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Physics

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Friday 4 September

Strongly Correlated Electrons

Dipolar and quadrupolar spin supersolid states in a spin-1 triangular antiferromagnet

Yixuan Huang, Yuan Gao, Wei Li et al. (+2 more)

We present a systematic numerical study of the spin-1 antiferromagnetic Heisenberg model on the triangular lattice in an out-of-plane magnetic field, using Density Matrix Renormalization Group (DMRG) methods. By mapping out the quantum phase diagram as a function of the single-ion anisotropy $D_z$ and magnetic field, we identify distinct dipolar and quadrupolar spin supersolid states, characterized by spontaneous U(1) symmetry breaking with finite spin superfluid stiffness coexisting with longitudinal translational symmetry breaking. At zero field, the dipolar spin supersolid with a 'Y'-type spin configuration persists down to $D_z = 0$, whereas the quadrupolar spin supersolid prevails at large $D_z$. At intermediate fields, the phase diagram is dominated by an up-up-down phase. At high fields below saturation, a quadrupolar spin superfluid emerges in the large-$D_z$ regime, whereas a dipolar spin supersolid with a 'V'-type spin configuration dominates at small $D_z$. These phases are characterized through their order parameters and spin superfluid stiffness using calculations on various system sizes. Furthermore, the dynamical spin structure factor is obtained across the phase diagram, where characteristic spectral signatures of different phases are observed, including the gapless Goldstone mode and the roton-like minima. These features are directly accessible to inelastic neutron scattering experiments. Our results provide a theoretical understanding of the interplay between frustrations, anisotropy, and Zeeman interactions in driving distinct spin supersolid phases in the spin-1 system, which are relevant to various triangular-lattice antiferromagnets such as Na$_2$BaNi(PO$_4$)$_2$ and K$_2$Ni(SeO$_3$)$_2$.
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All authors Yixuan Huang, Yuan Gao, Wei Li, Seiji Yunoki, Sadamichi Maekawa

Astrophysics of Galaxies

The dispersal law of young star clusters: free expansion – A Gaia/eROSITA census of Orion and Sco–Cen

João Alves, Stefan Meingast and Alena Rottensteiner

We measure how young star clusters disperse over time in the two nearest star-forming complexes. Our sample comprises 44 SigMA-Gaia-defined clusters in Orion and 31 in Sco–Cen, with isochronal ages of 2–25\,Myr. We extend each cluster's census with eROSITA-selected young stars that share its parallax and motion and lie within the distance they could have traveled ballistically since birth. By 10–30\,Myr, about one in three former cluster stars lies outside the cluster's cataloged boundary. Across both complexes and the full age range, we find that (1) the half-member radius increases linearly with age, $\rfifty \simeq \sigbirth t$, (2) the velocity dispersion shows no measurable evolution, and (3) all studied clusters are unbound. These results support free expansion. Young clusters in Orion and Sco-Cen emerge unbound from their birth clouds and coast at their birth velocity dispersion without significant relaxation or a characteristic dispersal timescale. We further show that memberships defined by density contrast preferentially omit the fastest stars, making the same clusters appear to expand more slowly ($\propto t^{0.6}$), cool with age, and approach equilibrium.
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Superconductivity

Transparency-engineered SQUID cells for Kerr-free three-wave-mixing Josephson metamaterials

Claudio Guarcello, A. Mert Bozkurt, Carlo Barone et al. (+3 more)

We introduce a transparency-engineered rf-SQUID cell for Kerr-free three-wave-mixing Josephson metamaterials. This design replaces the conventional tunnel-junction element with an effective Josephson element formed by two junctions in series, yielding a non-sinusoidal energy-phase relation that can be used as a tunable nonlinear design resource. We show that the asymmetry between the two series junctions and the applied flux bias provide independent control over the local expansion of the rf-SQUID potential, enabling operating points where the leading quartic Kerr term is suppressed while the cubic nonlinearity remains finite. We derive the corresponding Kerr-free condition, identify the resulting operating ridge in parameter space, and analyze the local stability and passive-matching constraints that bound its physically accessible portion. Our results provide a compact unit-cell design principle for three-wave-mixing Josephson metamaterials and suggest a route toward Kerr-suppressed Josephson traveling-wave parametric amplifiers.
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All authors Claudio Guarcello, A. Mert Bozkurt, Carlo Barone, Giovanni Filatrella, Alessandro Bruno, Sergio Pagano

Astrophysics of Galaxies

PPN–spin degeneracies in mock S62-like stellar-orbit inference

Shant Khlghatyan

We investigate the degeneracies between black hole (BH) spin effects and parametrized post-Newtonian (PPN) parameters in the relativistic orbital dynamics of S2-like and S62-like stars orbiting Sagittarius A$^{\ast}$. Using a 1PN+SO Hamiltonian framework and synthetic astrometric and radial velocity datasets, we perform Bayesian parameter inference. For current baseline observational precisions, the dominant relativistic observable–the Schwarzschild periapsis advance–allows the recovery of the effective precession parameter $\Upsilon$, while leaving the individual PPN parameters $\gamma$ and $\beta$ degenerate. Assuming microarcsecond-level astrometric precision, the spin-induced Lense-Thirring signal becomes partially detectable; fixing the PPN sector to General Relativity allows the BH spin magnitude to be constrained to an uncertainty of $\sim10^{-2}$. However, simultaneously varying PPN and spin parameters reveals a strong, approximately linear covariance between $\Upsilon$ and the dimensionless spin parameter $\chi$. To overcome this limitation, we demonstrate that joint multi-star inference can disentangle the degeneracy by combining a wider-orbit star, which constrains the dominant 1PN sector, with a compact relativistic orbit that is sensitive to Lense-Thirring frame dragging.
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Applied Physics

What Photocurrent Versus Effective Voltage Tells Us About Charge Generation in Organic Solar Cells

Ardalan Armin, Austin M. Kay, Drew B. Riley et al. (+2 more)

The photocurrent of an organic solar cell is routinely plotted against an effective voltage and used to extract an exciton dissociation probability, and through it a free-charge generation efficiency. The photocurrent measures neither. Using a drift-diffusion model in which free-charge generation is field independent and losses occur only by bimolecular recombination, we show that the apparent dissociation probability returned by this procedure lies well below unity even for complete dissociation. Across wide variations of carrier mobility and recombination strength it is a single-valued function of the fill factor and coincides with the short-circuit charge collection efficiency, reporting neither the generation yield nor anything about collection beyond what the fill factor already shows. Even for ideal transport the normalised photocurrent saturates below unity at an intensity-independent first-order limit set by recombination of photogenerated carriers with injected equilibrium charge. Applied to four organic solar cells whose generation efficiencies are known independently, the apparent dissociation probabilities track the short-circuit collection efficiency rather than the generation yield. We therefore suggest this construction not be used, particularly in the high-efficiency non-fullerene acceptor systems that are now state of the art.
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All authors Ardalan Armin, Austin M. Kay, Drew B. Riley, Oskar J. Sandberg, Paul Meredith

General Relativity and Quantum Cosmology

Cosmological Evolution of the Randall-Sundrum II Model with Running Vacuum: A Special Class of Solutions

Hao Yu, Jin Li and Zi-Chao Lin

In this work, we construct a novel cosmological framework by integrating the running vacuum model into the Randall-Sundrum II braneworld scenario. We derive a special class of analytical solutions in the model. Our investigation focuses on the complete evolutionary trajectory of the universe, with particular emphasis on the realization of primordial inflation and the evolution of cosmic entropy. We evaluate the model's viability across three scenarios: dust-dominated, radiation-dominated, and general perfect fluid-dominated universes. Our findings show that while the hybrid model is in principle capable of supporting inflation, producing enough e-fold number demands either severe fine-tuning of the parameter or unreasonably large (and thus physically unnatural) value of the parameter.
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General Relativity and Quantum Cosmology

Spherically symmetric inextendibility of weak null singularities with Christoffel symbols in $L^s_{\text{loc}}$

Peter Cameron and Jan Sbierski

Motivated by the strong cosmic censorship conjecture in general relativity, we prove the inextendibility of spherically symmetric weak null singularities as spherically symmetric Lorentzian manifolds with a continuous metric and Christoffel symbols in $L^{s}_{\text{loc}}$ for $s>1$. The result assumes a suitable blow-up condition on the derivative of the area-radius function transverse to the weak null singularity in combination with a rigidity result on continuous spherically symmetric extensions across null boundaries proven in [1]. In particular we show that these assumptions are satisfied by the Reissner-Nordström-Vaidya spacetime as well as by a class of spacetimes arising from small and generic spherically symmetric perturbations of subextremal Reissner-Nordström under the Einstein-Maxwell-scalar field system.
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High Energy Physics (Theory)

The endless journey towards the horizon of a quantum black hole

Victor Franken, Thomas G. Mertens and Bruno de S. L. Torres

It is a problem of great importance in quantum gravity whether quantum effects lead to nontrivial structure near black hole horizons, and if their interiors are emergent features of a large $N$ limit. We show that the strongly chaotic nature of black holes, captured by random matrix statistics of their spectrum, makes it so that a suitably gravitationally dressed infalling observer takes an infinite amount of proper time to reach the horizon. This makes the black hole interior operationally inaccessible to any outside observer, marking a sharp breakdown of the large $N$ causal structure of black holes in quantum gravity. To model the experience of an infalling observer, we study the response of an infalling particle detector coupled to a matter field in a 2d quantum black hole background, finding a peak in the detector's excitation probability as it enters an infinitely long non-perturbative journey close to the black hole horizon.
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Materials Science

Neural-field design of broadband Rayleigh-wave carpet cloaks under microstructure realisability constraints

David Aznaurov, Davit Piliposyan, Danila Rukhovich et al. (+1 more)

Transformation elasticity provides appropriate material distributions for elastodynamic cloaks but the required stiffness tensors generally violate the minor symmetries of Cauchy elasticity and are difficult to realise using conventional materials. Existing approaches restore these symmetries by modifying the transformed tensor, producing only an approximate cloak. In this work rather than modifying the transformed tensor we seek the best performing cloak within the class of Cauchy materials. We formulate 2D Rayleigh wave carpet cloak design as an optimisation problem governed by partial differential equations. Using a coordinate based neural-field and a differentiable finite element model solver we optimise symmetric stiffness and density fields by minimising wave field distortion. Both single frequency and broadband optimisation are considered, with the broadband model trained over multiple frequencies. Physical realisability is addressed using a database of homogenised microstructures through conditional diffusion, neural-field inverse design, and nearest-neighbour selection. FEM simulations show that the optimised Cauchy design approaches the ideal transformation-based cloak. After projection onto explicit microstructures, the homogenised representation recovers approximately 97% of the defect free reference surface-displacement magnitude, while direct FEM simulation of the fully resolved microstructured geometry recovers approximately 76%
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All authors David Aznaurov, Davit Piliposyan, Danila Rukhovich, Sebastien Guenneau

Soft Condensed Matter

Glassy dynamics, crossover temperature and density scaling in fragile glass-formers

Ankit Singh, Vinay Vaibhav, Swarn Lata Singh et al. (+1 more)

We investigate the slowing down of dynamics in a glass-forming mixture interacting via an inverse-power-law (IPL) potential using a combination of theory and large-scale molecular dynamics simulations. We measure the static pair-correlation function, configurational entropy, inherent-structure energy, and structural relaxation time. We employ a theoretical framework to calculate the structural relaxation time $\tau_{\alpha}$, which is found to be in very good agreement with the simulation results. The theory identifies a local structural order which defines the cooperativity of the relaxation and brings forth a fluctuation induced parameter $\psi ( T )$ and a crossover temperature $T_a$ that characterize the density and temperature dependence of the glassy dynamics. Furthermore, we determine a crossover temperature using independent dynamical and thermodynamic criteria and compare with the theoretically predicted crossover temperature $T_a$. Relaxation dynamics is shown to obey density-temperature scaling, similar to thermodynamic properties, in terms of a variable $\Gamma$ formed by an appropriate combination of density and temperature, characteristic of IPL interactions. Finally, we show that, when the excess thermodynamic and dynamic quantities obtained at different densities are plotted as functions of the reduced temperature $T/T_a$ (or $T_a/T$), the data collapse onto master curves with excellent agreement between theory and simulation. These scaling relations provide a unified description of the thermodynamics and dynamics in IPL systems, enabling the prediction of relaxation behavior over a wide range of densities from data at a single state point.
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All authors Ankit Singh, Vinay Vaibhav, Swarn Lata Singh, Yashwant Singh

Quantum Physics

AxQM: A Textbook-Scale Benchmark for Formal Proof Synthesis in a Library of Finite-Dimensional Quantum Mechanics

Weichen Winston Yin, Jacob M. Taylor, Dirk R. Englund et al. (+1 more)

Formalizing mathematics in a proof assistant, where a machine checks every definition, statement and proof, has set a new standard of rigor. Large language models are now capable of formalizing autonomously, even at the scale of whole textbooks. We bring this standard of rigor to physics, where theoretical arguments carry idealizations that are rarely stated fully, and any logical gaps could have a cascading effect on interdependent results. Recognizing the need to evaluate autoformalization systems for physics, we release AxQM, 1,019 kernel-checkable proof-synthesis tasks over 479 items drawn from the textbook Quantum Computation and Quantum Information by Nielsen and Chuang. The tasks are stated in a custom Lean library of finite-dimensional quantum mechanics. By task count, it is the largest proof-synthesis benchmark in physics by a factor of four. AxQM is derived from a near-complete formalization of the formal portions of the textbook, so every task is guaranteed a solution, which we keep private. Grading of the benchmark is done deterministically by the Lean kernel, which checks that the proof compiles, that no sorry appears in it or in any declaration it depends on, and that it introduces no new axioms.
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All authors Weichen Winston Yin, Jacob M. Taylor, Dirk R. Englund, Frank H.L. Koppens

Cosmology and Nongalactic Astrophysics

Euclid. A two-point correlation approach to diagnosing star-related systematics in the Euclid spectroscopic survey

Euclid Collaboration: I. Risso, B. R. Granett, E. Branchini et al. (+297 more)

The Euclid spectroscopic survey will measure galaxy clustering with unprecedented precision, requiring stringent control of observational and instrumental systematics. Star-related effects may contaminate spectroscopic images through photometric persistence and imperfect masking of stars. We characterized their impact on galaxy clustering analyses, focusing on angular features identifiable in the data. We used angular and spatial auto- and cross-correlation statistics. For galaxies, we used mock spectroscopic catalogues from the EuclidLargeMocks in a 330 deg2 region of the Euclid Wide Survey (EWS). For stars, we used Gaia and 2MASS catalogues in the same area. To simulate photometric persistence, we implemented a simplified detector-level model calibrated on spectroscopic measurements and varied its strength to introduce different interloper fractions. For stellar masking, we modelled inconsistencies between the mask applied to the data and to the random catalogue. We measured star-star, galaxy-galaxy, and star-galaxy angular correlation functions using the Landy–Szalay estimator, and quantified deviations from the expected null star-galaxy correlation. We also evaluated the large-scale impact of such systematics through the three-dimensional two-point correlation function (2PCF). Photometric persistence produces a characteristic feature in the star-galaxy angular cross-correlation at scales of order 100", corresponding to the Euclid dithering pattern and grism dispersion geometry, and a spurious positive signal approximately constant up to 1{\deg}. Star-galaxy cross-correlation can detect residual persistence at contamination levels as low as 10% in a Data Release 1 spectroscopic catalogue. In contrast, stellar-mask mismatches produce strong small-scale angular signatures but have negligible impact on the large-scale 2PCF under realistic EWS conditions.
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All authors Euclid Collaboration: I. Risso, B. R. Granett, E. Branchini, A. Veropalumbo, B. Kubik, P. Monaco, J. Comparat, A. Hall, N. Aghanim, B. Altieri, A. Amara, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, A. Balestra, S. Bardelli, P. Battaglia, A. Biviano, M. Bolzonella, M. Brescia, S. Camera, G. Cañas-Herrera, V. Capobianco, C. Carbone, J. Carretero, F. J. Castander, M. Castellano, G. Castignani, S. Cavuoti, A. Cimatti, C. Colodro-Conde, G. Congedo, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, H. Degaudenzi, S. de la Torre, G. De Lucia, H. Dole, F. Dubath, X. Dupac, S. Dusini, S. Escoffier, M. Farina, R. Farinelli, S. Ferriol, F. Finelli, N. Fourmanoit, M. Frailis, E. Franceschi, M. Fumana, L. Gabarra, S. Galeotta, K. George, W. Gillard, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, L. Guzzo, S. V. H. Haugan, S. Hemmati, W. Holmes, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, M. Kümmel, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, M. Magliocchetti, G. Mainetti, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, N. Mauri, E. Medinaceli, M. Melchior, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, C. Moretti, L. Moscardini, R. Nakajima, C. Neissner, S.-M. Niemi, J. W. Nightingale, C. Padilla, S. Paltani, F. Pasian, W. J. Percival, V. Pettorino, A. Pezzotta, S. Pires, G. Polenta, M. Poncet, L. A. Popa, F. Raison, A. Renzi, J. Rhodes, G. Riccio, F. Rizzo, E. Romelli, M. Roncarelli, B. Rusholme, R. Saglia, Z. Sakr, A. G. Sánchez, D. Sapone, B. Sartoris, P. Schneider, T. Schrabback, M. Scodeggio, A. Secroun, E. Sihvola, C. Sirignano, G. Sirri, L. Stanco, P. Tallada-Crespí, A. N. Taylor, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, J. Valiviita, T. Vassallo, Y. Wang, J. Weller, G. Zamorani, F. M. Zerbi, E. Zucca, M. Ballardini, E. Bozzo, C. Burigana, R. Cabanac, M. Calabrese, A. Cappi, F. Caro, T. Castro, J. A. Escartin Vigo, J. García-Bellido, T. Gasparetto, J. Macias-Perez, R. Maoli, R. B. Metcalf, A. A. Nucita, M. Pöntinen, E. Sarpa, V. Scottez, M. Sereno, M. Tenti, M. Tucci, M. Viel, M. Wiesmann, J. A. Acevedo Barroso, Y. Akrami, I. T. Andika, S. Anselmi, M. Archidiacono, G. Aricò, F. Atrio-Barandela, M. Baes, L. Bazzanini, J. Bel, D. Bertacca, M. Bethermin, F. Beutler, L. Blot, M. Bonici, M. L. Brown, S. Bruton, B. Camacho Quevedo, P. Carrilho, C. S. Carvalho, F. Cogato, T. E. Collett, S. Conseil, S. Contarini, A. R. Cooray, P. Corcho-Caballero, B. Csizi, O. Cucciati, S. Davini, T. de Boer, F. De Paolis, G. Desprez, A. Díaz-Sánchez, S. Di Domizio, J. M. Diego, V. Duret, A. Enia, Y. Fang, A. Farina, A. Finoguenov, A. Franco, Y. Fu, K. Ganga, E. Gaztanaga, Z. Ghaffari, F. Giacomini, F. Gianotti, G. Gozaliasl, A. Gruppuso, M. Guidi, C. M. Gutierrez, H. Hildebrandt, J. Hjorth, M. Jauzac, J. J. E. Kajava, Y. Kang, V. Kansal, D. Karagiannis, J. Kim, C. C. Kirkpatrick, A. Kovács, I. Kovačić, K. Koyama, S. Kruk, M. C. Lam, F. Leclercq, L. Legrand, M. Lembo, G. Leroy, G. F. Lesci, J. Lesgourgues, T. I. Liaudat, L. Linke, S. J. Liu, F. Mannucci, F. R. Marleau, C. J. A. P. Martins, M. Miluzio, G. Morgante, S. Nadathur, K. Naidoo, A. Navarro-Alsina, S. Nesseris, L. Nicastro, F. Oppizzi, F. Pace, D. Paoletti, G. Parimbelli, F. Passalacqua, K. Paterson, L. Patrizii, C. Pattison, R. Paviot, A. Pisani, D. Potter, G. W. Pratt, S. Quai, M. Radovich, G. Rodighiero, W. Roster, S. Sacquegna, M. Sahlén, D. B. Sanders, A. Schneider, D. Sciotti, E. Sellentin, S. Serjeant, L. C. Smith, J. G. Sorce, I. Szapudi, M. Talia, K. Tanidis, C. Tao, F. Tarsitano, G. Testera, R. Teyssier, S. Tosi, A. Troja, C. Uhlemann, C. Valieri, A. Venhola, D. Vergani, G. Verza, S. Vinciguerra, M. von Wietersheim-Kramsta, N. A. Walton, L. Wang, A. H. Wright

Quantum Physics

Fanout Complexity of Symmetric Boolean Functions in $\mathsf{QAC}^0$

Boyan Xu and Lvzhou Li

Whether $\mathsf{QAC}^0$ can compute $\mathtt{PARITY}_n$ remains open. Computing $\mathtt{PARITY}_n$ is equivalent to implementing $\mathtt{FANOUT}_n$ under $\mathsf{QAC}^0$ reductions. This raises a more general question: for an arbitrary symmetric Boolean function $f:\{0,1\}^n\to\{0,1\}$, what fanout size is necessary and sufficient for computing $f$ in $\mathsf{QAC}^0$? We show that the answer is exactly the transition radius $\rho(f)$: computing $f$ and implementing $\mathtt{FANOUT}_{\rho(f)}$ are equivalent under $\mathsf{QAC}^0$ reductions. In particular, if $\rho(f)\ge n^\delta$ for some constant $\delta>0$, then computing $f$ is $\mathsf{QAC}^0_{\mathrm{f}}$-complete. Combined with Paturi's theorem, our characterization implies that if $\mathtt{PARITY}_n \notin \mathsf{QAC}^0$, then any Boolean function in $\mathsf{QAC}^0$ of approximate degree $n^{1/2+\Omega(1)}$ must be nonsymmetric.
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Materials Science

Interfacial Accommodation as a Candidate Ductility Pathway in Intermetallic-Rich Alloys

Avik Mahata

Heterophase interfaces are increasingly recognized as active participants in plastic deformation, yet quantitative methods for comparing their strain-accommodation capacity remain limited. Here, we present an atomistic framework for quantifying interface-mediated strain accommodation using molecular dynamics simulations. Interface broadening, roughening, and migration are extracted from atomistic trajectories and combined into an Interface Accommodation Index, with a normalized counterpart accounting for differences in initial interface structure. A weighting sensitivity analysis demonstrates that the relative ranking of interfaces is robust to the specific form of the index. The framework is demonstrated for three experimentally motivated interfaces, Al/Al3Ti, Al/Al9M2, and Al9M2/Al3Ti (M = Fe, Co, Ni), under tensile, compressive, and shear loading. Bulk simulations show that Shockley partial dislocations dominate plastic deformation, with alloy chemistry governing the transition toward mixed-character dislocation networks. Tensile loading produces the greatest interface accommodation, while shear produces comparatively limited structural evolution. The Al9M2/Al3Ti interface exhibits both the highest yield resistance and the largest accommodation response, suggesting that intermetallic-intermetallic interfaces can simultaneously sustain load and redistribute strain. These simulations quantify structural accommodation rather than ductility or fracture directly; their connection to macroscopic ductility therefore requires experimental validation. The framework provides a transferable approach for comparing interface accommodation in multiphase alloys and identifies interface chemistry and crystallography as important design variables for damage-tolerant structural materials.
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Nuclear Theory

Signals for Nuclear Solid-Liquid Phase Transition in Clustering Nuclei

Xi-Guang Cao, Yong-Hao Jin, Chun-Wang Ma et al. (+2 more)

The nuclear phase diagram remains a fundamental challenge, where uncovering how the cluster degree of freedom evolves with temperature and energy is essential to understand the intriguing crossover between cluster, nucleon, and nuclear astrophysics. A new first-order phase transition, the nuclear solid-liquid phase transition (SLPT), emerges spontaneously from nucleonic degrees of freedom in low-energy heavy-ion collisions. Clear signals of the SLPT are identified as a region of negative heat capacity in smaller systems (e.g., $^{12}\text{C} + ^{12}\text{C}$ and $^{16}\text{O} + ^{12}\text{C}$) and a caloric plateau in larger systems (e.g., $^{28}\text{Si} + ^{12}\text{C}$ and $^{40}\text{Ca} + ^{12}\text{C}$), along with prominent behaviors in the number of fragment species and information entropy. Moreover, the pairwise distance probability density function provides a direct spatial fingerprint of the melting, where long-range crystalline $\alpha$-cluster peaks vanish above the transition temperature, giving way to a liquid-like distribution. This new phase transition unifies the many-body dynamics of finite constituents, extending from nanoscale clusters to nuclear systems. Beyond advancing nuclear structure and phase diagrams, these insights offer profound implications for astrophysics, notably linking structural evolution to astrophysical phase transitions via nuclear cluster dissolution in supernovae.
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All authors Xi-Guang Cao, Yong-Hao Jin, Chun-Wang Ma, Wen-Bo Liu, Yu-Gang Ma

Exactly Solvable and Integrable Systems

A note on the integrability status of a 'mysterious' case of a quadratic Hamiltonian

Ognyan Christov

We present a simple algebraic proof of meromorphic non-integrability of a 'mysterious' case of a quadratic Hamiltonian studied by Sokolov and Wolf. The result is obtained by applying the Morales-Ramis method, based on differential Galois theory.

Strongly Correlated Electrons

Environment-assisted transport in a strongly correlated boundary-driven Fermi-Hubbard chain

Hakan Yeler and Özgür Çak{\i}r

We study steady-state transport in a one-dimensional Fermi-Hubbard chain coupled to particle reservoirs at the boundaries and to local dephasing baths at each site, using the time-evolving block decimation (TEBD) method to solve the Lindblad master equation. In the absence of dephasing, the current exhibits two well-separated maxima as a function of the boundary driving rate, reflecting the distinct charge and spin energy scales of the strongly correlated regime. Upon introducing dephasing, we find two distinct dephasing-induced transport-enhancement regimes, in contrast to the single enhancement previously reported for spinless fermions. Analysis of the non-equilibrium steady state in the Hamiltonian eigenbasis reveals that the two regimes originate from distinct dephasing-induced redistribution processes: the first involves redistribution within the uppermost Hubbard band, while the second involves transitions between Hubbard bands. Our results demonstrate how many-body correlations shape the interplay between coherent driving, dephasing, and quantum Zeno physics in strongly correlated open systems.
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Chemical Physics

Polarizable Embedding for Photoelectron Spectroscopy and Photoelectron Circular Dichroism in Solution: Core-Level Ionization of Aqueous Alanine

Giovanni Nottoli and Piero Decleva. Chiara Cappelli

We present a polarizable quantum-mechanics/molecular-mechanics formulation for the calculation of molecular photoionization observables in solution. The approach couples the static-exchange density-functional-theory treatment of bound and continuum electronic states with a fully atomistic polarizable embedding described with the fluctuating-charge force-field. The fluctuating charges are determined self-consistently with the ground-state quantum-mechanical density and are subsequently included in the static-exchange Hamiltonian to account for the outgoing electron. The numerical behavior of the coupled scheme is validated and applied to the X-ray photoelectron spectrum and photoelectron circular dichroism of zwitterionic L-alanine in aqueous solution, using an ensemble of configurations extracted from molecular dynamics. Calculated spectra reproduce experimental profiles remarkably well, demonstrating that atomistic solvent structure and environmental polarization must be treated together to reliably model photoelectron observables in aqueous solution.
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Earth and Planetary Astrophysics

Stability of circumbinary planets: the role of binary properties and migration scenarios

Romain Grane, Nicolás Cuello, Mario Sucerquia et al. (+4 more)

Among the thousands of exoplanets detected to date, only a very small fraction are classified as circumbinary planets, and this number becomes negligible when considering low-mass planets. This rarity may partly result from observational biases, but also from the challenging dynamical environment of binary systems, which can prevent the long-term stability of planetary orbits. It is therefore essential to investigate the conditions that enable the formation and survival of stable circumbinary planets, particularly in the low-mass regime. To this end, we performed N-body simulations coupled with a planet migration prescription to study the post-formation dynamics of two 10 Earth-mass circumbinary planets in a protoplanetary disc. Based on more than 1,000 simulations, we find that inward migration can, in some cases, be halted through resonance capture with the binary. In contrast to some previous purely N-body studies, these configurations appear to remain stable over long timescales. We further find that the binary mass ratio $q_B$ and eccentricity $e_B$ strongly influence the stability of multi-planet systems. Within the explored parameter space, some regions support long-term stability, whereas others are highly unstable. These stability regions are also sensitive to the migration timescales, and therefore to disc properties and planetary masses. Finally, our simulations suggest that systems in which two planets enter resonance while migrating together are more likely to form stable multi-planet configurations, particularly around highly eccentric binaries. These results provide a first step toward identifying binary star systems that are most promising for hosting multiple low-mass circumbinary planets.
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All authors Romain Grane, Nicolás Cuello, Mario Sucerquia, Emmanuel Gianuzzi, Milenne Ávila-Bravo, Carolina Charalambous, Amaury H. M. J. Triaud

Materials Science

Semiclassical thermoelectric transport in disordered Dirac electron system Ag2Te

Kentaro Kuga, Keisuke Hirata, Daiki Goto et al. (+3 more)

We investigated the thermoelectric effects of the Dirac electron system Ag2Te under magnetic field. Our anal-ysis based on the Boltzmann semiclassical model associated the disorder with the unconventional magnetic field responses such as linear magnetoresistance, linear Nernst effect, step-like Nernst effect, and sign change in Nernst effect. The analysis also revealed the impurity band near the Fermi energy. We simultaneously clari-fied the serious impact of the thermal Hall effect on the measurement of the Nernst effect, and we proposed the definitive solution. Our careful measurement and analysis will be the standard for the thermoelectric study under magnetic field.
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All authors Kentaro Kuga, Keisuke Hirata, Daiki Goto, Ryogo Ishihara, Masaharu Matsunami, Tsunehiro Takeuchi

Materials Science

Anharmonic Lattice Dynamics and Anisotropic Electron-Phonon Coupling in Quasi-1-Dimensional Charge Density Wave Ta2NiSe7

Prithwija Mandal, S. Nanthini, Aditya Singh et al. (+4 more)

The microscopic origin of charge density wave formation in quasi one dimensional Ta2NiSe7 remains actively debated, particularly regarding the relative contributions of Fermi surface nesting, electron phonon coupling, and lattice instabilities. Here, we combine temperature and orientation dependent polarized Raman spectroscopy with first principles calculations to uncover the anisotropic electronic and lattice interactions governing the CDW state in Ta2NiSe7. Heat capacity and electrical transport measurements identify an incommensurate CDW transition at 61 K. Raman spectroscopy reveals pronounced in plane anisotropy, with e ph coupling strength along intrachain b axis exceeding five times that along interchain c axis, whereas lattice anharmonicity is enhanced by threefold along c axis. First principles calculations identify Ta2 Se octahedral vibrations and Ta Se electronic states near the Fermi level as dominant channels mediating the anisotropic e ph interaction. Exceptionally strong and directional e ph coupling along b axis establishes lattice driven electronic instability as the primary mechanism underlying CDW modulation and highlights the dominance of intrachain interactions in strongly coupled Ta2NiSe7. Despite this strong coupling, the CDW remains incommensurate, indicating that lattice anharmonicity provides an additional degree of freedom. Enhanced anharmonicity along c axis suggests that anisotropic phonon phonon interactions reshape the free energy landscape and contribute to stabilizing incommensurate phase. These findings reveal a cooperative interplay between anisotropic e ph coupling and lattice anharmonicity in governing CDW formation in low dimensional quantum materials.
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All authors Prithwija Mandal, S. Nanthini, Aditya Singh, Kewal S. Rana, Dibyendu Dey, Kanishka Biswas, Ajay Soni

Solar and Stellar Astrophysics

Can isolated binaries form unequal-mass binary black-hole mergers with a high-spin primary black hole?

Xiao-Tian Xu, Dong Lai and Bin Liu

GWTC-5 has revealed a subpopulation of merging binary black holes (BBHs) with a high-spin primary black hole (BH) and possibly unequal BH masses. GW241110 additionally exhibits a large spin-orbit misalignment, which suggests a hierarchical-merger origin. However, other formation scenarios are possible or even likely, especially for events without constraints on spin-orbit misalignment. As an alternative to hierarchical mergers, we investigate whether binary evolution can produce unequal-mass BBH mergers with a high-spin primary BH. Rather than performing comprehensive population-synthesis calculations, we examine the evolutionary pathways of forming merging BBHs and assess their uncertainties. We identify two possible pathways for producing unequal-mass BBHs with a high-spin primary. In initially wide binaries, mass-ratio reversal can make the tidally spun-up second-born BH both more massive and more rapidly rotating than the first-born BH; alternatively, in an initially close, unequal-mass binary, the primary star may evolve chemically homogeneously, while the secondary star evolves normally, producing a high-spin first-born BH that is more massive than its companion. Generally, large spin-orbit misalignment can be produced by large natal kicks or tertiary-induced nodal precession and/or Zeipel-Lidov-Kozai oscillations. We conclude that hierarchical mergers are not uniquely required to produce unequal-mass BBHs with a high-spin primary BH, although each isolated-binary pathway faces important theoretical constraints. Future detections of more merger events with primary BH spins around 0.7 would discriminate between binary evolution and hierarchical merger origin.
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Disordered Systems and Neural Networks · Cross-listed from cs.LG

Coarse-Graining Hidden Representations: Unsupervised Neuron Selection via Mapping Entropy

Margherita Mele, Andrea Castagna, Roberto Menichetti et al. (+2 more)

Overparameterized neural networks carry far more hidden units than a task nominally requires, raising the question of which neurons are essential and whether that distinction is legible in the representation itself, without labels or gradients. We cast neuron selection as the problem of coarse-graining the hidden layer by retaining a subset of its neurons, and score each putative selection by the mapping entropy (ME). This quantity measures the loss of discriminatory power inherent in discarding part of the network neurons, and the selection that minimises the ME is taken as particularly informative. This criterion is fully unsupervised, in that it depends only on hidden-activation statistics. In teacher-student networks, ME optimisation recovers the minimal teacher-consistent representation and retains extra units in proportion to the hidden layer's residual variability; in a non-linear Gaussian process task, it selects coherent functional-class mappings whose preferred class shifts across training. On this task and on translation-augmented MNIST, ME-selected subnetworks outperform random subsets of equal size, most clearly under strong compression - linking configurational distinguishability to predictive performance.
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All authors Margherita Mele, Andrea Castagna, Roberto Menichetti, Raffaello Potestio, Alessandro Ingrosso

Quantum Physics

Non-local games and communication complexity with noisy entanglement

Srijita Kundu and Olivier Lalonde

We study the impact of noise on the theories of quantum nonlocality and entanglement-assisted communication complexity. We consider non-local games and entanglement-assisted communication complexity in a model where Alice and Bob may share arbitrarily many noisy EPR pairs. We study four noise models: depolarizing noise, unital noise, biased reset noise, and erasure noise. Our results are as follows: 1. We upper bound the value of the CHSH game under all these noise models in terms of the noise parameter, without any assumptions on the measurements used in the strategy. 2. We prove a parallel repetition theorem for general non-local games under all noise models except biased reset noise; we prove an improved parallel repetition theorem for unique games. Our parallel repetition rate is smaller than the quantum parallel repetition rate for CHSH in a nontrivial noise regime. 3. Using our unique-game parallel repetition theorem and a relation defined by the CHSH game, we prove a separation between communication complexity with noisy vs noiseless entanglement. This implies an $\Omega(n)$ two-way communication lower bound for distilling $n$ EPR pairs from noisy EPR pairs, in the same nontrivial noise regime. 4. We show that any interactive entanglement-assisted communication protocol can be simulated by an SMP communication protocol with noisy shared randomness, with an exponential blowup in communication. This generalizes a known result on the simulation of noiseless shared randomness with noisy shared randomness. 5. We show a polynomial lower bound on the number of copies of noisy EPR pairs required to compute the Equality function with constant communication, under all four noise models. The previous result gives a matching upper bound, and moreover, this answers an open question in the literature on whether logarithmically many noisy shared bits suffice for communication.
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Statistical Mechanics

On the growth of operator entanglement in brickwork circuits with Yang–Baxter gates

Balázs Pozsgay

We study the operator entanglement of local operators in one-dimensional brickwork circuits whose two-site gate satisfies the braid relation; throughout this work, we call such a gate a Yang–Baxter gate. We establish upper bounds for several structured, overlapping classes of Yang–Baxter gates. We show that the operator Schmidt rank remains uniformly bounded in time for all qubit Yang–Baxter gates and, in arbitrary local dimension, for permutation gates obtained from non-degenerate Yang–Baxter maps. We also show that it grows at most polynomially for involutive dual-unitary Yang–Baxter gates and for arbitrary phase dressings of permutation gates obtained from non-degenerate Yang–Baxter maps. These results imply, respectively, constant and logarithmic upper bounds on the operator entanglement. Conversely, we construct a seven-state involutive Yang–Baxter gate without dual unitarity and a one-site operator whose exact operator Schmidt rank grows exponentially, although the corresponding operator entropies remain undetermined. Entanglement growth in the general Yang–Baxter case remains open. All proofs and selected examples were constructed by ChatGPT 5.6 Sol.
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Materials Science

Symmetry-protected triplet Weyl complexes

Yun-Yun Bai, Ke-Xin Pang, Yan Gao et al. (+2 more)

The Nielsen-Ninomiya theorem dictates that Weyl nodes must appear in pairs of opposite chirality to preserve global charge neutrality. However, in crystals, specific crystalline symmetries can stabilize multi-Weyl nodes, circumventing this pairwise constraint and enabling compensated Weyl complexes with mixed chiral charges. The minimal configuration of this type is a triplet Weyl complex (TWC), comprising exactly three Weyl nodes. Here, we systematically investigate the symmetry conditions required to realize TWCs. By screening all 1651 magnetic space groups (MSGs) in both spinless and spinful systems, we establish that: (i) Only TWCs with charge magnitudes of $\{1,1,2\}$ and $\{1,2,3\}$ are permitted; (ii) the $\{1,1,2\}$ configuration can be realized in 166 spinless MSGs and 70 spinful MSGs; and (iii) the $\{1,2,3\}$-TWCs, which has not been reported before, can occur in 10 MSGs for both spinless and spinful cases. We explicitly demonstrate the existence of $\{1,2,3\}$-TWC in a tight-binding model. Furthermore, we present the first electronic realization of $\{1,1,2\}$-TWC topological semimetal state in the chiral carbon allotrope DZQH-C$_{36}$, in which the three Weyl nodes form a collinear configuration, leading to a characteristic “S”-shaped surface Fermi arc pattern. Our findings uncover novel topological states featuring mixed chiral charges and provide guidance for exploring their physics in concrete material systems.
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All authors Yun-Yun Bai, Ke-Xin Pang, Yan Gao, Weikang Wu, Shengyuan A. Yang

General Relativity and Quantum Cosmology

Probing Neutron Star Equation of State Universality with Gravitational Waves

Praveer Tiwari, Ajit Kumar Mehta and K. G. Arun

Current neutron star equation-of-state inferences assume that a common equation of state describes all neutron stars. However, {poorly understood dense-matter physics may give rise to distinct long-lived stellar subpopulations following different mass–tidal-deformability relations, invalidating this assumption. In this Letter, we demonstrate that next-generation gravitational-wave observatories enable neutron star equation-of-state universality to be transformed from an assumption into a testable hypothesis. By combining hierarchical Bayesian inference with a piecewise-polytropic parametrization of the neutron star equation of state, we establish a framework for testing equation-of-state universality with next-generation gravitational-wave observatories. We find that about 30 (50) loud binary neutron star mergers with network SNRs above 100 are sufficient to provide compelling evidence for departures from equation-of-state universality, even if only 20% (10%) of the population exhibits one of the representative non-universality parametrizations considered here.
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High Energy Physics (Phenomenology)

The axial-vector nucleon form factor in the meson dominance picture: the role triangle singularities from a dispersive view

Enrique Ruiz Arriola and Pablo Sanchez-Puertas

The nucleon axial form factor is analyzed in terms of a dispersion relation comprising chiral perturbation theory (ChPT) and perturbative QCD (pQCD) in the low- and high-momentum regimes respectively, which implies a set of superconvergence sum rules for the $A \to N \bar N$ spectral function. In the timelike region below the $N \bar N$ production threshold we include the $a_1$ and $a_1'$ resonances, with finite-width effects modeled through $\rho \pi$ and $\sigma \pi$ intermediate states. Above the $N \bar N$ threshold, we model an infinite tower of radially excited $1^{++}$ resonances with a non-integer power fall-off, eventually matching pQCD. In this setup, we find that both the ChPT and pQCD contributions are tiny. In turn, the dominant $\rho\pi$ triangle provides the leading deviations from axial meson dominance. Our calculation is not a fit; it contains parameters with a priori uncertainties estimates. The axial radius is predicted to be $r_A^2 =(0.28-0.33)~\textrm{fm}^2 = ( 0.47-0.57~\textrm{fm})^2$ in agreement with recent lattice QCD results but inconsistent with the MINER$\nu$A determination. A simple semiempirical formula is provided accounting for the main physical effects.
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Lattice Field Theory

Equation of state of dense magnetized QCD matter via a robust analytic continuation

S. Borsányi, B. B. Brandt, G. Endrődi et al. (+4 more)

We compute the equation of state of dense and magnetized strongly interacting matter using lattice QCD at a non-zero value of the lattice spacing. Our simulations employ $2+1+1$ dynamical flavors of rooted staggered quarks with masses tuned to the physical point. To conform with experimental constraints, we impose strangeness neutrality and isospin asymmetry on our observables. We circumvent the sign problem by simulating imaginary values of the chemical potential and applying the $T'$-expansion scheme to carry out the analytic continuation of our observables to the real chemical potential axis. This novel scheme, adapted to the setup with nonzero magnetic fields, is demonstrated to produce significantly smaller systematic errors in the final observables, compared to the standard analytical continuation at fixed temperature, allowing for better-controlled extrapolations. Our results for the pressure, the entropy density and the interaction measure are tabulated for direct use in heavy-ion phenomenology applications.
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All authors S. Borsányi, B. B. Brandt, G. Endrődi, J. N. Guenther, G. Markó, M. A. Petri, A. D. M. Valois

Earth and Planetary Astrophysics

Modelling Palomar Transients: Constraints from Reflection Geometry and Orbital Altitude

Beatriz Villarroel, Alina Streblyanska, Hichem Guergouri et al. (+3 more)

Recent searches of digitised photographic plates from the Palomar Observatory have uncovered tens of thousands of short-lived transients, each visible in only a single exposure. Their morphologies indicate sub-second flashes, consistent with specular reflections from highly reflective objects in near-Earth orbits. In this paper, we present a modelling study using geometric shadow modelling, Monte Carlo simulations, and photometric constraints to infer their physical properties. We examine the observed groupings and alignments, which appear to be consistent with sudden changes in attitude. Assuming a spherical-shell model, the angular profile of the measured transient deficit around the antisolar point is consistent with a population at characteristic altitudes of $\sim 20,000$–25,000 km. A complementary estimate, based on the altitude dependence of the global Earth-shadow deficit, yields a broader characteristic range of $\sim$ 20,000–35,000 km above Earth's surface, extending into the geosynchronous orbital (GSO) region. Under simplified geometric and photometric assumptions and assuming $\sim20{,}000$ to $35{,}786$ km above the Earth's surface, the inferred sizes of the specularly reflecting facets range from centimetre scales up to $\sim3$ m, with characteristic flash durations of $\sim320$ ms and slow rotation rates. We explore both natural and non-natural toy models consistent with the data, and provide constraints to guide future observational searches.
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All authors Beatriz Villarroel, Alina Streblyanska, Hichem Guergouri, Brian Doherty, Matthew Shultz, Stephen Bruehl