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Physics

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Monday 24 August

Accelerator Physics

White Paper on a Novel FFA-Based CEBAF Upgrade to 22 GeV

S. A. Bogacz, R. M. Bodenstein, K. E. Deitrick et al. (+11 more)

We present a conceptual design for a cost-effective upgrade of the Continuous Electron Beam Accelerator Facility (CEBAF) to 22 GeV using non-scaling fixed-field alternating-gradient (FFA) arcs built from Halbach-style permanent magnets. Building on the eight-pass energy-recovery demonstration at the Cornell–BNL CBETA test accelerator, the design replaces the highest-energy recirculation arcs with a pair of FFA arcs that simultaneously transport six passes spanning a factor-of-two momentum range. We describe the machine layout; including the injector, recirculating linacs, spreaders and recombiners, FFA arcs, splitters, transition and extraction regions; together with beam-dynamics validation studies covering emittance growth, synchrotron-radiation-driven depolarization, and orbit correction, and we summarize permanent-magnet design, prototyping, and radiation-resiliency results. This white paper documents the accelerator physics underpinning a staged path to 22 GeV that preserves CEBAF's multi-hall, high-luminosity, polarized-beam capabilities.
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All authors S. A. Bogacz, R. M. Bodenstein, K. E. Deitrick, B. R. Gamage, R. Kazimi, D. Khan, E. Nissen, S. Ogur, Y. Roblin, P. Rossi, J. S. Berg, S. J. Brooks, D. Trbojevic, V. Morozov

Quantum Physics

Dual-Isotope Sympathetic Cooling in a Long Ion Chain

Tianyi Wang and Marko Cetina

Owing to their high controllability and connectivity, one-dimensional ion chains are attractive building blocks for near-term quantum computers. However, long ion chains are susceptible to motional heating caused by fluctuating external electric fields. To enable deep computations, this source of noise must be suppressed without inducing qubit decoherence or degrading qubit connectivity. We demonstrate steady-state mid-circuit sympathetic cooling of all computationally-relevant motional modes of a 23-ion chain consisting of \qubit qubit and \coolant coolant ions without using any qubit operations. In a room-temperature system, our cooling scheme preserves the mean phonon occupations of the long-wavelength axial and radial modes near their values following state preparation, while keeping the modes used to implement entangling gates near their ground states throughout a 56-ms circuit. Crucially, we show that our cooling sequence preserves qubit coherence, and evaluate its impact on single- and two-qubit gate operations. Additionally, we demonstrate a parallel qubit reset protocol leveraging the shared radial mode coupling between species. Our sympathetic cooling scheme represents a critical step toward reducing gate errors in individually-addressed long ion chains and establishes a versatile platform for simulating open quantum systems.
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Astrophysics of Galaxies

FASHI DR2: A Catalog of 132 Low-Redshift HI 21 cm Absorption Systems

Chuan-Peng Zhang, Ming Zhu, Peng Jiang et al. (+7 more)

We present an untargeted survey of 21 cm HI absorption systems based on the second data release of the FAST All Sky HI survey (FASHI DR2), covering approximately 19,500 deg$^{2}$ at $z\lesssim0.09$. A total of 132 HI absorbers are identified, including approximately 60 new discoveries, forming one of the largest homogeneous samples of low-redshift HI absorbers assembled to date. The sample extends to continuum flux densities as low as 2.6 mJy, substantially below the limits of previous flux-limited surveys. The absorber population is dominated by narrow systems ($W_{50}<100$ km s$^{-1}$), while broad absorbers ($W_{50}>200$ km s$^{-1}$) account for 13.6% of the sample. Most absorbers are optically thin, with a median optical depth of $\tau_{\rm HI}\approx0.14$. The velocity-offset distribution is broadly symmetric about the systemic velocities of the host galaxies. The associated absorbers are preferentially found in massive, actively star-forming galaxies. We find tentative evidence for a weak anti-correlation between HI column density and stellar mass, although the relation exhibits substantial scatter. These results provide the first statistical characterization of the low-redshift HI absorber population based on the FASHI DR2 sample and establish a valuable benchmark for future HI absorption surveys with next-generation radio facilities.
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All authors Chuan-Peng Zhang, Ming Zhu, Peng Jiang, Hong Guo, Yizhou Gu, Cheng Cheng, Jin-Long Xu, Nai-Ping Yu, Xiao-Lan Liu, Bo Zhang

Materials Science

FUCrIMODo: structure recovery from atomistic descriptors via multi-stage genetic algorithms

Louis Boehm, Martin Kuban and Claudia Draxl

Data-driven approaches to materials discovery rely on numerical representations of atomic structures as input for machine learning models. Inverting these descriptors - recovering atomic structures from their representations - is essential for most generative material design pipelines, yet it remains challenging, particularly for periodic systems. Existing inversion methods are either tailored to specific invertible descriptors or require candidate structures with similar atomic arrangements and compositions, limiting the exploration of novel regions in chemical and configurational space. Here, we propose a generalizable, similarity-driven sampling approach, powered by a novel stage-wise optimization strategy, to recover atom types, atomic positions, and unit cell shapes directly from a descriptor. Our approach requires only descriptor features and parameters as input without any prior structural knowledge. The capability of our method is demonstrated by the averaged Smooth Overlap of Atomic Positions (SOAP) descriptor.
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Quantum Physics

Quantum-Geometric Length Scale for Long-distance Squeezing in Bosonic Bogoliubov Systems

Sonu Verma, Sangmo Cheon, Myung-Joong Hwang et al. (+1 more)

Multimode squeezing is a key resource for continuous-variable quantum technologies, but its spatial range in bosonic lattices is usually tied to dispersive propagation. Here we show that parametric pairing can create an exactly flat Bogoliubov band spanned by compact Bogoliubov generators, while producing phase-sensitive anomalous correlations and sub-vacuum collective-mode squeezing that extend far beyond their finite support. Each compact generator mixes annihilation and creation operators, thereby encoding the Bogoliubov squeezing structure, and neighboring translated generators can have nonzero commutator overlap. Enforcing canonical bosonic commutation relations therefore requires spatially extended linear combinations of these translated compact generators, which define the canonical Bogoliubov modes. The squeezing transformation of these modes varies with momentum and is quantified by the squeezing-sector symplectic quantum metric. A complex-momentum singularity of the analytically continued canonical Bogoliubov modes sets both the anomalous-correlation decay length and the momentum-space width of this metric, defining an intrinsic quantum-geometric length scale. This singularity can be tuned continuously while preserving exact flatness, thereby controlling the spatial range of correlations and squeezing. Away from exact flatness, long-distance correlations persist through multiple decay channels, while modes localized by defects and dimerized boundaries provide complementary probes of the underlying quantum geometry. In the weak-damping limit, the same quantum-geometric length scale can be extracted from frequency-filtered two-port correlations. Our results establish the quantum geometry of canonical Bogoliubov modes as a mechanism for spatially extended quantum resources arising from compact Bogoliubov generators.
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All authors Sonu Verma, Sangmo Cheon, Myung-Joong Hwang, Moon Jip Park

Strongly Correlated Electrons

A DQMC study of the spectral and conductive properties of the two-dimensional Holstein model

J. Neuhaus, B. Cohen-Stead, N. Mannella et al. (+1 more)

We study the dynamical properties of the two-dimensional square lattice Holstein Hamiltonian using numerically exact determinant quantum Monte Carlo simulations. In particular, we report systematic calculations of the model's single-particle spectral function and optical conductivity over a range of phonon energies, electron-phonon coupling strengths, carrier concentrations, and temperatures. In doing so, we map the evolution of the system from a dressed metallic phase to a (bi)polaron liquid/insulator to a charge-density-wave insulator as the carrier concentration is tuned from dilute values to half-filling. We corroborate these results using several equal-time correlation measurements and related proxy quantities reconstructed from time-displaced correlation measurements. This paper is also accompanied by an extensive open data set, covering over 16,640 unique parameter values.
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All authors J. Neuhaus, B. Cohen-Stead, N. Mannella, S. Johnston

High Energy Physics (Theory)

Landau theory, effective temperature, and tricritical phenomena in a holographic nonequilibrium steady state

Motohiro Kanazawa, Masataka Matsumoto and Shin Nakamura

We investigate the critical exponents $(\gamma,\nu)$ at the current-driven tricritical point (TCP) associated with chiral symmetry breaking in a nonequilibrium steady state described by the D3/D7 model. In the symmetry-broken phase, we find that, unlike in the conventional Landau theory, both $\gamma$ and $\nu$ can take values different from those predicted by the Landau theory and depend on the path along which the TCP is approached in the phase diagram. However, when the TCP is approached with the ratio of the effective temperature to the heat bath temperature, $T_{*}/T$, held fixed, the critical exponents agree with those of the Landau theory. These results suggest that the critical phenomena at the current-driven TCP may be described by the Landau theory along the $T_{*}/T$-fixed line, whereas a nontrivial extension of the Landau theory is required for a more general description of the critical phenomena along arbitrary paths.
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Quantum Physics

Entanglement-enhanced fluctuation-free daemonic ergotropy with random measurements

Saptarshi Roy, Pritam Halder, Tamal Guha et al. (+1 more)

Optimized daemonic ergotropy can make entanglement thermodynamically dispensable in measurement-assisted work extraction: for a fixed system marginal, quantum-classical states can reproduce the maximal work obtainable by optimizing the auxiliary measurement. We show that this equivalence is broken when the auxiliary measurement is randomized. For qudit-qubit quantum-classical states under Haar-random projective measurements, we derive upper bounds on the averaged daemonic gain and prove a gain-fluctuation trade-off, showing that any positive randomized gain necessarily entails measurement-induced fluctuations. In sharp contrast, a family of two-qubit entangled pure states attains the algebraic maximum of the gain allowed by a system marginal while remaining fluctuation-free for every measurement basis, yielding at least twice the gain achievable by any quantum-classical state with the same marginal. We further demonstrate that such conclusion holds when general two-qubit separable states are considered positioning randomized gain as a sufficient criterion for entanglement certification. Finally, we show that the entanglement advantage persists under partially randomized measurements sampled from a polar cap around the optimal basis. These results establish randomized daemonic ergotropy as a thermodynamic probe of entanglement and exhibit the connection between measurement-induced work fluctuations on the type of correlations: quantum entanglement vs classical.
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All authors Saptarshi Roy, Pritam Halder, Tamal Guha, Hyunseok Jeong

Instrumentation and Detectors

Performance Evaluation of a High-Granularity LYSO-SiPM-Based Position-Sensitive Detector for a One-Shot Gamma-Scanning System with Sub-Millimeter Spatial Resolution

Katyayni Tiwari, Arzoo Sharma, Jürgen Gerl et al. (+5 more)

A compact position-sensitive {\gamma}-detector based on a thin monolithic LYSO crystal and a 96-channel SiPM array is developed for the spatial characterization and calibration of segmented {\gamma}-ray detector systems used in nuclear-physics experiments. The detector is designed to provide localized irradiation and rapid two-dimensional response mapping. A 7 cm diameter and 3 mm thick LYSO crystal is optically coupled to the SiPM array, and the position of the incident {\gamma}-ray interaction is reconstructed from the relative scintillation-light signals collected by neighboring SiPM channels. An asymmetry-based charge-sharing method is employed to determine the interaction position from the spatial distribution of the detected scintillation light. Detailed GEANT4 simulations, including optical photon transport, were performed to investigate the detector response and estimate its intrinsic spatial resolution. The simulations predict a spatial resolution of approximately 0.5 mm for 60 keV and 511 keV {\gamma}-rays under idealized conditions. A prototype detector was developed and experimentally characterized using coincidence measurements with the {\gamma}-scanning facility at GSI, Germany. The experimental measurements demonstrate a spatial resolution better than 1 mm in the central detector region, while the position-dependent response and degradation near the detector boundaries are investigated. The experimental results are compared with GEANT4 predictions to identify the contributions of optical photon transport, charge sharing, and detector geometry to the measured spatial resolution. The developed detector provides a compact solution for the three-dimensional characterization of highly segmented {\gamma}-ray detector arrays in nuclear physics experiments.
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All authors Katyayni Tiwari, Arzoo Sharma, Jürgen Gerl, Ivan Kojouharov, P. Herrmann, H. Schaffner, G. Aggez, Pushpendra P. Singh

Materials Science

Giant Surface-driven Nonlinear Hall Effect in BiTeCl at Room Temperature

Zhihua Liu, Ziheng Wang, Yongbo Lv et al. (+9 more)

The nonlinear Hall effect (NLHE) provides a pathway to generate a Hall response in time-reversal-symmetric yet inversion-symmetry-broken systems. NLHE can rectify an alternating current into a transverse direct voltage, making it attractive for radio-frequency rectification, energy harvesting, and terahertz detection, applications for which device miniaturization remains a central pursuit. In this context, the inherent inversion symmetry breaking at surfaces is particularly appealing: because symmetry is necessarily broken at the surface of any crystal, irrespective of whether its bulk is centrosymmetric, surface-driven nonlinear responses lift the stringent constraint on bulk symmetry and open a route toward compact device architectures. Here we report the observation of a giant, surface-driven second-order nonlinear Hall effect in the Rashba-type polar semiconductor BiTeCl at room temperature. The determined second-order nonlinear Hall susceptibility at 300 K reaches 1.68 $\mu$mV$^{-1}$, which is 80 times larger than that of the best previously reported surface-dominated systems. We attribute this giant response to the synergistic interplay between BiTeCl's polar crystal structure and its rich surface states: the polar stacking renders the top and bottom surfaces inequivalent, so that the nonlinear response originates from a single surface without compensation from the other. Symmetry and scaling analyses suggest that both skew-scattering and side-jump mechanisms contribute to the observed effect. Our findings not only identify BiTeCl as a promising platform for future applications utilizing the NLHE, but also establish the asymmetry between the opposite surfaces of a polar crystal as a general design principle for discovering surface-driven materials with larger nonlinear Hall responses.
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All authors Zhihua Liu, Ziheng Wang, Yongbo Lv, Hanru Feng, Zhiwei Zhang, Bo Zhang, Feng Liu, Guohua Wang, Shengwei Jiang, Hao Chu, Hui Li, Dong Qian

Cosmology and Nongalactic Astrophysics

Black holes from a Higgs-like field in the radiation era

Ethan Milligan, Luis E. Padilla and David J. Mulryne

Light spectator fields during inflation can acquire superhorizon fluctuations that cross a potential barrier between positive and negative regions of their potential. Motivated by the Standard Model Higgs instability, in this work we study the subsequent evolution of patches where this occurs in the radiation era after inflation ends for a Higgs-like spectator field. We utilise fully nonlinear, spherically symmetric numerical relativity. Across the black hole forming configurations in our investigation we find a robust two-stage evolution. First, the central negative potential region reverses its expansion, becomes kinetic dominated, and forms a primordial black hole that hides the runaway core. The positive potential barrier that survives outside this first horizon then determines one of two late-time branches. In the subcritical branch the original apparent horizon grows smoothly and engulfs the remaining scalar structure. In the supercritical branch, however, the potential energy of the barrier dominates the local evolution. The result is a transient wormhole throat, a bifurcating trapping horizon, and an inflating child universe branch. In both branches the parent radiation dominated universe is ultimately left with an ordinary primordial black hole whose subsequent growth is governed by radiation accretion.
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Solar and Stellar Astrophysics

Breakout/Interchange Reconnection as a driver of Jets, Fast Coronal Mass Ejection, and Solar Energetic Particles

Pankaj Kumar, Judith T. Karpen, David Lario et al. (+4 more)

Understanding how energetic particles are accelerated and released from the low corona into the interplanetary medium during solar eruptions is crucial for space weather research. Here, we present multiwavelength observations of a solar eruption that are consistent with breakout reconnection playing an important role in driving a fast coronal mass ejection (CME) and the associated solar energetic particle (SEP) event. Extreme-ultraviolet and radio observations reveal evidence of breakout reconnection within a fan-spine topology. The filament eruption begins after the pre-eruption opening, accompanied by quasiperiodic jets and associated downflows near the null point, as well as recurrent faint Type III radio bursts during the ongoing slow breakout reconnection. Furthermore, the observations also reveal the formation of pre-eruption coronal rain via slow interchange reconnection near the null point. A large-scale circular ribbon, along with simultaneous four hard X-ray footpoint sources and intense Type III radio bursts, was observed during the explosive breakout reconnection that enabled opening of field lines and allowed energetic particles to escape into interplanetary space. In situ measurements by PSP and Wind confirm the prompt injection of electron beams consistent with the timing of the explosive breakout reconnection. A fast shock associated with the erupting flux rope during interchange reconnection played a major role in producing the gradual SEP event. These observations highlight the key role of breakout reconnection in producing a fast CME/shock with the SEP release and acceleration process. These results have broader implications for particle acceleration and release processes in multiscale null-point topologies, which produce a continuum of eruptions ranging from small-scale jets to large-scale CMEs.
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All authors Pankaj Kumar, Judith T. Karpen, David Lario, Benjamin J. Lynch, Peter F. Wyper, Spiro K. Antiochos, P. K. Manoharan

Optics

Nonlocality is the missing design rule for topological photonics

Fatemeh Davoodi

Topological photonics has provided powerful design rules for routing and localizing light through geometry, symmetry and engineered coupling. However, fabricated nanophotonic and plasmonic devices rarely realize only the local or short-range interaction networks assumed in compact topological models. Long-range near-field coupling, retardation, radiation leakage, substrate-assisted hybridization, material dispersion and fabrication disorder can reshape the optical modes that are interpreted as topological. In this Perspective, I argue that nonlocality should be treated as a design parameter rather than as a residual perturbation. This shift requires moving from ideal phase labels toward calibrated interaction models, finite-structure observables, robustness maps and graded confidence measures. I discuss how full-wave simulations, experiments and physics-informed learning can connect geometric design variables to effective electromagnetic interaction networks. Such calibrated workflows can clarify when a topological design rule is reliable, when it fails, and how nonlocal coupling can be exploited for robust nanophotonic devices.
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General Relativity and Quantum Cosmology

Scalar charge bounds for extremal black hole formation

Berend Schneider

I prove that a collapsing charged scalar field with scalar charge $\mathfrak{e}$ that forms an exactly extremal Reissner–Nordström black hole à la Kehle–Unger with radius $r_+$ must satisfy $|\mathfrak{e}|r_+ > \frac{1}{3}$. In contrast, I also show that no such bound exists for subextremal collapse: a scalar field with an arbitrary $\mathfrak{e} \ne 0$ can form a subextremal black hole with an arbitrary (subextremal) charge-to-mass ratio. Complementing the extremal bound, I prove that a Schwarzschild black hole can become extremal if $|\mathfrak{e}|r_+ > \sqrt{\frac{3 + \sqrt{33}}{3}}$. The fact that $|\mathfrak{e}|r_+$ can be taken to be of order unity could be considered evidence that the third law of black hole mechanics in vacuum is false.
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Solar and Stellar Astrophysics

Preparing for the Early eVolution Explorer: Photometric Diagnostics of Magnetospheric Accretion Geometry in Young Stellar Objects

Laura Venuti, Connor E. Robinson, Ann Marie Cody et al. (+13 more)

The inner disk truncation radius, $R_T$, plays a crucial role in the regulation of star-disk interaction and the early evolution of star-disk-planet systems; however, measuring this parameter is observationally challenging. We present a new method for determining $R_T$ in young accreting systems that hinges on the color dependence of the accretion shock emission in multi-band time-domain surveys. Based on the accretion simulations of Robinson et al. (2017, 2021), we produce synthetic color-magnitude diagrams at near-UV and optical wavelengths that predict the loci of accreting stars as a function of $R_T$. We test these model predictions on young stars with interferometric $R_T$ estimates, finding very good agreement in our results. We apply this novel technique to a pilot survey of 26 classical T Tauri stars in Taurus and Upper Scorpius. We find a predominance of sources with small truncation radii, $R_T < 4\ R_\star$, and an overall distribution of $R_T$ that is statistically similar to that inferred from interferometric studies, while differing from those inferred from emission line modeling. Finally, we discuss the application of this technique to NASA's mission concept EVE, with the goal to provide simultaneous measurements of inner disk truncation radii, corotation radii and mass accretion rates for hundreds of young stars across the Galaxy. The unprecedented survey of inner disk properties that the mission would produce would enable the first stringent test of angular momentum evolution theories in young stars and reveal the impact of the inner disk conditions on early planet architectures.
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All authors Laura Venuti, Connor E. Robinson, Ann Marie Cody, Eric Gaidos, Meredith A. MacGregor, Neal J. Turner, Mark R. Swain, George Zhou, Sydney Vach, Lukas Gehrig, Christopher M. Johns-Krull, Zhaohuan Zhu, Jennifer A. Burt, Ward S. Howard, Damon Landau, Evgenya Shkolnik

Optics · Cross-listed from q-bio.OT

Beyond chlorophyll: machine learning estimates of diagnostic phytoplankton pigments from multispectral ocean colour data

David Moffat, Angus Laurenson, Victor Martinez-Vicente et al. (+4 more)

Phytoplankton play a central role in marine ecosystems and the global carbon cycle, with different groups contributing differently to ocean biogeochemical processes. While standard techniques exist for monitoring phytoplankton concentration from ocean-colour data, their community composition remains difficult to observe at large scales. Chlorophyll-a, widely available from satellite ocean-colour observations, is commonly used as a measure of phytoplankton biomass but provides limited information on taxonomic composition. Accessory pigments, some of which are diagnostic of important phytoplankton groups, offer additional information on community structure, but their retrieval from ocean-colour data is challenging because of limited spectral resolution and strong covariance with chlorophyll-a. In this study, we evaluate machine learning methods for estimating diagnostic pigment concentrations from multispectral satellite observations. Using a global dataset of 33,640 High Performance Liquid Chromatography (HPLC) measurements matched with ESA Ocean Colour Climate Change Initiative (OC-CCI) reflectance data, we compare Random Forest and TabPFN models trained on multispectral reflectance with baseline models using chlorophyll-a alone. A temporally stratified validation scheme is employed to reduce the effects of autocorrelation. Results show that multispectral models consistently outperform approaches based solely on satellite-derived chlorophyll-a, demonstrating that ocean-colour reflectance contains additional information relevant to pigment discrimination. Improvements vary by pigment, with those strongly correlated with chlorophyll-a showing limited gains, while others exhibit substantial improvement. These findings highlight the potential of machine learning to extract ecologically relevant information from satellite data beyond conventional chlorophyll-based approaches.
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All authors David Moffat, Angus Laurenson, Victor Martinez-Vicente, Gemma Kulk, Xuerong Sun, Robert J. W. Brewin, Shubha Sathyendranath

Materials Science

Determination of the ferrimagnetic structure of monoclinic TbFe$_{2}$D$_{4.2}$ deuteride and its evolution versus temperature and high magnetic field

Valerie Paul-Boncour and Olivier Isnard

The magnetic properties of monoclinic TbFe$_{2}$D$_{4.2}$ have been investigated by combining different magnetic measurements, including those involving a high pulsed magnetic field, with neutron diffraction experiments versus temperature and applied field. TbFe$_{2}$D$_{4.2}$ displays a ferrimagnetic ground state with M$_{Tb}$ = 8.2(2) $\mu$$_{B}$ and M$_{Fe}$ = 2.1(2) $\mu$$_{B}$. At 4.2 K a large magnetic anisotropy related to the Tb moments is observed, as saturation is not reached at 50 T. In addition, two metamagnetic transitions are observed for fields of 3 and 29 T. Upon heating, the Tb moment decreases progressively whereas the Fe moment remains constant up to 150 K. At 160 K both Tb and Fe moments sharply decrease, and a 0.38% contraction of the cell volume is observed due to an itinerant electron metamagnetic behavior of the Fe sublattice. This transition temperature is 76 K higher than that of YFe$_{2}$D$_{4.2}$ due to an increase in cell volume, as well as exchange interactions between the Fe and Tb moments. The deuteride becomes paramagnetic above 220 K.
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Mathematical Physics

Instantons in a Double-Well are Poisson Distributed

Jacob Shapiro

We give a rigorous realization of the dilute instanton picture for a semiclassical Schrödinger operator with a symmetric double-well potential on $\mathbb{R}^n$. Using a localized Feynman–Kac representation, we decompose the heat-kernel trace according to the number of passages made by a Brownian bridge between shrinking neighborhoods of the two wells. We identify the weight of one passage with a hopping coefficient $\rho_\lambda$, $\displaystyle \rho_\lambda = \int_{\partial\Omega} \left( \nabla\overline{\varphi_{\lambda,0}^{\Omega}}\, \varphi_{\lambda,0}^{-\Omega} - \overline{\varphi_{\lambda,0}^{\Omega}}\, \nabla\varphi_{\lambda,0}^{-\Omega} \right)\cdot\nu. $ On the exponentially long time scale $\beta=N/\lvert\rho_\lambda\rvert$, the number of passages converges, for every fixed $N>0$, to a Poisson random variable of mean $N$. We identify $-\frac{1}{\lambda}\log\lvert\rho_\lambda\rvert\to S(d,-d)$ and obtain $\displaystyle E_1(\lambda)-E_0(\lambda) = 2\lvert\rho_\lambda\rvert\left(1+o(1)\right). $ Thus the familiar instanton expansion of the double-well eigenvalue splitting emerges directly from a factorization of the heat-kernel trace.
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Strongly Correlated Electrons

Anomalous stabilization of excitons by metallic proximity

Jeongkeun Song, Uksam Choi, Shan Lin et al. (+6 more)

Metallic environments are generally expected to suppress excitons through strong dielectric screening, yet their influence can differ in composite systems where metallic and insulating regions coexist. Here, we investigate excitonic states in PdxCu1-xCrO2 thin films across a percolation-driven metal-insulator transition. Optical spectroscopy and many-body GW calculations show that CuCrO2 hosts strongly bound excitons with a binding energy of about 489 meV. With increasing Pd substitution, the system approaches an insulator-to-metal transition near x = 0.5, consistent with the site-percolation threshold of a triangular lattice. In the pre-percolation regime, the excitonic resonance redshifts by 241 meV while the Tanguy continuum onset remains nearly unchanged, consistent with a substantial increase in exciton binding energy before metallization. An image-charge-based excitonic hydrogen model shows that isolated metallic regions can enhance electron-hole binding through image-charge interactions, whereas conventional screening is recovered once a continuous metallic network forms. Although this model provides a possible interpretation of the observed excitonic evolution, an alternative scenario in which metallic and excitonic responses originate from electronically distinct states and evolve independently cannot be excluded. These results reveal unusual metallic-excitonic coexistence near a percolation-driven metal-insulator transition and suggest nanoscale metallic proximity as a possible route for modifying excitonic interactions.
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All authors Jeongkeun Song, Uksam Choi, Shan Lin, Du Li, Baekjune Kang, Li Yang, Ambrose Seo, Changhee Sohn, Ho Nyung Lee

Computational Physics

First-Principles Electron-Magnon Coupling with Machine-Learning Hamiltonians: From Band Renormalization to Transport

Shixu Liu, Xingding Li, Haozhe Li et al. (+4 more)

In analogy to electron-phonon coupling (EPC), electron-magnon coupling (EMC) is expected to shape electronic structure, transport, and possibly unconventional superconductivity in magnetic materials. However, unlike EPC, which is now routinely treated within first-principles frameworks, a quantitative description of EMC, especially for transport, remains elusive because of the lack of theoretical formalism. Consequently, even for elemental iron, EPC-only calculations miss both the magnitude and the $T^2$ component of resistivity. This discrepancy has long been attributed to EMC, although direct computational evidence has been lacking and the underlying transport mechanism remains unresolved. Here we develop a unified first-principles formalism for EMC in collinear magnetic systems within many-body perturbation theory, complemented by machine-learning spinful Hamiltonians that supply quantities not directly accessible from conventional first-principles methods. Our framework enables ab initio transport calculations including EMC effects for the first time. Applied to ferromagnetic $\alpha$-Fe, our approach yields electron spectral functions consistent with previous studies. More importantly, we recover the full $T^2$ component of resistivity with a coefficient in quantitative agreement with measurement and reveal that the $T^2$ component cannot be attributed solely to EMC, as has long been assumed, but is dominated by the strong EPC-EMC interplay. Extending to antiferromagnetic K-doped $\mathrm{BaMn_2As_2}$, our method captures the ARPES-observed magnon-induced kink and a large EMC strength of $\sim 3$ comparable to experimental measurements, demonstrating the generality of the framework. Our work closes a longstanding gap in the quantitative understanding of transport in magnetic systems and provides a predictive foundation for examining magnon-mediated phenomena.
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All authors Shixu Liu, Xingding Li, Haozhe Li, Yang Zhong, Hongjun Xiang, Xin-Gao Gong, Ji-Hui Yang

High Energy Physics (Phenomenology)

Radiative decays of the isoscalar $S$-wave $D\bar D$ molecule

Yuan-Jun Gao, Gang Li, Shi-Dong Liu et al. (+1 more)

In the hadronic molecular picture, an isoscalar $S$-wave $D\bar{D}$ molecule is naturally expected as the spin-0 partner of $X(3872)$. Assuming this state, denoted by $X_0$, to be a pure $D\bar D$ molecule with quantum numbers $J^{PC}=0^{++}$, we investigate its radiative decays $X_0\to\gamma V (V=\rho^0,\omega)$ within an effective Lagrangian framework. The decay amplitudes are generated by intermediate charmed-meson loops, with electromagnetic gauge invariance consistently maintained throughout the calculation. We evaluate the partial decay widths and examine their dependence on the $X_0$ mass and the cutoff. Although the individual decay widths exhibit a sizable dependence on the cutoff, their ratio is remarkably stable. In particular, we obtain that the ratio for the decays $X_0\to\gamma\rho^0$ and $X_0\to\gamma\omega$ is approximately 2.26, which is insensitive to the variation of the cutoff. This robust ratio provides a useful model-insensitive signature of the molecular structure of $X_0$.
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All authors Yuan-Jun Gao, Gang Li, Shi-Dong Liu, Pan-Pan Shi

High Energy Physics (Theory)

Perturbative Anomaly Inflow on Orbifolds

Hao Y. Zhang

We study perturbative anomaly inflow for effective theories supported on orbifold fixed loci of the internal geometry. Donnelly's equivariant APS theorem gives a fixed-point density, whose degree-$(d+2)$ component is identified as the anomaly polynomial of the $d$-dimensional effective theory. We apply the construction to six-dimensional A-type orbi-instanton theories engineered by $N$ M5-branes probing a transverse $\mathbb{C}^2/\mathbb{Z}_k$ singularity at an end-of-the-world M9-brane. For a flat $E_8$ connection specified by $\rho:\mathbb{Z}_k\to E_8$, we compute the non-identity ALE fixed-point class on the M9 wall. Its degree-eight component agrees with the complete Kac-label-dependent remainder conjectured in \cite{MOTZ} by Mekareeya-Ohmori-Tachikawa-Zafrir, including the $SU(2)_R$ and tangent-bundle curvatures. Together with the known M5/Hořava–Witten and ALE/Hořava–Witten terms, this reproduces the unflavored tensor-branch anomaly polynomial. This local equality further suggests a complete M-theory corner-inflow interpretation. The same prescription also be extended to include flavor symmetries as the centralizer of $E_8$.
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General Relativity and Quantum Cosmology

Kerr Black Hole Uniqueness

Qing Han, Marcus Khuri, Gilbert Weinstein et al. (+1 more)

We prove the black hole uniqueness conjecture in the axially symmetric, stationary vacuum setting: there is no regular, asymptotically flat equilibrium configuration with more than one horizon component. More precisely, we establish that in every such multi-horizon configuration, the logarithmic angle defect along every bounded axis rod is negative, which implies that the net interaction force across each such segment is attractive. The proof is based on a refined asymptotic analysis of the associated singular harmonic maps, partially drawn from the companion work [16], together with a global maximum principle bound for the Weyl conformal factor arising from a novel scalar curvature related differential inequality.
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All authors Qing Han, Marcus Khuri, Gilbert Weinstein, Jingang Xiong

Quantum Physics

Exact Cahill-Glauber Hierarchy for the Double-Morse Ground State

Firoz Chogle, Berihu Teklu and Mauro F. Pereira

Phase-space and quasiprobability methods now play operational roles in quantum technologies, characterizing localization, non-Gaussianity, nonclassical resources, and coarse-graining. We develop an exact, representation-consistent analysis of the lowest quasi-exact ground state of the symmetric double-Morse oscillator. In the double-Morse potential, the dimensionless parameter $A$ controls the separation of the minima and the central barrier, thereby changing the physical ground state. At fixed $A$, the Cahill–Glauber parameter $s$ labels the quasiprobability $W_A^{(s)}(q,p)$: $s=0$, $-1$, and $1$ give the Wigner, Husimi $Q$, and Glauber–Sudarshan $P$ representations, respectively. Although the potential is double-welled for $0<A<1$, the exact ground-state amplitude is single-peaked at the origin and lies above the barrier; as $A$ approaches unity, the merged well remains locally quartic rather than harmonic. Closed analytical expressions are obtained for the Wigner function and Weyl characteristic function. The Wigner function displays the $A$-dependent exchange between position and momentum localization and retains negative regions, certifying nonclassicality and, for this pure state, non-Gaussianity. The Weyl function is its Fourier dual, generates symmetrically ordered moments and cumulants, and yields the full $s$-ordered hierarchy. For $s<0$, isotropic Gaussian smoothing suppresses fine sign-changing structure while preserving the large-scale localization envelope. The Husimi endpoint is nonnegative without implying classicality, whereas the $P$ representation remains distributional. Thus, $A$ controls the physical phase-space geometry, while $s$ controls how the same non-Gaussian and nonclassical state is resolved across complementary representations
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High Energy Astrophysical Phenomena

Binary Neutron Star Merger Simulations with Microphysical Equation of State using Spritz

Fatemeh Hossein Nouri, Jay V. Kalinani, Bruno Giacomazzo et al. (+2 more)

We present the first binary neutron star merger simulations performed with the general-relativistic magnetohydrodynamics (GRMHD) Spritz code employing a finite-temperature tabulated equation of state. Two magnetized binaries with the LS220 equation of state and a GW170817-like chirp mass, differing only in their mass ratios ($q=1$ and $q=0.7$), are evolved from the late inspiral through merger, hypermassive neutron-star (HMNS) formation, and delayed collapse to a black hole (BH). We investigate how the binary mass ratio influences the postmerger evolution, jet-launching conditions, and matter ejection. We find that the equal-mass binary forms a slightly longer-lived HMNS, allowing more efficient magnetic-field amplification during the post-merger evolution. As a result, it accumulates larger magnetic fluxes, develops a magnetically dominated funnel, and launches a collimated magnetically driven polar outflow. In contrast, the unequal-mass binary ejects approximately 50% more mass but exhibits weaker magnetic-field amplification, with the polar region remaining turbulent and baryon loaded throughout our simulation, suggesting that the development of a magnetically dominated funnel is likely delayed.
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All authors Fatemeh Hossein Nouri, Jay V. Kalinani, Bruno Giacomazzo, Riccardo Ciolfi, Albino Perego

Materials Science

Absence of lateral domain wall mobility in Zn1-xMgxO thin films

Jack Eckstein, Kyle P. Kelley, William Prudnick et al. (+4 more)

Polarization reversal in ferroelectrics arises from the coupled processes of domain nucleation and subsequent growth, yet the governing mechanisms differ fundamentally between classical perovskite oxides and emerging wurtzite ferroelectrics. While switching in perovskites is typically governed by mobile domain walls whose field-driven propagation dominates macroscopic kinetics, here we show that polarization reversal in wurtzite Zn1-xMgxO proceeds through a qualitatively different pathway. Using scanning oscillator microscopy, in combination with point pulse-imaging methods, we directly map local switching events and domain wall responses, revealing that domain walls in Zn1-xMgxO exhibit negligible lateral mobility (sub 10nm) and that polarization reversal proceeds predominantly through the nucleation of vertically extended columnar filaments with a lateral size on the order of the grains. This nucleation-controlled switching contrasts sharply with the growth-mediated dynamics characteristic of perovskite ferroelectrics and explains the abrupt, spatially localized switching behavior observed in wurtzite systems. These results establish nucleation-dominated filamentary reversal as a defining switching mechanism in Zn1-xMgxO and point towards the need for further studies to understand correlation lengths and nucleation processes across a range of grain sizes.
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All authors Jack Eckstein, Kyle P. Kelley, William Prudnick, Jon-Paul Maria, Stephen Jesse, Neus Domingo, Rama K. Vasudevan

Statistical Mechanics · Cross-listed from cs.IT

Breakdown of Edgeworth Expansion in Finite-Blocklength Regime and Exact Absorption via $q$-Deformation

Hiroki Suyari

This paper addresses the structural breakdown of the Edgeworth expansion in the finite-blocklength (FBL) regime, where conventional asymptotic approximations yield unphysical negative probabilities in the deep-tail region. We propose a $q$-deformed framework that resolves this inconsistency by replacing additive polynomial perturbations with a geometric deformation of the information density space. Motivated by the linearization of nonlinear dynamics, we prove that dynamically scaling the $q$-logarithmic parameter exactly absorbs the third-order skewness while preserving global nonnegativity. We establish a universal asymptotic matching, demonstrating that the framework encapsulates higher-order asymptotic scales. Numerical results confirm that the proposed method matches the state-of-the-art precision of the Cornish-Fisher bound without the risk of negative probabilities. The framework offers a robust and computationally stable foundation for evaluating operational limits in ultra-reliable communications such as 6G and URLLC.
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High Energy Physics (Theory)

The ETH matrix model for DSSYK: non-perturbative corrections and intersection theory

Eleonora Alfinito and Matteo Beccaria

At leading order in the genus expansion the ETH matrix model for DSSYK reproduces its correlators by construction, while its higher-genus corrections are conjectured to capture higher-topology contributions in the dual sine-dilaton gravity – a correspondence established so far only for the disk and the wormhole. At fixed genus the correlators are built from discrete volumes $N_{g,n}$, polynomial in $q$-deformed zeta values $\zeta_q(2k)$ with $q=e^{-\lambda}$, $\lambda$ being the DSSYK coupling. These lie in the ring of quasimodular forms generated by the Eisenstein series $E_2,E_4,E_6$, whose $S$-duality yields an exact closed form for the leading non-perturbative correction as $\lambda\to0$, controlled by $\widetilde q=e^{-4\pi^2/\lambda}$. Known at disk level, this scale is shown here to govern the fixed-genus, higher-boundary amplitudes as well. We show that the term linear in $\widetilde q$, at leading order in $\lambda$, is captured entirely by the $q$-deformed Weil–Petersson volumes, and reduces to a finite sum of intersection numbers of $\kappa$-classes on the moduli space $\overline{\mathcal M}_{g,n}$ of stable curves, computable without repeating the topological recursion that produced the $N_{g,n}$. We tabulate it for every $(g,n)$ whose $q$-deformed volume is known in closed form, and extend it to $(3,1),(3,2),(4,1)$, where none is available. The construction is not restricted to leading order: we work out $O(\widetilde q^2)$ for the same cases.
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Chemical Physics

Tracking molecular hydrogen formation from ionized water in real time

Chuan Cheng, Chi-Hong Yuen, Eleanor Weckwerth et al. (+8 more)

Removing an electron from a water molecule can drive its two hydrogen atoms to pair up and depart as molecular hydrogen. However, even for this elementary reaction, the route from start to finish has remained hidden because measurements have yet to follow the electronic and nuclear motion simultaneously. Combining correlated photoelectron and ion imaging, few-femtosecond pump–probe measurements, and nonadiabatic simulations, we track the complete pathway in isolated heavy water (D$_2$O) molecules. The reaction takes an indirect route and dissociates along three distinct pathways (direct, roaming, and delayed) with formation times of about 34 and 72 femtoseconds for the direct and delayed branches. Yet bond formation requires the molecule to first break its own symmetry. Only random asymmetric motion enables the electronic-state switch at a conical intersection, joining the two hydrogen atoms before the oxygen–hydrogen bond breaks. These results establish a time-resolved picture of molecular hydrogen formation from water and provide a general strategy for linking electronic excitation to chemical outcomes in settings from radiation damage to hydrogen production.
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All authors Chuan Cheng, Chi-Hong Yuen, Eleanor Weckwerth, Ian Gabalski, Aaron M. Ghrist, Haoran Ma, Andrew J. Howard, Mathew Britton, Yunquan Liu, Eric Wells, Philip H. Bucksbaum

Mesoscale and Nanoscale Physics

Quantum Geometry Driven Optical Responses in 1T-MX$_2$ Monolayers: A Symmetry-Constrained Slater-Koster Tight-Binding Approach

Bikram Baruah, Snehasish Nandy and Subhasis Panda

Centrosymmetric 1T-MX$_2$ monolayers(MLs) have attracted considerable attention owing to their intriguing transport properties and potential technological applications arising from the interplay among quantum geometry, electronic band structure, and band-gap characteristics. Despite this rich physics, a comprehensive microscopic tight-binding(TB) description that simultaneously captures these properties remains insufficiently established, while first-principles approaches can be computationally demanding for systematic investigations across different materials and perturbations. Here, we develop a transferable eleven-band Slater-Koster TB description of ML 1T-MX$_2$ TMDs and use it to establish a connection among their microscopic electronic structure, quantum geometry, and optical response. The model is constructed in an orthogonal orbital basis from the crystal geometry and symmetry-constrained SK parameters, with material-specific parametrizations obtained from DFT calculations for ML ZrS$_2$ and HfS$_2$. The resulting geometry-based Hamiltonian accurately describes the low-energy electronic structures and provides a natural framework for extending the analysis to the broader isostructural 1T-MX$_2$ family. We find that the pristine MLs possess a finite quantum metric, with the dominant contribution concentrated in the two highest occupied bands owing to the small near-gap energy separation and strong metal-chalcogen $p$-$d$ hybridization. Furthermore, we verify the interband $f$-sum rule, which directly relates the integrated optical spectral weight to the Brillouin-zone-averaged quantum metric. Our results establish optical spectral weight as an experimentally accessible probe of the quantum geometry of occupied Bloch states and provide a unified microscopic framework for connecting electronic structure, quantum geometry, and measurable optical responses across the 1T-MX$_2$ family.
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