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Tuesday 7 July

Mathematical Physics · Cross-listed from math.NA

On low-rank tensor train approximability for linear nearest neighbor systems

Patrick Gelß, Sebastian Matera, Reinhold Schneider et al. (+1 more)

Low-rank tensor methods are an important tool in the numerical treatment of equations with a high-dimensional state space. Nearest neighbor interaction systems like the Ising model or more general Markov jump processes, as well as 1D finite-state quantum systems are examples of such problems. While low-rank tensor train/matrix product state models have been shown to be highly efficient for the simulation of such systems, providing theoretical justification for this remains a challenging task. One approach for obtaining estimates on required ranks for certain accuracies is to investigate the rank increase in Krylov subspace methods for solving the problem at hand. In the context of area laws for ground states of 1D spin systems, nontrivial results on rank-increasing properties of nearest neighbor operator polynomials have been obtained in work of Arad et al. [arXiv:1301.1162] by studying the partial commutativity of local operators. In the present work, this technique is applied to polynomial methods for definite linear equations and dissipative linear ODEs with nearest neighbor structure. This allows to derive corresponding low-rank approximability statements for solutions of such problems which are independent of the system size. Numerical simulations of high-dimensional nearest neighbor systems illustrate the theoretical findings.
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All authors Patrick Gelß, Sebastian Matera, Reinhold Schneider, André Uschmajew

Earth and Planetary Astrophysics

Size, shape, density, and atmospheric limit of (50000) Quaoar revealed from 14 years of stellar occultation

Giuliano Margoti, Felipe Braga-Ribas, José Luis Ortiz et al. (+173 more)

We present results from 28 stellar occultations by the large Trans-Neptunian Object (50000) Quaoar registered between 2018 and 2025. By performing a joint analysis of this occultation data-set, along with other 9 published events, we were able to fit an oblate ellipsoid shape, with equatorial semi-axes, a and b of 566.1+2.5-2.2 km, and a polar semi-axis, c, of 511.2+3.6-3.7 km. It provides an equivalent volumetric diameter of 1094.4 +/- 4.6 km and polar oblateness of 0.097 +/- 0.011. Considering an absolute magnitude of H = 2.79 +/- 0.35, we derive a geometric albedo of pV = 0.125 +/- 0.038. We have derived new upper limits to the surface pressure of a CH4 atmosphere of 0.15 nbar (1-sigma) and 0.65 nbar (3-sigma). We also provide a table with the 36 new astrometric positions for Quaoar. Using the new system mass derived from Weywot's orbit around Quaoar, we calculated a density of 1.760 +/- 0.109 g/cm3. Moreover, from the derived size and rotation period (8.8394 +/- 0.0002 hours (Ortiz et al. 2003)), we calculate that, if Quaoar is in Maclaurin hydrostatic equilibrium state, it would have a density of 1.859 +/- 0.200 g/cm3. This result, within the error bars, is compatible with the value we found. Therefore, this work shows that Quaoar can be a Maclaurin object, being eligible as a dwarf planet.
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All authors Giuliano Margoti, Felipe Braga-Ribas, José Luis Ortiz, Bruno Sicardy, Josselin Desmars, B. E. Morgado, Eros de Oliveira Gradovski, Chrystian Luciano Pereira, Pablo Santos-Sanz, Altair Ramos Gomes-Júnior, Julio Ignacio Bueno de Camargo, Marcelo Assafin, Vieira-Martins Roberto, Yucel Kilic, Damya Souami, René Duffard, Gustavo Benedetti-Rossi, Tiago Pinheiro, Maísa Poiani, Eduardo Rondón, Marcelo Emilio, Dave Herald, Rafael Sfair, Nicolas Morales, Francois Colas, Frédéric Vachier, Mónica Vara Lubiano, Rodrigo Boufleur, Mert Acar, Francisco J. Aceituno, Miguel R. Alarcon, Sinan Alis, Sergio Alonso, Javier Alonso-Santiago, Flavia Amadio, Laerte Andrade, Pascal André, Jonatã Arcas-Silva, Alper K. Ateş, David Lafuente Aznar, Michael Backes, Mehmed Naim Bagiran, Nelson Balcar, M. A. Barry, Khalid Barkaoui, Wolfgang Beisker, Kirk Bender, Zouhair Benkhaldoun, Svetlana Boeva, Eberhard H. R. Bredner, Richard Busuttil, A.~Y.~Burdanov, Oscar Canales, Javier Zaragoza-Cardiel, V. Casanova, Matheus Leal Castanheira, Peter Ceravolo, Steven J. Conard, Luciano Negrello Correa, Daniel V. Cotton, V. S. Dhillon, Serena Diamond, Vlad Dumitrescu, Joan Dunham, David W. Dunham, Christopher L. Duston, Eslam Elhosseiny, Orhan Erece, Sila Eryilmaz, Emilio J. Fernandez-García, Suleyman Fisek, R. Scott Fisher, Clyde Foster, Eric Frappa, Antonio Frasca, Jonah Frey, José María Gómez-Limón Gallard, Jose Luis Maestre Garcia, Dave Gault, Kosmas Gazeas, Kai Getrost, Michael Gillon, Alan Gilmore, Robert Glassey, K. D. Green, William Hanna, Nicholas J. Haigh, Dean Hooper, Kamil Hornoch, Dragana Ilic, Cristóvão Jacques, Felix~Jankowsky, Emmanuel Jehin, Selami Kalkan, Roxanne Kamin, Monika K. Kamińska, Shai Kaspi, J. J. Kavelaars, Stephen Kerr, Ulrich Kolb, Richard Komvzik, Dogan T. Koseoglu, Mike Kretlow, Sangeeta Kuchibhotla, Jean Lecacheux, Arnaud Leroy, Alexios Liakos, Luana Liberato, Peter Lindner, S. P. Littlefair, Jose M. Madiedo, Natalio Maícas, Marcio Malacarne, Paul Maley, Jan Mánek, Anna Marciniak, Patrick Martinez, Ramón Iglesias-Marzoa, Graeme McKay, Steve Messner, Zdeněk Moravec, Eduardo Fonseca Morato, Messias Fidêncio Neto, John Newman, Vadim Nikitin, Richard Nolthenius, Peter Nosworthy, Mohammad Odeh, W. Ogloza, Sibel Otken, Sacit Özdemir, Andras Pal, Ashley Pennell, Amauri Pereira, Carles Perello, Jean Perkins, Konstantin von Poschinger, Thiago do Prado, Theodor Pribulla, Sohrab Rahvar, Giovana Ramon, Seth Redfield, Claudine Rinner, Jean-Pierre Rivet, Johannes Antunes Nascimento Ro, rigues Antonio Román-Reche, Flavia Luane Rommel, T. de Santana, T. Santana-Ros, Antoni Selva, Christoph M. Schaefer, Andrew Scheck, Carles Schnabel, Olivier Schreurs, Andreas Schweizer, M. Serra-Ricart, Ned Smith, Colin Snodgrass, Eda Sonbas, A. Sota, Rafael Ribeiro de Sousa, Fabio Augusto Spina, Theodore Swift, Robert Szakats, Ali Takey, Mohammad F. Talafha, Ramachrisna Teixeira, Zahide Terzioğlu, Qiushi Chris Tian, Vagelis Tsamis, Eyüp Kaan Ülgen, Oliver Vince, Marcos Rincon Voelzke, Christian Weber, Julien de Wit, Michal Zejmo

Soft Condensed Matter

Dimensional Crossover of Thermal Transport in Nanoconfined Liquids Driven by the Interplay of Quasi-One-Dimensional Structure and Wall Dissipation

Kenta Hisamoto, Yusei Kobayashi, Takahiro Ikeda et al. (+2 more)

Heat transport in nanoconfined liquids can deviate from ordinary Fourier behavior because confinement alters liquid structure and interfacial dissipation. Although such changes may lead to quasi-one-dimensional transport or overdamped sound relaxation, the conditions under which length-dependent transport persists remain unclear. Here we use molecular dynamics simulations of monatomic liquid argon confined in carbon nanotubes with systematically varied radii and lengths. We find a radius-controlled crossover: length-dependent axial thermal conductivity persists over long tube lengths in single-file and single-shell states, but is strongly truncated or nearly saturated once mixed-shell or multilayer packing develops. This crossover is accompanied by the loss of clear acoustic-like axial modes and enhanced wall–liquid friction. Thus, tube radius controls whether length-dependent heat transport persists or is truncated by coupling confined-liquid structure to wall-induced dissipation.
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All authors Kenta Hisamoto, Yusei Kobayashi, Takahiro Ikeda, Eiji Yamamoto, Masashi Yamakawa

General Relativity and Quantum Cosmology

Starting inflation in asymptotically flat spacetimes

Sam E. Brady, Thomas W. Baumgarte and Katy Clough

A key question in early universe cosmology is whether inflation can be successfully seeded by a generic, localised fluctuation in the inflaton field that probes the inflationary part of the potential. Past simulations have mainly considered periodic spacetimes representing either a closed universe of a specific size or a typical patch of a larger one, and as a result have needed to impose restrictive conditions on the extrinsic and intrinsic curvatures, which are arguably not generic. In this work we consider initial fluctuations in asymptotically flat spacetimes, allowing more general profiles of the intrinsic and extrinsic curvature. Our findings confirm and generalise the result of Goldwirth and Piran that a fluctuation with proper size several times the inflationary scale $(G\rho_{\rm infl})^{-1/2}$ is required for successful inflation. We also discuss inherent restrictions on the initial data, and how imposing a periodic length close to the inflationary scale may bias results.
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Chemical Physics

An entropic bottleneck, dynamical gating, and outward redistribution of roaming in a designed Chesnavich-type model

Stephen Wiggins

Roaming reactions are organized not by potential-energy saddles but by transition states that are unstable invariant objects in phase space, periodic orbits in the two degrees of freedom studied here. To ask what controls roaming, we modify the Chesnavich model of a barrierless ion–molecule dissociation: its orientation-dependent angular hindrance is replaced by a transverse-stiffness ridge whose angular frequency peaks at an interior radius, and the classical dynamics are studied at a fixed energy just above the dissociation threshold. Comparing two ensembles that differ only in this angular interaction (same radial channel, energy, and inward initial conditions) isolates its effect. The ridge gates entry into the inner well, cutting inner capture from $57\%$ to $15\%$ and returning most of the incoming flux directly to reactants; it does not eliminate roaming but relocates it outward, suppressing it inside the ridge and switching it on farther out. The model retains analogues of the original model's three transition states (tight, free-rotor, and outer orbiting orbits), which we locate as unstable periodic orbits. The tight orbit spans a dividing surface that coincides, within numerical accuracy, with the variational minimum-flux surface, and it carries no barrier along the reaction coordinate: a deep entropic bottleneck placed at an interior radius by the stiffness maximum. Its entropic character is shared with the original model. Strength-matched monotone controls show that the gating tracks the hindrance strength at the bottleneck radius; what the interior maximum supplies is placement, concentrating that strength where it gates most effectively. The trajectories it admits roam nonstatistically, with nonexponential gap-time distributions: the entropic bottleneck governs how much is captured, not the dynamics that follow.
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General Relativity and Quantum Cosmology

Observationally Constrained Cosmological model in $f(Q,\mathcal{L}_{m})$ Gravity with $H(z)$ parameterization

Vinod Kumar Bhardwaj, Maxim Khlopov, Maxim Krasnov et al. (+1 more)

In the present work, we explore an observationally constrained cosmological model in the framework of $f(Q,\mathcal{L}_{m})$ gravity, where $Q$ denotes the non-metricity scalar and $\mathcal{L}_{m}$ represents the matter Lagrangian density. To derive the modified Friedmann field equations, we consider a flat FLRW space-time. We have considered a specific parameterization of the Hubble parameter $H(z)$ to explore the cosmic evolution, which successfully describes the shift of the cosmos from its initial decelerated expansion period to the current accelerated scenario. The free model parameters are constrained using recent observational datasets including Cosmic Chronometers (CC), Pantheon+SH0ES, Union 3.0, DESI-BAO, and CMB distance priors using MCMC approach through the $\chi^2$-minimization process. The derived results indicate that the present model remains consistent with recent cosmological observations. We note that the deceleration parameter exhibits a signature flipping behavior at transition redshift $z_t \approx 0.643$, confirming the transition from matter-dominated deceleration to dark-energy-driven acceleration. The equation of state (EOS) parameter remains in the quintessence region and exhibits an asymptotical approach to the $\Lambda$CDM limit at late times. Moreover, the estimated cosmic age can be found as $13.724^{+0.087}_{-0.048}$ Gyr, which agrees well with recent observational estimations. The statefinder and Om diagnostics support the quintessence nature of the model. At the same time, the examination of energy conditions reveals that two specific energy conditions, viz. Null Energy Condition (NEC) and Dominant Energy Condition (DEC) are fulfilled, while the Strong Energy Condition (SEC) is violated, validating the accelerated expansion of the universe.
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All authors Vinod Kumar Bhardwaj, Maxim Khlopov, Maxim Krasnov, Saibal Ray

Quantum Physics

Unbiased Estimation of Conditional Covariance for Quantum Optomechanics

Katsuta Sakai and Nobuyuki Matsumoto

Continuous measurements can prepare macroscopic mechanical oscillators in conditional quantum states, but their covariance is difficult to verify. The conventional retrodictive estimator assumes a forward–backward covariance symmetry and can be biased, because physical dynamics such as feedback damping reduces the observability of the state from future records. Here, we derive an exact linear-Gaussian estimator from causal, retrodictive, and smoothed trajectories. For a milligram-scale mirror, it agrees with a Riccati prediction based on parameters fixed independently, while the conventional estimate exhibits a covariance-space bias of $d_M\simeq3.5$. Our method paves the way toward unbiased testing of macroscopic entanglement within a calibrated linear-Gaussian model, applicable to both tabletop mirrors and kg-scale gravitational-wave test masses.
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Strongly Correlated Electrons

Instabilities of Fermi Liquids with Arbitrary Forward Scattering: Exact Approach

Dmitry Miserev, Joel Hutchinson, Herbert Schoeller et al. (+2 more)

In this work, we consider $N$-fold degenerate $D$-dimensional electron gas with spherical Fermi surface and arbitrary forward-scattering density-density interaction transferring small momentum compared to the Fermi momentum $k_{\mathrm{F}}$. The dimensional reduction that is mathematically equivalent to the Haldane patch construction and similar multidimensional bosonization techniques, provides a natural map of two-point $D$-dimensional correlation functions (fermion Green function, susceptibilities etc.) onto effective one-dimensional (1D) correlators with the same diagrammatic structure, which can be evaluated exactly within a 1D bosonizable (Gaussian) theory. We then apply this formalism to evaluate the fermion Green function, pair and charge/flavor susceptibilities, as well as the composite correlation functions for the case of a finite-range interaction, where the interaction range $R_{\mathrm{s}} \gg 1/k_{\mathrm{F}}$ is large compared to the Fermi wavelength. First, we find that the single-particle spectral function remains Fermi-liquid-like which is fully consistent with the previous research. In contrast to the single-particle sector, the many-body channels are efficiently dressed by finite-range interactions, and this dressing is fully equivalent to the one-loop renormalization group (RG), which is also in line with previous multidimensional bosonization results. Within the forward-scattering model, stable long-range order is not possible, and relevant susceptibilities demonstrate singular power-law scaling with temperature $T$ at $T \to 0$. The rest of the abstract is in the PDF.
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All authors Dmitry Miserev, Joel Hutchinson, Herbert Schoeller, Jelena Klinovaja, Daniel Loss

Computational Physics · Cross-listed from math.NA

Nested Volume-Surface Integral Equations for Acoustics

Danilo Aballay and Elwin van 't Wout

The simulation of high-frequency acoustic wave propagation in unbounded domains with local heterogeneous materials and high-contrast interfaces poses significant challenges to numerical methods. The volume-surface integral equation (VSIE) method is an attractive approach as it automatically satisfies the radiation condition at infinity via Green's functions, handles heterogeneous materials via Newton potentials, and models scattering at high-contrast interfaces via surface integral operators. However, its effectiveness in practical simulations has been limited by high computational costs, sensitivity to sharp interfaces, and insufficient computational verification. This study extends the applicability of VSIE by deriving integral formulations for nested heterogeneous materials with parameter jumps at interfaces. We also develop extensive benchmarks against coupled finite-element and boundary-element methods to verify the VSIE's accuracy and mesh convergence. The various benchmarks using open-source software demonstrate the effectiveness of VSIE for large-scale acoustic simulations.
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Mathematical Physics · Cross-listed from math.DS

Topological Dynamics of Pullback Maps on Full Shifts

Alonso Castillo-Ramirez and Luguis De Los Santos Baños

Let $G$ be a group, let $A$ be a finite alphabet, and let $\phi: G \to G$ be an endomorphism. We study the topological dynamics of the pullback map $\phi^* : A^G \to A^G$, given by $\phi^*(x)=x\circ\phi$, a canonical example of a generalized cellular automaton. In the one-dimensional case, where $G=\mathbb Z$ and $\phi_k(n)=kn$, we prove a sharp dichotomy: $\phi_k^*$ is equicontinuous precisely for $k\in\{-1,0,1\}$, and cofinitely sensitive otherwise. Although the fixed identity coordinate prevents transitivity on the full shift, the restriction to the natural invariant components is topologically mixing exactly when $k\notin\{-1,0,1\}$. We then extend the analysis to countable groups, showing that $\phi^*$ is equicontinuous if and only if every element of $G$ is eventually periodic under $\phi$, while the existence of a non-eventually-periodic element is equivalent to cofinite sensitivity and to the absence of equicontinuous points. Finally, we characterize Bernoulli measure preservation and strong mixing on the punctured configuration space in terms of injectivity and eventual periodicity.
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High Energy Astrophysical Phenomena

Finite-Field QED Corrections to Vacuum Birefringence and Magnetar Polarization Transport

S. Abbassi, F. A. Chishtie and S. R. Valluri

We study low-energy photon propagation in a constant magnetic field within the finite-field one-loop Heisenberg–Euler framework and apply the resulting mode-dependent refractive indices to magnetar polarization transport. In a centered-dipole model, the polarization-limiting radius is unchanged to better than $10^{-12}$ because mode decoupling occurs at $\sim10^2R_{\rm NS}$, where $B\ll B_{\rm cr}$. Near the surface, however, the weak-field Cotton–Mouton expression overestimates the accumulated birefringent phase by up to a factor $2.9$ at $10^{15}$~G. At the plasma–vacuum resonance, finite-field corrections reduce the resonance density by $32\%$ and raise the adiabatic conversion energy by $14\%$ for 1E~1547.0$-$5408; the corresponding changes are factors $2.6$ and $1.37$ for 1RXS~J1708$-$4009, and factors $9.7$ and $2.13$ for SGR~1806$-$20, the latter controlled by the strong-field asymptote. The parallel-mode magnetic response remains positive and exhibits a broad maximum near $17B_{\rm cr}$. Its strict $\mathcal O(\alpha)$ expansion is monotonic, indicating that the detailed position and profile of the maximum are not controlled beyond the present approximation and require higher-loop assessment. These results identify vacuum-resonance observables as the most sensitive channel for testing finite-field QED in magnetars.
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Computational Physics

Gradient-Based Inverse Design of Free-Energy Landscapes with Diffusion Models

Eli Zick and Dan Mendels

Free-energy surfaces govern the populations of metastable states and the barriers that control transitions between them, making their direct optimization a central challenge in molecular and materials design. In this work, we introduce Gradient-Based Free Energy Surface Optimization (GB-FESO), an inverse design framework that uses a trained conditional diffusion model as a differentiable surrogate for the ensemble distribution. After training, the diffusion model is frozen, and the conditioning variables defining the system are optimized so that the generated ensemble reproduces a prescribed target free-energy surface. The optimization is carried out by backpropagating a distribution-level loss, based on kernel density estimates of the Kullback-Leibler divergence, through a deterministic diffusion sampling trajectory. We first validate GB-FESO on one-dimensional Gaussian ensembles, demonstrating that both continuous and relaxed discrete conditioning variables can be optimized to recover target distributions, including those outside the training domain. We then apply the method to a four-particle Lennard-Jones toy peptide exhibiting multiple metastable conformational states. In this more physically motivated setting, GB-FESO successfully optimizes the interaction parameters to reproduce target free-energy landscapes in the majority of test cases, with optimization performed either in the full internal-coordinate space or in a reduced collective-variable representation. These results establish GB-FESO as a promising first step toward an ensemble-level inverse design framework for molecular systems with prescribed thermodynamic and kinetic behavior.
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Strongly Correlated Electrons

Skyrmion Phase Control by Magnetic Dipole-Dipole Interaction and Electric Field in Centrosymmetric Materials

Raz Rivlis, Alexander Petrović and Yuri Dahnovsky

Establishing precise control over the helicity and spatial configuration of magnetic skyrmions will be essential to realize their promise in classical, analog and quantum computation applications. In this work, we explore the role of magnetic dipole-dipole interactions, external electric fields, and magnetic fields in controlling these parameters within a triangular lattice centrosymmetric skyrmion host. We demonstrate that dipole-dipole interactions strongly favor Bloch helicity. Notably, a zero magnetic field skyrmion phase appears upon raising the dipole-dipole coupling strength, with substantial potential for cost-effective quantum device applications. We also report the emergence of a meron/antimeron lattice phase, in the absence of any Dzyaloshinskii-Moriya interaction. In contrast, applied electric fields stabilize high density Néel skyrmion crystals. The interplay between dipole-dipole interactions and external electric fields creates a continuous transition between the two skyrmion types, rather than an abrupt switch. Applied electric fields can therefore be used as a continuous tuning mechanism for skyrmion helicity, and hence a control handle for tuning two-level systems in skyrmion qubits.
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Optics

Terahertz-driven four-wave mixing at glass surfaces: Probing vibrational resonances and structural regimes

Mathias Hedegaard Kristensen, Jérôme Degert, Theo Guillaume et al. (+3 more)

Disordered materials such as glasses exhibit complex structural dynamics that are challenging to probe with conventional spectroscopies. We demonstrate that terahertz-driven four-wave mixing (FWM) at glass surfaces provides direct access to low-frequency vibrational modes and structural evolution in amorphous solids. Applied to a compositional series of PbO-silicate glasses (20-54 mol% PbO), this technique resolves distinct contributions from collective Boson-peak excitations and Pb-O / Si-O network stretching modes, and tracks their systematic evolution across structurally distinct compositional regimes. The dominant vibrational frequency blueshifts with PbO content, reflecting the progressive evolution of the Pb$^{2+}$ network role from silicate-modifier to ward network-former. A pronounced enhancement of the FWM signal near 44 mol% PbO coincides with the emergence of medium-range Pb-Pb correlations, while in-plane-to-out-of-plane FWM intensity ratio ($I_{\rm SS}/I_{\rm PS}$) tracks $\chi^{(3)}$ tensor anisotropy tied to Pb$^{2+}$ lone-pair spatial correlations. The non-monotonic peak in both observables at 44 mol% PbO - a composition where NMR finds no change in local Pb-O coordination and Pb-O-Pb free-oxide linkages are negligible - provides direct evidence that a collective lone-pair reorganization occurs in the medium-range structure independently of nearest-neighbor bonding. These results establish terahertz-driven FWM as a bulk-sensitive, near-surface depth-confined ($\sim$50 nm) nonlinear spectroscopy sensitive to vibrational and electronic structural fingerprints inaccessible to linear infrared, Raman, and terahertz time-domain probes.
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All authors Mathias Hedegaard Kristensen, Jérôme Degert, Theo Guillaume, Emmanuel Abraham, Laetitia Dalstein, Eric Freysz

Chemical Physics

Economised path integrals

Zezhu Zeng and David E. Manolopoulos

The Hessian of the ring polymer spring potential in the standard Trotter path integral is a $P\times P$ symmetric circulant matrix with a centroid eigenvalue of zero. All such matrices commute and are diagonalised by the same bead to normal mode transformation matrix, and their eigenvalues contain $\lceil P/2\rceil-1$ degenerate pairs by symmetry. However, this still leaves some freedom to improve on the Trotter approximation: one can optimise the remaining $\lfloor P/2\rfloor$ independent non-zero normal mode frequencies to fit the exact quantum mechanical radii of gyration of harmonic ring polymers with frequencies in the range $0\le\omega\le\omega_{\rm max}$, where $\omega_{\rm max}$ is the maximum physical frequency in the problem of interest. The optimisation involves solving a simple least squares problem for the optimum (economised or "Eco") internal mode frequencies. The remainder of the calculation then proceeds in the same way as a Trotter path integral calculation. An example application to hexagonal ice shows that the convergence of the Eco path integral is comparable to that of the 4th order Suzuki-Chin path integral, but with purely 2nd order Trotter effort. There is no need to calculate the projected Hessians that arise in the Suzuki-Chin method by finite differences, there is no need to develop any new estimators for observables, and once the Eco frequencies have been calculated the implementation of the Eco path integral involves changing just a few lines of a Trotter path integral code. To provide a more impressive example we have implemented the Eco method in GPUMD and used it to converge the (negative) thermal expansion coefficient and the constant pressure heat capacity of MOF-5 with a machine-learned neuroevolution potential.
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Quantum Physics

Geometric obstructions to quadratic time scaling in multiparameter quantum estimation

Eoin O'Connor, Jiayu He, Matteo G. A. Paris et al. (+1 more)

Unitary encoding of a single parameter provides quadratic enhancement in precision, with the quantum Fisher information scaling quadratically with the encoding time. However, when estimating multiple parameters simultaneously, this fundamental scaling is not guaranteed. Here, we establish a universal geometric obstruction that dictates when multiparameter quantum metrology fails to achieve simultaneous $t^{-2}$ scaling. By decomposing the Hamiltonian derivatives into components that commute and do not commute with the system Hamiltonian, we prove that linear dependence among the commuting components inevitably generates a slow parameter direction whose Fisher information remains bounded as O$(t^0)$, limiting the overall estimation precision. We demonstrate this mechanism in both discrete- and continuous-variable setups, including collective spin magnetometry and a generalized quantum harmonic oscillator, and contrast it with the Lipkin–Meshkov–Glick model where $t^{-2}$ decay is preserved. Remarkably, while the slow direction fundamentally limits the achievable precision, the measurement incompatibility between fast and slow directions decays as $1/t$, rendering the symmetric logarithmic derivative bound asymptotically saturable. Our framework provides a readily computable diagnostic, given by the Gram matrix of the diagonal generators, for identifying such obstructions in arbitrary multiparameter estimation problems. We further show that the bottleneck can be circumvented by relegating slow directions to nuisance parameters or by employing adaptive quantum control.
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All authors Eoin O'Connor, Jiayu He, Matteo G. A. Paris, Marco G. Genoni

Exactly Solvable and Integrable Systems

Asymptotic analysis of N-elliptic localized solutions for the Fokas–Lenells equation

Feng-Bao Feng, Wang Tang and Guo-Fu Yu

This paper investigates the N-elliptic localized solutions of the Foka-Lenells equation. Based on the corresponding Lax pair, the Weierstrass elliptic functions are adopted to construct the elliptic function solutions and the fundamental solution matrix of the equation. The N-elliptic localized solutions are further derived via the N-fold Darboux-Backlund transformation. By virtue of the Cauchy determinant expressed with sigma functions, the asymptotic behaviors of the obtained solutions are systematically analyzed along and between their propagation directions, and the symmetry properties of these solutions are established.
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Optics

Bright solitons in hybrid-dispersion photonic crystal microresonators

Alexander E. Ulanov, Lukas Bengel, Bastian Ruhnke et al. (+2 more)

Bright dissipative Kerr solitons in optical microresonators provide chip-scale sources of ultrashort pulses and frequency combs. Their properties are defined by the cavity dispersion for which fundamentally conflicting requirements exist: short pulses and broadband spectra require weak dispersion, whereas strong dispersion is associated with predictable dynamics. Here, we resolve this conflict by introducing a localized strong-dispersion section spanning several modes around the pump resonance within an otherwise weakly dispersive system. We implement this hybrid-dispersion scheme in a photonic crystal microresonator and reveal a new soliton attractor of backward-propagating solitons, accessible at low pump power in a thermally stable manner within the blue-detuned regime. The conflicting requirements for broadband spectra and low-noise single-soliton formation are reconciled, even in microwave-repetition-rate resonators, which otherwise are prone to uncontrollable multi-soliton formation. These results highlight the potential to achieve previously incompatible characteristics in nonlinear photonic systems through hybrid-dispersion attractor shaping.
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All authors Alexander E. Ulanov, Lukas Bengel, Bastian Ruhnke, Alexandra Sakharova, Tobias Herr

Quantum Physics

Bosonic quantum error-correcting codes with finite stellar rank

Rui Wang, Adithi Udupa, Timo Hillmann et al. (+3 more)

Bosonic quantum error correction (QEC) relies on non-Gaussian bosonic encodings whose preparation cost is a central practical constraint. In this work, we use stellar rank as a resource measure to design and benchmark bosonic codes under finite non-Gaussian resources. For fixed cat and Gottesman–Kitaev–Preskill (GKP) code families, we show that finite stellar rank creates a trade-off among state approximability, energy, and logical protection under photon loss and photon-number dephasing, evaluated with optimal recovery. This trade-off implies that codewords with better ideal error-correction properties need not be optimal once finite-rank preparation constraints are imposed. Going beyond fixed-target codewords, we directly optimize bosonic encodings at fixed stellar rank, revealing noise-adapted code structures and concrete resource thresholds. Grid-like encodings emerge under photon loss, whereas approximately rotation-symmetric encodings arise under dephasing. In the optimized search, stellar rank k=2 suffices to surpass break-even for all dephasing strengths considered, while under photon loss the required rank increases with the loss rate. These results establish stellar rank as an operationally meaningful resource measure for bosonic QEC under practical state-preparation constraints.
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All authors Rui Wang, Adithi Udupa, Timo Hillmann, Ulysse Chabaud, Alessandro Ferraro, Giulia Ferrini

Other Condensed Matter

Spontaneous emission of light by non-equilibrium phonons

J. Plo, P. Valvin, M. Moret et al. (+8 more)

When a system is brought out of equilibrium by an external excitation, its relaxation to thermodynamic equilibrium generates phonons. These non-equilibrium phonons degrade via cascaded anharmonic decay processes, progressively leading to a thermal population of phonons following a Bose-Einstein distribution at the system temperature. Preceding heat dissipation by convection, conduction and incandescence, this early phase of the relaxation dynamics is commonly assumed to be exclusively non-radiative. Here, we demonstrate that the radiative emission by phonons can be an efficient relaxation pathway competing with the intrinsic anharmonic decay. Optical spectroscopy under femtosecond two-photon excitation in boron nitride unveils a photoluminescence signal in the mid-infrared spectral range, stemming from the spontaneous emission of light by non-equilibrium phonons. This observation of non-thermal radiation from phonons introduces a new paradigm for out-of-equilibrium physics, mid-infrared optics, and thermal management.
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All authors J. Plo, P. Valvin, M. Moret, T. Taliercio, J. Batista, T. Sohier, A. Vasanelli, C. Sirtori, B. Gil, W. Desrat, G. Cassabois

Quantum Physics

Attosecond metrology of bright quantum light

P. Stammer, J. Rivera-Dean, E. Pisanty et al. (+1 more)

Attosecond metrology is the ability to measure ultrafast optical light-wave oscillations, yet its approach has been limited to classical fields. Hence, the influence of the fluctuations of a quantum field on attosecond measurements has remained unexplored. Here, we close this gap by showing that the attosecond streaking measurement of bright quantum light is sensitive to quantum fluctuations of the optical field on the attosecond timescale. The distinct sub-cycle modulations allow to extract the properties of the squeezed field quadrature in regimes where conventional state tomography approaches reach their limitation. With the full quantum optical attosecond streaking scheme developed here, we provide a certification method that can measure quantum squeezing below the shot noise limit, thereby overcoming the problem of tomographically measuring bright quantum light. This opens the way towards quantum optical metrology of field fluctuations with attosecond temporal resolution.
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All authors P. Stammer, J. Rivera-Dean, E. Pisanty, M. Lewenstein

Instrumentation and Methods for Astrophysics

slicersim: A python package to simulate image slicer spectroscopic observations – application to the Lazuli Spectrograph

M. Rigault, Y. Copin, G. Aldering et al. (+8 more)

Integral Field Spectroscopy (IFS) is a key technique to study galaxies, stellar and planetary systems, and transients, by spatially splitting the scene and dispersing this light onto the detector. This technique is now central for many modern telescopes, including the Lazuli Space Observatory which will host a low spectral-resolution image slicer spectrograph. To prepare for future IFS-equipped instruments and to better understand the systematics of current ones, realistic simulations are needed. We present slicersim, a Python package designed to simulate IFS observations. slicersim is a modular and flexible tool that allows the user to build a scene, define a telescope, a spectrograph, and a detector, and to simulate the resulting observation, including various sources of noise and instrumental effects. The package is designed to be easily extensible to any IFS, with a current focus on that from the Lazuli Space Observatory. In this paper, we present the structure and logic of the package, detailing its main components, and providing an example of its usage. Using slicersim we demonstrate the feasibility of a large cosmology campaign on Lazuli – a sample of 8000 Type~Ia Supernovae uniformly distributed between $z=0$ and $z=1.5$, observed within the first few years of its operations for a typical average signal-to-noise of 25 per resolution element rest-frame optical wavelengths.
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All authors M. Rigault, Y. Copin, G. Aldering, J. Edelstein, G. Furesz, J. Lasker, T. Miller, S. Perlmutter, A. Roy, E. Schlawin, G. Stefansson

Superconductivity

Effect of charge-imbalance potential relaxation on the high-frequency vortex dynamics and kinetic inductance of superconducting circuits

R. I. Kinzibaev, V. S. Stolyarov and A. S. Mel'nikov

We show that relaxation of the charge-imbalance potential plays a key role in the retarded dynamics of Abrikosov vortices in a type-II superconducting sample carrying a microwave current. Starting from the time-dependent Ginzburg–Landau equations we derive the vortex equation of motion accounting both the dissipation and retardation effects. The retardation is governed by the dynamics of the charge-imbalance potential and reveals itself at characteristic timescales diverging near the superconducting critical temperature $T_{c}$. These retardation effects in vortex dynamics strongly affect the kinetic inductance of superconducting circuits being, thus, responsible for the magnetic field dependence of characteristics of different superconducting devices in the high frequency range.
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Optics

Sectorial customized corneal crosslinking for keratoconus: an inverse biomechanical design study with an anisotropic reduced shell finite-element surrogate

J. Sumaya-Martinez and A. Altamirano-Torres

We propose an inverse biomechanical design framework for sectorial customized corneal crosslinking in keratoconus. The cornea is modeled as an anisotropic reduced shell with spatially varying crosslinking-induced stiffening, enabling the optimization of localized treatment patterns rather than uniform irradiation profiles. Numerical simulations show that sectorial stiffening can redistribute curvature, reduce localized steepening, and improve corneal regularity in decentered keratoconus models while preserving biomechanical plausibility. These results support the use of patient-specific computational planning for customized crosslinking protocols and provide a basis for future integration with corneal tomography and programmable ultraviolet delivery systems.
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High Energy Physics (Theory)

Unitary matrix models, quantized symmetric functions and spin chain

Gao-fu Ren

We construct a correspondence between a broad class of unitary matrix models and vacuum correlation functions in quantum spin-chain Hilbert spaces. The key step is to lift symmetric functions to operators acting on the $N$-magnon sector in a way that preserves the relevant ring structure. For any unitary matrix model whose integrand admits a factorized expansion in symmetric functions, the Schur orthogonality of the unitary group integral is then translated into the inner product of quantized Schur states. We illustrate the construction for the Gross–Witten–Wadia model, superconformal indices of $\mathcal{N}=4$ super Yang–Mills theory with classical gauge groups, and Toda tau functions. The resulting operator formulation provides a unified algebraic bridge between unitary matrix integrals, quantum integrable systems and symmetric function theory.
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Chaotic Dynamics

When a common price signal is present, network topology leaves no fingerprint on a storage fleet's collective dynamics

Stelios Savva

Price-based mean-field models of battery storage coordination usually assume that each agent responds to the true population-average charging power. Under that assumption, communication topology is irrelevant because the broadcast price already carries the coupling that matters. We study a nearby regime in which agents respond to a shared noisy forecast of the average, with correlation rho between agents' forecast errors. Analytically and in simulation, we find that topology remains undetectable in the effective-dimensional response of the fleet, even when neighbour observation is the only explicit communication signal. The mechanism is structural: the correlated forecast error projects onto the graph-invariant consensus mode, while topology acts through transverse modes. As rho N grows, the consensus-mode variance dominates and the spectral participation ratio approaches one independently of graph topology. Simulations on linear, star, and small-world graphs confirm that topology-induced variation is below the variation caused by redrawing the forecast noise. The result is not a claim that topology has no dynamical effect, but that shared stochastic forcing can mask topology-dependent modes in decentralized storage fleets.
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Chemical Physics

Reaction Pathway Detection using Machine-Learned Energy Potentials – Decomposition of Energized CF$_3$CHOO

Cangtao Yin and Markus Meuwly

Characterization of the decomposition products of energized Criegee intermediates is essential for assessing their impact on the chemical evolution of the atmosphere. Here, a generic and microscopically resolved approach is used to determine the molecular fragmentation pathways and products for CF$_3$CHOO. They include, among others, direct formation of CO$_2$ + CHF$_3$ (HFC-23), HF + CO$_2$ + CF$_2$, and fragmentation routes that are not evident from static reaction path calculations alone. The computed probability for formation of HFC-23 of 14 % qualitatively agrees with a value of $(7.9^{+0.4}_{-0.2})$ % from recent measurements, given the differences in the two approaches. Non-statistical dynamics is found for almost all decomposition pathways and the simulations show that excess energy can redirect reaction outcomes away from minimum-energy pathways. The results highlight the power of machine-learned PESs to elucidate multi-step reaction mechanisms of atmospherically relevant intermediates beyond traditional Master equation/electronic structure approaches to provide molecular-level understanding of the role of dynamics.
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High Energy Physics (Theory)

Axioms for physical reasoning: codifying the Seiberg–Witten solution in Lean

Michael R. Douglas

Mathematicians have embraced interactive theorem provers with growing enthusiasm – building large shared libraries and machine-checking a string of landmark results. Theoretical physics is different: most of its results are not theorems but justified by arguments the community trusts without a rigorous proof. For many – the one we treat here among them – no rigorous proof is within reach. For 4d Yang–Mills theory, deriving exact rigorous results from first principles would first require constructing the interacting theory nonperturbatively, which is a sizable piece of one of the Clay Millennium prize problems. We argue here that an interactive theorem prover can be used to verify some non-rigorous physics arguments. The method is to postulate a short list of explicit, named physical postulates, which imply the physical results by virtue of a machine-checkable proof. The trust that remains then rests on that short, inspectable list, and the prover can report, for any downstream result, exactly which assumptions it used. We carry this out for the Seiberg–Witten solution of ${N}=2$ $SU(2)$ super-Yang–Mills – the genus-one case – formalized in Lean 4; the higher-genus $SU(N)$ generalization is developed in the same repository as an axiomatized skeleton and left to future work. We describe what is proved, what is assumed, how the assumptions are checked – external review and an independent numerical oracle – and why this discipline is a sound standard for validating AI-generated results in theoretical physics. What we offer is a discipline, reviewable on its own terms: a reader may take the Seiberg–Witten mathematics on trust and still assess the formalization method.
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Soft Condensed Matter

Hybrid Dynamical Simulation Reveals Apparent Stiffening of Flexible Protein Lattices Driving Membrane Bending

Samuel L. Foley and Margaret E. Johnson

Membrane-deforming protein lattices play a central role in essential and pathogenic remodeling processes, including clathrin-mediated endocytosis and viral budding. Simulating these systems at biologically relevant length and time scales requires mesoscale approaches that preserve structural detail. We present a hybrid simulation framework that couples a particle-based flexible protein lattice to a continuum membrane model, enabling systematic investigation of how lattice geometry and rigidity influence membrane remodeling. We validate the coupled model by comparing simulation results with theoretical predictions for membranes under increasing tension. Using buckling-based deformations of pre-assembled clathrin lattices, we quantify the lattice flexural rigidity and establish a direct relationship between the force constants in the coarse-grained energy function and the emergent lattice mechanics. We then compare this flexural rigidity, $\kappa_{l,\mathrm{flex}}$, to an effective rigidity, $\kappa_{l,\mathrm{eff}}$, commonly used in continuum descriptions of sphere-forming protein assemblies. Although $\kappa_{l,\mathrm{flex}}$ is set solely by the energy function, $\kappa_{l,\mathrm{eff}}$ depends on lattice size and connectivity, with the two measures converging for weakly-connected lattices. As a result, with lattice growth, the effective rigidity relevant for spherical bud formation increases and the relaxation timescale decreases. This size-dependent stiffening highlights the importance of structural details in interpreting lattice mechanics and cautions against assuming a single constant stiffness. We demonstrate the generality of the method by applying it to pre-assembled viral lattices generated with reaction-diffusion simulations. This work provides a validated framework for simulating deformable protein assemblies of diverse geometry coupled to membrane dynamics and remodeling.
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High Energy Physics (Theory)

An Intermediate Scale R-axion & the QCD Axion

James Unwin

An intermediate scale R-axion faces an immediate obstruction from the Dine-Festuccia-Komargodski (DFK) bound on the superpotential, $2|\langle W\rangle|\leq f_R F$, since for a nearly Minkowski vacuum it typically follows that $f_R\gtrsim M_{\rm Pl}$. We show that this lower bound on $f_R$ can be relaxed in an effective construction with the scalar potential tuned near zero via a mixed $F$- and $D$-term uplift, leading to a metastable vacuum in which the usual Planckian-$f_R$ inference from the DFK argument is avoided locally. Validity of the effective field theory and metastability of the small $f_R$ vacuum generically both imply a relaxed bound: $ f_R \gtrsim \sqrt{m_{3/2}M_{\rm Pl}} $. We also highlight that if the R-symmetry has a QCD anomaly, this potentially permits the R-axion to play the role of the QCD axion. TeV-scale supersymmetry permits $f_R\sim10^{11}$ GeV, this not only evades certain astrophysical and cosmological axion constraints, but notably lies in the window for which the observed dark matter abundance can be reproduced by the R-axion via the misalignment mechanism.
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