Strongly Correlated Electrons
Extended symmetric quantum phase in a honeycomb Heisenberg model with sublattice-selective interactions
Nai Chao Hu, Xing-Yu Zhang, Yuchi He et al. (+1 more)
Motivated by two-dimensional
bilayer systems we numerically study an anti-
ferromagnetic spin-$1/2$ Heisenberg model on the honeycomb
lattice with a nearest-neighbour exchange coupling $J_1$, and a next-nearest-neighbour exchange coupling $J_2'$ for the B sublattice sites only. Using infinite Projected Entangled-Pair States (iPEPS), variational uniform
matrix-product states on cylinders, and exact diagonalization, we find an extended symmetric regime $0.4\lesssim J'_2/J_1\lesssim0.6$, in which local observables show no
magnetic, valence-bond, or
chiral spin order. At $J'_2/J_1=0.5$, the PEPS correlation length grows systematically with bond dimension, and an inverse-correlation-length extrapolation favors a vanishing limit. We also find that various observables scale algebraically with the finite bond-dimension-induced correlation length, which points to a gapless
spin liquid ground state. We propose a $\mathbb{Z}_2$ Dirac
spin liquid parton state, with Dirac points that are protected by translation, time-reversal and three-fold rotation
symmetry, as a promising candidate state to explain the numerical results. We also discuss the possibility that the symmetric ground state is a featureless, short-range entangled state with a small gap.
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All authors Nai Chao Hu, Xing-Yu Zhang, Yuchi He, Nick Bultinck
Strongly Correlated Electrons
From Effective Temperature to Non-Boltzmann State Selection in Driven-Dissipative Quantum Criticality
Tiago Jorge, Jens Paaske and Pedro Ribeiro
Whether a nonequilibrium
quantum-critical steady state can be described by an effective temperature remains an open question. We address it in a voltage-biased electronic Lipkin–Meshkov–Glick model, a minimal driven-dissipative model of a collective
spin coupled to metallic leads. A controlled large-$N$ treatment reveals an overdamped open
quantum-critical regime distinct from the closed model. The surrounding
quantum critical fan, organized by temperature and voltage, is explored and fluctuations are found to be governed by an effective temperature $T_{\rm eff}$. At strong bias, the transition becomes first-order through a tricritical point. Remarkably, the same $T_{\rm eff}$ governs the strongly driven regime, but now varies across the entire order-parameter landscape. The steady state is therefore selected by a non-Boltzmann rule, shifting the first-order transition away from the equal-depth point of a deterministic potential. Driven criticality thus remains organized by an effective temperature while revealing non-thermal state selection.
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General Relativity and Quantum Cosmology
Reconnection of Gravitational Fields
Luca Comisso and Felipe A. Asenjo
In a tetrad formulation of general relativity, an ideal Ohm-type condition for the gravitational field implies the conservation of gravitational fluxes and the preservation of the connectivity of gravitational field sheets. We investigate the consequences of departures from ideal gravitational
evolution by developing a theory of gravitational reconnection, defined as a change in the connectivity of gravitational field sheets arising from the breakdown of the ideal frozen-in
evolution of the gravitational field. We derive quantitative measures of the gravitational reconnection rate, show that gravitational reconnection alters the energy-momentum exchange between the gravitational and matter sectors, and determine how it modifies the
evolution of gravitational helicity. Our results provide a quantitative framework for describing changes in gravitational connectivity and their consequences in dynamical spacetimes.
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General Relativity and Quantum Cosmology
Frozen-In Gravitational Fields
Felipe A. Asenjo, Maricarmen A. Winkler and Luca Comisso
Spacetime can undergo complex nonlinear
evolution, as governed by the Einstein field equations, and a central challenge is to understand the
geometric structures that arise, persist, and interact throughout its
evolution. Using a formulation of Einstein equations that parallels nonlinear electrodynamics of continuous media, we show that general relativity admits gravitational field connections—two-surfaces and associated field lines whose connectivity is maintained by the spacetime dynamics. This gravitational frozen-in behavior is enabled by an ideal Ohm-type condition for the gravitational field. We further show that the same framework naturally leads to a conserved “gravitational
magnetic” flux. A conserved gravitational helicity also emerges, with a clear topological interpretation in terms of gravitational field-line structures. These results identify well-defined topological constraints on admissible spacetime
evolution and provide an organizing principle underlying the nonlinear dynamics of spacetime.
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History and Philosophy of Physics
Before WIMPs: Neutrinos and the origins of particle dark matter
Jaco de Swart
After four decades of null-results, the experimental quest to discover a dark matter particle ardently continues. While confidence in the leading candidate, the Weakly Interacting Massive Particle (WIMP), is waning, its explanatory success still shapes current experimental approaches and theoretical expectations - from underground detecting efforts in Europe, China, and the U.S. to modern theories of
cosmic structure. This paper traces the origins of this particle-based paradigm to a critical predecessor: the
neutrino-dominated universe. Proposed in the early 1970s as a solution to extra-
galactic anomalies,
neutrinos became the leading explanation of 'missing matter' following experimental hints of
neutrino mass in 1980. Although short-lived, the model's coherent picture of
cosmic evolution and structure formation set strong conceptual and methodological standards - providing critical impetus to the field of particle cosmology. Examining this history invites renewed reflection on how such past aims and expectations continue to guide dark matter inquiry today.
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High Energy Physics (Theory)
Functional Dimensional Regularization
Piero Beretta and Alessandro Codello
We introduce and develop Functional Dimensional Regularization (FDR), a novel functional renormalization group (RG) framework that extends the principles of dimensional regularization beyond the perturbative $\varepsilon$-expansion. The key insight is to define the FDR beta functions, valid in any continuous dimension $d$ and characterized by threshold functions, as a sum over all critical dimensions of the corresponding scheme-independent beta functions computed in DR. We demonstrate that this formalism exhibits all the hallmarks of a fully-fledged functional RG. Within the local potential approximation, we perform a general fixed point analysis, recovering the $\varepsilon$-expansion for all multi-critical models and establishing a direct connection to functional scaling solutions, spike plots, and eigen-perturbation spectra. Extending the framework to the second order of the derivative expansion, we compute the critical exponents for the Ising universality class in $d=3$, providing estimates for the anomalous dimension $\eta$ and RG spectrum that converge rapidly and show favorable agreement with state-of-the-art results. We present a detailed comparison with non-perturbative and proper-time RG approaches, highlighting structural similarities and key differences. In particular, we introduce a “
distillation” procedure that allows one to systematically derive the FDR flow from any other one-loop-exact RG scheme. Our results establish FDR as a self-contained and competitive RG framework that combines the technical simplicity of dimensional regularization with the versatility of the functional approach.
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Machine Learning
Trains but Doesn't Learn: A Post-Training Delivery Benchmark for LLM Agents as Forward-Deployed Engineers
Weihang Ding and Junfei Zhan
Post-training is becoming a service (PTaaS): a customer hands an operator data and a goal, and a forward-deployed engineer (FDE) returns a fine-tuned, evaluated, and deployed model under a budget, a human-approval gate, and reproducibility requirements. Seating an LLM
agent in the FDE seat raises a question existing
benchmarks cannot answer: not whether an
agent can raise a metric, but whether it can be trusted to deliver. We answer it on a governed delivery plane, where an
agent drives ten stages and an oracle scores each stage from platform-recorded facts. The central silent failure is the run that trains but does not learn (TBDL): loss falls, every signal stays green, and the delivered model is no better than the base. An operator-run acceptance gate catches every such run before payment, and a detector calibrated on known-corrupted runs flags severe corruption mid-run. We ran four frontier
agents (Claude Opus 5, GPT-5.6-luna, Gemini 3.7 Flash, DeepSeek V4-Pro) end to end on metered L40S, A100, and H200 GPUs across 8B to 70B open bases, certifying every scenario before scoring. We also ran a human FDE arm under the same oracle and compare every
agent against it.
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General Relativity and Quantum Cosmology
Higher derivative Hořava-Lifshitz fermions: from superconductivity to atomic spectroscopy
A. A. Araújo Filho, K. E. L. de Farias, N. Heidari et al. (+2 more)
We investigate an isotropic Hořava-Lifshitz
fermion theory supplemented by a dimension-six spatial derivative operator, preserving first order time
evolution while modifying the ultraviolet dispersion relation. Within the regime of validity of the derivative expansion, we develop three complementary consequences of the $z=2$ sector. First, a Bardeen-Cooper-Schrieffer/Nambu-Jona-Lasinio (BCS/NJL) mean field treatment of
fermion pairing yields the particle and antiparticle quasiparticle spectra, the finite temperature gap equation, and the gauge invariant criterion for a stable superconducting phase. The modified dispersion alters both the density of states governing the pairing scale and the electromagnetic vertices entering the Meissner response. Second, using the scalar pole denominator as a minimal
spin independent exchange kernel, we derive an exponentially damped and oscillatory massive potential and obtain the corresponding Born scattering amplitudes. The quartic momentum dependence renders both the forward and total cross sections finite and produces a large transfer behavior distinct from Rutherford scattering. Finally, we evaluate the induced shifts of the hydrogenic $1S$, $2S$, and $2P$ levels in closed form, retaining the full dependence on the interaction range. In other words, these latter results gives direct spectroscopic constraints on the product of
nuclear and leptonic couplings, with muonic atoms, showing the respective sensitivity to the short distance Hořava-Lifshitz sector.
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All authors A. A. Araújo Filho, K. E. L. de Farias, N. Heidari, M. Paganelly, A. F. Santos
Solar and Stellar Astrophysics
The oldest low-$\alpha$ thin disc stars
Riano E. Giribaldi, Laura Magrini, Marco Palla et al. (+1 more)
The formation pathway of the $\alpha$-poor Milky Way thin disc remains under debate. The latest observational data indicates the presence of comparable numbers of old
stars in both the low- and high-$\alpha$ disc components, suggesting either coeval or overlapping formation epochs. Using GALAH DR4, we provide evidence that the $\alpha$-poor
stars coexist with $\alpha$-rich
stars up to $\sim$12.5 Gyr.
Stellar ages of 0.5 Gyr precision were re-derived for nearly $30\,000$ subgiant
stars using accurate effective temperatures ($T_{\rm{eff}}$) from the infrared flux method (IRFM) together with distances based on
Gaia parallaxes. About 22% of the sample constitutes a population peaking at 9.2 Gyr, with evidence for an extended old-age tail reaching 12.5 Gyr. Among
stars older than 10 and 11 Gyr, between 20 and 30% have relative low [$\alpha$/Fe] and
solar-like
metallicities ($-0.5 \leq \mathrm{[Fe/H]} \leq +0.5$ dex). These
stars exhibit kinematics consistent with those of near
solar-age $\alpha$-poor
stars in the thin disc. These
stars can be evolved Sun-like
stars, i.e. old
solar analogues, whose $T_{\rm{eff}}$ and
gravity modified with the time. Comparison with a well-tested
Galactic disc chemical
evolution model supports the presence of a significant fraction of old, $\alpha$-poor disc
stars, confirming the plausibility of our selection criteria. We provide a catalogue with the selected sample to facilitate spectroscopic follow-ups at high resolution.
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All authors Riano E. Giribaldi, Laura Magrini, Marco Palla, Carlos Viscasillas Vázquez
Earth and Planetary Astrophysics
Probing Exoplanetary Rings with Asterodensity Profiling: A PhotoRing Analysis of Kepler-51
Jorge I. Zuluaga, Sebastian Numpaque, David M. Kipping et al. (+1 more)
The Kepler-51 system hosts transiting super-puff
planets whose extremely low bulk densities challenge structural models, possibly because unresolved rings inflate their inferred radii. We test this hypothesis by combining asterodensity profiling with TTV-aware transit fits of Kepler long-cadence photometry. For Kepler-51b we measure a density ratio $\Psi\equiv\rho_{\star,\mathrm{obs}}/\rho_{\star,\mathrm{true}} = 1.18\pm0.06$, a $2.9\sigma$ offset from $\Psi=1$; for Kepler-51d we find $\Psi=1.04\pm0.08$ ($0.6\sigma$), consistent with no anomaly. Unmodelled eccentricity is disfavoured for
planet b by TTV-derived dynamical constraints ($p=0.007$) but remains viable for
planet d ($p=0.33$). The offset of Kepler-51b is also compatible with the PhotoRing (PR) effect of unmodeled rings. Using a
geometric ringed-transit forward model and
Bayesian retrieval, we identify ring configurations that reproduce the transit observables and the measured density ratios. The preferred solutions are consistent with compact, moderately inclined rings that raise the true bulk densities by factors of $2-5$. Conversely, the absence of a large PR offset excludes extended, optically thick, high-obliquity rings at $99\%$ credibility for b and $70\%$ for d from archival photometry alone. These objects may thus be "puff ringed
planets" although recent JWST observations of Kepler-51d show no direct signature of an opaque ring. While the required impact parameters and
stellar densities show tension with independent constraints -attributable to Kepler's 30-minute cadence- this study presents the first complete application of the PR effect, offered as a methodological demonstration and exclusion experiment rather than as evidence that rings are present. All code is publicly available to support applications to other systems.
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All authors Jorge I. Zuluaga, Sebastian Numpaque, David M. Kipping, Jaime A. Alvarado-Montes
High Energy Astrophysical Phenomena
Early NIR echo and the time variable mass loss history of Type IIn SN 2024kgi
Naveen Dukiya, Kuntal Misra, Andrea Pastorello et al. (+30 more)
We present a comprehensive analysis of the long-term photometric and spectroscopic monitoring campaign of the Type IIn
Supernova (SN) 2024kgi. The SN reaches at peak an $r$-band absolute magnitude of $-19.81 \pm 0.06$ mag and a bolometric luminosity of $\sim 2 \times 10^{43}$ erg s$^{-1}$. We observe a break in the lightcurve at day $\sim 312$, after which the luminosity decline changes from $t^{-1.0}$ to $t^{-4.5}$, likely due to the shock sweeping the dense CSM. We introduce a semi-analytical lightcurve modeling approach for CSM-interaction in transients that accounts for variable
diffusion time. We hence estimate a CSM mass of $2.34^{+11.8}_{-1.6} M_{\odot}$ and with a density profile $\rho_{csm} \propto r^{-2.74}$, indicating progressively increasing mass loss toward the SN explosion. The ejecta signatures emerge as broad H, He, and Ca II triplet lines, at day $\sim 80$, much earlier than expected from a spherically symmetric CSM, suggesting asymmetry in the CSM. After the lightcurve break, the H lines exhibit a wavelength-dependent deficit in the red-wing flux, indicating new
dust formation in the ejecta and/or in the post-shock gas. We observe an NIR excess from day $\sim 40$ onwards. We attribute the early NIR excess before the lightcurve break solely to the NIR echo from pre-existing
dust, as there are no other indications for new
dust formation. The late-time NIR excess likely has contributions from both the preexisting and newly formed
dust. The steady increase in mass loss, slow CSM velocity, and asymmetric CSM favor a binary interaction-induced mass loss.
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All authors Naveen Dukiya, Kuntal Misra, Andrea Pastorello, Andrea Reguitti, Anjasha Gangopadhyay, Aravind P. Ravi, Brian Hsu, Noah Franz, David J. Sand, Nathan Smith, Jennifer E. Andrews, Moira Andrews, K. Azalee Bostroem, Collin Christy, Monalisa Dubey, Joseph R. Farah, Archana Gupta, Estefania Padilla Gonzalez, Emily Hoang, D. Andrew Howell, Curtis McCully, Darshana Mehta, Megan Newsome, Jeniveve Pearson, Nicolas Meza Retamal, Jeonghee Rho, Manisha Shrestha, Bhagya Subrayan, Giacomo Terreran, Lina Tomasella, Stefano Valenti, Giorgio Valerin, Kathryn Wynn
Quantum Physics
Strong coupling of a reconfigurable ${}^{171}$Yb atom array to a tunable telecom-band nanofiber cavity
Hideki Ozawa, Neville Chen, Yusuke Hisai et al. (+13 more)
Nanophotonic cavities provide strong atom-
photon coupling in a compact, directly fiber-coupled geometry, while a reconfigurable array of $^{171}$Yb atoms combines high-fidelity gates with a metastable
qubit state coupled directly to a telecom-band transition, making the two a natural interface between neutral-atom
quantum processors and telecom
quantum networks. Here, we realize strong atom-cavity coupling on the ${}^{3}\mathrm{P}_0 \leftrightarrow {}^{3}\mathrm{D}_1$ transition of ${}^{171}\mathrm{Yb}$, establishing, to our knowledge, the first neutral-atom cavity-QED system to reach the single-atom strong-coupling regime on a telecom-band atomic transition. Reflection spectroscopy of a single-sided cavity yields a single-atom internal cooperativity of $C_{\mathrm{in}}=5.6(1.0)$ and collective coupling following $\sqrt{N}$ scaling up to $N=5$ atoms, with homogeneous coupling at antinodes over $\sim$200 $\mathrm{\mu}$m along the nanofiber. Thermal tuning of a fiber Bragg grating provides in situ control of the cavity outcoupling rate over two orders of magnitude from the undercoupled to the overcoupled regime, relevant for various atom-cavity protocols. We confirm compatibility with reconfigurable atom arrays by demonstrating 99.95(6)% imaging fidelity and trap lifetimes comparable to free-space array, at 1 $\mathrm{\mu}$m from the nanofiber axis. Moreover, the diameter-engineered antireflection design of the nanofiber enables tweezer-based atom transport across the nanofiber with no measurable loss or heating at 4.5 $\mathrm{\mu}$m above the nanofiber, supporting a two-layer architecture for the nanofiber-integrated atom array. From the demonstrated atom-cavity coupling, atom capacity, and cavity mode profile, we project time-multiplexed remote atom-atom
entanglement generation at 40 kHz, with prospects for further scaling through technical enhancements and channel multiplexing.
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All authors Hideki Ozawa, Neville Chen, Yusuke Hisai, Shunichiro Hashimoto, Kenichi N. Komagata, Remi T. Oddon, Shanjou Yang, Seitaro Horikawa, Seigo Kikura, Shigehito Miki, Takao Aoki, Tadayuki Yoshitake, Hideki Konishi, Shinichi Sunami, Akihisa Goban, Ryotaro Inoue
Probability
Systems of rough stochastic differential equations I: weak existence and Yamada–Watanabe
Florian Huber
For systems of rough
stochastic differential equations in the sense of Friz–Hocquet–Lê, with a fixed deterministic rough driver, we prove two results. The first is weak existence with unbounded coefficients. The Itô data is assumed continuous and of linear growth, with no Hölder or Lipschitz continuity and no ellipticity. The rough vector field is a controlled pair of linear growth with bounded derivatives, subject either to a norm-
curvature decay or to diagonality with coordinatewise
curvature decay; in the diagonal case a coordinatewise upper bound on the
diffusion matrix is added. The existing results ask the Itô data and the rough field to be bounded. We remove that boundedness, and ask in exchange for a
curvature hypothesis on the rough field, bounds on its derivatives, and a narrower index configuration. The conclusion is weaker on two counts: the bounds that define a solution are imposed in the mean rather than uniformly on the probability space, and the solution's moments stop at the order the initial law carries. The second is the Yamada–Watanabe implication for rough equations: weak existence, together with pathwise uniqueness, yields a strong solution and joint uniqueness in law. A solution here is not defined by a pathwise identity but by two bounds on a remainder, one of them conditional, and an arbitrary enlargement of the filtration need not preserve that one. The enlargements the Yamada–Watanabe construction produces are immersions, however, and along an immersion both bounds transfer unchanged.
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High Energy Physics (Phenomenology)
Cosmological stasis and the coupled dark sector of the Dark Dimension
Alexander Stewart
We study cosmological stasis in coupled dark matter and dark energy models in which a scalar field drives the dark energy and sets the dark matter mass, with the Dark Dimension as the motivating realization. Treating dark matter, dark energy,
baryons, and radiation as an autonomous dynamical system, we show that exact stasis requires exponential slopes along the trajectory, and that running slopes give exact stasis or a drifting quasi-stasis depending on whether the running is integrable. The constant abundance solutions are the stationary solutions of coupled quintessence, which we read as stasis epochs with computable lifetimes and exits. Anchoring the cosmology to the measured abundances at matter-radiation equality and today, we show that the stasis region for this model cannot accelerate for any initial conditions, and that the total equation of state is never phantom although the effective dark energy of a $\Lambda$CDM fit can appear so. For the Dark Dimension, capture into stasis in the future is excluded for
geometric sources of the potential once dark fifth-force bounds are imposed, and dark matter production from the Standard Model brane supports a further stasis which the standard scenario does not reach. The stasis solutions provide analytic exclusions of the parameter space which do not depend on initial conditions.
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High Energy Physics (Phenomenology)
Fast Surrogate for the Earth Matter Effect on Solar Neutrinos
Saeed Ansarifard
We present a deep-learning surrogate for the Earth matter effect on
solar neutrinos. The model uses a residual convolutional network conditioned on the
solar neutrino oscillation parameters and is trained on numerical solutions computed over a grid of parameter values. It predicts the Earth-induced transition probabilities across
neutrino energy and zenith angle, providing a fast approximation to the direct numerical calculation. For the reference electron-
neutrino survival probability, the surrogate achieves a pointwise relative accuracy of approximately $2\%$ and a speed-up of about a factor of 60 in a laptop-CPU test. Since the network learns only the Earth-crossing propagation, it can be applied without retraining to new-physics scenarios that leave this propagation unchanged. The surrogate can also be retrained using alternative numerical implementations or extended parameter sets, providing a flexible and computationally efficient approach for
solar-
neutrino analyses. The code and simulation data are publicly available at \href{https://github.com/AI-Driven-HEP/NuMatterSurrogate}{\faGithub}.
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General Relativity and Quantum Cosmology
Accurate Black Hole Quasinormal Modes, Regge Poles, and Greybody Factors from Light Ring Ladder Symmetry
Rajes Ghosh, David Pereñiguez, Jaime Redondo-Yuste et al. (+1 more)
The characteristic oscillations of a black hole can be understood in terms of null rays trapped near its unstable light ring, with this correspondence becoming exact in the high-frequency limit. In this regime, we uncover a hidden ladder
symmetry in the perturbation equations, which maps the calculation of quasinormal modes, Regge poles, and greybody factors for a spherically symmetric black hole onto the
quantum-mechanical problem of an anharmonic oscillator. This provides a systematic, efficient framework for computing the black hole response, with improved convergence properties compared with existing approximation schemes. As an explicit application, we analytically compute all three quantities for a Schwarzschild black hole through eighteenth order in inverse angular momentum, obtaining highly accurate results. We explore different resummation schemes and find that they can further improve the accuracy of the Regge poles and, particularly, the greybody factors. Our framework can be readily extended to rotating black holes and to modified theories of
gravity.
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All authors Rajes Ghosh, David Pereñiguez, Jaime Redondo-Yuste, Emanuele Berti
Quantum Physics
Localized Decoherence as a Constructive Tool: An Optical Simulation of Matter-Wave Interference
Hadis Torbatiyan, Bedir Halc{\i}, Adrian Udovičić et al. (+2 more)
Decoherence is conventionally regarded as a detrimental process that suppresses
quantum coherence and limits the performance of
quantum technologies. Contrary to this view, we show that spatially localized decoherence can instead be exploited as an interferometric tool. Beyond its conceptual implications, localized decoherence provides a novel approach to prepare arbitrary macroscopic spatial superpositions for testing
quantum physics with massive particles. We demonstrate the proof of principle by making use of the correspondence between optics and matter-waves through the equivalence of the respective propagation functions. By employing
stochastic phase fields to the optical counterpart to model the decoherence, our experiments confirm the expected interference. The results establish localized decoherence as a resource for
quantum state engineering.
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All authors Hadis Torbatiyan, Bedir Halc{\i}, Adrian Udovičić, Lara Ulčakar, Rainer Kaltenbaek
Disordered Systems and Neural Networks
Disorder-promoted stability
Arthur N. Montanari, Pietro Zanin and Adilson E. Motter
Previous studies of network dynamics have suggested that heterogeneity among nodes inhibits stability, at odds with the ubiquity of inherently heterogeneous natural and engineered systems. Here, we show that this conclusion arises from model reductions introduced for mathematical tractability and breaks down when nodal dynamics are higher-dimensional, yielding non-Hermitian Jacobians. In such systems, including neural, power-grid, and material networks, nodal heterogeneity can instead enhance stability, even when parameters are randomly disordered. Non-Hermiticity also underlies the stabilizing effects of network heterogeneity, which can arise even in one-dimensional nodal dynamics through nonreciprocal interactions, as shown for ecological networks. Our framework reveals disorder not as a liability but as a general resource for stabilizing complex systems.
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General Relativity and Quantum Cosmology
Gravitational wave signatures of subsolar neutron star formation in collapsar disks
Vishal Baibhav, Valerio De Luca, Loris Del Grosso et al. (+3 more)
Standard models for
stellar core collapse predict the birth of
neutron stars with masses exceeding a
solar mass. In the collapsar model, a rapidly rotating massive
star collapses to a black hole surrounded by a dense,
neutrino-cooled
accretion disk, whose outer regions may in some cases fragment into
neutron-rich clumps that collapse to form subsolar-mass
neutron stars. These disk-formed objects can then merge either with one another or, following possibly hierarchical
evolution, with the central black hole. In this work, we characterize the gravitational-wave signatures of these binaries, focusing on distinctive features of the collapsar environment: Doppler and other phase modulations from orbital motion about the central black hole, gas-driven migration in the disk, and
tidal interactions during inspiral. We show that the combination of anomalously low component masses with these environmental imprints produces unique waveform signatures that can distinguish the collapsar channel from other subsolar merger scenarios. Current and next-generation detectors have good prospects for identifying the intrinsic properties of such objects and, if subsolar mergers are discovered, for testing and constraining the collapsar formation pathway.
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All authors Vishal Baibhav, Valerio De Luca, Loris Del Grosso, Emanuele Berti, Brian D. Metzger, Lam Hui
Astrophysics of Galaxies
Gone with the wind? Potential gas inflow in the broad-line region of a QSO at $z=0.287$ traced by time-varying Balmer absorption
Xihan Ji, Dominic J. Walton, Francesco D'Eugenio et al. (+6 more)
We report spectroscopic observations of a remarkable QSO, J115724.80-000455.56 at $z=0.287$ from the Dark Energy Spectroscopic Instrument (DESI) survey. This QSO exhibits variability in its hydrogen Balmer absorption over a time interval of 10 months in the observed frame between 2021 and 2022. The observed Balmer absorption can be decomposed into two components with distinct kinematics: a non-varying, "stationary" component and a varying, "dynamic" component. Both absorbers have gas column densities of $N_{\rm H}\sim 10^{22}~{\rm cm^{-2}}$ and likely have densities of $n_{\rm H}\gtrsim 10^{8}~{\rm cm^{-3}}$. We inferred small effective physical sizes of $\lesssim 10^{-3}$ pc for the absorbers, which, together with the time variability, suggests that the absorption occurs in the broad-line region (BLR). The reshifted centroid velocities of both absorbers imply an inflow, where the inferred mass inflow rate is comparable to the single-epoch mass
accretion rate of this QSO. The 2022 epoch of this QSO further reveals a 10% change in the column density over 2 months, indicating the gas inflow might be continuous. We also obtained new X-ray observations using the $\it Einstein~Probe$, which reveals an X-ray-to-bolometric luminosity ratio significantly below the general AGN population. The X-ray weakness is consistent with strong gas obscuration with $N_{\rm H}= 4.0^{+ 1.6}_{- 1.5}\times10^{23}~{\rm cm^{-2}}$. The substantially higher gas obscuration seen in the X-rays compared to the optical possibly indicates a warm absorber inside the BLR or merger-driven enhancement of the
galactic scale obscuration consistent with optical imaging. This QSO might thus represent an active feeding phase after a recent gas-rich merger.
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All authors Xihan Ji, Dominic J. Walton, Francesco D'Eugenio, Ignas Juodžbalis, Vasily Belokurov, Andrew C. Fabian, Roberto Maiolino, Jiamu Huang, Douglas N.C. Lin
Mesoscale and Nanoscale Physics
Scaling of qubit coherence in quantum dot based Majorana chains: Rabi and Ramsey oscillations of Majorana qubits formed by four and six quantum dots
Haining Pan and Sankar Das Sarma
We present a theoretical study of the Rabi and Ramsey coherence time of Majorana-based
qubits formed by double $N$-site
quantum-dot artificial Kitaev chains, following the recent experimental realization arXiv:2607.09511. We generalize the
qubit to two chains of arbitrary length and compare the Rabi and Ramsey oscillations of the four-dot and six-dot
qubits, simulated with realistic disorder for three sets of parameters: small and large superconducting gaps, and the experimental parameters. We find that, in the pristine limit, the Rabi oscillation is independent of the chain length, whereas the Ramsey oscillation of the six-dot
qubit suffers from larger leakage, because the third site suppresses the unwanted energy splitting away from the sweet spot but at the same time makes the deliberate splitting difficult to achieve, which requires a larger detuning that could excite the bulk. In reality with disorder, neither coherence time improves universally with the chain length. The Rabi coherence is set by the competition of three dephasing channels, and the additional dots pay off only if the fluctuation of the interchain tunneling is suppressed; the Ramsey coherence is set by the fluctuation of the energy splitting during the $\sigma_z$ rotation, which for the four-dot
qubit is fixed by the sweet-spot disorder alone and does not depend on the mean splitting, whereas for the six-dot
qubit the detuning that generates the splitting adds a fluctuation growing with the splitting itself, so the additional dots pay off only for small splittings. This implies that a longer chain is thus a better
quantum memory but not necessarily a better
qubit under manipulation. Although topological protection is expected in a longer Kitaev chain
qubit, observing it in the current Rabi and Ramsey measurement protocols remains an experimental challenge.
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General Relativity and Quantum Cosmology
Gravity-Informed Neural Networks for Post-Newtonian Binary Dynamics
Gabriele Barbagallo and Javier Matulich
We introduce a
gravity-informed neural-network (GravINNs) framework for learning post-Newtonian binary orbital dynamics. The method incorporates the equations of motion directly into the training phase and is developed at three complementary levels. First, we construct single-orbit surrogates for conservative post-Newtonian dynamics and assess their accuracy across different orbital configurations. We then extend the approach to a parametric model spanning a four-dimensional parameter space defined by the initial separation, radial and tangential momenta, and symmetric mass ratio, allowing a single trained network to represent entire families of orbits and replace repeated numerical integrations. Finally, we consider dissipative dynamics by including the leading radiation-reaction contribution at $2.5$PN order. In this regime, the network reproduces the orbital
evolution and the associated secular energy loss, starting from a conservative 2PN warm start and without using dissipative reference trajectories in the training. These results show that physics-informed neural-networks (PINNs) can provide accurate and flexible representations of both conservative and dissipative post-Newtonian dynamics. The complete implementation and the models used in this work are publicly available through the GravINNs repository.
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Astrophysics of Galaxies
The KAGG survey: KCWI Analysis of Gas around Galaxies at z~3-5
Grecco A. Oyarzún, Marc Rafelski, J. Xavier Prochaska et al. (+5 more)
We present the KCWI Analysis of Gas around
Galaxies (KAGG) survey of Ly$\alpha$ emission around Damped Ly$\alpha$ Absorbers (DLAs) at z~3-5 with the Keck
Cosmic Web Imager (KCWI) integral-field spectrograph. The KAGG survey is characterized by the sample of 36 DLAs spanning a wide
metallicity range, the wide search area for associated Ly$\alpha$ emission (impact parameter b$~\lesssim 120~$kpc), and the high emission sensitivity, reaching Ly$\alpha$ luminosities $\lesssim10^{42}$ erg s$^{-1}$. We identify 7 DLA Ly$\alpha$ emitters that are likely DLA
galaxy candidates due to the good match between the Ly$\alpha$ emission and DLA
redshifts. Based on a composite sample of 11 DLA Ly$\alpha$ emitters from KAGG and MAGG (MUSE Analysis of Gas around
Galaxies), we find that the impact parameters of DLA Ly$\alpha$ emitters decrease with DLA
metallicity, from b$~>50~$kpc at [M/H]~-2 to b$~<50~$kpc at [M/H]~-1. Including Ly$\alpha$ emitters at larger velocity offsets and at larger impact parameters from the DLAs, we construct samples of 35 "Group" Ly$\alpha$ emitters and 17 "Large-scale" Ly$\alpha$ emitters. We find that their impact parameters and incidence rates also depend on DLA
metallicity. Based on simulations of our survey and comparisons with models of
galaxy formation, we conclude that higher DLA
metallicities are associated with higher
halo masses. The low Ly$\alpha$ emission detection rate at low impact parameters suggests that most DLA
galaxies either have low
stellar masses (M$~\lesssim10^{8}M_{\odot}$) or have their Ly$\alpha$ emission suppressed due to HI resonant scattering and/or
dust absorption.
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All authors Grecco A. Oyarzún, Marc Rafelski, J. Xavier Prochaska, Nissim Kanekar, Marcel Neeleman, Marie Wisz, Michele Fumagalli, Regina A. Jorgenson
Astrophysics of Galaxies
Dark matter haloes from dwarf to massive galaxies: no systematic inner-density tension with {\Lambda}CDM hydrodynamical simulations
Pavel E. Mancera Piña, Justin I. Read, Jorge Sarrato-Alós et al. (+1 more)
Two of the most prominent small-scale challenges to the cold dark matter (CDM) paradigm are the cusp-core and diversity-of-rotation-curves problems. The former concerns the shallow inner DM density profiles inferred for many
galaxies compared with the cusps predicted by collisionless CDM, while the latter concerns the wider range of inner DM densities and rotation curve shapes inferred observationally than hydrodynamical simulations traditionally reproduce. Robust observational constraints on DM core sizes and
halo densities are therefore essential for testing both the nature of DM and the impact of
galaxy formation processes. We analyse the inner DM distribution of a curated sample of 48 gas-rich
galaxies and 8 Milky Way gas-poor satellites, spanning 6 orders of magnitude in $M_\ast$. We find substantial scatter in DM core sizes and degrees of coreness, with both cuspy and cored
haloes occurring over a broad $M_\ast$ range. The cores are energetically consistent with
stellar feedback, requiring modest
supernova energy coupling efficiencies of order $0.1-1\%$. Comparisons with the NIHAO, FIRE-2, and EDGE simulations reveal broad agreement in the inner DM densities and logarithmic slopes of observed and simulated
galaxies. The main residual differences concern the steep slopes of some massive simulated
galaxies and differences in SHMRs. Using a rotation-curve diversity diagnostic from previous work, we find that extreme discrepancies with simulations are absent from our curated sample and largely attributable to uncertain kinematics or baryonic mass distributions. Within the scope of our analysis, we find no evidence of a systematic inner-density tension between our
galaxy sample and current $\Lambda$CDM hydrodynamical simulations. Together with the modest energetic requirements for core formation, this substantially alleviates the cusp-core and diversity-of-rotation-curves problems.
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All authors Pavel E. Mancera Piña, Justin I. Read, Jorge Sarrato-Alós, Claudia Muni
High Energy Physics (Phenomenology)
A Unitary Fixed Point Away from Threshold: Momentum-Surface EFT for Strong Mixing
Lorenzo De Ros and Javier Reig Navarro
Radiative capture in a non-relativistic system can become non-perturbative even when the underlying transition interaction is weak. We demonstrate this mechanism in a simple
quantum-mechanical two-channel model with a systematic power counting, where strong mixing between scattering and bound states develops in a narrow region around a finite momentum $k_0$, leading to a perturbative violation of unitarity. In this regime, the enhanced contributions factorize, reducing the dynamics to a free scattering state interacting through a strong local coupling. Under RG
evolution in the factorization scale, this local interaction approaches a
unitary fixed point, analogous to that of systems with an anomalously large scattering length. This motivates an EFT organized around the finite-momentum surface $|\mathbf{k}|=k_0$, describing
fermions at unitarity with a linear dispersion relation. The resummation resulting from the EFT restores unitarity and provides a systematic expansion for both elastic scattering and radiative capture.
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General Relativity and Quantum Cosmology
The BTZ black hole, the Third Law and gravitational collapse
Aidan M. McSharry, Harvey S. Reall and Jorge E. Santos
We prove that a Third Law of black hole mechanics holds for the BTZ black hole in 3d
gravity coupled to matter obeying the dominant energy condition. This law states that initial data containing a trapped surface cannot evolve in finite time to a black hole that coincides with extremal BTZ on the event horizon, for any choice of boundary conditions at infinity. The result is proved by defining a quasilocal energy and angular momentum and using spinorial methods to establish a BPS inequality that is saturated by the extremal BTZ solution. Nevertheless, we show that gravitational collapse of a massless scalar field can result in the formation of an extremal BTZ black hole in finite time. The difference between these results arises because gravitational collapse occurs in the Neveu-Schwarz sector, whereas extremal BTZ is supersymmetric in the Ramond sector. Solutions that settle down to extremal BTZ in infinite time along the event horizon are also discussed.
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High Energy Physics (Phenomenology)
Morgan Del Gratta, Fabio Maltoni, Davide Pagani et al. (+1 more)
We investigate the limitations of the two-qutrit
quantum tomography in
Higgs-
boson decays to four charged
leptons. At next-to-leading order, the standard reconstruction can yield an operator that is not positive semidefinite, even when radiatively improved
spin-analysing powers are used. We trace this failure to the coherent combination of
photon- and Z-mediated contributions to the off-shell dilepton system, whose distinct production and decay structures invalidate the assumed universal decay analysers. Nevertheless, the rank-two angular sector remains accessible and perturbatively stable, enabling a robust lower bound on the squared concurrence, and hence a reliable assessment of
entanglement beyond leading order.
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All authors Morgan Del Gratta, Fabio Maltoni, Davide Pagani, Giovanni Pelliccioli
Solar and Stellar Astrophysics
The white dwarf binary pathways survey - XI. The Gaia-GALEX UV Excess Sample for systems within 350 pc
James A. Garbutt, S. G. Parsons, N. Gentile Fusillo et al. (+9 more)
White
dwarfs (WDs) with F, G or K type binary companions are the last common ancestor to a zoo of exotic phenomena. Finding a clean sample of such systems is difficult, as WDs in such binaries are usually outshone at optical wavelengths by their non-degenerate companion. It is useful to have a sample of such binaries - they can be studied to investigate binary
evolution, as they may have undergone a previous phase of mass transfer. Using
Gaia data release 3 and GALEX, we compile a sample of 2597 candidate WD + FGK systems within 350 pc. These were identified via their ultraviolet excesses relative to MESA Isochrones and
Stellar Tracks (MIST) model predictions consistent with the
Gaia parameters of their non-degenerate companions. We estimate the mass, surface
gravity and effective temperature of the WDs by fitting the excess ultraviolet flux to models, or through interpolation where only one ultraviolet band was available. We also estimate the age of the system where possible, by comparing against any wide WD companions in higher-order
stellar systems, or by checking if the system is a member of a cluster. On comparing against Simbad, we estimate the level of contamination within our sample to be between 10-35 per cent. This is a valuable sample for investigating WD + FGK binaries, particularly those containing hotter WDs (Teff,WD >~ 25 kK), and systems with post-main sequence companions.
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All authors James A. Garbutt, S. G. Parsons, N. Gentile Fusillo, B. T. Gänsicke, M. S. Hernandez, F. Lagos-Vilches, R. Raddi, A. Rebassa-Mansergas, J. J. Ren, M. R. Schreiber, O. Toloza, M. Zorotovic
High Energy Physics (Theory)
Bulk OPE Coefficients of the $E$-Series Virasoro Minimal Models
Amaury Lhoste, Jiaxin Qiao and Masahito Yamazaki
We present bulk-primary operator-product coefficients for every Virasoro minimal model with an $E_6$, $E_7$, or $E_8$ modular invariant. Dividing by a universal product of
chiral generalized-minimal-model OPE coefficients reduces the conformal bootstrap problem to a finite algebraic problem governed by root-of-unity
quantum-group $6j$ symbols. The exceptional factors of the OPE coefficients can be chosen independent of the second Kac indices $s$, and their dependence on the central charge reduces to finitely many reference cases and explicit phases. A finite computer-assisted calculation yields candidate algebraic $s=1$ seed data and high-precision numerical evidence for existence and uniqueness modulo primary-field signs. We prove that exact existence and uniqueness for these seeds imply the corresponding result for all Kac labels within the genus-zero bulk locality and crossing equations; the finite seed step remains uncertified. The three families require $18$, $32$, and $107$ representative reduced OPE coefficients for $E_6$, $E_7$, and $E_8$, respectively. We provide reconstruction conventions and coefficient tables for both
unitary and nonunitary models. Our calculation assumes only Virasoro
symmetry, bulk locality (permutation
symmetry) and OPE associativity (crossing equations).
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Quantum Physics
Nonlocal advantage of quantum coherence in tau-lepton pairs from electron–positron collisions
Yoav Afik, Juan Ramón Muñoz de Nova, Sarthak Sharma et al. (+1 more)
Quantum correlations have recently attracted significant
attention in
collider physics, with Nonlocal Advantage of
Quantum Coherence (NAQC) representing the strongest form of
quantum correlation studied so far. Owing to its strength, NAQC is considerably more challenging to observe than Bell nonlocality since it is only present in narrower regions of phase space. Unlike other systems, tau-
lepton pair ($\tau^+\tau^-$) production in electron–positron ($e^+e^-$) collisions provides an ideal testing ground, as it exhibits strong
quantum correlations and, in particular, NAQC over a large region of phase space. In this paper, we investigate NAQC in $e^+e^- \to \tau^+\tau^-$ production at center-of-mass energies of 10.58 and 91.19~GeV, corresponding to the ongoing Belle~II and future FCC-$ee$ experiments, respectively. Remarkably, for our experimental proposal, we develop a dedicated NAQC witness, which allows to certify NAQC presence by measuring one single magnitude. We estimate the experimental sensitivities needed to establish the presence of NAQC, finding that a large fraction of the number of events (specifically, 0.18 for Belle~II and 0.31 for FCC-$ee$) contribute to the NAQC signal. A 5$\sigma$ observation of NAQC requires a precision of approximately 1% at Belle~II, while a precision of a few percent is sufficient at FCC-$ee$. The resulting observation would constitute the strongest form of
quantum correlation measured in a
collider to date. In addition, we design an experimental scheme to implement the steering game leading to the NAQC definition, representing the first implementation of a steering game in a high-energy
collider. Our results are easily extendable to other electron–positron
colliders with different center-of-mass energies.
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All authors Yoav Afik, Juan Ramón Muñoz de Nova, Sarthak Sharma, Surya Sundar Raman