Posch et al. (+1 more)

The KP equation is a prototypical $(2+1)$-dimensional integrable PDE. Its soliton solutions are famously parametrized by the Sato Grassmannian. In seminal work, Kodama and Williams made the surprising discovery that the combinatorics of soliton solutions are intimately related to the combinatorics of the totally positive Grassmannian as pioneered by Postnikov. They introduced novel algorithmic methods inspired by polyhedral structures arising from tropical geometry. Soliton solutions to the 2D Toda lattice and the Davey–Stewartson equation, two closely related integrable systems with soliton solutions, are also classified by the Sato Grassmannian. Kodama suggested that the methods of his work with Williams could generalize to these two integrable equations. In this work, we show that this is indeed the case. We derive algorithms to produce contour plots from elements in the totally nonnegative Grassmannian in both cases. In the asymptotic setting, we recover and refine previous work of Biondini and Wang; as well as Biondini, Kireyev and Maruno.
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All authors Rodrigo Navarro Betancourt, Marvin Anas Hahn, Vera Posch, Vincenzo Reda

General Relativity and Quantum Cosmology

Intermittency in Quantum Graviton-Phonon Conversion

Yuna Gouin, Sugumi Kanno and Jiro Soda

A graviton can be converted into a phonon in a resonant bar detector. First-order perturbation theory predicts a strong enhancement of this conversion for coherent and squeezed graviton states, but the probability can exceed unity when the coherent or squeezing parameter is large. Since a conversion probability must satisfy the unitarity bound, we solve the graviton-phonon quantum dynamics exactly within the rotating-wave approximation. For an initial coherent state, we find that the conversion occurs intermittently through narrow bursts separated by intervals of strong suppression. For an initial squeezed state, the departure from perturbative behavior occurs earlier, and the conversion is strongly suppressed after its initial growth. These effects may provide signatures of quantum graviton-phonon dynamics relevant to single-graviton detection.
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Mathematical Physics

Explicit Hamiltonian structure of the Flaschka-Newell Painlevé II hierarchy via symmetry reduction of the Painlevé IV hierarchy

Olivier Marchal, Mohamad Alameddine and Sergej Laub

We study the Hamiltonian structure of the Flaschka-Newell Painlevé II hierarchy via symmetry reduction of the associated space of meromorphic connections. Building on the realization of this hierarchy as a reduction of the Painlevé IV hierarchy via a $\mathbb{Z}_2$-symmetry, we construct a set of Darboux coordinates adapted to the involution. After a suitable change of trivialization, the symmetry acts diagonally in these coordinates, allowing the fixed-point locus to be explicitly described as a symplectic submanifold. This enables us to derive the reduced Hamiltonians after symmetry, thereby obtaining explicit expressions for the Hamiltonians and the Lax matrices of the Flaschka-Newell Painlevé II hierarchy. This strategy also illustrates how symmetry-adapted canonical Darboux coordinates enable explicit reductions of isomonodromic systems at the level of their underlying symplectic geometry.
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Quantum Physics

Schrödinger's real-valued equation revisited

Oliver Passon and Bernd Rosenow

The Schrödinger equation can be rewritten as a second-order equation for a single real-valued scalar field. Taken at face value, however, this one-field reduction obscures several local structures of quantum mechanics: the Born density and current, the role of momentum as a generator, and the usual derivation of the uncertainty relation. We argue that these difficulties do not show that real variables fail. They show that the reduced equation is not, by itself, a complete local representation of the theory. Its coherent real form is obtained by restoring the underlying Hamiltonian phase-space structure, where the missing component reappears as a canonical partner. In this real phase-space formulation, the standard structures reappear locally, and minimal magnetic coupling reveals an internal \(SO(2)\) gauge structure. Thus, the symbol \(i\) can be removed, but the symplectic and complex structure it encodes cannot.
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Mesoscale and Nanoscale Physics

Frequency-Division Multiplexing in Magnonic Waveguides

Alina-Cristina Bunea, Laurentiu Stoleriu, Giacomo Talmelli et al. (+3 more)

Frequency-division multiplexing is a key functionality for wave-based information processing, enabling multiple information channels to coexist within the same physical medium. Here, we experimentally investigate spin-wave multiplexing in a CoFeB waveguide using all-electrical excitation and detection. Two independently generated microwave signals are simultaneously coupled into the same spin-wave waveguide through inductive antennas and characterized using broadband vector network analyzer measurements. The transmission spectra obtained under single-channel and multiplexed operation exhibit excellent agreement, demonstrating that spin waves with different frequencies and wavelengths propagate simultaneously without measurable interaction in the linear regime. The observation is confirmed using both dual-sweep and sweep-plus-single-tone excitation schemes. A theoretical analysis based on linear superposition and phase-sensitive detection explains the absence of observable inter-channel interference for independent microwave sources. Micromagnetic simulations further confirm that the amplitudes and wavevectors of the individual spin-wave modes remain unchanged during co-propagation, demonstrating the absence of interaction over the entire propagation distance. The results provide direct experimental evidence that independent spin-wave channels can coexist in a single waveguide and support the implementation of frequency-division multiplexing in future magnonic computing and microwave signal-processing architectures.
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All authors Alina-Cristina Bunea, Laurentiu Stoleriu, Giacomo Talmelli, Dan Neculoiu, Christoph Adelmann, Florin Ciubotaru

Soft Condensed Matter

Inferring activity from fluid flow in continuum models of active matter

Aditya Mohapatra, Sagarika Adhikary and Rajesh Singh

Active matter systems are driven out of thermodynamic equilibrium by localized, microscale energy dissipation. While hydrodynamic continuum frameworks are highly successful at simulating these non-equilibrium phenomena (the forward problem), characterizing real-world active materials is fundamentally bottlenecked by the difficulty of measuring active stresses directly. This paper addresses the inverse problem using deep learning: model inference and model selection from observable flow field data of active fluids. We formulate a generalized hydrodynamic inversion framework applied to two cornerstone paradigms of active continuum physics: Active Model H (representing scalar active matter) and Active Nematics (representing active systems with orientational order). We demonstrate that the kinetic energy spectrum obtained from the fluid flow fields preserve a high-fidelity signature of activity to infer parameters of active model H and active nematics. Our deep learning method presents a principled way to bear upon questions of model inference and selection given the flow field data in continuum models of active matter.
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Mathematical Physics · Cross-listed from math.DS

Scattering Dynamics and Chaotic Motions in a Relativistic Two-Centre Problem

Stefano Baranzini and Gian Marco Canneori

We study the planar relativistic two-centre problem at fixed energy, including a class of perturbations of the Keplerian potential. Up to a reparametrisation of time, the relativistic dynamics is equivalent to a classical two-centre system with critical strong-force singularities. This reduction allows us to apply variational methods based on the Maupertuis functional. We construct collision-free relativistic trajectories with prescribed symbolic itineraries and obtain a coding of the dynamics by admissible sequences. In particular, we prove the existence of bounded orbits, scattering solutions with prescribed asymptotic directions, and trapped trajectories that are asymptotically free in one time direction and exhibit prescribed symbolic behaviour in the other.
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Superconductivity

Power-Law Suppression of Superfluid Stiffness in High-Kinetic-Inductance NbN Films

Meenakshi Sharma, Hrishikesh Borah, Sandeep Singh et al. (+8 more)

Disorder is a powerful route to high kinetic inductance in superconducting ultrathin films, enabling compact high-impedance quantum circuits. This functionality, however, comes at the cost of reduced phase rigidity and potentially anomalous electrodynamics. Here, we use NbN microwave resonators with thicknesses down to 2.8 nm and sheet kinetic inductance up to 300 pH per square to probe how this trade-off reshapes the superconducting response. In the thinnest films, transport shows signatures of a Berezinskii-Kosterlitz-Thouless transition, while the microwave response reveals a pronounced low-temperature power-law suppression of the superfluid stiffness, inconsistent with Mattis-Bardeen theory. With increasing thickness, this anomalous regime is progressively suppressed, marking a continuous crossover toward conventional, gap-dominated electrodynamics. Cross-sectional transmission electron microscopy reveals a nanocrystalline twin-domain structure, pointing to oriented microstructural disorder as a crucial factor in the observed response. Overall, the crossover is governed by the ratio of superfluid stiffness to pairing energy, Theta(0)/Tc, identifying this ratio as a parameter governing the boundary between phase-fluctuation-dominated and gap-dominated superconducting electrodynamics in disordered nanofilms.
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All authors Meenakshi Sharma, Hrishikesh Borah, Sandeep Singh, Berit H. Goodge, Edouard Lesne, Sandra Nestler, Surinder P. Singh, Haolin Jin, Yejin Lee, Bernd Büchner, Uri Vool

Physics and Society

Corruption as a self-sustained collective state in political systems

Nuno Crokidakis and Jaime L. C. da C. Filho

Political corruption is often interpreted as the result of individual misconduct or isolated institutional failures. However, persistent corruption patterns observed in real-world political systems suggest that systemic corruption may instead emerge as a self-sustaining governance arrangement supported by reinforcing interaction structures. In this work, we introduce a minimal compartmental model for the dynamics of systemic political corruption and the formation of corruption-supporting relational structures. The concentration of political power is treated as an emergent macroscopic observable arising from these coupled dynamics. Despite its simplicity and mean-field character, the model exhibits a nontrivial phase transition separating regimes of low corruption from structurally captured states sustained by self-reinforcing interaction mechanisms. The model predicts that, above a critical interaction strength, the captured state becomes dynamically stable, with small perturbations of the macroscopic variables naturally relaxing back to the stationary state. We argue that this mechanism provides a possible explanation for the persistence of corruption across successive electoral cycles and institutional crises. In particular, the political dynamics observed in the state of Rio de Janeiro, Brazil, provide a qualitative illustrative example of several mechanisms discussed by the proposed framework rather than a quantitative application of the model. More broadly, the results suggest that long-term political capture may emerge spontaneously from reinforcing interactions between systemic corruption and the relational structures that sustain it, without requiring centralized coordination or complex strategic behavior.
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Mesoscale and Nanoscale Physics

Exact theory of chirality-dependent p-wave magnetism and Edelstein effect in spin spirals

Börge Göbel, Tom G. Saunderson, Freia Opfermann et al. (+3 more)

Spin-momentum locking is widely regarded as a hallmark of relativistic spin-orbit coupling. Here we demonstrate analytically that it can instead emerge solely from magnetic chirality. Solving the minimal tight-binding model of electrons coupled to a spin spiral using a generalized Bloch theorem, we show that the spiral generates chirality-dependent p-wave magnetism characterized by the antisymmetric spin texture $\boldsymbol{s}(\boldsymbol{k})=-\boldsymbol{s}(-\boldsymbol{k})$. The exact solution further yields closed-form expressions for the electrical conductivity and the spin Edelstein susceptibility, revealing a microscopic mechanism by which magnetic chirality alone can generate spin polarization without spin-orbit coupling, with direct implications also for chirality-induced spin selectivity. In the strong exchange-coupling regime, the spin-dependent physics of the spin spiral becomes directly analogous to the orbital-dependent physics of electrons propagating through a non-magnetic helix. Our work establishes a minimal exactly solvable model of chirality-induced spin-momentum locking and spin-charge conversion beyond the conventional spin-orbit coupled paradigm.
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All authors Börge Göbel, Tom G. Saunderson, Freia Opfermann, Lennart Schimpf, Ersoy Şaş{\i}oğlu, Samir Lounis

2607.20094 · 22 Jul · 6 pages, 4 figures. This work was supported by the EIC Pathfinder OPEN grant 101129641 "Orbital Engineering for Innovative Electronics" and by Deutsche Forschungsgemeinschaft (DFG): Project No. 328545488 - CRC/TRR 227, Project No. B12 and by the German Excellence Strategy -EXC3112/1 -533767171 (Center for Chiral Electronics)

Abstract PDF $SPIN ×14$MAG ×3$THRM ×1

Astrophysics of Galaxies

A universal chromosome map for globular clusters: chemical calibration and environmental regulation of the multiple populations

C. Lardo, M. Salaris, N. Bastian et al. (+7 more)

Chromosome maps (ChMs) are two-dimensional diagrams of UV/optical pseudocolours widely used to diagnose the multiple stellar populations (MPs) phenomenon in globular clusters. Their raw morphology is affected by the metallicity-dependent response of the photometric filters, preventing unbiased comparisons across clusters of different metallicities. We identify a cross-cluster ChM framework that accounts for this dependence, enabling an unbiased investigation of the physical drivers of MP diversity. We analyse ChMs for 23 Galactic globulars and devise a technique to correct the raw maps for the clusters' different metallicities. On the resulting "universal" ChM we define a new photometric enrichment index $S_{\rm ChM,z}$, validated against APOGEE spectroscopy. We compare this index with cluster masses, structural parameters, orbital quantities, and accretion-origin classifications. $S_{\rm ChM,z}$ correlates with the multivariate chemical abundance ranges of the enriched population and with the aluminium spread. Across the sample it increases with initial mass but correlates most strongly with a family of orbital-confinement quantities ($z_{\max}$, vertical action, apocentre, Galactocentric radius, orbital energy). The corrected ChMs provide a chemically meaningful, population-level measure of the enriched sequence. $S_{\rm ChM,z}$ does not trace a single abundance ratio but captures the cluster-to-cluster amplitude of the combined light-element variations, with particular sensitivity to the high-temperature Mg-Al/O component of proton-capture processing. Its dependence on both cluster potential depth and orbital confinement suggests that 2P chemical diversity is shaped by internal enrichment physics together with an environmental imprint, whether inherited at formation, modified by early evolution, or filtered by subsequent orbital survival.
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All authors C. Lardo, M. Salaris, N. Bastian, C. Charbonnel, E. Dalessandro, E. Dondoglio, M. Gieles, M. G. H. Krause, F. Martins, S. Monty

Statistical Mechanics

Logarithmic scaling correction in quench dynamics of the J1-J2 Potts model

Kun Li and Wanzhou Zhang

In conventional quench dynamics governed by the Kibble-Zurek mechanism (KZM), the defect density generally decays as a pure power law of the quench rate. However, the KZM scaling of the two-dimensional (2D) XY model with topological phase transitions features prominent logarithmic corrections. Nevertheless, it remains unclear whether such logarithmic scaling corrections emerge in discrete-spin systems that host two successive topological phase transitions under thermal quenches. This work investigates the J1-J2 antiferromagnetic Potts model and constructs its equilibrium phase diagram. Based on the temperature ranges of the paramagnetic phase, quasi-long-range ordered (QLRO) phase, long-range ordered phase, and zero-temperature ground state, we design four quench protocols with distinct temperature intervals. Our results demonstrate that quenches terminating in the QLRO phase exhibit logarithmically corrected KZM scaling of the excess energy density, consistent with the dynamical universality class of the 2D XY model. In contrast, quenches ending in the LRO phase, including both finite-temperature and zero-temperature protocols, follow conventional power-law scaling. Our results clearly uncover the characteristic scaling corrections of the J1-J2 Potts model and offer theoretical guidance for future experimental investigations of KZM via photonic simulation platforms.
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Astrophysics of Galaxies

Galactic Science with the LiteBIRD satellite: Spectral characterization of diffuse Galactic polarized emission at the angular power spectrum level

S. Vinzl, J. Aumont, L. Vacher et al. (+108 more)

Detection of primordial $B$-mode polarization in the cosmic microwave background (CMB) from tensor perturbations generated during inflation is a major scientific goal of future CMB missions. Its success will strongly depend on the characterization of polarized foregrounds, a challenge that the LiteBIRD satellite aims to tackle with its 15 frequency bands ranging from 40 to 402 GHz. In this work, we forecast the ability of LiteBIRD to characterize polarized dust and synchrotron emission in the diffuse interstellar medium (ISM), at the angular power spectrum level. From simulated LiteBIRD intensity and polarization maps with different foreground complexities, we compute cross-frequency angular power spectra and fit them to dust and synchrotron spectral energy distributions, which are modeled by a modified black body and a power law, respectively. We find that LiteBIRD will be able to measure the dust temperature, dust and synchrotron spectral indices and spatial correlation with dispersions as low as $\sigma(T_{\rm d})\sim0.2$ K, $\sigma(\beta_{\rm d})\sim0.006$, $\sigma(\beta_{\rm s})\sim0.04$ and $\sigma(\rho)\sim10^{-2}$, as well as to detect and quantify deviations from the proposed parametric model due to variations of the emission properties in the three dimensions of our Galaxy. Additionally, LiteBIRD is likely to rule out the power-law model of polarized foreground angular power spectra suggested by Planck data. It will also be able to detect differences in the values of $\beta_{\rm d}$, $T_{\rm d}$, and $\beta_{\rm s}$ between $E$ modes, $B$ modes, and intensity in the diffuse ISM for the first time, highlighting the joint variations of the physical conditions and the magnetic field structure across the Galaxy. We conclude that in addition to detailed studies of CMB polarization, LiteBIRD will open a new window onto the physical conditions governing the ISM of the Milky Way.
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All authors S. Vinzl, J. Aumont, L. Vacher, R. T. Génova-Santos, D. Adak, A. Rizzieri, H. Akamatsu, E. Allys, A. Anand, C. Baccigalupi, M. Ballardini, A. J. Banday, R. B. Barreiro, N. Bartolo, S. Basak, A. Basyrov, M. Bersanelli, N. Brancadori, T. Brinckmann, E. Calabrese, P. Campeti, A. Carones, F. Carralot, F. J. Casas, J. Chandran, M. Citran, F. Columbro, A. Coppolecchia, P. de Bernardis, E. de la Hoz, M. De Lucia, S. Della Torre, C. Dickinson, P. Diego-Palazuelos, K. Ebisawa, H. K. Eriksen, J. Errard, F. Finelli, C. Franceschet, U. Fuskeland, G. Galloni, M. Galloway, M. Gerbino, M. Gervasi, T. Ghigna, S. Giardiello, E. Gjerløw, M. Gomes, S. E. Harper, L. T. Hergt, E. Hivon, H. Ishino, K. Kikuno, K. Kohri, N. Krachmalnicoff, L. Lamagna, M. Lattanzi, C. Leloup, F. Levrier, A. I. Lonappan, M. López-Caniego, G. Luzzi, D. Maino, V. Maranchery, S. Masi, S. Matarrese, T. Matsumura, S. Micheli, M. Migliaccio, M. Monelli, L. Montier, G. Morgante, L. Mousset, R. Nagata, T. Namikawa, P. Natoli, A. Occhiuzzi, L. Pagano, A. Paiella, D. Paoletti, G. Pascual-Cisneros, G. Patanchon, V. Pavlidou, V. Pelgrims, F. Piacentini, G. Piccirilli, M. Pinchera, G. Polenta, L. Porcelli, M. Remazeilles, J. A. Rubiño-Martín, M. Ruiz-Granda, Y. Sakurai, L. Salvati, J. Sanghavi, V. Sauvage, Y. Sekimoto, M. Shiraishi, S. Stellati, R. M. Sullivan, R. Takahashi, A. Tartari, K. Tassis, K. Tateoka, L. Terenzi, M. Tomasi, M. Tristram, B. van Tent, P. Vielva, G. Weymann-Despres, E. J. Wollack

Materials Science

From MLIPs to Microstructure: A High-Throughput Computational Framework to Design Spinodal Alloys in High-Dimensional Composition Spaces via Analytic Derivatives of CALPHAD Model Predictions

Courtney Kunselman, Doguhan Sariturk, Siya Zhu et al. (+2 more)

Identifying regions of design space subject to spinodal decomposition is a critical component of alloy design in high-dimensional composition spaces. In cases where designers are seeking to exploit spinodal microstructures to tailor alloy properties, prediction of microstructure evolution and morphology is also needed. In this work, we present a Machine Learning Interatomic Potential (MLIP)-trained, CALPHAD-based, open-source workflow for high-throughput microstructure stability analysis and visualization. In this workflow, coherent strain contributions are captured via high-throughput MLIP elastic constant calculations. To predict microstructure morphology for compositions of interest, MLIP-generated thermodynamic models are fed into an elasto-chemical phase field simulation. Both stability analyses and phase-field simulations utilize analytically-derived Gibbs energy Hessians to improve computational efficiency and accuracy over finite difference approximations. We demonstrate this workflow by investigating microstructure stability in the Hf-Nb-Ti-V quaternary system.
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All authors Courtney Kunselman, Doguhan Sariturk, Siya Zhu, Vahid Attari, Raymundo Arroyave

Quantum Gases

Two- and three-body bound states in one-dimensional Fermi bipolaron with three-body interaction

O. Hryhorchak and V. Pastukhov

We discuss the ground-state properties of two bosonic (or spin-1/2 fermionic in a singlet spin state) impurities immersed in a one-dimensional ideal Fermi gas with only the three-body contact interaction accounted for. Despite its simplicity, the considered model is found to demonstrate a variety of medium-induced few-body bound states. Particularly, using variational calculations with trial wave functions that correctly take into account one particle-hole excitation, we predict the emergence of a dimer state and several trimer states over a wide range of the three-body coupling parameter.
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Other Condensed Matter

Core and valence photoemission spectra of atoms and molecules from a multichannel Dyson equation

Stefano Paggi, J. Arjan Berger and Pina Romaniello

We recently presented multichannel Dyson equations for the ab initio simulation of various spectroscopies. In particular, we introduced a multichannel Dyson equation for the description of photoemission spectra. In this work, we apply our approach to the simulation of photoemission spectra of atoms and molecules. We introduce a numerically efficient approach to calculate their spectral functions. We compare the spectra obtained within the multichannel Dyson equation to those obtained with full configuration interaction and the $GW$ method. We are thus able to show that the satellite features due to shake-up processes are significantly better described by the multichannel Dyson equation than by $GW$. Finally, we also discuss the slow convergence of the satellite energies with the size of the basis set and we propose a simple extrapolation method to reach the complete basis-set limit.
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Fluid Dynamics

Water entry of small hydrophobic spheres on an axisymmetric wavefield

Chase T. Gabbard, Mario Ibrahim, Joseph Quinton et al. (+3 more)

When a sphere crosses an air-water interface it can entrain a significant volume of air, a process relevant to numerous naval, industrial, and environmental settings. While air entrainment through sphere impact onto quiescent interfaces has been extensively studied, real-world interfaces are inherently unsteady, and the influence of surface waves is less understood. In this work, we systematically investigate the effect of waves on air entrainment in a highly controlled setting: small hydrophobic spheres impacting an axisymmetric standing wavefield. By analyzing the resulting cavity across a wide parameter space, including wave phase, driving amplitude, and frequency, we reveal that local interface deformation dramatically alters the maximum cavity volume. This effect is driven by a geometric modulation of the splash curtain, which shifts the transition between cavity closure modes. We demonstrate that the influence of waves in our setting is well parameterized by the instantaneous interface slope evaluated at the radius of the sphere, successfully collapsing our experimental data alongside the traditional Weber and Bond numbers.
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All authors Chase T. Gabbard, Mario Ibrahim, Joseph Quinton, Eli Silver, Jesse Belden, Daniel M. Harris

Materials Science

Kinetically-Arrested Phase Separation leads to Tunable Domain Structures in Vapor-Deposited Glasses

A T M Mahbub Alahe, Thomas J. Ferron and Camille E. Bishop

The characteristic length scale of phase-separated organic thin film blends is a critical structural parameter governing the performance and functionality of organic electronic devices. The arrested morphologies of vapor-deposited organic thin films result from the interplay between thermodynamic driving forces and kinetic constraints during deposition. Here, we aim to isolate the role of kinetic effects in phase separation by varying the deposition rate at a constant substrate temperature for a co-deposited molecular glass blend of N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) and Disperse Orange 37 (DO37). The dependence of morphology on deposition rate is quantified using power spectral density (PSD) analysis of atomic force microscopy (AFM) images. Two distinct deposition rate-dependent length scales at the surface reveal how deposition kinetics directly influence domain size and film topography. Complementary Resonant Soft X-ray Scattering (RSoXS) measurements indicate that phase separation extends throughout the film thickness. These observations are consistent with the surface equilibration mechanism previously described for homogeneous vapor-deposited films, in which enhanced surface mobility allows molecules in the growing film to partially equilibrate into distinct surface-templated states during deposition. In the current work, this mechanism allows the multi-component blend to phase separate and coarsen into a structure with multiple length scales before kinetically arresting to an extent that depends on the deposition rate. The demonstration of finely tunable domain size with deposition rate provides strategies to design new organic electronic devices with desired morphologies.
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General Relativity and Quantum Cosmology · Cross-listed from math.DG

Null distance on cosmological spacetimes and monotone convergence

Miguel Prados-Abad and Omar Zoghlami

The metric theory of spacetimes studies Lorentzian manifolds using tools of metric geometry. This is achieved via the null distance, which is a definite distance constructed from a time function on a spacetime. This enables the study of Gromov-Hausdorff-type convergence of spacetimes, a program recently initiated by Sakovich and Sormani. In this paper we study such notions of convergence for cosmological spacetimes with compact slices, i.e., $(a,b)\times M$ endowed with a Lorentzian metric $-dt^2+h_t$, where $h_t$ is a family of Riemannian metrics on the compact manifold $M$. Assuming mild extension properties of $h_t$, we first establish that these spacetimes are causally-null compactifiable and future developed. We then study monotone sequences with a uniform upper bound on the spatial diameter, obtaining uniform convergence of the null distances, as well as convergence of the associated timed metric spaces in the future developed Gromov-Hausdorff sense. Finally, we prove that causally-null compactifiable spacetimes satisfying a mild causal accessibility condition are causally-null, and relate the causally-null distance induced by the limit distance with the null distance induced by the (possibly non-smooth) limit metric tensor. Examples are provided to motivate the necessity of our hypotheses.
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Quantum Physics

Physics-Informed Graph-Neural Decoding of the Surface Code: the Logical Signal as an Exact Topological Pairing

P. E. Trevisanutto, S. Dhanpal, S. Basak et al. (+2 more)

We develop a physics-informed graph neural network (GNN) decoder for the surface code that solves a discrete Poisson equation on the syndrome graph, with the syndrome as the charge source. We compare four readout architectures for extracting the logical-error probability: a potential-based readout that maps the Poisson field through a multilayer perceptron, two current-based readouts under single- and two-sink Dirichlet boundary conditions, and a diffusion-based variant. Comparing these, we show that the solver's edge current is a pure gradient flow whose harmonic (circulating) part vanishes identically. The logical signal therefore cannot be read as a component of the current itself; it is instead a topological pairing between the syndrome and a boundary-fixed harmonic coordinate that distinguishes the two code boundaries linked by the logical operator. We prove that this pairing is evaluated exactly and in closed form, with no learned readout parameters, as the net current drained between the two boundary sinks. On the rotated surface code under circuit-level depolarising noise, this single closed-form scalar matches the best full-field readout and, at larger code distance, significantly exceeds the single-sink current pool, so that isolating the pairing helps more, not less, as the field grows larger and sparser. The decoder is not intended to surpass minimum-weight perfect matching, near-optimal for this noise model; its contribution is an interpretable characterisation of the logical signal itself.
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All authors P. E. Trevisanutto, S. Dhanpal, S. Basak, L. Petit, J.Thiyagalingam

Mesoscale and Nanoscale Physics · Cross-listed from cs.AI

Reading and Steering Representations of Materials-Science Mechanisms in an Open-Weight Language Model

Markus J. Buehler

Large language models can answer scientific questions, yet a correct output does not reveal whether the model represents or uses the governing physics. Here, using three open-weight Gemma 4 models (google/gemma-4-E4B-it, google/gemma-4-12B-it, google/gemma-4-31B-it) we identify three experimentally separable signatures of materials-science mechanism information: selective concept readability, relational encoding of qualitative constitutive orientation, and causal, context-dependent control of constrained engineering answers. We combine matched direct and Jacobian vocabulary readouts, option-free state geometry, a 60-law counterfactual benchmark and causal interventions. In 50 held-out materials descriptions, three independently fitted Jacobian lenses reproduced concept ranks, and target-free word sets from both readouts enabled blinded identification of 9 of 10 mechanism families. A separate 72-prompt benchmark produced mechanism-specific hidden-state neighborhoods, but an exact graph audit showed that this apparent physical organization was equally explained by numerical comparison. We therefore compared otherwise identical prompts in which only the direction of the physical input was reversed, asking whether the resulting hidden-state movement followed the supplied constitutive law. These state transformations ordered direct, physically neutral and inverse laws across 60 frozen relations and correctly oriented 39 of 40 directional laws, whereas lexical controls were near chance. Bidirectional interventions shifted answer probabilities toward or away from the physically appropriate outcome across all 12 matched cases, while counterfactual state patches transferred opposing decision signals across mechanisms and answer formats. Physical relationships were therefore more visible in controlled state changes than in absolute states alone.
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