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Physics

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Friday 21 August

High Energy Physics (Experiment)

On-Detector Machine Learning for Beam-Induced Background Rejection at a 10 TeV Muon Collider

Daniel Abadjiev, Eliza Howard, Tsz Ngong You et al. (+35 more)

A 10 TeV Muon Collider is a compelling candidate for a future energy-frontier facility, offering unprecedented opportunities to explore the fundamental laws of particle physics. Muon decays in the collider ring produce intense beam-induced background (BIB) that can overwhelm detector occupancy and exceed readout bandwidth constraints. We investigate the potential of on-detector Machine Learning for BIB rejection in the vertex detector, exploiting pixel cluster shapes to distinguish background from collision products. We study three classes of lightweight neural-network architectures, and evaluate their implementation feasibility using high-level synthesis. Selected architectures achieve 88 to 90% data reduction at 99% signal efficiency, while requiring hardware resources compatible with potential ASIC implementation. These results demonstrate the potential of performing substantial BIB rejection directly in the pixel readout, providing a strategy for meeting the tracker readout requirements at a future Muon Collider.
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All authors Daniel Abadjiev, Eliza Howard, Tsz Ngong You, Ryan Michaud, Benjamin Ryan Roberts, Benjamin Rosser, Karri Folan Di Petrillo, Doug Berry, Arghya Ranjan Das, Jennet Dickinson, Giuseppe Di Guglielmo, Harshul Gupta, Farah Fahim, Abhijith Gandrakota, Lindsey Gray, James Hirschauer, David Jiang, Shiqi Kuang, Ron Lipton, Mira Littmann, Miaoyuan Liu, Nicholas Manganelli, Petar Maksimovic, Corrinne Mills, Mark S. Neubauer, Aidan Nicholas, Benjamin Parpillon, Jannicke Pearkes, Adam Quinn, Danush Shekar, Ricardo Silvestre, Chinar Syal, Morris Swartz, Nhan Tran, Amit Trivedi, Keith Ulmer, Mohammad Abrar Wadud, Benjamin Weiss

Cosmology and Nongalactic Astrophysics

Diversity of Galaxy Centers from Small-Scale Isocurvature

Jessica N. Lopez-Sanchez and Wen Yin

The observed diversity of galaxy centers motivates the possibility that the local dark matter composition may vary among galaxies. In conventional multicomponent dark matter scenarios, however, large stochastic variations in the relative abundances are not generically expected, with the cold component typically remaining dominant. We perform $N$-body simulations with a subdominant ultralight dark matter component carrying significant large-amplitude small-scale isocurvature perturbations. We find that although nonlinear evolution largely homogenizes its fraction on galactic scales,ultralight dark matter can still be enhanced and even dominate the centers of small halos because large initial ultralight dark matter fluctuations seed early potential wells that later form halo centers. The ultralight-dominated region can extend beyond $0.01R_{\rm vir}$ and account for more than half of the central dark matter density, even for a cosmological ultralight dark matter fraction below $O(10\%)$. This central segregation provides a possible route to stochastic cusp–core diversity, potentially explaining the observed diversity of galaxy centers.
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Chemical Physics

Machine learning predictions of the Hessian matrix for peptides chains and small proteins

Giorgio Domenichini

Molecular Hessians have a key role in describing molecular vibrations, trajectories and optimization paths. An explicit calculation of them through standard quantum mechanical methods can be computationally expensive for medium-large systems, and in many applications not even needed. Machine learning methods can be a shortcut to tackle efficiently the computational difficulties. This paper will present a ML model able to predict the Hessian matrix of biological system made of thousands of atoms. The method, based on learning the Hessian in internal coordinates is intrinsically invariant to molecular rotations and translations, and has a very good scaling with the systems' size. The training was performed on a dataset of simple aminoacids, as they constitute the building blocks of larger proteins. From the predicted Hessian matrix it is possible to calculate thermochemical properties within the harmonic approximations, among them enthalpies, entropies, Gibbs' free energies, and zero point vibrational energies.
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Quantum Physics

Hypothesis testing between quantum ensembles

Jian Yao and Quntao Zhuang

Quantum state ensembles are important in quantum information processing. For example, quantum $t$-designs model highly entangled states in complex systems, while projected ensembles appear in generative quantum machine learning and studies of thermalization. With their sample state accompanied by a classical label, these ensembles contain operational information beyond their average density operators. Yet an ensemble differs from a classical-quantum state because it is invariant under permutations of labels. We formulate binary hypothesis testing between finite quantum ensembles and derive fundamental limits on error probability. Given an observed label pattern, we show that the joint sampled state can be described by power-weighted ensemble moments. This yields the Bayes-optimal measurement and exact finite-sample error, revealing that discrimination is governed by the full moment hierarchy up to the number of samples. In the many-sample limit, we derive Chernoff bounds and obtain exact error exponents for finite uniform pure-state ensembles. We apply these results to optical communication and $t$-designs. For finite uniform pure-state $t$-designs with large $t$, the maximal discrimination exponent scales sharply as $\sim t^{-2}$, while equal-prior fixed-error testing requires $\sim t^2$ samples.
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High Energy Astrophysical Phenomena

VLASS Discovery of a Luminous Galactic Radio Transient Evolving on Decade Timescales

Jessie M. Miller, Gregg Hallinan, Dillon Dong et al. (+10 more)

We present a multiwavelength analysis of the radio transient VT J1906+0849, discovered as a 70 mJy source in Epoch 1 of the Very Large Array Sky Survey (VLASS), 21 yr after an NRAO VLA Sky Survey (NVSS) non-detection. Radio observations reveal the source was first detected in 2005, peaking at $\gtrsim200$ mJy in 2014, then declining until a late 2025 rebrightening. The transient sits at a Galactic latitude of $\approx0.74^\circ$ and the properties of its optical-infrared counterpart support a Galactic origin. At $d\gtrsim15$ kpc, the extreme radio luminosity is likely powered by sustained accretion onto a compact object. However, a Swift-XRT non-detection shows it is X-ray faint relative to the Galactic X-ray binary population, and the radio emission is distinct from X-ray binaries in its temporal and spectral behavior. Broadband radio spectra suggest synchrotron self-absorption, but size constraints from equipartition and very long baseline interferometry show little to no expansion in the radio-emitting region over 5+ yr, despite significant spectral evolution. Near-infrared spectroscopy reveals a single broad emission line with a stable centroid but variable width and luminosity. We attribute this feature to blueshifted Br$\gamma$ tracing a persistent asymmetric $\approx2000$ km s$^{-1}$ outflow. These properties are unlike any previously identified Galactic radio source. One possible interpretation is that VT J1906+0849 is a young analog of the microquasar SS 433, with a dense disk wind confining a continuously powered synchrotron outflow. This jet-wind interaction explains the compact, slowly expanding radio source and may contribute to the absence of bright X-ray emission.
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All authors Jessie M. Miller, Gregg Hallinan, Dillon Dong, Adolfo S. Carvalho, S. T. Myers, Jean Somalwar, Casey Law, B. M. Gaensler, Vikram Ravi, Laura Chomiuk, Assaf Horesh, Delina Levine, Yuyang Chen

High Energy Physics (Theory)

Inclusive Radiation and Backreaction from the Phase-Space S-Matrix

Nathan Moynihan

We develop a phase-space description of classical scattering in which the matter sector of the Dyson S-matrix is partially Weyl transformed while the radiation sector remains operator valued. The resulting S-matrix symbol provides a common origin for several classical observables: we show that the inclusive waveform, the classical displacement in phase-space (i.e. the impulse and position shift), and the angular momentum arise as different projections of the same object. We show that the partially Weyl-transformed $S$-matrix admits an exponential organisation in terms of an elastic phase and connected radiation kernels, while its inclusive one-point projection admits a coherent representative with waveshape $\alpha_I$ describing classical radiation, extending our recent proposal. Furthermore, we show explicitly how nonlinear gravitational memory can be derived from an inclusive coherent waveshape. The dependence of the waveshape on the hard scattering data naturally leads to a quantum geometry, including an induced Berry connection on the space of waveforms, whose contribution to the phase-space displacement captures both radiation-reaction and static-field effects. We illustrate this structure by deriving static contributions to the position shift and field angular momentum in both scalar QED and gravity.
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Strongly Correlated Electrons

Ultralow-Field Triplon Condensation in a Spin-Ladder Magnet

Ankit Labh, Ross H. Colman, Jakub Šebesta et al. (+12 more)

We realise the first ultralow-field Bose-Einstein condensation of triplons in a spin-ladder magnet, uncovering a quantum critical point at only $\mu_0 H_{c1}=0.17$ T in Henmilite ($\mathrm{Ca_2Cu(OH)_4[B(OH)_4]_2}$). Unlike dimer magnets, a ladder retains extended one-dimensional correlations in its gapped parent state, making this limit strongly fluctuation dominated. Thermodynamic, magnetoelastic, $\mu$SR, and neutron-diffraction measurements overturn the previous assignment of zero-field antiferromagnetic order, establishing a quantum-disordered coupled-ladder parent state with persistent low-energy dynamics. The weak low-temperature anomaly instead marks a gap-controlled crossover from the correlated ladder regime into the activated quantum-disordered state. These measurements further reveal an exceptionally asymmetric ordered dome extending to $\mu_0 H_{c2}\simeq 8.2$ T. Quantum Monte Carlo simulations for the relevant spin Hamiltonian place Henmilite just on the gapped side of the zero-field ladder-ordering instability, naturally accounting for the strong separation between the exchange and residual-gap scales and the tiny critical field. Our findings extend ultralow-field triplon condensation beyond the dimer paradigm and establish Henmilite as a platform for controlled tuning across quantum criticality in a fluctuation-dominated spin ladder.
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All authors Ankit Labh, Ross H. Colman, Jakub Šebesta, Noah Oefele, Elsa Lhotel, Adam Berlie, Paul Steffens, Oksana Zaharko, Pascal Manuel, Iurii Kibalin, Philipp Gegenwart, Dominik Legut, Johanna K. Jochum, Alexander A. Tsirlin, Petr Čermák

Chemical Physics

Machine-Learned NMR Shieldings in Molecular Solids with Built-In Hybrid-Functional Molecular Corrections

Matthias Kellner, Ruben Rodriguez-Madrid, Jacob B. Holmes et al. (+4 more)

Fast and accurate chemical shielding estimators are essential for shielding-driven Nuclear Magnetic Resonance (NMR) crystallography. Machine-learning models for shielding predictions have matured significantly and today are primarily limited by the electronic structure reference data they are trained on. Here, we introduce ShiftML4, a shielding-tensor model trained directly on monomer-corrected calculations that approximate PBE0, rather than the PBE reference targeted by earlier ShiftML models. ShiftML4 is trained on a diverse set of structures containing 12 of the most common NMR nuclei in molecular organic solids. On experimental benchmark sets, the 13C isotropic RMSE against experiment is 1.67 ppm, compared with 2.34 ppm for GIPAW-PBE on the same geometries. ShiftML4 gives a similar 1H prediction RMSE to ShiftML3 (0.5 ppm) and improves the 15N RMSE from 7.24 to 6.08 ppm. The model also reduces errors in the shielding-tensor anisotropy, with an RMSE of 4.63 ppm on 13C CSA principal components against 5.85 ppm for GIPAW. The improvements in prediction accuracy are retained on better geometries. Basing shift predictions on structures relaxed with PET-MOLS, a recent machine-learned interatomic potential that reaches approximate hybrid-DFT geometries in seconds, lowers the ShiftML4 errors further to 0.48 ppm (1H), 1.49 ppm (13C) and 3.66 ppm (15N).
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All authors Matthias Kellner, Ruben Rodriguez-Madrid, Jacob B. Holmes, Pablo A. Unzueta, Gregory J. O. Beran, Lyndon Emsley, Michele Ceriotti

Quantum Physics

Tomographic Limits of the Petz Recovery Map

Peter Sidajaya, Clive Cenxin Aw, Mingxuan Liu et al. (+1 more)

The Petz recovery map is considered one of the key candidates for the quantum analogue of Bayesian inference and Jeffrey's conditionalization. Since, there seems to be a natural connection between Bayesian inference and the notion of state tomography, it is natural to ask if the Petz recovery can be used for this latter task. In this paper, we discuss such recent results on iterated Petz recovery and relate them to Bayesian approaches to quantum state tomography. We highlight the limitations of direct Petz iteration and show how an extended Petz construction, by lifting the inference problem to a classical distribution over candidate quantum states, recovers the structure of Bayesian and maximum likelihood tomography. This provides perspective on the modifications or nuances required for a Petz approach to quantum retrodiction to perform quantum state tomography.
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All authors Peter Sidajaya, Clive Cenxin Aw, Mingxuan Liu, Valerio Scarani

Mathematical Physics

The spin-1/2 Heisenberg XXZ chain and the Lorentz mirror model with loop weight 2

Kieran Ryan

We prove that for the spin-1/2 Heisenberg XXZ chain in the range $\Delta\in[-1,1/2]$, the ground state on the torus of length $L$ converges to an infinite volume ground state $\langle\cdot\rangle$ as $L\to\infty$, and that the spin-spin correlation $\langle S_0^{(1)}S_x^{(1)}\rangle$ decays polynomially fast in $x$. In the range $\Delta\in[-1,0]$ we have the stronger results: that the convergence holds for several finite-volume, finite temperature states, that $L$ and $\beta=1/T$ can be taken to infinity in any order, that the convergence holds on (Euclidean) dynamic correlators, and that $\langle S_0^{(1)}S_x^{(1)}(t)\rangle$ decays to zero in $|(x,t)|$, and cannot decay exponentially fast. The convergence of the ground state in infinite volume is known rigorously by Bethe Ansatz methods, while our correlation decay results (apart from the points $\Delta=0,-1$), the convergence on dynamic correlators and the interchangeability of limits are new at the rigorous level. Moreover our methods are new and do not use any Bethe Ansatz techniques, using only the following related probabilistic models. In the Lorentz mirror model with loop weight 2, a model of random loops on the square lattice, in a large range of parameters we prove that connection probabilities tend to 0, and do so polynomially fast in the symmetric case of the model. Our proof uses two couplings of this mirror model with the six-vertex model, one of which is new. The main input is the delocalisation of the height function of the six-vertex model proved by several authors. We further prove that the height function of a certain space-time version of the six-vertex model delocalises and then prove through analogous couplings to those mentioned above that connection probabilities converge to 0 in the loop representation of the XXZ model introduced by Ueltschi.
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Quantum Physics

Random quantum circuits, chaos and quantum thermalization

J. T. Chalker

These notes accompany lectures given in June 2025 at the summer school Fundamental Problems in Statistical Physics XVI. They offer a short introduction to random quantum circuits as simple models for generic many-body quantum systems. They give an outline of the motivation for introducing these models, starting from ideas of random matrix theory. They also provide a sketch of calculations of some of the quantities of most physical interest, based on an average over an ensemble of systems. These quantities give insights into operator spreading, entanglement dynamics and spectral correlations.
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Materials Science

Chemical Control of Electronic Structure and Topology in Tellurium-Encapsulated Silicene

Gabriel Elyas Gama Araujo, Andre Luis de Oliveira Batista, Willian Oliveira Santos et al. (+3 more)

We investigate chemical control of the electronic, optical, and topological properties of two-dimensional \ce{Si2X2Te2} (\ce{X} = \ce{B}, \ce{Al}, \ce{Ga}, and \ce{In}) monolayers using first-principles calculations. All compounds are dynamically stable semiconductors, with their vibrational and electronic properties evolving systematically upon group-III substitution. Hybrid-functional calculations including spin–orbit coupling reveal predominantly $p$-orbital band edges and increasingly pronounced relativistic effects from B to In. Most notably, the calculated $\mathbb{Z}_2$ invariant identifies \ce{Si2In2Te2} as a candidate quantum spin Hall insulator, while the B-, Al-, and Ga-based monolayers remain topologically trivial. Bethe–Salpeter calculations further show that electron–hole interactions redistribute oscillator strength near the absorption onset while preserving a weak in-plane optical anisotropy. Our results establish group-III substitution as a simple chemical route to tune the electronic structure and drive a transition from trivial to nontrivial topology in \ce{Si2X2Te2} monolayers.
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All authors Gabriel Elyas Gama Araujo, Andre Luis de Oliveira Batista, Willian Oliveira Santos, Alexandre Amaral Leitao, Alexandre Cavalheiro Dias, Andreia Luisa da Rosa

Astrophysics of Galaxies

The Random Magnetic Field of the Milky Way

Michael Unger and Glennys R. Farrar

We constrain the large-scale isotropic random component of the Galactic magnetic field using the Planck reconstruction of the 408 MHz synchrotron sky. Our analysis simultaneously fits the random-field structure, the synchrotron contributions of the coherent field and local foregrounds, and isotropic and dipolar offsets. A new element of the analysis is the use of excess polarized emission at 30 GHz to model local foregrounds, allowing us to retain 97% of the sky without absorbing these structures into Galaxy-wide features of the magnetic field. Across variations in the coherent-field model, cosmic-ray electron distribution, sky mask, and field profile, we consistently find that the dominant random-field component is a vertically compact disk with a local rms strength of about 4 $\mu$G and a 1/e scale height of approximately 1 kpc, substantially thinner than in most previous models. An annular enhancement in the inner Galaxy improves the fit to the data, whereas we find no evidence for either a large-scale spiral pattern or a thick random-field disk. The fits also yield an intensity monopole of 4-7 K, whose possible origin we discuss. We quantify the implications of the inferred random field for the angular smearing of ultrahigh-energy cosmic rays. Compared with previous models, the sky-median smearing angle is smaller by up to a factor of 1.7, and by up to 2.4 in individual directions.
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Strongly Correlated Electrons

Neural quantum states in condensed matter: advances, best practices, and prospects

Jonas B. Rigo, Björn J. Wurst, Rajah Nutakki et al. (+2 more)

Neural quantum states provide flexible variational representations of quantum many-body wave functions by combining neural-network parametrizations with Monte Carlo sampling. In this perspective, we review recent advances in their application to condensed-matter systems, focusing on frustrated quantum magnets, interacting lattice fermions, and non-equilibrium dynamics. We discuss the architectures, symmetry constraints, optimization methods, and sampling strategies underlying state-of-the-art calculations, and summarize practical guidelines for reliable simulations. We also examine the principal remaining challenges, including learning non-trivial sign and phase structures, controlling variational bias, enforcing physical symmetries, scaling optimization to large networks, and achieving stable real-time evolution. Finally, we outline promising directions in which neural quantum states may extend the reach of classical simulations of strongly correlated quantum matter.
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All authors Jonas B. Rigo, Björn J. Wurst, Rajah Nutakki, Markus Schmitt, Dante Kennes

Earth and Planetary Astrophysics

Does Cumulative XUV Unify the Neptunian Desert?

Qunfeng Jiang

The Neptunian desert is the scarcity of roughly $2$-$10\,R_{\oplus}$ planets on orbits of a few days. Atmospheric escape driven by stellar X-rays and extreme-ultraviolet (XUV) radiation may shape its lower boundary by stripping hydrogen-helium envelopes. Because M dwarfs and F-, G-, and K-type stars have different activity histories, present bolometric irradiation may not trace the cumulative high-energy dose that drives escape. We ask whether cumulative XUV yields a common boundary across spectral type and whether the convergence survives star-to-star variation in age and rotation. Using 1850 Kepler and TESS planets, Model for Rotation of Stars (MORS) activity tracks, and a global boundary model, we find that the offset between M dwarfs and FGK stars shrinks from $-1.065$ dex in bolometric flux to $-0.369$ dex for a common 5 Gyr median-rotation XUV history. Assigning plausible ages and initial rotations to individual hosts preserves the smaller XUV offset in every trial, with a median reduction of 69.1%. A common-period null yields comparable alignment. Cumulative XUV therefore substantially reduces the host-type dependence, but the present data do not establish a universal XUV threshold independent of orbital period.
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Strongly Correlated Electrons

Two distinct gap structures in the mid-infrared optical conductivity of the Hubbard model

Dongwook Kim and Karsten Held

Mid-infrared (MIR) optical conductivities in cuprate superconductors show universal features. In this study, we demonstrate that these originate from two distinct gaps: the pseudogap mediated by antiferromagnetic spin fluctuations and the Mott-Hubbard gap. The MIR spectra from these two gaps show a characteristic and distinct shape and doping dependence, and can thus be distinguished. Specifically, the Mott-Hubbard correlations, while rendering a peak in the visible spectrum for small dopings, yield a broad optical response starting in the MIR when a “waterfall” develops in the one-particle spectrum at larger dopings. The numerically and analytically determined doping-dependence of both gaps consistently reproduce experiments, and provide a unified microscopic understanding of the cuprate MIR optical conductivity.
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General Relativity and Quantum Cosmology

Static electric and magnetic traversable wormholes in $(2+1)$-dimensional nonlinear electrodynamics

Mauricio Cataldo

Every traversable wormhole reported so far in static (2+1) gravity coupled to nonlinear electrodynamics has come from a power-Maxwell Lagrangian L propto |F|^k restricted to k=1/2, always forcing the cosmological constant to a fixed sign or zero. We show these restrictions are artefacts of that single choice, not physical requirements, and give a complete classification of static traversable wormholes in this theory. Of the three mutually exclusive electromagnetic configurations compatible with the symmetry, the radial electric branch admits no throat for any Lagrangian or Lambda. In each remaining branch, azimuthal electric and magnetic, the field equations admit exactly two regimes: either the redshift function is fixed, leaving the shape function b(r) completely free with Lambda absorbed without constraint; or the redshift is generic, in which case b(r) becomes fixed instead. We solve both regimes in closed form in both branches, and show that fixing the Lagrangian to any single power k forces Lambda nonzero and determines b(r) up to finitely many constants: this freedom requires the Lagrangian to be genuinely unrestricted. One azimuthal-electric family reproduces the static BTZ mass function, turning the vacuum black hole into a wormhole once sourced by the nonlinear field. Applied to the unique conformal power-Maxwell theory, k=3/4, previously known only as a radial-branch charged black hole, the same Lagrangian yields genuine wormholes in the azimuthal and magnetic branches, showing the electromagnetic configuration, not the Lagrangian, decides between a horizon and a throat; Born-Infeld electrodynamics admits no throat in any branch.
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Optics

Oblique Bragg-Doppler scattering at relativistic grating created by backward Raman amplification in hydrogen

Wenhong Lai, Jiapeng Huang, Haozhe Guo et al. (+1 more)

We report the first observation of relativistic "Bragg-Doppler" reflection, which occurs when a light beam is incident on a fine-period phase grating moving at close to the speed of light. The grating is created in hydrogen-filled hollow-core fibre by seeded backward stimulated Raman scattering, which creates an intense coherence wave of molecular vibrations at 125 THz, with wavelength 299 nm, moving at ~c/8. When this grating is obliquely probed at a generalized Bragg angle, a reflected beam emerges, Doppler-shifted by 125 THz. The effect is also uni-directional, as phase-matching is strongly violated when the probe beam is reversed, so may be viewed as an ultra-high frequency Bragg-cell frequency-shifter. The wide transparency window of hydrogen allows frequency shifting of radiation from the visible to the vacuum UV, simply by tuning the incident angle. The results open up new opportunities for spatio-temporal studies of coherence wave dynamics, frequency conversion in difficult-to-access spectral regions such as the deep and vacuum UV, and quantum-state-preserving frequency conversion of single photons.
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All authors Wenhong Lai, Jiapeng Huang, Haozhe Guo, Philip St.J. Russell

Astrophysics of Galaxies

The [Ne V] AGN Diagnostic in SDSS-IV/eBOSS: An Anticorrelation Between Ionization State and AGN Luminosity in Low-Redshift Coronal-Line Galaxies

Owen S. Matthews Acuña, Christy A. Tremonti, Nikko J. Cleri et al. (+6 more)

Traditional narrow-line diagnostics fail at high redshift, where low metallicity drives star-forming galaxies and Active Galactic Nuclei (AGN) into overlapping regions of the Baldwin-Phillips-Terlevich (BPT) diagram. Coronal lines, with ionization potentials exceeding 100 eV, offer a robust alternative: they cannot be produced by normal stellar populations, arise almost exclusively from AGN or fast shocks, and are insensitive to abundance evolution. Among these, the [Ne V] doublet is the brightest optical coronal line tracer of AGN activity. Existing coronal line catalogs contain only about 1750 objects, too few to statistically assess the completeness and purity of [Ne V]-selected AGN samples. We identify 33,817 galaxies with [Ne V] S/N > 5 at z = 0.147-1.12 in the Sloan Digital Sky Survey IV extended Baryon Oscillations Spectroscopic Survey (SDSS-IV/eBOSS), exceeding the combined literature total by more than an order of magnitude. [Ne V] preferentially selects rapidly accreting, relatively unobscured AGN; only 41.5% of BPT AGN show detectable emission. By stacking spectra that lack [Ne V] on a grid of black hole mass and [O III] luminosity, we recover [Ne V] in the majority of bins, implying that non-detections reflect limited survey sensitivity rather than a deficit of coronal emission. We find [Ne V]/[Ne III] is only weakly correlated with [O III]/[O II]. Galaxies with high [Ne V]/[Ne III] for their [O III]/[O II] ratio have lower Eddington ratios and are more likely classified as LIERs or Composites. The [Ne V]/[O III] ratio shows a strong anticorrelation with [O III] luminosity, with the most extreme coronal-line strengths found among the lowest-luminosity AGN, in analogy with the accretion states of stellar-mass black holes. Comparison with a sample of z=2-9 [Ne V]-detected galaxies suggests some, but not all, high-redshift AGN follow the same relations.
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All authors Owen S. Matthews Acuña, Christy A. Tremonti, Nikko J. Cleri, Kyle B. Westfall, Bee R. Erena, Jacob B. Stimac, Britt Lundgren, Drake Miller III, Aleksandar M. Diamond-Stanic

Fluid Dynamics

A Variational Principle for the Vorticity Equation

Ahmed Farooq

We present a variational formulation of the incompressible vorticity equation based on Gauss's principle of least constraint using the Gauss constraint functional $\Zvec_\omega$. The central result is the Euler–Lagrange equation $\mathbf{Z}_\omega = -\nabla h$, where $h = \mathbf{u} \cdot\boldsymbol{omega}$ is the helicity density. This reveals that the helicity gradient $\nabla h$ acts as the constraint force maintaining the solenoidality of the vorticity field, exactly as the pressure gradient $\nabla p$ maintains incompressibility in Taha et al.'s pressure-gradient minimization principle. The helicity density naturally emerges as the Lagrange multiplier enforcing $\nabla \cdot \boldysmbol{omega}=0$, and at the solution the flow minimizes the norm of the helicity gradient $\|\nabla h\|^2$. This establishes the exact duality: helicity is to vorticity as pressure is to velocity. We apply the variational principle to the Burgers vortex and verify the the Euler-Lagrange equation. The variational principle connects to Moffatt's helicity conservation theorem, Arnold's geometric formulation of ideal fluid flow, and Kambe's gauge-theoretic formulation. This work provides a unified variational framework for fluid dynamics that spans classical mechanics, geometric mechanics, and topological field theory. We discuss how this work may provide a theoretical foundation for understanding the role of helicity gradients in boundary layer dynamics, with potential implications for the formation of coherent structures and the onset of transition. These applications are reserved for future work.
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Superconductivity

Superconducting ground state study of Cr-based equiatomic high-entropy alloy through $\mu\text{SR}$

Sonika Jangid, Rhea Stewart, Adrian D. Hillier et al. (+1 more)

High-entropy alloy superconductors, characterized by extreme chemical disorder and complex electronic environments, have attracted significant attention as model systems for exploring superconductivity in disordered materials. Here, we investigate a Cr-based equiatomic HEA, Cr-V-Ti-Nb-Ta, which contains a magnetic 3d element, providing an opportunity to examine the influence of magnetic elements on superconductivity in highly disordered systems. Despite expected magnetic pair-breaking, this alloy exhibits bulk type-II superconductivity with a transition temperature of $T_c = 2.33(3)$ K and a high upper critical field. Transverse-field $\mu$SR measurements reveal an s-wave superconducting gap close to the BCS value, while zero-field $\mu$SR suggests preserved time-reversal symmetry. These results establish Cr-V-Ti-Nb-Ta as a promising platform for exploring the interplay between disorder, magnetism and superconductivity in high entropy alloys.
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All authors Sonika Jangid, Rhea Stewart, Adrian D. Hillier, R. P. Singh

General Relativity and Quantum Cosmology

On the Emergence of the Hysteresis Effect in Gravitational Systems

Raihaneh Moti and Ali Shojai

Previously, it was shown that the interplay between the gravitational memory effect and the thermodynamics of an ensemble of spinning objects gives rise to a hysteresis effect, which can be termed Gravo-Thermo memory. This effect can be studied either through a statistical approach or via kinetic theory. Here, we present a general kinetic theory model for the general case of a fluid composed of spinning extended objects in the presence of gravity.
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High Energy Astrophysical Phenomena

Generation of TeV Photons by PeV Neutrinos in Dense Astrophysical Environments

Jun-Chen Wang, Hanlin Song, Hao Li et al. (+2 more)

Recent observations by IceCube and KM3Net of PeV-scale ultra-high-energy (UHE) neutrinos, together with detections of TeV-PeV photons from various sources such as the Crab Nebula, the Galactic Center, and gamma-ray burst by ground-based observatories including Tibet AS$\gamma$, MAGIC, Carpet-3, and LHAASO, point to the existence of extreme astrophysical environments capable of accelerating particles to ultra-high energies. These findings motivate investigations of possible connections between UHE neutrinos and photons in such environments. Theoretically, dense regions surrounding compact objects can efficiently produce UHE neutrinos. In this work, we calculate the production of UHE photons from neutrino-nucleon interactions, and note that if these interactions occur in the outer, optically thin regions of dense environments, the resulting photons could potentially be observed. In our model, an incident neutrino scatters off a nucleon, generating secondary partons that hadronize into pions and subsequently decay into UHE photons. We calculate the resulting photon energy spectra and find that for incident (anti)neutrinos with energies above 1 PeV, the probability of producing photons with energies exceeding 1 TeV is greater than 13%. As a concrete application, we show that this mechanism can quantitatively account for the preburst TeV photons observed in GRB 221009A, providing a natural explanation for both their energies and lead times. These findings establish a plausible mechanism linking UHE neutrino events to gamma-ray observations, providing new insights into hadronic processes in extreme astrophysical environments and supporting multi-messenger astronomy studies.
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All authors Jun-Chen Wang, Hanlin Song, Hao Li, Jie Zhu, Bo-Qiang Ma

Soft Condensed Matter

LCST and Closed-Loop Phase Behavior in Non-Associating Fully Symmetric Multicomponent Polymer Systems

Artem Petrov and Alfredo Alexander-Katz

Multicomponent liquids can phase separate upon heating, exhibiting a lower critical solution temperature (LCST). Moreover, a narrow class of materials can undergo disordering transition upon further heating, yielding closed-loop phase diagrams. Previously, it was shown that LCST or closed-loop phase behavior can appear in the models of liquids in which components are asymmetric or interaction potentials have a specifically designed attraction. Here, we show theoretically that LCST and closed-loop phase behavior can occur in a significantly wider set of models. In particular, we found that these phenomena can be exhibited by the simplest and widely used coarse-grained (CG) models of any multicomponent liquid in which species are fully symmetric and where all particles interact via an arbitrary repulsive potential. In addition, we discovered that LCST and closed-loop phase behavior in these models emerges merely due to the basic property of CG liquid models, namely, the appearance of strong monomer-monomer positional correlations at low monomer number density $\rho$. We simulated the models of fully symmetric binary blends and diblock copolymer melts where nonbonded monomers interacted via a generic T-independent purely repulsive harmonic potential. As predicted, LCST and closed-loop phase behavior emerged at $\rho$ sufficiently low to cause strong monomer-monomer correlations leading to a strong T-dependence of the effective coordination number, which, in turn, induced a nonmonotonic T-dependence of the Flory-Huggins parameter. To summarize, we discovered that the simplest fully symmetric non-associating CG models of multicomponent liquids can exhibit complex temperature response due to a mechanism stemming from the basic nature of any CG liquid model. This mechanism might contribute to the emergence of LCST and closed-loop phase behavior in many existing polymer materials.
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Statistical Mechanics

Meandering stripes in the frustrated $J_1$-$J_2$ Ising model on the honeycomb lattice

Denis Gessert, Martin Weigel and Wolfhard Janke

We study the frustrated $J_1$-$J_2$ Ising model on the honeycomb lattice with ferromagnetic nearest-neighbor couplings fixed at $J_1=1$ and strong antiferromagnetic next-nearest-neighbor interactions, i.e., $J_2 \leq -1/4$. Little is known for this range of $J_2$, whereas for less negative values of $J_2$ the system orders ferromagnetically at low temperatures and appears to remain in the Ising universality class. In previous work it was shown that the model has a largely degenerate ground state, and it was conjectured that there is some kind of phase transition. We introduce a complex-valued nematic order parameter, which can differentiate between the high-temperature paramagnetic phase and the observed partially-disordered stripe phase at lower temperatures. Configurations in this phase consist of stripes of spins parallel with respect to one lattice direction, which collectively meander along the remaining two, producing partially disordered ground states. The sharp peaks in the specific heat observed in earlier work only appear when using periodic boundary conditions and are absent for free boundaries. Additionally, we reveal a striking dependence of the behavior on the aspect ratio of the considered samples. Ultimately, even a careful finite-size scaling analysis for $J_2 = -0.5$ and $J_2 = -1$ is unable to clearly discern between a crossover without any singularities and some form of continuous transition, including the possibility of an infinite-order transition of the Berezinskii-Kosterlitz-Thouless (BKT) type. For $J_2=-1/4$ we find that the system remains disordered at all temperatures and that it exhibits a finite ground-state entropy per site, for which our simulations provide the accurate asymptotic estimate $S(T=0)/N = 0.230\,960\,93(14)$ in the thermodynamic limit $N\rightarrow\infty$.
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Lattice Field Theory

Exponential-in-$N_c^2$ cost reduction of product-formula-based quantum simulations of quantum chromodynamics

Zohreh Davoudi and Jesse R. Stryker

Quantum algorithms for simulating quantum chromodynamics (QCD) have matured steadily since the pioneering work of Byrnes and Yamamoto [PRA 73, 022328 (2006)]. The most popular strategies for Hamiltonian simulation involve product-formula decompositions. However, the application of product-formula methods to SU($N_c$) lattice gauge theories by Byrnes and Yamamoto leads to $O(\Lambda^{8(N_c^2-1)})$ gate complexity per Trotter step, where $\Lambda$ is the bosonic cutoff in the electric (i.e., irreducible-representation) basis. A seminal work by Kan and Nam [arXiv:2107.12769 (2021)] significantly improves over such an undesirable cost and reports an $O\big(\Lambda \text{polylog}(\Lambda)\big)$ scaling, yet it still calls for an unrealistically large number of quantum gates. Here, we illuminate one of the reasons behind this high cost estimate and show that a factor of size $O(2^{4(N_c^2-1)})$ can be removed from the per-Trotter-step cost estimate by Kan and Nam. We specifically show that, by using methods developed in our past works [PRD 112, 014508 (2025); Quantum 7, 1213 (2023)], exponentiated-Hamiltonian decomposition—a necessary step in the application of product-formula algorithms—can be performed far more efficiently than previously thought. Our method reduces the T-gate cost estimate of QCD simulations using a second-order product formula by a factor of nearly $10^{14}$, independent of simulation parameters and sizes. Focusing on simulations in the electric basis, we further contrast our results with other methods: the local-multiplet basis approach of Ciavarella, Klco, and Savage [PRD 103, 094501 (2021)] and the near-optimal algorithm of Rhodes, Kreshchuk, and Pathak [PRX Quantum 5, 040347 (2024)]. This work highlights the importance of continued algorithmic improvement to bringing the quantum-simulation cost of QCD within reach of realistic quantum computers.
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Cosmology and Nongalactic Astrophysics

Model independent lensing sub-structure detection with multiply-imaged star clusters constellations

Leo W.H. Fung, Tom Broadhurst, Sung Kei Li et al. (+3 more)

A broad class of dark matter (DM) models predicts the existence of sub-structures residing in DM haloes on sub-resolvable angular scales. Techniques to extract such a generic feature from diffraction-limited observations are lacking. In this work, we propose a model-independent 'super-resolving' method applicable to strong gravitational lens systems that is fully data-driven, without reference to any lens models. This method relies on a specific way of applying the optical Liouville theorem across multiple scales in the imaging data, a technique we refer to as geometrical-duality. We test this method using realistic simulations and apply it to a 'constellation' consists of 11 compact star clusters seen in two giant arcs in the lensing cluster SMACS0723 imaged by JWST as a proof-of-concept. We find reasonable self-consistency with the expectation of non-detection given the statistical sensitivity, except for one pair of star clusters. Such an outlier can be explained in the context of CDM as sub-haloes lensing in the mass range $M_{\rm sub} = 10^8 - 10^9\,M_\odot$, for which the corresponding Einstein radius is smaller than the diffraction limit of JWST.
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All authors Leo W.H. Fung, Tom Broadhurst, Sung Kei Li, Jeremy Lim, Giorgio Manzoni, George F. Smoot

Strongly Correlated Electrons

Emergent Vibronic Spectral Hierarchy in a Kagome Flat-Band Insulator

Jun Shu, Jun Shen, Yanmin Zhang et al. (+17 more)

Electron-phonon coupling is usually understood in terms of electronic quasiparticles interacting with dispersive lattice vibrations. Much less is known about the complementary limit in which the relevant phonon mode is itself localized or weakly dispersive. Here we investigate this regime in the kagome compound Rb$_{2}$Ni$_{3}$S$_{4}$, which undergoes an unconventional insulating transition near $T^{*} \approx$ 260-280~K. Combining polarization-resolved Raman spectroscopy with temperature-dependent x-ray diffraction, scanning tunneling microscopy, and electrical, thermal, and magnetic measurements, we show that the transition involves electronic localization without a conventional structural or magnetic order parameter. Raman spectra reveal a giant Franck-Condon progression associated with a nearly dispersionless 333.7~cm$^{-1}$ phonon, decorated by an equally spaced comb-like fine structure with a characteristic spacing of 40.6~cm$^{-1}$. The comb spacing is insensitive to magnetic field, whereas its spectral weight is strongly field tunable. Rather than treating either hierarchy alone as pure phonon effect, we interpret their nested coexistence as evidence for a strongly coupled electron-vibrational manifold involving a localized lattice coordinate. These results identify dispersionless phonons as an active route to vibronic correlations in solids and suggest that such electron-vibrational self-trapping is closely associated with the insulating phase of Rb$_{2}$Ni$_{3}$S$_{4}$.
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All authors Jun Shu, Jun Shen, Yanmin Zhang, Hong Du, Qingsong Wang, Zeyuan Wang, Bin Wang, Zeliang Xu, Dengjing Wang, Hengfu Lin, Zunming Lu, Lei Qin, Jie Yuan, Jinbo Peng, Zhida Song, Fedor V Kusmartsev, Anna Kusmartseva, Kui Jin, Ruidan Zhong, Ge He

Quantum Physics

Eavesdropper-Blind Remote State Preparation and Applications to Quantum Public-Key Encryption

Kaniuar Bacho and Alexandru Cojocaru

Remote state preparation (RSP) is a central primitive in quantum cryptography, enabling classical parties to remotely construct quantum states using only classical communication. As a result, RSP serves as a key building block in numerous protocols involving classical clients and quantum servers, allowing classical parties to leverage the advantages offered by powerful quantum computers. All known constructions of RSP rely on strong cryptographic assumptions, typically variants of trapdoor claw-free functions (TCFs). In this work, we initiate the study of a weaker form of remote state preparation, which we call eavesdropper-blind remote state preparation (EB-RSP). Informally, EB-RSP requires blindness only against external observers who see the transcript of the honest protocol, rather than against the quantum server itself. Despite this relaxed adversarial model, the resulting notion remains sufficient for useful cryptographic applications. In particular, we show that two-message EB-RSP already suffices to construct quantum public-key encryption with classical public keys and quantum ciphertexts. We then construct two-message EB-RSP protocols from specific one-way group actions, yielding a first step toward RSP-type primitives based on assumptions that do not rely on trapdoors. Finally, we observe that existing RSP constructions are likely naturally adaptable to the two-message EB-RSP notion; we demonstrate this explicitly for a concrete TCF-based RSP construction.
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High Energy Physics (Theory)

$G_2$-Manifolds from 4d $\mathcal{N}=1$ Quivers

Andreas P. Braun, Oscar Lewis, Matteo Sacchi et al. (+1 more)

Inspired by quantum field-theoretic constructions of 4d $\mathcal{N}=1$ quiver gauge theories that flow to superconformal field theories (SCFTs), we construct 7d manifolds of $G_2$-holonomy, which geometrically engineer these quivers in M-theory. Field theoretically, the 4d quivers are obtained by flux torus compactifications of 6d $\mathcal{N}=(1,0)$ SCFTs. The 6d theory compactified on a circle gives rise to a 5d KK-theory, which has a geometric realization as M-theory on a non-compact elliptically fibered Calabi-Yau threefold. Following the field-theoretical prescription, these local geometries are fibered over a circle to realize (topological) $G_2$-holonomy manifolds. We carry this out concretely in the case of the rank 1 E-string theory and its 4d quivers and construct new families of $G_2$-holonomy spaces.
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All authors Andreas P. Braun, Oscar Lewis, Matteo Sacchi, Sakura Schafer-Nameki