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2603.10185 2026-03-12 astro-ph.IM astro-ph.GA astro-ph.SR

Attaining Spectral Energy Distributions With Sub-Percent Uncertainties: All-Sky DA White Dwarf Spectrophotometric Standard Stars For Large Telescopes And Surveys

Abhijit Saha, Edward W. Olszewski, Benjamin M. Boyd, Thomas Matheson, Tim Axelrod, Gautham Narayan, Annalisa Calamida, Jay B. Holberg, Ivan Hubeny, Ralph C. Bohlin, Susana Deustua, Armin Rest, Jenna Claver, Sean Points, Christopher W. Stubbs, Elena Sabbi, John W. Mackenty

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We present a synopsis of the project to establish thirty-two new faint ($ 16.5 \leq V \leq 19.8 $) DA white dwarfs as spectrophotometric standards distributed over the whole sky. Our results validate the use of fully radiative pure hydrogen model fluxes for hot DA white dwarfs to predict the observed broadband fluxes from near ultraviolet through the near infrared to accuracies of a few parts per thousand. After fitting the line of sight reddenings simultaneously with the model spectral energy distributions of these stars against spectroscopic and multi-band photometric observations, we have shown that residuals have an rms of typically 0.4 percent. This indicates that the complications from interstellar dust extinction have been adequately mitigated. Our stars supplement the three brighter DA white dwarfs that define the flux scale of CALSPEC. The consequent photometric accuracy, their all sky coverage, and their brightness range that matches the dynamic range of large telescopes, constitutes an unprecedented ensemble of standard stars for both ground as well as space based use. This paper targets readers who may wish to use these as standard stars, and provides for them the essential content to understand their strengths and limitations, without traversing the technical details of analysis that are already captured in a series of papers since 2016. The narrative here describes the motivation, justification, and evolution of the analysis methods; the input data that constrain the modeling; as well as the stability of our results in the face of future improvements in models.

2603.10183 2026-03-12 hep-th

Induced current by a magnetic flux in $(1+2)-$dimensional conical spacetime in a Ho{ř}ava-Lifshitz Lorentz-violating scenario

E. R. Bezerra de Mello, H. F. Santana Mota

Comments 16 pages and 3 figures

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We investigate the vacuum expectation value of bosonic current induced by a magnetic flux in a $(2+1)-$dimensional conical spacetime in the presence of a circular boundary, in a Ho{ř}ava-Lifshitz Lorentz violation symmetry scenario. We assume that the circular boundary is concentric with magnetic flux, and the massive scalar quantum field obeys the Robin boundary condition on the boundary. In order to develop this analysis, we calculate the positive frequency Wightman functions for both regions, inside and outside the boundary. Using these functions, we obtain analytical expressions for the vacuum expectation bosonic currents. As we will see, these functions are presented in the form of the sum of boundary-free and boundary-induced parts. As to the boundary-induced currents, some asymptotic behaviors are investigated for specific limiting cases; moreover, in order to provide a better understanding about the behavior of the currents, some plots are given.

2603.10182 2026-03-12 cond-mat.mes-hall

Deep learning statistical defect models on magnetic material dynamic and static properties

C. Eagan, M. Copus, E. Iacocca

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The modeling of realistic magnetic materials requires the inclusion of defects. Based on the pseudospectral Landau-Lifshitz description of magnetisation dynamics, we propose a statistical model that takes into account defects, specifically vacancies. This statistical model can be integrated with deep learning techniques that correlate defect thresholds with relevant physical observables. We develop a convolutional neural network and a physics-informed neural network combined with theory of functional connections to predict the dispersion relation given defect parameters and physical constraints. A two-branch convolutional neural network is developed to predict domain-wall widths depending on defects threshold, taking into account the spatial profile and domain-wall width separately to achieve a prediction. The proposed physics-informed approaches leverage deep-learning and achieve statistical predictions measured in physical units. This is a stepping stone towards the discovery of new materials and the determination of minimal defect thresholds required for desired dynamics, states, or topological textures.

2603.10181 2026-03-12 math.AG math.KT

Vector bundles over certain Koras-Russell threefolds of the third kind

Tariq Syed

Comments 10 pages; comments welcome!

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Let $k$ be an algebraically closed base field of characteristic $0$ and let $α_{1}, α_{2}, α_{3}, d \geq 2$ be integers such that $α_{1}, α_{2}, α_{3}$ are pairwise coprime and $gcd (α_{1},d-1) = 1$. Then consider the Koras-Russell threefold $Y := \{ x + x^d y^{α_{1}} + z^{α_{2}} + t^{α_{3}} = 0\} \subset \mathbb{A}^{4}_{k}$. We prove that the Chow groups $CH^{i}(Y)$ are trivial for $i=1,2,3$ and therefore all algebraic vector bundles over $Y$ are trivial. If $α_{1}$ is odd, we also prove that the Chow-Witt groups $\widetilde{CH}^{i}(Y, \mathcal{L})$ are trivial for $i=1,2,3$ and any line bundle $\mathcal{L}$ over $Y$.

2603.10179 2026-03-12 astro-ph.CO

A modern halo streaming model for redshift space distortions

Cheng-Zong Ruan, Baojiu Li, Carlton M. Baugh, Sownak Bose, Alexander Eggemeier, David F. Mota

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Accurate modelling of redshift-space distortions (RSD) in galaxy clustering is essential for extracting cosmological information from current and forthcoming large-scale structure surveys. While perturbation theory is reliable on large scales, much of the constraining power lies at intermediate and small separations, where nonlinear dynamics within and between dark matter haloes dominate. We present a halo streaming model for nonlinear galaxy clustering in redshift space that is accurate and physically interpretable. Our framework combines the streaming model for RSD with a halo-model decomposition of the galaxy clustering into central/satellite and one-/two-halo contributions. We build dedicated emulators for the key physical ingredients, trained on a suite of $N$-body simulations: halo mass functions, real-space halo two-point correlation functions, and pairwise velocity moments. By emulating these modular building blocks rather than the final redshift-space observable, this approach preserves physical transparency, enables targeted optimisation for each ingredient, and remains flexible to changes in tracer populations and galaxy-halo connection models. The resulting halo streaming model reproduces the simulated nonlinear anisotropic clustering signal down to highly nonlinear scales, while achieving the computational efficiency required for cosmological parameter inference. This framework is designed to support full-shape RSD analyses for surveys such as DESI and \textit{Euclid}, facilitating precision measurements of structure growth and tests of gravity. All codes and trained emulators are publicly available in the \href{https://github.com/chzruan/freyja}{\texttt{freyja}} repository.

2603.10177 2026-03-12 cs.DB

K-Join: Combining Vertex Covers for Parallel Joins

Simon Frisk, Austen Fan, Paraschos Koutris

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Significant research effort has been devoted to improving the performance of join processing in the massively parallel computation model, where the goal is to evaluate a query with the minimum possible data transfer between machines. However, it is still an open question to determine the best possible parallel algorithm for any join query. In this paper, we present an algorithm that takes a step forward in this endeavour. Our new algorithm is simple and builds on two existing ideas: data partitioning and the HyperCube primitive. The novelty in our approach comes from a careful choice of the HyperCube shares, which is done as a linear combination of multiple vertex covers. The resulting load with input size $n$ and $p$ processors is characterized as $n/p^{1/κ}$, where $κ$ is a new hypergraph theoretic measure we call the reduced quasi vertex-cover. The new measure matches or improves on all state-of-the-art algorithms and exhibits strong similarities to the edge quasi-packing that describes the worst-case optimal load in one-round algorithms.

2603.10176 2026-03-12 astro-ph.GA astro-ph.CO

Radio selection of heavily obscured AGN in the J1030 field: unraveling a missing Compton-thick population

Giovanni Mazzolari, Roberto Gilli, Marco Mignoli, Marcella Brusa, Isabella Prandoni, Fabio Vito, Ivan Delvecchio, Giorgio Lanzuisi, Alessandro Peca, Andrea Comastri, Stefano Marchesi, Marco Chiaberge, Marisa Brienza, Cristian Vignali, Matilde Signorini, Quirino D'Amato, Fabrizio Gentile, Kazushi Iwasawa, Colin Norman, Alberto Traina, Federica Loiacono, Pietro Baldini, Marianna Annunziatella, Roberto Decarli

Comments Accepted for publication on A&A. 15 pages + appendix. Main figures: Fig. 3 (radio-excess selection), Fig. 5 (column density distribution of radio-excess sources non detected in the X-rays), Fig. 8 (radio-selected Compton-thick AGN number density)

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We tested the effectiveness of radio selection to discover heavily obscured AGNs, particularly at high-z, and we measured their abundance for the first time from a radio perspective. We consider the radio sources detected in the J1030 field, which is one of the fields with the deepest combination of 1.4 GHz radio and X-ray observations. We defined a radio excess parameter as the ratio between the star formation rate (SFR) that would correspond to the observed radio luminosity and the one directly derived from the spectral energy distribution (SED) fitting, $\rm REX=SFR_{1.4GHz}/SFR^{corr}_{SED}$. We then select as radio excess AGN those sources with $\rm REX>8.5$, corresponding to a $3σ$ excess above the median value. In this way, we find 145 radio-excess sources falling into the \textit{Chandra} X-ray image footprint but without X-ray detection. From the deep X-ray upper limits, we estimated a lower limit to the obscuration of each radio-excess AGN, finding on average $\log (N_H/\rm{cm^{-2}})>23.7$. A CTK AGN scenario is also supported by the results of the X-ray stacking analysis performed on sources at $z>1.5$, which revealed X-ray luminosities and hardness ratios compatible with very highly obscured AGN. Finally, we computed the number density of these radio-selected CTK AGN. While at $z\sim 2$ the radio number density agrees well with the CTK AGN predictions of different population synthesis models, at $z\sim3$ the radio selection returns a CTK AGN number density $\sim 2-3$ times larger than what is predicted by the X-ray models and observations. This result supports the effectiveness of radio emission in selecting the most obscured sources, unraveling a population of AGN potentially missed by X-rays surveys at $z>3$, paving the way to a synergistic use of the future radio and X-ray facilities such as the \textit{SKAO} and \textit{NewAthena}.

2603.10171 2026-03-12 hep-th

States of 2D Yang-Mills and Large-Volume Entanglement

Dmitry Melnikov, Jefferson T. Oliveira, Valmir Peixoto, Marcia Tenser

Comments 36 pages, 28 figures

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We study entanglement in two-dimensional Yang-Mills theory, viewed as a quasi-topological model of emergent space. The most familiar class of states in this theory are states defined by Euclidean path integrals over Riemann surfaces. Bipartite states of this class have thermofield double structure, with entanglement consistently reducing with total area and the number of topological defects, turning separable in the infinite-area limit. In contrast, Wilson lines and loops generate rich non-monotonic behavior of the entanglement entropy. Most notably, we find that for a certain discrete set of configurations, entanglement remains finite at infinite area. The reduced density matrices, in such configurations, take the form of finite-dimensional projectors onto non-trivial vacuum sectors. We also discuss the implications of the large-volume effects for confinement and find that special asymptotic configurations are related to transitions in the confining force.

2603.10170 2026-03-12 astro-ph.HE gr-qc

Kick matters: The impact of a new recoil model on the retention of hierarchical black-hole remnants in globular clusters

Tousif Islam, Digvijay Wadekar, Konstantinos Kritos

Comments 17 pages, 11 figures

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In globular clusters, hierarchical mergers are among the most promising pathways to forming massive black holes such as GW231123. A key factor determining whether a merger-remnant black hole will be retained in these environments and thus participate in subsequent hierarchical mergers is the recoil kick velocity. Analytic models for the recoil velocity are currently employed in nearly all population-synthesis frameworks. We instead use a state-of-the-art recoil-kick model gwModel_flow_prec developed from a combination of numerical-relativity and black-hole perturbation-theory data, together with data-driven techniques such as normalizing flows and the post-Newtonian structure of the kick. Employing both back-of-the-envelope estimates and detailed N-body as well as semi-analytical cluster simulations, we show that gwModel_flow_prec leads to a noticeable increase in the retention probability of hierarchical-merger remnants compared to the previously used analytic model and changes the mass and spin distribution of the black holes formed through hierarchical mergers. Additionally, we discuss the implications of our results in the context of massive binaries such as GW231123.

2603.10169 2026-03-12 stat.ME stat.AP

Novel g-computation algorithms for time-varying actions with recurrent and semi-competing events

Alena Sorensen D'Alessio, Lucas M. Neuroth, Jessie K Edwards, Chantel L. Martin, Paul N Zivich

Comments 22 pages, 2 figures, 5 tables

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Background: A core aspect of epidemiology is determining the impacts of potential public health interventions over time. With long follow-up periods, epidemiologists may need to consider semi-competing events, in which a terminal event, like death, precludes a non-terminal event, like hypertension. Time-varying confounding poses an additional challenge when studying time-varying interventions or actions. Existing methods do not simultaneously address semi- competing events and time-varying confounding. Methods: We propose two novel g-computation algorithms for causal effects with semi- competing events and time-varying actions. To explore performance of our novel g-computation estimators, we conducted a Monte Carlo simulation study. We then applied our estimator to investigate how cigarette smoking prevention throughout young and middle adulthood might impact prevalent hypertension using data from Waves III (aged 18-26 years) - VI (aged 39-51 years) of the National Longitudinal Study of Adolescent to Adult Health. Results: Our simulations show that the novel g-computation estimators had little bias and appropriate confidence interval coverage. They outperformed existing alternative estimators across sample sizes. In the illustrative application, the novel estimator identified a small reduction in prevalence of hypertension and risk of death in midlife had all cigarette smoking been prevented across follow-up compared to the observed smoking patterns. Conclusion: As long-running cohorts progress in age, death within the study sample will become an increasing concern for studies of aging-related outcomes, life course analyses, and investigations into chronic disease development. Our novel g-computation estimators provide a simultaneous solution.

2603.10168 2026-03-12 hep-th

Towards Two-to-Two Scattering of Scalars in Asymptotically Safe Quantum Gravity

Angelo P. Chiesa, Jan M. Pawlowski, Manuel Reichert

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We compute the graviton-mediated two-to-two scattering amplitude and cross section for scalar particles in asymptotically safe quantum gravity. Specifically, we compute the full momentum dependence of the scalar-graviton three-point scattering vertex for spacelike momenta with the functional renormalisation group. We also discuss the analytic continuation to the Minkowski branch, and in particular its angular dependence. Then, the timelike part of the vertex is reconstructed and used to compute the scattering amplitude and cross-section. We show that the cross-section reduces to that in General Relativity at small energies, and it respects unitarity in the UV.

2603.10167 2026-03-12 astro-ph.HE

Neutrinos from extreme astrophysical sources

Xavier Rodrigues

Journal ref New Astron.Rev. 102 (2026) 101747

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In this paper I review recent results on high-energy neutrino astronomy and what they can reveal about some of the most extreme cosmic accelerators. I discuss recent measurements of the diffuse TeV-PeV cosmic neutrino spectrum by the IceCube observatory and the current flux limits in the ultra-high-energy regime, contextualizing the recent detection of an ultra-high-energy neutrino by the KM3NeT observatory. I review the recent emergence of a TeV signal from nearby Seyfert galaxies such as NGC 1068, the potential of $γ$-ray blazars as neutrino sources above the PeV regime, and the current status of tidal disruption events and other transient classes as possible neutrino sources. For each of these topics, I discuss ongoing developments in source models and their current limitations. I argue for the indispensable role of next-generation multi-messenger facilities, such as IceCube-Gen2, in solidifying current source associations, probing the ultra-high-energy regime, and resolving vast transient populations that remain unidentified with current statistics.

2603.10164 2026-03-12 cond-mat.stat-mech

Integrability-breaking-induced Mpemba effect in spin chains

Adam J. McRoberts

Comments 4 pages, 4 figures

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We show that there are two distinct mechanisms that can cause the symmetry-restoration Mpemba effect in spin chains with \textit{weakly broken} integrability, such that the asymptotic equilibration is diffusive, but the lifetime of anomalously fast spin hydrodynamics at low temperature is parametrically large. In particular, we consider isotropic spin chains quenched out of equilibrium by suppressing the $z$-components, without inducing any net magnetisation. Initially, the restoration of isotropy is faster in hotter systems -- because they have more phase space available to scramble their initial conditions -- which may cause the equilibration curves to cross at early times in both integrable and non-integrable systems. At later times, however, the equilibration is effectively hydrodynamic, and the \textit{colder} systems start to equilibrate faster as the lifetime over which they evince superdiffusive spin hydrodynamics is parametrically larger -- but only in \textit{non}-integrable models. Depending on the details of the temperatures and the extent of the initial symmetry-breaking, two isotropy-restoration curves may have a crossing at early time, late time, neither, or both.

2603.10157 2026-03-12 astro-ph.CO gr-qc hep-th

Thermal enhancement of inflationary magnetic fields

Arjun Berera, Suddhasattwa Brahma, Zizang Qiu, Rudnei O. Ramos

Comments 13 pages, 1 figure, comments welcome including citation requests;

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We investigate primordial magnetogenesis by assuming the gauge field is prepared in a thermal state during inflation rather than the standard Bunch-Davies vacuum. The temperature $\mathcal{T}$ introduces a physical scale that breaks conformal invariance at the level of the state while preserving the standard Maxwell action. This modification results in a {\it dissipative boost} that alters the magnetic energy density scaling from $a^{-4}$ to $a^{-3}$, resulting in a present-day magnetic field $B_0$ enhancement that can potentially range from about $10^{8}$ to $10^{16}$ on galactic scales. While this toy model alone does not satisfy observational lower bounds, it demonstrates that thermal initial conditions can significantly mitigate the conformal obstruction. Our results suggest that embedding this mechanism within a fully dynamical warm inflation framework, where dissipation continuously maintains the thermal bath, provides a highly promising path towards successfully realizing a minimal model of inflationary magnetogenesis without the need to invoke non-minimal couplings, anomalous background dynamics or nonlinear extensions of electrodynamics.

2603.10155 2026-03-12 econ.GN q-fin.EC

Towards macroeconomic analysis without microfoundations: measuring the entropy of simulated exchange economies

Yihang Luo, Robert S. MacKay, Nick Chater

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The theory of thermal macroeconomics (TM) analyses economic phenomena within the mathematical framework of classical thermodynamics, using a set of axioms that apply to the purely macroscopic aspects of an economy [CM]. The theory shows that the possible macro-behaviours are governed by an entropy function. In simple idealised cases, the entropy function can be calculated from the rules governing the interactions of individual agents. But where this is not possible, TM predicts that the entropy can nonetheless be measured empirically through an economic analogue of calorimetry in physics. We show using computer simulations the in-principle feasibility of this approach: an entropy function can successfully be measured for a range of simulated economies that we tested. In cases where entropy can be calculated analytically from microfoundational assumptions, the measured entropy agrees well. In more complex cases, where microfoundational analysis is infeasible, our method of measuring entropy still applies and is validated by demonstrations that entropy is a state function of an economic system, i.e., exhibits path independence. This appears to hold even for some systems to which we don't have a proof that the Axioms of TM apply. Furthermore, in all cases tested, entropy is concave, as predicted by TM. As shown in [CM], once the entropy function is established for a simulated exchange economy, it is possible to derive prices, the value of money and various other quantities, and make predictions about the effects of putting two or more economies in contact.

2603.10154 2026-03-12 cond-mat.mtrl-sci

Intertwined Swirling Polarization States in BaTiO$_3$ with Embedded BaZrO$_3$ Nanoregions

R. Machado, F. Di Rino, M. Sepliarsky, M. G. Stachiotti

Comments Accepted for publication in Phys. Rev. Lett

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Ferroelectric materials embedded with dielectric inclusions offer a unique platform for exploring novel topological polar textures. Using first-principles-based atomistic simulations, we investigate the polarization behavior of a BaTiO$_3$ matrix containing segregated BaZrO$_3$ nanoregions. We demonstrate that the polar texture in three-dimensionally ordered arrays of dielectric inclusions is governed by their size and spacing, revealing three distinct regimes. At large separations, the nanocomposite exhibits bulk-like BaTiO3 phase transitions, while at smaller spacings, interconnected swirling polarization patterns give rise to vortex supercrystal states. We analyze the stabilization mechanisms of these states and show that each regime is characterized by distinct switching behavior. Furthermore, we find that nanocomposites with randomly distributed dielectric inclusions exhibit swirling polarization textures, giving rise to an amorphous network of entangled vortices. Our findings provide new insights into the physics of relaxor ferroelectrics, are consistent with recent experimental observations, and open up new possibilities for designing materials with emergent topological functionalities.

2603.10152 2026-03-12 econ.EM

Shrinkage Regularization for (Non)Linear Serial Dependence Test

Francesco Giancaterini, Alain Hecq, Joann Jasiak, Aryan Manafi Neyazi

Comments 10 pages

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This paper introduces a regularized test of the null hypothesis of the absence of linear and nonlinear serial dependence for high-dimensional non-Gaussian time series. Our approach extends the portmanteau test introduced in Jasiak and Neyazi (2023) to the high-dimensional setting.

2603.10151 2026-03-12 astro-ph.HE

Relativistic \(^{56}\text{Ni}\) Decay Lines in GRB 221009A

Rahim Moradi, Emre S. Yorgancioglu, Shao-Lin Xiong, Yan-Qiu Zhang, Shuang-Nan Zhang, Roland Diehl, Yu Wang

Comments Accepted for publication in Communications Physics

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Long Gamma Ray Bursts are thought to originate from the core collapse of massive stars that give rise to energetic broad-lined Type Ic supernovae. The brightest burst ever recorded, GRB 221009A, has been linked to a broad-lined Type Ic supernova through late-time observations by the James Webb Space Telescope. An emission line evolving from $\sim$37 to $\sim$6~MeV is detected during the prompt phase. We propose that this time-evolving line is consistent with Doppler-boosted radioactive decay of nickel synthesized in the associated supernova and entrained in the relativistic jet, corresponding to the boosted 158~keV decay branch. We also report evidence for an additional higher-energy excess near $\sim$24~MeV at 290--300~s, detected at moderate statistical significance and consistent with the boosted 270~keV decay branch. The observed kinematics and flux evolution are compatible with expectations from radioactive decay, providing direct spectroscopic evidence linking prompt emission to supernova nucleosynthesis.

2603.10150 2026-03-12 astro-ph.HE astro-ph.SR

Accreting White Dwarfs: An Unreview

Simone Scaringi, Christian Knigge, Domitilla de Martino

Comments 46 pages, 5 figures. Accepted in Space Science Reviews. We thank the International Space Science Institute in Bern for hosting a workshop on the first 50 years of research on accretion discs

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Accreting white dwarfs (AWDs) are among the best natural laboratories for understanding disk accretion. Their proximity, brightness, and purely classical nature make them ideal systems in which to probe the fundamental physics that governs the transport of angular momentum, the generation of outflows, and the coupling between disks, magnetospheres, and accretors. Yet despite decades of study, many critical questions remain unresolved. In this ``unreview'', we therefore focus not on what is known, but on what is unknown. What drives viscosity and sustains accretion in largely neutral disks? How are powerful winds launched, and how do they feed back on the disk and binary evolution? Why do so many systems show persistent retrograde precession, and what drives bursts in magnetic AWDs? By identifying these open problems -- and suggesting ways to resolve them -- we aim to motivate new observational, numerical, and theoretical efforts that will advance our understanding of accretion physics across all mass scales, from white dwarfs to black holes.

2603.10147 2026-03-12 cond-mat.stat-mech physics.optics

Bridge Scaling in Conditioned Henyey-Greenstein Random Walks

Claude Zeller

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We study fixed-length bridge paths -- half-space excursions that start and end at a planar boundary -- for three-dimensional random walks with Henyey-Greenstein scattering angles and exponentially distributed step lengths, using Monte Carlo simulation over asymmetry parameter g from 0 to 0.95 and path lengths from 4 to 200 steps. The key structural feature is that the walk evolves on a two-dimensional Markovian state space (depth, direction cosine) rather than the scalar depth coordinate alone. Four anomalies with respect to classical Brownian-excursion theory are reported. The mean amplitude scales super-diffusively, as path length to a power of 0.57--0.58 for isotropic scattering, nine standard deviations above the Brownian prediction of 0.5, with no sign of convergence out to 200 steps. The diffusion coefficient scales as the transport mean free path to the power 0.415 rather than the predicted 1.0. The midpoint depth distribution is Rayleigh rather than half-normal, consistent with a two-dimensional Bessel process. The bridge-conditioned mean direction cosine converges to minus two-thirds at the final step, independently of the asymmetry parameter and initial direction -- the classical Milne result anchored by the H-function moment identity. All anomalies are attributed to the two-dimensional state-space structure. The two anomalous exponents sum to approximately unity, suggesting a common geometric origin. Whether this constitutes a permanent universality-class shift or an anomalously slow crossover to Brownian-excursion behaviour remains the primary open question.

2603.10144 2026-03-12 cond-mat.mes-hall cond-mat.quant-gas cond-mat.stat-mech

Geometry of Contact Terms in Linear Response: Applications to Elasticity

Ian Osborne, Gustavo Monteiro, Barry Bradlyn

Comments 18 pages, 2 figures, 3 authors

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Employing the Kubo linear response formalism to calculate the elasticity of anisotropic systems has been shown to yield odd elastic moduli. For Hamiltonian systems, this result seems to be contradictory as it would violate energy conservation. To resolve this discrepancy, we examine the predictions of quantum linear response in the context of our expectation from classical elasticity theory. Our framework reveals that the geometry of the space of strain perturbations introduces correction factors to the correspondence between the Kubo formula and the elastic moduli which resolves the contradiction. We use a two-dimensional gas of electrons in a magnetic field as a pedagogical example. We use generalized f-sum rules to demonstrate how contact terms may reveal themselves in experimental measurements. Finally, we discuss the implications of our results for interpreting more general linear response functions.

2603.10142 2026-03-12 cond-mat.mtrl-sci

Endohedral Derivatives of the Recently Synthesized Two-Dimensional Fullerene Networks: Electronic and Optical Insights from First-Principles Calculations

Marcelo L. Pereira Junior, Raphael M. Tromer, Luiz A. Ribeiro Junior, Douglas S. Galvao

Comments 14 pages and 6 figures

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The quasi-hexagonal phase of the two-dimensional fullerene network (qHPC$_{60}$), recently synthesized, has emerged as a stable carbon-based material with distinct structural and electronic features. In this work, we employed density functional theory (DFT) calculations to investigate the electronic and optical properties of its endohedral derivatives. The encapsulation of nitrogen, cerium, and strontium atoms inside fullerene cages was systematically analyzed at different concentrations. Our results show that encapsulation preserves the semiconducting backbone of pristine qHPC$_{60}$ while introducing localized electronic states that alter the bandgap and enable new transition channels. Nitrogen encapsulation produces intragap states with potential relevance for discrete optical emission, whereas cerium and strontium generate intraband states near the conduction edge. These modifications induce a red shift of the absorption onset into the visible spectrum, accompanied by enhanced refractive and absorptive responses. The robustness of the electronic structure under reduced concentrations indicates that the fully encapsulated limit adequately represents the system. Overall, the findings highlight impurity-endowed qHPC$_{60}$ as a promising platform for optoelectronic and light-harvesting applications.

2603.10137 2026-03-12 q-fin.CP

Uncertainty-Aware Deep Hedging

Manan Poddar

Comments 16 pages, 4 figures, 12 tables

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Deep hedging trains neural networks to manage derivative risk under market frictions, but produces hedge ratios with no measure of model confidence -- a significant barrier to deployment. We introduce uncertainty quantification to the deep hedging framework by training a deep ensemble of five independent LSTM networks under Heston stochastic volatility with proportional transaction costs. The ensemble's disagreement at each time step provides a per-time-step confidence measure that is strongly predictive of hedging performance: the learned strategy outperforms the Black-Scholes delta on approximately 80% of paths when model agreement is high, but on fewer than 20% when disagreement is elevated. We propose a CVaR-optimised blending strategy that combines the ensemble's hedge with the classical Black-Scholes delta, weighted by the level of model uncertainty. The blend improves on the Black-Scholes delta by 35-80 basis points in CVaR across several Heston calibrations, and on the theoretically optimal Whalley-Wilmott strategy by 100-250 basis points, with all improvements statistically significant under paired bootstrap tests. The analysis reveals that ensemble uncertainty is driven primarily by option moneyness rather than volatility, and that the uncertainty-performance relationship inverts under weak leverage -- findings with practical implications for the deployment of machine learning in hedging systems.

2603.10136 2026-03-12 stat.ME

Pseudo Empirical Best Prediction of Multiple Characteristics in Small Areas

William Acero, Domingo Morales, Isabel Molina

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Small area estimators that ignore the sampling design lack design consistency when the sampling mechanism is complex and may be severely biased under informative designs. Existing procedures that account for the survey weights under unit-level models typically focus on a single response variable. This paper addresses the estimation of area means for several dependent target variables under a multivariate nested error regression (MNER) model. We propose a multivariate pseudo-empirical best linear unbiased predictor that accounts for the sampling mechanism. Moreover, by aggregating the MNER model, we derive a unified predictor that can be obtained from either unit-level or area-level data. Bootstrap procedures are proposed to estimate the mean squared errors (MSEs) of the proposed predictors. Simulation experiments are conducted to examine the properties of the proposed small area estimators and the MSE estimators. Finally, an application with housing data illustrates the proposed methods.

2603.10135 2026-03-12 astro-ph.GA

Three Hundred Quasars from the Couch: A first look at high-redshift quasar discovery with SPHEREx

Frederick B. Davies, Sarah E. I. Bosman, Arpita Ganguly, Eduardo Bañados, Silvia Belladitta, Daniel Stern, Javier A. Acevedo Barroso, Daming Yang, Joseph F. Hennawi, Feige Wang, Jinyi Yang, Xiaohui Fan

Comments 12+4 pages, 11+2 figures, submitted to A&A

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Photometric selection of luminous high-redshift ($z\gtrsim4$) quasars is plagued by contamination from numerous low-mass Galactic stars, reddened lower-redshift quasars, as well as compact luminous red galaxies. Confirmation of these rare objects thus requires extensive spectroscopic campaigns on 4 and 8-meter-class telescopes with relatively low success rates. Here we demonstrate the utility of SPHEREx spectrophotometric survey data for quasar confirmation with no ground-based follow-up required, "from the couch," applied to candidates from a purposefully simplistic photometric and astrometric Gaia+WISE selection down to low Galactic latitudes ($|b|\geq8^\circ$). Primarily from the detection of their strong broad H$α$ emission lines, we discover 87 new luminous $4.0 < z < 5.7$ quasars with median $M_\text{1450} = -27.5$, including 19 quasars at $z>5$, and recover 219 previously published quasars at $z>4$. We validate our SPHEREx selection with a 100% confirmation rate in ground-based spectroscopic follow-up of 29 of our new $z>4$ quasars, including 11 unpublished archival spectra. We also discover 203 additional lower-redshift quasars at $0.3 < z < 4$, consisting primarily of relatively rare highly-reddened and strong broad-absorption-line objects that are likely missed by traditional quasar surveys. Finally, we show that the Ly$α$ absorption breaks and H$α$ lines of luminous quasars are already detectable at redshifts $5.7\lesssim z\lesssim6.5$ after the completion of only the first of four all-sky surveys to be performed by SPHEREx during its planned two-year mission.

2603.10134 2026-03-12 physics.plasm-ph

Interpretive Modeling of plasma evolution during fueling experiments at CMFX

S. Mackie, J. G. van de Lindt, J. L. Ball, A. Perevalov, W. Morrissey, Z. Short, B. L. Beaudoin, C. A. Romero-Talamas, J. Rice, R. A. Tinguely

Comments 6 pages 3 figures

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英文摘要

The Centrifugal Mirror Fusion Experiment (CMFX) is an axisymmetric magnetic mirror with a central cathode which generates an azimuthal, radially sheared, supersonic \( E \times B \) flow. The induced rotation stabilizes, confines, and heats the plasma. The diagnostic set on CMFX is sparse, giving limited insight to the state of the plasma. In this work, we developed a time-dependent interpretive analysis framework that uses applied voltage, input power, and measured neutron yield rate to infer evolving plasma conditions throughout a discharge. The 0D MCTrans++ code serves as the core physics model, incorporating centrifugal effects, viscous heating, and angular momentum confinement to infer plasma parameters from operating conditions and experimental observables. An iterative Newton's method was implemented to solve for the plasma state evolution consistent with experimental measurements averaged over successive time intervals. The interpretive analysis was applied to experiments comparing different fueling strategies, revealing a path to improved performance via several short puffs of fuel spread across the discharge. This insight led to operations at voltages up 70 kV. Deuterium neutron yields up to \(1.5 \times 10^7\) n/s were measured, and ion temperature was inferred to reach 950 eV. Until CMFX gains a more complete diagnostic set, this interpretive analysis framework provides useful insight into the evolution of centrifugal mirror plasmas.

2603.10127 2026-03-12 cond-mat.mtrl-sci

ALD Oxidant as A Tuning Knob for Memory Window Expansion in Ferroelectric FETs for Vertical NAND Applications

Ranie Jeyakumar, Prasanna Venkatesan, Lance Fernandes, Salma Soliman, Priyankka Ravikumar, Taeyoung Song, Chengyang Zhang, Woohyun Hwang, Kwangyou Seo, Suhwan Lim, Wanki Kim, Daewon Ha, Shimeng Yu, Suman Datta, Asif Khan

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英文摘要

Dielectric inserts are widely used to expand the memory window (MW) in ferroelectric FETs (FeFETs) for vertical NAND applications, with prior efforts focused primarily on material selection and stack positioning. Here, we demonstrate that the ALD oxidant used for the Al2O3 interlayer serves as a process-level tuning knob for MW engineering. H2O-grown Al2O3 yields a significantly larger MW (7-8 V) compared to O3 (4 V) for both gate-injection (12/3) and tunnel dielectric (8/3/8) configurations. While the tunnel dielectric (8/3/8) stack maintains robust retention up to 1e4s at 125C despite the larger MW, the gate-injection (12/3) configuration exhibits pronounced retention degradation for the H2O case. The enhanced MW is attributed to higher interlayer leakage associated with H2O-based ALD. These results establish oxidant choice as a key process parameter for co-optimizing MW and retention in ferroelectric NAND technologies.

2603.10124 2026-03-12 astro-ph.HE

Quantifying the impact of relativistic precession on tidal disruption event light curves

Diego Calderón, Ondřej Pejcha, Brian D. Metzger, Paul C. Duffell, Stephan Rosswog

Comments 7 pages and 4 figures. Proceedings of "X-ray Quasi-Periodic Eruptions and Repeating Nuclear Transients", 16-19 June 2025, ESAC, Madrid. Accepted for publication in Astronomische Nachrichten

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英文摘要

The tidal field of a black hole can turn a star into a gas stream whose orbit can precess, especially if the a black hole is rapidly spinning. In this work, we investigate the impact of precession on the light curves of tidal disruption events (TDE). To do so, we perform two-dimensional radiation-hydrodynamic simulations of the interaction of the TDE wind and luminosity with the precessed stream wrapped around the black hole. Our results show that in events with black holes of $\sim10^6~\text{M}_{\odot}$ and no orbit-spin inclination, the line of sight has little effect on the light curves, since the stream covers a small fraction of the solid angle as the precession is confined to the orbital plane. In the case of black holes of $\gtrsim10^7~\text{M}_{\odot}$ and high inclination ($i\sim90^{\circ}$), the light curve peaks can be delayed by $\sim$100 days due to presence of the precessed stream blocking the radiation in the early phase of the event. We also discuss our efforts to model self-consistently the hydrodynamic evolution of a tidal stellar stream on curved spacetimes by the presence of a massive black hole.

2603.10122 2026-03-12 astro-ph.HE

The baryon content of magnetically arrested black hole disks and jets

Anthony Chow, Lorenzo Sironi, Bart Ripperda, Amir Levinson

Comments 16 pages, 17 figures

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英文摘要

We study the transport of baryons in magnetically arrested accretion flows and relativistic jets using general relativistic magnetohydrodynamic simulations that incorporate a passive Eulerian tracer. The tracer allows us to reconstruct a proxy for the physical baryon density supplied by the accretion disk while excluding the mass injected numerically to maintain stability in highly magnetized, low-density regions. Applying this method to axisymmetric black hole simulations with varying spin, we show that baryon loading of the jet is intrinsically episodic and regulated by magnetic flux eruption cycles occurring in the inner accretion flow. Each eruption evacuates baryons from the innermost equatorial region, drives reconnection in extended current sheets, and expels moderately magnetized disk material along the funnel wall, establishing a recurrent mass-loading channel. In spinning black holes, shear-driven waves along the jet boundary further enhance baryon entrainment, whereas this mechanism is suppressed in the non-spinning case. For parameters representative of the black hole accretion flow in M87, we map the global structure and time evolution of the Goldreich-Julian screening boundary, defined as the surface separating regions where the plasma density is sufficient to supply the charges required to screen electric fields parallel to the magnetic field from regions that are charge starved. For spinning black holes, we find that the electromagnetic power of the jet is predominantly carried by baryon-poor plasma, with extended time intervals of charge starvation. Our results provide a framework for diagnosing jet composition, charge starvation, and reconnection-driven mass loading in magnetically arrested black hole systems, with direct implications for particle acceleration and non-thermal emission in low-luminosity accretion flows.

2603.10121 2026-03-12 cond-mat.mes-hall cond-mat.mtrl-sci

A unifying framework for sum rules and bounds on optical, thermoelectric and thermal transport from quantum geometry

M. Nabil Y. Lhachemi, Jennifer Cano

Comments 11 pages

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英文摘要

We present a geometric formulation of optical, thermoelectric, and thermal linear response in clean, zero temperature band insulators based on a single object: a generalized time-dependent quantum geometric tensor (g-tQGT) built from correlations of projected particle and heat polarization operators. Within this framework, the AC transport tensors admit compact expressions that make their geometric content explicit. The response splits into a Berry curvature contribution that remains finite in the DC limit and a frequency correction governed by the quantum metric, implying geometry driven effects even in topologically trivial insulators. At equal times, the g-tQGT recovers the usual integrated QGT and yields energy-weighted thermal analogs whose antisymmetric parts are fixed by orbital and heat magnetization. Importantly, in the thermal channel, a thermal quantum geometric tensor is obtained. Casting the theory in a Hilbert-Schmidt inner product form yields a bound on the trace of the thermal QGT, an uncertainty relation on the projected polarization operators and a purely geometric upper bound on the finite-time accumulated response. The latter is used in the optical channel to derive a geometric upper bound on the electric current. Finally, time derivatives of the g-tQGT are used to generate a hierarchy of generalized thermoelectric and thermal sum rules, and bounds on these sum rules are obtained. These bounds are used to find inequalities between different physical objects such as the optical mass, susceptibility functions and magnetizations.