Instrumentation and Detectors
Radiation Hardness of Commercially Available NUV-MT Silicon Photomultipliers
T. Avgitas, M. Axiotis, Z. Balmforth et al. (+5 more)
Silicon Photomultipliers (SiPMs) based on the near-ultraviolet, metal-filled trench (NUV-MT) technology offer improved
photon detection efficiency and reduced correlated noise relative to earlier designs, making them attractive for a broad range of particle- and astroparticle-physics applications. As such devices may be deployed in high-radiation environments, quantifying their performance after irradiation is essential. Commercially available Broadcom AFBR-S4N series NUV-MT SiPMs were irradiated with 1 MeV
neutrons to fluences between 2x10^{9} and 1.1x10^{10} n_{eq}/cm^2 at the TANDEM accelerator facility of NCSR "Demokritos" in Athens, and characterised before and after irradiation and over successive thermal-annealing stages. Irradiation increased the dark noise by up to three orders of magnitude and degraded the single-
photon resolution by up to a factor of ten, with resolution lost entirely at the highest fluence, while no shift in breakdown voltage was observed. Thermal annealing partially recovered the performance, reducing the dark noise by up to a factor of two and restoring the single-
photon resolution.
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All authors T. Avgitas, M. Axiotis, Z. Balmforth, I. Manthos, K. Nikolopoulos, E. Taimpiri, C. Toukmenidis, A. Ziagkova
Strongly Correlated Electrons
Evolution from Kitaev to XXZ spin chains via distortion: Application to BaCo$_2$V$_2$O$_8$
Philip Richard, Mandev Bhullar and Hae-Young Kee
BaCo$_2$V$_2$O$_8$ is a prototypical
spin-orbit-coupled Ising-chain antiferromagnet that provides a unique platform for studying field-induced
quantum magnetism. Under a transverse
magnetic field, it exhibits unusual
magnetic properties, including an anomalous staggered magnetization and a pronounced anisotropy of the critical field with respect to the in-plane field direction. While these phenomena have been attributed phenomenologically to a site-dependent anisotropic $g$-tensor, a recent microscopic theory has shown that
spin-orbit coupling naturally generates bond-dependent Heisenberg, Kitaev, and $\Gamma$ exchange interactions. Here, we unify these two pictures by extending the microscopic theory to incorporate distortions of the CoO$_6$ octahedra. We show that the distortions not only generate the site-dependent anisotropic $g$-tensor but also renormalize the staggered exchange interactions through a distortion-induced contribution that partially compensates the Kitaev-derived staggered term. Using point-charge calculations to estimate the $g$-tensor of BaCo$_2$V$_2$O$_8$, we demonstrate that the strong anisotropy of the critical field originates from the combined effects of the modified exchange interactions and the anisotropic $g$-tensor. Our work provides a unified microscopic framework for understanding the
magnetic anisotropy of
spin-orbit-coupled Ising-chain materials.
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General Relativity and Quantum Cosmology
Exploration of Zero-Complexity Compact Stars in Higher Dimensions under the Finch-Skea Background
Shyam Das, Megandhren Govender, Kevin Reddy et al. (+1 more)
Motivated by the recent extension of Herrera's gravitational complexity to arbitrary higher-dimensional spacetimes, we investigate exact compact-
star models that satisfy the vanishing-complexity condition within the Finch–Skea geometry in $(n+2)$-dimensional Einstein
gravity. By combining the higher-dimensional Einstein field equations with the generalized complexity formalism, we obtain a new class of exact interior solutions describing anisotropic fluid spheres with zero complexity. The physical properties of these models are evaluated by analyzing the behavior of the matter variables, pressure anisotropy, and
equilibrium conditions, alongside the standard requirements of regularity, energy conditions, causality, and stability. We further explore the influence of spacetime dimensionality on the structural characteristics of the
stellar configurations, demonstrating that the presence of extra dimensions significantly modifies the internal matter distribution while preserving physical viability. The solutions presented here represent the first exact higher-dimensional Finch–Skea compact-
star models constructed within this recently developed generalized complexity framework \cite{choudas}. These results provide a natural extension of zero-complexity
stellar configurations beyond four-dimensional General Relativity and offer a robust framework for investigating self-gravitating systems in higher- dimensional
gravity.
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All authors Shyam Das, Megandhren Govender, Kevin Reddy, Bikram Keshari Parida
Solar and Stellar Astrophysics
Chemical evolution of Na, Mg, and Al in the Galactic bulge from UVES data
R. P. Nunes, B. Barbuy, C. Chiappini et al. (+9 more)
The formation of the
Galactic bulge remains incompletely understood, with evidence pointing to different
stellar populations, including a bar-driven component, an inner-disk population, and an older spheroidal component. Chemical abundances provide critical constraints on the origin of these populations, particularly for odd-Z elements such as Na and Al, as well as Mg, whose behaviour at high
metallicity is still a matter of debate. We aim to investigate the presence of overabundances of Na, Mg, and Al in
Galactic bulge
stars, with particular emphasis on the metal-rich regime, and to evaluate their consistency with predictions from chemical
evolution models. We re-derived the abundances of Na, Mg, and Al for a sample of 55 bulge red
giants previously analysed in the literature. Our study is based on high-resolution UVES spectra obtained with the ESO Very Large
Telescope and employs spectrum synthesis using the Turbospectrum code, with updated atomic and molecular line lists. We find somewhat lower abundances of Mg and Al at the metal-rich end than previous studies, while a fraction of the metal-rich
stars still exhibit significant Na enhancements. These enhancements persist when different sets of
stellar parameters are adopted, indicating that they are robust. The presence of Na-enhanced
stars at high
metallicity is difficult to reconcile with standard chemical
evolution models and suggests additional enrichment processes in the bulge, or a particular behaviour of
stellar yields with
metallicity. The Na enhancement could be due to
metallicity-dependent yields from massive
stars, not taken into account in available models, and/or enrichment by asymptotic
giant branch
stars, or due to second-generation
stars evaporated from globular clusters, the latter option arising because for the metal-rich ([Fe/H]>0)
stars a Na-O anti-correlation appears to occur.
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All authors R. P. Nunes, B. Barbuy, C. Chiappini, A. Friaça, M. C. Jelin, V. Hill, M. Zoccali, A. Renzini, A. Pérez-Villegas, H. Ernandes, S. O. Souza, M. J. Castro
Quantum Physics
Quantum Representation Learning Beyond Pairwise Fidelity
Junpeng Hou and Changbin Lu
Quantum contrastive, metric, and self-supervised learning often expose encoded
quantum states to the learner through transition probabilities, especially fidelity.
Quantum states are known to possess higher-order relational invariants, but their consequences for learned representations remain unclear. Here we show that a transition-probability-only learning interface can possess exact continuous blind directions in certain
quantum-state families. We recover this missing information with a batch operator, built from coherent overlap amplitudes and negative masking, where its second moment $q_-$ retains four-state interference. Moreover, $q_-$ is directly measurable through two-copy interference and can enter variational learning via methods like parameter shift. In relational quartets derived from toric-code and double-semion states, this fidelity-blind signal encodes inequivalent modular data despite identical pairwise fidelities. Finally, in a four-
photon benchmark with preparation drift, augmenting all six pairwise fidelities at two orthogonal probes with the corresponding normalized $q_-$ reduces the mean out-of-distribution phase error by $86\%$ at equal total shot budget. These results establish multistate relational observables as measurable, trainable, and physically consequential signals for
quantum representation learning beyond pairwise fidelity.
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Astrophysics of Galaxies
Dark Matter Halo Tumbling Induced by Torques from Massive Mergers
Neil Ash and Monica Valluri
Dark Matter
halos exhibit slow tumbling known as `figure rotation'. Figure rotation occurs in roughly $80\%$ of isolated $\Lambda$CDM
halos and is relatively unaffected by baryonic feedback, making it an attractive and relatively unexplored test for $\Lambda$CDM. However,
galaxy mergers are capable of exerting strong torques on a host
halo's quadrupole, warranting an investigation of whether such interactions are capable of influencing figure rotation. Using isolated $N-$body simulations and 6 TNG50
halos containing MW analog
galaxies, we investigate figure rotation in the context of massive mergers. For isolated
galaxies we find that massive mergers elicit rotation of the host
halo in both a rapid transient phase during the satellite infall with pattern speeds between $10^\circ-60^\circ$ Gyr$^{-1}$, and post-merger as a steady tumbling with pattern speeds between $2^\circ-40^\circ$ Gyr$^{-1}$ lasting for at least $6-8$ Gyr. Both transient and long-lived tumbling depend on the trajectory of the infalling satellite. We find that figure rotation can be induced by radial mergers with no orbital angular momentum, suggesting that
tidal torques from the satellite are a driving mechanism. Meanwhile, TNG50
halos show quadrupole tumbling modified during major mergers in both pattern speed (3/6
halos) and rotation axis orientation (6/6
halos). Quadrupole tumbling remains stable after the last major merger in 5 of our 6
halos. Our results suggest that, rather than tracing the early
tidal shear, figure rotation at present day may instead retain a dynamical
memory of a
halo's last major merger.
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Plasma Physics
Revisiting the MRX Electron Current Sheet Width with Semi-Collisional Kinetic Simulations at Hydrogen Mass Ratio
Sung Hyun Son, Adam Stanier, William Daughton et al. (+3 more)
For over eighteen years, the electron current sheet measured in the
Magnetic Reconnection Experiment (MRX) has stood a factor of 2–5 wider than predicted by MRX-like kinetic simulations, and the measured electron force balance has not closed with the classical terms alone. As a consequence, the dominant nonideal terms responsible for breaking the frozen-in condition have remained unexplained. Here, two-dimensional kinetic simulations with binary Coulomb collisions are performed in a cylindrical geometry representative of MRX, at the realistic hydrogen mass ratio $m_i/m_e = 1836$ and at MRX-relevant collisionality. For the first time, these simulations reproduce the measured electron current sheet half-width. The simulated value, $\delta_{BT} = 0.744 \pm 0.054$~cm or $6.26 \pm 0.45$ electron skin depths ($d_e$), lies within the experimental range of 5.5–7.5~$d_e$. The electron force balance closes through the classical channels alone: the pressure-tensor divergence supports 76% of the nonideal electric field and collisional friction the remainder. The historical force-balance deficit reappears only when the simulated layer is sampled at the experimental 3~cm
outflow resolution, suggesting that the deficit reflects probe resolution rather than anomalous dissipation. Beyond this reproduction, an analytic model of the layer width is developed that orders the meandering electrons by the coherence of their orbits against collisions. In this model, the Dreicer ratio $E_D/|E_y|$ selects the electrons whose current-carrying motion survives, and the resulting width prediction brackets the measured values across a wide collisionality scan. A discrepancy remains in the width normalized to the local electron gyroradius ($\rho_e$), whose measured value lies a factor of 3–6 above both the model and the simulations.
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All authors Sung Hyun Son, Adam Stanier, William Daughton, Jongsoo Yoo, Tongnyeol Rhee, Hantao Ji
Earth and Planetary Astrophysics
Precise Stellar Age Constraints and Habitable Zone Evolution in Exoplanet Systems
Grace Henry, Ted von Hippel and Anna Childs
Accurate
stellar ages are fundamental to interpreting the evolutionary histories of habitable zone (HZ)
planets. Because
stellar luminosity evolves over time, HZ boundaries migrate outward, meaning that present-day HZ
planets may have experienced different irradiation environments earlier in their
evolution. Accurate ages are therefore required to estimate HZ residence times and place planetary habitability in an evolutionary context. We use the
Bayesian Analysis of
Stellar Evolution with nine parameters (BASE-9) code to constrain ages and masses for
exoplanet host
stars with
planets located in the HZ. Our sample includes single
stars with effective temperatures of 4475-7200 K that host
planets within their calculated HZ boundaries. We fit isochrones to broadband photometry from
Gaia DR3, Pan-STARRS, and 2MASS jointly with
Gaia parallaxes, spectroscopic
metallicities, and extinction estimates, and assess the resulting age posterior distributions. Using these age constraints, we track HZ migration along
stellar evolutionary sequences to estimate continuous HZ residence times, allowing us to identify ideal targets for followup high resolution characterization. Because isochrones separate most strongly near and beyond the main-sequence turnoff, our analysis emphasizes evolved and turnoff hosts, where BASE-9 produces the tightest constraints. We quantify age precision across the sample, yielding highly precise ages for subgiants and evolved main-sequence or turnoff
stars, and less precise but measurable ages for lower main-sequence hosts. The final catalog provides our age constraints for 149 HZ
planets around 146 host
stars and supports evolutionary interpretations of planetary histories.
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Earth and Planetary Astrophysics
IFU Observations of Comet 3I/ATLAS = C/2025 N1 (ATLAS) using the Hobby-Eberly Telescope with the VIRUS Instrument
Anita Cochran, Gregory Zeimann, Emmanuel Jehin et al. (+2 more)
We observed interstellar object 3I/ATLAS = C/2025 N1 (ATLAS) on 9 December 2025 UT with the VIRUS spectrograph on the Hobby-Eberly
Telescope. VIRUS is a low spectral resolving power, multi-IFU, optical spectrograph. We used a single IFU for the observations and were able to obtain spectra spaced every one arcsec (1327 km) from the optocenter out to about 85,000 km in the sunward direction. The spectra include molecular features normally seen in the optical for spectra of
Solar System comets, with the addition of many very strong lines of FeI and NiI. We modeled these observations using the Haser (1957) model framework and find that the data can only be fit if we assume that the
outflow velocity of the gas is half that of comets in our
Solar System observed at the same heliocentric distance. We derived Haser model scale lengths for three NiI and four FeI lines. We discuss the implication of the similarities and differences between this object and normal
Solar System comets. The excellent spatial resolution of VIRUS, coupled with a FOV of 50X50 arcsecs and a geocentric distance of 1.83 au, allowed us to probe the coma of 3I in great detail.
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All authors Anita Cochran, Gregory Zeimann, Emmanuel Jehin, Hideyo Kawakita, Adam McKay
High Energy Astrophysical Phenomena
The Mass-Ratio Distribution of the Low-Mass Binary Black Hole Subpopulation: A Natural Outcome of Isolated Binary Evolution
Monica Gallegos-Garcia, Anarya Ray, Vicky Kalogera et al. (+7 more)
The observed merging binary black hole population is increasingly consistent with being composed of a mixture of subpopulations, each likely the result of different formation mechanisms. In particular, the low-mass subpopulation, with primary black hole masses below $\approxeq 15\,M_{\odot}$, has been attributed to mergers formed through isolated binary
evolution. We use the binary population synthesis code POSYDON to study the mass ratio $(q)$ distribution of binary black hole mergers from isolated binary
evolution and compare to the observed low-mass subpopulation. We explore variations in
supernova remnant prescriptions, common-envelope efficiency, and black hole
accretion efficiency. We find that our models have a preference for asymmetric $q$, most with a broad peak near $q\approxeq0.5-0.7$, and a near-equal-mass component whose relative strength varies across models. This resultant $q$ distribution is consistent with the $q$ distribution of the low-mass subpopulation observed with gravitational waves. We find that for the majority of models these features arise from physically distinct formation subchannels: the asymmetric peak reflects contributions from common-envelope and stable mass-transfer systems, while the near-equal-mass component traces double-core common envelope and contact systems. We conclude that the features in the $q$ distribution of the observed low-mass subpopulation emerge naturally from isolated binary
evolution across a range of model assumptions. As the gravitational-wave catalog continues to grow, the relative strength of these $q$ features will provide an increasingly powerful diagnostic of isolated binary
evolution and its formation subchannels.
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All authors Monica Gallegos-Garcia, Anarya Ray, Vicky Kalogera, Max Briel, Michael Zevin, Abhishek Chattaraj, Zepei Xing, Jeff J. Andrews, Seth Gossage, Philipp M. Srivastava
Geophysics
TREMORS: An Agentic Assistant for Multi-Datacenter Seismic Data Acquisition
Ryley G. Hill, Richard Alfaro-Diaz, Jonathan MacCarthy et al. (+2 more)
Seismology increasingly depends upon large data
retrieval across multi-datacenter platforms. Yet, data procurement often demands domain expertise, user burden, and is difficult to reproduce. As archives continue to grow, translating scientific intent into structured workflows that operate across multiple repositories and produce high quality, AI ready data is becoming an increasingly urgent challenge. We present TREMORS (Text Referenced Event Mapping and Output Renderer for Seismographs), an agentic framework that uses large
language model
reasoning within a constrained execution graph to automate seismic data
retrieval. TREMORS translates natural
language queries into a structured intermediate schema, which drives execution through a constrained LangGraph workflow. Example workflows demonstrate support for both event-based and continuous waveform acquisition. The framework is designed to extend across heterogeneous multi-datacenter systems through a portable schema and modular workflow components. This work positions agentic workflows as the catalyst that will connect scientific intent with distributed seismic data systems, enabling a future of reproducible, data-driven inquiry while reducing the burden of routine acquisition tasks.
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All authors Ryley G. Hill, Richard Alfaro-Diaz, Jonathan MacCarthy, Jonas A. Kintner, Christopher W. Johnson
Quantum Physics
GadIR: A Spatial-Topology Preserving Compiler for Quantum Many-Body Systems Simulation
Xiangyu Ren, Yuexun Huang, Zhaohui Yang et al. (+5 more)
Simulating
quantum many-body systems has been one of the most important applications of
quantum computation. For simulation, the
Hamiltonian of a physical system is compiled into
quantum programs with native instructions for
quantum hardware. In previous works, the
Hamiltonian is represented as Pauli strings, then compiled and optimized based on the
quantum circuit model. Such representation paradigm neglects the spatial
topology of original physical models, which is vital information to reducing the overhead of compiling many-body systems
Hamiltonians. To address such neglect, we introduce a spatial-
topology preserving compiler for
quantum many-body simulation. Using Pauli gadgets as the representations of the
Hamiltonian, we introduce our intermediate representation – GadIR, to preserve the spatial-
topology information of original physical models. Our compiler frontend performs the group reduction
algorithm based on Pauli gadget model, which is a hardware-independent optimization. Our compiler backend performs trotterization and scheduling on Pauli gadgets, then synthesizes the Pauli gadgets into hardware-native
quantum programs. We evaluate our compiler on all the canonical
quantum many-body system models, while achieving a significant reduction on compilation overhead regarding four major
quantum architectures. Overall, our spatial-
topology preserving IR exploits the compilation optimization space for
quantum many-body systems
Hamiltonian.
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All authors Xiangyu Ren, Yuexun Huang, Zhaohui Yang, Yuchen Zhu, Tsung-Wei Huang, Tsung-Yi Ho, Zhiding Liang, Antonio Barbalace
Mathematical Physics · Cross-listed from math.PR
Support of Dyson Brownian Motion
Jiaoyang Huang and Shengjing Xu
We consider beta-Dyson Brownian motion, with $\beta >= 1$, started from a deterministic configuration with uniformly bounded support. Let $\mu_t$ be the semicircular free-convolution flow issued from the initial empirical measure, and set $S_t = supp(\mu_t)$. For every fixed $T, \epsilon > 0$, with probability at least $1 - C \exp(-(log n)^2)$, every particle remains within an epsilon-neighborhood of $S_t$ for all $0 <= t <= T$. The result holds from time zero, requires no regularity assumption at the initial spectral edges, and applies to multi-cut supports with macroscopic interior gaps. A key ingredient is a deterministic local resolvent exclusion principle: an $o((n \eta)^(-1))$ comparison of Stieltjes transforms on a complex disc above a real point separated from the reference support excludes
eigenvalues from the corresponding real interval. This gives a model-independent mechanism for converting local resolvent estimates into spectral confinement.
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Statistical Mechanics
Piston-Like Information Engine II: Boundary-Controlled Optimum in Active Matter
Laura Hoek, Neta Ben Ari, Rémi Goerlich et al. (+2 more)
Information engines convert information into extractable work through measurements and feedback. We realize an engine that employs information to compress a gas of self-propelled bristle bots. Its work per measurement, $\bar{W}$, is controlled by the size of the detection region $\Delta x$ and the probability $p_1$ that this region is vacant. In thermal systems, $\bar{W}$ follows the universal form $-p_1 \ln p_1$, whereas the active engine shows a qualitatively modified relation. As particle density increases, the maximum of $\bar{W}(\Delta x)$ switches between two distinct operating regimes. Notably, this transition is also found in the solutions that maximize power output for finite-time cycles with dynamics affected by dry friction. We attribute this nonequilibrium feature to the accumulation of active particles near the boundaries.
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All authors Laura Hoek, Neta Ben Ari, Rémi Goerlich, Saar Rahav, Yael Roichman
Optics
Reciprocal asymmetric transmission in self-shadowed metallized gratings
Can Yesilyurt
A single oblique metallization step gives conventional gratings one-sided silver decoration, established by electron microscopy and elemental mapping. Opposite-face reversal measurements yield finite-aperture red/green/blue transmission ratios up to 1.74 for a 1-$\mu$m grating and 1.5-1.8 for a 30-$\mu$m grating, with reference-normalized transmittances for the latter. Flat-side coating and reduced silver dose give ratios near unity. Maxwell calculations on self-shadowed growth profiles reproduce the directional sign qualitatively and attribute the contrast to diffraction-channel redistribution. The structure remains reciprocal, including its normal-incidence zeroth-order transmission. These results establish directional metallization as a route to direction-selective optical transmission without multilayer
alignment or overlay lithography.
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Other Condensed Matter
Phase synchronization of fish schools through spatial gaps
Elena G. de Lamo, Óscar Sánchez, M. Carmen Miguel et al. (+1 more)
We investigate how sensory coupling mediates phase coherence between spatially separated, confined active systems. Using two fish schools separated by a water-filled transparent gap, we isolate
vision as the primary interaction channel. Under boundary confinement, each school's center-of-mass heading exhibits noisy bistable dynamics, spontaneously switching between two antiparallel directions along the partition wall. Turning events in one school bias the orientation of the other, driving distance-dependent phase synchronization. We model this behavior using two coupled
stochastic bistable oscillators whose exact solution quantitatively reproduces the empirical results. Our work establishes a precise connection between nonequilibrium active systems and coupled
stochastic oscillators, offering insight into boundary-spanning information transfer in living collectives.
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All authors Elena G. de Lamo, Óscar Sánchez, M. Carmen Miguel, Romualdo Pastor-Satorras
Mathematical Physics · Cross-listed from math.AP
The entropy production is not always monotone for hard spheres or for Maxwell molecules
Luis Silvestre
In 1966, McKean asked whether the
entropy production of the Boltzmann equation must be monotone decreasing in time. We show that this is not the case even in the space-homogeneous setting for the Boltzmann collision operator with a constant angular cross section and the kinetic parameter $\gamma \in [0,1]$. This recovers the classical case of hard spheres and the simplest case of Maxwell molecules. Our examples are radially symmetric mixtures of Maxwellians.
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Quantum Physics
$\mathcal{N}$-bein formalism for degenerate states in the parameter space of quantum geometry
Jorge Romero, Carlos A Velasquez and J David Vergara
Recently, we introduced a
geometric object analogous to an orthonormal frame in the Cartan formalism to study the parameter space of
quantum systems; we called it $\mathcal{N}$-bein, with $\mathcal{N}$ being the number of parameters that characterize the
quantum system. Acting as the “square root” of the
quantum geometric tensor (QGT), the $\mathcal{N}$-bein allows us to define new tensors to improve our understanding of the structure beneath the parameter space of
quantum mechanics. In this work, we extend this mathematical framework surrounding the $\mathcal{N}$-bein to analyze the parameter space of
quantum systems with degenerate spectra. As in the non-degenerate case, we define a non-Abelian two-state QGT to identify possible transitions between degenerate states after two consecutive parameter variations. Additionally, using the Wilczek-Zee connection, we introduce a torsion-like tensor as the covariant derivative of the $\mathcal{N}$-bein. This torsion captures the noncommutativity of successive parameter variations and coincides with the antisymmetric part of the two-state QGT. We also present a geometrical formulation using differential forms and discuss the physical implications of the newly defined tensors. Furthermore, we construct several gauge-invariant observables from the $\mathcal{N}$-bein and its derivatives to highlight the utility of the new tensors. Finally, to illustrate the convenience and applications of this formalism, we apply the theoretical framework to a system of coupled harmonic oscillators immersed in an electric field. The coupling between the oscillators results in a degenerate system. Thus, using the new formalism, we found correlations among the
quantum states quantified by the new invariants.
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Plasma Physics
The Fusion Equilibrium Challenge: Inferring Magnetic Geometry Without Magnetic Diagnostics
Tapan Ganatma Nakkina, Matthew Waller, Craig Michoski et al. (+6 more)
Next-generation fusion reactor devices such as SPARC, ARC, and CFETR will operate in extreme
neutron environments that compromise the
magnetic sensors traditionally used to reconstruct
plasma equilibria. However, reliable knowledge of the
plasma equilibrium–including
magnetic flux surfaces, safety factor profiles, and shaping parameters–is indispensable for real-time control, disruption avoidance, and physics interpretation. The Fusion
Equilibrium Challenge invites the NeurIPS community to confront a deceptively simple but scientifically rigorous inverse problem: reconstruct the two-dimensional poloidal flux function psi(R,Z) and a suite of scalar
equilibrium parameters from non-
magnetic diagnostics alone, namely external poloidal-field coil currents and Thomson-scattering electron temperature/density profiles. The challenge provides the first open-access, harmonized multi-machine
benchmark for fusion, releasing a curated
dataset of 9,113 DIII-D shots and 2,416 MAST shots–filtered for Thomson-diagnostic availability, feature completeness, and EFIT-reconstruction quality. Each shot is packaged into a standard Parquet file containing approximately 260 (DIII-D) / approximately 80 (MAST) EFIT flux maps and rich high-rate diagnostics. Two complementary awards reward intra-machine reconstruction fidelity (S_model) on DIII-D and zero-shot cross-machine generalization (G_ratio) to the topologically distinct MAST spherical tokamak. We argue that the challenge functions as a
benchmark for reactor-ready
equilibrium inference and as a probe of how far machine learning can be pushed toward truly machine-agnostic
plasma state estimation.
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All authors Tapan Ganatma Nakkina, Matthew Waller, Craig Michoski, Brian Sammuli, David R. Hatch, William Boyes, Mitchell Clark, Raffi Nazikian, Sterling Smith
Quantum Physics
Reliable Sample-Level Quantum Error Mitigation via Dominance-Aware Clustering
Mohsen Ghodrati, Kausthubh Chandramouli and Dror Baron
Many
quantum algorithms for classically difficult optimization tasks must return high-quality bitstrings from finitely many
circuit executions, whereas most
quantum error-mitigation methods target expectation values. We study sample-level recovery when measured probability mass is distributed around multiple latent bitstrings, called centers. Each component of the measured probability mass is called a source and we assume that each center is associated with one source. We identify dominance-at every coordinate, more than half of a retained region's probability mass comes from one source and agrees with its center-as a sufficient condition under which majority voting recovers that center with exponentially decreasing error probability. We show that nearest-center assignment, as used in clustering
algorithms such as the $k$-modes
algorithm, can fail to produce dominated regions even when the true centers are known. This failure motivates responsibility thresholding and a local dominance screen, whose combination we call dominance-aware (DA) refinement. Synthetic and simulated MaxCut-QAOA experiments show that DA refinement favors precision, while $k$-modes with DA refinement improves overall center recovery. All procedures are classical post-processing and require no additional
quantum-
circuit executions.
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Astrophysics of Galaxies
Virgo Filaments VIII: Characterizing the Structural Parameters of Virgo Galaxies with Machine Learning to Probe Environmental Quenching
Kim Conger, Gregory Rudnick, Rose A. Finn et al. (+9 more)
A persistent challenge in
galaxy evolution involves disentangling the many correlated properties in order to isolate the effects of a
galaxy's environment on its
star formation history. To address this multidimensionality problem, we apply k-means clustering to 2831
galaxies in the extended regions around the Virgo cluster to define objective, reproducible subsets of structurally similar
galaxies. Using measurements of size, light distribution, and
stellar mass, k-means partitions these
galaxies into three feature classes (FCs):
dwarfs, spheroids, and large disks. In addition to being structurally different, these FCs show distinct offsets from the
star-forming main sequence to $>3\sigma$ significance, with the spheroid population systematically shifted to lower
star formation rates. Examining environmental dependence within each FC, we find that denser environments are associated with progressively stronger quenching. However,
star formation for the
dwarf and large disk
galaxies is not strongly affected until the rich group and cluster environments. For the spheroid
galaxies,
star formation instead smoothly decreases as environment density increases. We verify that these trends are not driven by differences in Sersic index within each environment, suggesting that the effectiveness of environmental quenching depends on the
galaxy's structural class. Our results speak to the utility of a simple machine learning model to create broad classes of structurally similar
galaxies based on a small set of parameters, which has important implications for navigating this data rich era of astronomy.
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All authors Kim Conger, Gregory Rudnick, Rose A. Finn, Rebecca A. Koopmann, Benedetta Vulcani, Dennis Zaritsky, Gianluca Castignani, Francoise Combes, Gabriella De Lucia, Matteo Fossati, Gautam Nagaraj, Daria Zakharova
Instrumentation and Methods for Astrophysics
Learning and Predicting the Nonlinear Variability of X-ray Binaries with the Koopman Operator
Eric Miao, Ruo-Yu Shang, Kaya Mori et al. (+1 more)
X-ray variability in compact-object binaries encodes the nonlinear dynamics of corona-jet interactions and
accretion disk instabilities. Standard timing techniques characterize periodic and quasi-periodic variability well, but do not model underlying nonlinear dynamics or forecast their
evolution. We apply Koopman operator theory and a data-driven approximation, extended dynamic mode decomposition (EDMD), to X-ray light curves for the first time. Koopman theory represents nonlinear
evolution as an infinite-dimensional linear operator $\mathcal{K}$, whose eigendecomposition separates a complex system into independently evolving linear modes. We derive that each Koopman eigenfunction contributes a Lorentzian peak to the power spectrum, giving quasi-periodic oscillations a dynamical interpretation in which process noise damps modes and broadens their peaks. In both chaotic Duffing oscillator simulations and $\sim$30 yr of RXTE ASM and MAXI monitoring of the X-ray binary 4U 1705-44, the slowest-varying eigenfunction partitions state space into low- and high-flux regimes, changing sign days to weeks before transitions become visible in the light curve. Iterating $\mathcal{K}$ additionally yields flux forecasts on days-to-weeks horizons. The strengths of this framework are its generality across linear and nonlinear systems, its intrinsic interpretability through decomposed modes carrying explicit dynamical meaning, and its predictive power from propagating learned dynamics forward. These results establish Koopman operator theory as a new frontier of astrophysical timing and help advance interpretable machine learning for scientific discovery and understanding.
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All authors Eric Miao, Ruo-Yu Shang, Kaya Mori, Reshmi Mukherjee
General Relativity and Quantum Cosmology
Exploring the construction of field equations for regular black holes with dynamical regularization scales
Raúl Carballo-Rubio and Jacopo Mazza
The study of the dynamics of regular black holes is an emergent area of research. Recent works have discussed how to deform the Einstein field equations to regularize spherically symmetric black hole solutions due to the introduction of a new physics scale acting as regulator. In this exploratory paper, we consider for the first time the problem of constructing field equations in which the regularization scale is a dynamical field. Such field equations may provide an effective description of the
evolution of the cores of regular black holes due to the backreaction of matter, and a novel avenue for constructing alternative dynamical solutions of theoretical and phenomenological interest. We discuss a general family of field equations describing spherically symmetric
gravity coupled to a scalar field, and study whether the sector with a constant scalar field contains solutions describing static regular black holes with no additional physics scales aside from the ones provided by the scalar field. We show that this question can be reduced to solving a linear partial differential equation for the coupling functions between the scalar and the metric degrees of freedom.
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High Energy Physics (Theory)
Truncated Polyakov bootstrap
Kaushik Kangshabanik, Apratim Kaviraj and Shailesh Lal
We set up a truncated numerical approach in the Polyakov bootstrap (PB) framework. We employ a gradient descent optimization to solve PB sum rules numerically, and hence solve crossing for arbitrary deformations of the generalized free field (GFF) spectrum in an iterative way starting from a perturbative solution. For
unitary deformations the solutions coincide with extremal CFT spectra. But more interestingly, our findings indicate that a general crossing solution, not necessarily
unitary (i.e. without positivity), can be uniquely identified by a smooth connection to GFF. The truncated Polyakov bootstrap approach is established through a number of examples in both single and mixed correlator settings.
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Materials Science
A Spatial Localizer for Constituent-Resolved Exciton Wannier Functions
Haylen Gerhard and Wladimir A. Benalcazar
Excitons are composite quasiparticles: beyond a center-of-mass position, each carries an internal electron-hole dipole governing its coupling to electric fields and other
excitons.
Exciton Wannier functions locally represent
exciton bands, but resolving this dipole requires localizing the electron and hole simultaneously. We show that, in one dimension, the projected electron and hole position operators fail to commute when the covariant derivative of the
quantum geometric dipole (QGD)
matrix (the difference between the hole and electron non-Abelian Berry connections) is nonzero. This precludes a common eigenbasis and bounds the joint electron-hole spread from below. For one band, the internal dipole is gauge invariant and center-of-mass methods suffice; for multiple bands, no existing construction yields a gauge minimizing both position uncertainties. We introduce an “
exciton spatial localizer,” a Hermitian operator
embedding both projected positions in a Clifford-
algebra structure. Its spectral minima locate the
exciton's center-of-mass and dipole coordinates, while its eigenvectors yield
exciton Wannier functions jointly localized in electron and hole coordinates without gauge fixing, an ansatz, or iterative optimization. In an interacting
bilayer model, combined reflection–time-reversal
symmetry or a nonsymmorphic particle–hole
symmetry forces the QGD
matrix to be traceless at every momentum while allowing it to remain nonzero. A two-band
exciton subspace with zero net internal dipole then decomposes into a
symmetry-related pair of
exciton Wannier functions with opposite center-of-mass positions and internal dipoles. Adding the interlayer dipole as a Clifford component further separates intralayer and interlayer
exciton Wannier functions in a six-band subspace.
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High Energy Physics (Phenomenology)
Tremaine-Gunn Control: Evading Bounds on Light Fermion Dark Matter
Joel Barir, Diego Blas, Anubhav Mathur et al. (+1 more)
Pauli exclusion is often regarded as imposing a model-independent lower bound on the mass of fermionic dark matter in
galaxies. We show that dark-sector interactions can substantially weaken this conclusion. In particular, eV-scale
fermions can form bound structures with the characteristic sizes and densities of
dwarf galaxies, thereby circumventing the conventional Tremaine-Gunn mass constraint. Within these objects, the degeneracy pressure is balanced by an attractive finite-range scalar Yukawa force that is significantly stronger than
gravity. The interaction acts on
dwarf-
galaxy scales while remaining screened on larger scales. We derive the
evolution of the resulting dark-matter fluid and identify a viable cosmological history in which structures first form gravitationally, with the new interaction becoming active only at late times. As a proof of concept, we construct a model in which a single late-time phase transition generates the required dynamics. These results provide a new route to exceptionally light fermionic dark matter and demonstrate that dark-sector interactions can qualitatively alter conventional phase-space limits.
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All authors Joel Barir, Diego Blas, Anubhav Mathur, Tomer Volansky
Quantum Physics
Non-Markovian interactions with pulses of quantum radiation
Julien Pinske and Stefan Scheel
The interaction of a traveling pulse of
quantum light with a localized
quantum system shows non-Markovian features when scattering takes place in a structured environment. Here, we devise a non-Markovian input-output theory by coherently coupling the scatterer to a pseudomode, which decays into a Markovian reservoir. This incorporates
memory effects of a structured environment without altering the cascaded nature of the Lindblad master equation, whose solution provides the
quantum state of the output field of any desired mode. We apply our theory to the stimulated emission by a two-level atom, and to transmission of a Gaussian pulse through a cavity. We observe that the non-Markovian revival of coherence in the scatterer distorts the single-mode nature of the incoming pulse, thus resulting in a multimode output field.
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Quantum Physics
Bilinear correlations in Fluctuating Gaussian States with anti-unitary symmetries
Xu Zhang
We study bilinear order-parameter correlations in a general class of sign problem-free systems that are described by what we call Fluctuating Gaussian States (FGS) with anti-
unitary symmetries, where the weight of each Gaussian measurement in the space-time path integral is positive-definite. Supported by Monte Carlo simulations on fluctuating Gaussian fermionic and bosonic examples, we argue that such systems generally exhibit two types of broken-
symmetry phases: a saddle point phase and a non-local contraction phase, with the competition between the two determined by the stability of the fluctuation saddle point of FGS. Due to the
Fermi liquid instability in fermionic FGS with anti-
unitary symmetries, we also discuss the possibility of representing fermionic FGS with a particular Projected Entangled-Pair State (PEPS) ansatz, which we argue a certain construction provides an efficient description for the saddle point phase, but not for the non-local contraction phase. Finally, we discuss the potential implication of our result in non-
equilibrium systems and stabilizing a target bilinear order.
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Earth and Planetary Astrophysics
From orbit to ground: pre-impact meteorite strewn field predictions for imminent impactors and meteorite recovery
Anna Moscati, Marco Fenucci, Laura Faggioli et al. (+3 more)
The flux of meteoroids reaching the Earth is continuous, ranging from microscopic grains to occasional metre and decametre scale bodies. The smallest ones fully ablate in the upper atmosphere, whereas sufficiently large or strong objects survive entry and deposit fragments on the ground as meteorites. Predicting where these fragments land, and reconstructing the atmospheric trajectory and fragmentation sequence that produced them, is central both to hazard assessment and to the recovery of freshly fallen material. The accuracy of such predictions, however, remains limited by poorly constrained fragmentation processes and by sparse, heterogeneous observational coverage of individual events. Traditional strewn field simulations rely on detailed fireball data and event-specific assumptions on fragment masses, aerodynamics, and breakup. These approaches are effective for well-instrumented events, but their applicability degrades rapidly when observations are sparse, often resulting in huge uncertainties. We present an ab initio framework predicting strewn fields of near-Earth asteroids directly from pre-impact orbital solutions. It propagates luminous trajectory and dark flight using a physics-based translational dynamics model and realistic atmospheric conditions, without requiring fireball triangulation or event-specific tuning. Validation against recent asteroid falls with recovered meteorites shows agreement with observations, with nominal solutions reproducing fall locations within 100-200 m. The new method has been integrated into the ESA Aegis pipeline, which now enables hours-ahead computation of impact locations, supporting recovery efforts, minimizing contamination, and, where warranted by object size and predicted ground hazard, civil-protection decision making.
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All authors Anna Moscati, Marco Fenucci, Laura Faggioli, Marco Micheli, Francisco Ocaña, Juan Luis Cano
Earth and Planetary Astrophysics
Mass constraints for the K2-223 system planets: An ultra-short-period sub-Earth, a short-period super-Earth, and a tentative long-period giant planet
Dawid Jankowski, Grzegorz Nowak, Gaia Lacedelli et al. (+23 more)
We present mass constraints of two short-period Earth-sized
planets transiting K2-223 based on high-precision radial velocity measurements from HARPS-N and ESPRESSO, as well as a tentative indication of an outer Jupiter-like
planet orbiting the G1V
dwarf K2-223. With a radius of $R_\mathrm{b}=0.79\pm0.10$ $\mathrm{R_{\oplus}}$ and a 3$\sigma$ upper mass limit $M_\mathrm{b}<2.8$ $\mathrm{M_{\oplus}}$, K2-223 b belongs to the small group of known sub-Earth
planets and is currently the smallest known ultra-short-period
planet ($P_\mathrm{b}\approx$ 0.5 day) transiting a
solar-type
star. With a radius of $R_\mathrm{c}=1.41\pm0.15$ $\mathrm{R_{\oplus}}$, a mass of $M_\mathrm{c}=4.2\pm1.3$ $\mathrm{M_{\oplus}}$, and a density of $\rho_\mathrm{c}=8.3\pm3.7$ $\mathrm{g\,cm^{-3}}$, K2-223 c is a short-period ($P_\mathrm{c}\approx$ 4.5 days) super-Earth. Based on almost 6.5 years of radial velocity monitoring of K2-223 with the HARPS-N spectrograph, we identified a tentative
giant planet with an orbital period of $P_\mathrm{d}=4.53^{+0.32}_{-0.34}$ $\mathrm{years}$ and a minimum mass of $1.29^{+0.23}_{-0.17}$ $\mathrm{M_{\rm Jup}}$. Two close-in small
planets accompanied by a distant candidate Jupiter-like companion would make K2-223 a system with a rare architecture. This is valuable for testing scenarios of planetary formation and
evolution. The extreme proximity of K2-223 b to the parent
star means that relativistic and
tidal perturbations to Newtonian
gravity need to be considered. We discuss the timescales and amplitudes of these effects in the context of the radial velocity model and dynamical simulations of the K2-223 multiple-
planet system. We also present a parametrisation of the
planets with directly measured masses, radii, and bulk densities in terms of the orbital period normalised by the Roche period. This provides an alternative representation in the context of the Neptune desert.
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All authors Dawid Jankowski, Grzegorz Nowak, Gaia Lacedelli, Enric Pallé, Krzysztof Goździewski, Thomas Masseron, Ilaria Carleo, Rafael Luque, Felipe Murgas, Davide Gandolfi, Artie P. Hatzes, William Cochran, Pedro Figueira, Rafael A. García, Samuel Geraldía-González, Judith Korth, Pierrot Lamontagne, John H. Livingston, Savita Mathur, Giuseppe Morello, Jaume Orell-Miquel, Dinil B. Palakkatharappil, Carina M. Persson, Seth Redfield, Atanas K. Stefanov, Vincent Van Eylen