Mathematical Physics
Szegő-type determinant asymptotics for generalized Hilbert matrices with edge eigenvalues
Martin Gebert and Heinrich Küttler
We compute the large-$N$ asymptotics of the determinant of the identity plus or minus a generalized
Hilbert matrix. For $N \in \mathbb{N}$ and $\delta \in \mathbb{R} \setminus \{-1, -2, \ldots\}$, let \[ H_N^\delta := \left( \frac{\sin((1+\delta)\pi)}{\pi(j+k+1+\delta)} \right)_{j,k=0}^{N-1} \] be the generalized
Hilbert matrix. For $\delta$ not a half-integer, we prove the large-$N$ power-law asymptotics of the determinant \[ \log \text{det}(I_N \pm H_N^\delta) = -\frac{\theta_\delta^2 \pm \theta_\delta}{2} \log N + O(1) \] where $\theta_\delta := \delta$ if $\delta < -1/2$, and $\theta_\delta := \frac 1 \pi \arcsin(\sin(\delta\pi))$ if $\delta \ge -1/2$ and $\arcsin \colon [-1,1] \to [-\frac{\pi}{2}, \frac{\pi}{2}]$ denotes the principal branch of $\arcsin$. For $\delta \geq -\frac 12$ the asymptotics is known. The novelty of the present paper is the regime $\delta < - \frac 12$ and understanding the dichotomy in the decay exponent. This stems from the $\pm 1$ edge
eigenvalues of the limiting operator appearing for $\delta < - \frac 12$. Most notably, we obtain for $\delta < -\frac12$ \[ \log \det\bigl(I_N - (H_N^\delta)^2\bigr) = -\delta^2 \log N + O(1). \] Such determinants arise in the study of Anderson's orthogonality catastrophe.
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Instrumentation and Methods for Astrophysics
Flux jump correction in the QUBIC TES data pipeline
Belen Costanza, Lucas Merlo Azzolina, Claudia G. Scoccola et al. (+20 more)
Flux jumps occur in the readout electronics of Transition Edge Sensor (TES) detectors coupled to Superconducting
Quantum Interference Devices (SQUIDs), as a consequence of the periodic transfer function of SQUIDs in the superconducting regime. These events manifest as discontinuities in the Time Ordered Data (TOD) and can significantly degrade the quality of the measured signals. In this work, we present an automated pipeline to identify and correct flux jumps in the calibration data of the QUBIC (Q & U Bolometric Interferometer for Cosmology) instrument, designed to measure the B-mode polarization of the
Cosmic Microwave Background (CMB). Using data from multiple observation campaigns, we characterize the statistical properties of flux jumps and compare them with expectations based on the electronic configuration of the instrument. The proposed pipeline successfully corrects these events, allowing the recovery of affected data and enabling their use in subsequent CMB analysis.
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All authors Belen Costanza, Lucas Merlo Azzolina, Claudia G. Scoccola, Nahuel Miron Granese, Elia Battistelli, Jean-Christophe Hamilton, Michel Piat, Damien Prele, Steve Torchinsky, Ismail Bekkaoui, Alessandro Coppolecchia, Paolo De Bernardis, Sofia Ferazzoli, Massimo Gervasi, Luca Gomez, Sabrina Marwede, Silvia Masi, Youssef Moulane, Alessandro Paiella, Mathias Regnier, Gustavo Romero, Federico Sanchez, Ivan Queirolo
Mesoscale and Nanoscale Physics
Entanglement from particle number fluctuations in a second-order topological insulator
Mahla Moridi Farimani and Kim Pöyhönen
Higher-order topological
insulators are materials with a bulk energy gap featuring gapless modes at $(d-n)$-dimensional edges, where $n > 1$. Despite this modified bulk-boundary correspondence, their nontrivial
topology can nevertheless be observed through the bipartite
entanglement spectrum. Inspired by works suggesting fluctuations in conserved quantities could be used to study
topology in one-dimensional systems, which likewise feature zero-dimensional edge modes, we extend this treatment to a two-dimensional second-order topological
insulator where corner states play an analogous role. We show that the standard bipartite
entanglement entropy and particle number fluctuation lack striking signals of topological phase transitions, both in the static case and in the time
evolution after a quench, obscured by an area-law term from the subsystem edges. By introducing a quadripartite construction of the subsystem, we show that it is possible to isolate the topological contributions, producing sharp transition peaks in both quantities, observable by studying subsystems much smaller than the full system. As particle number fluctuations are accessible in existing experiments, these results establish a concrete and scalable path to experimental detection of the
entanglement in higher-order topological
insulators.
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Quantum Physics
Optimization Landscape Geometry in VQE for Frustrated Quantum Spin Models
Vojtěch Novák, Ivan Zelinka, Swagatam Das et al. (+1 more)
We
benchmark eight classical optimizers for exact-statevector VQE calculations on a controlled hierarchy of frustrated
spin models, ranging from a diagonal Ising glass to transverse-field Ising and anisotropic Heisenberg models. The
benchmark includes local,
stochastic-gradient, evolutionary, covariance-adaptation, and swarm-based optimization methods under matched function-evaluation budgets. To understand their performance beyond final energies, we characterize the underlying
Hamiltonian–ansatz landscapes in terms of local minima, gradients,
curvature, and ground-state reachability. We use simple variational
circuits, from an $R_y$ product-state ansatz for the diagonal model to shallow $R_y$–CNOT hardware-efficient
circuits for the noncommuting models, and study how increasing
circuit depth changes their expressivity, reachability, and optimization geometry. We find that optimizer performance changes substantially across the model hierarchy and is closely connected to landscape structure, while the variational gap represents a separate source of error. These results show how classical optimization, variational expressivity, and landscape geometry jointly determine VQE performance for frustrated
spin models.
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All authors Vojtěch Novák, Ivan Zelinka, Swagatam Das, Martin Beseda
Quantum Physics
Codes for Quantum Secret Sharing with a Helper
Eric Chitambar, Sarah Hagen, David W. Kribs et al. (+3 more)
Helper
quantum secret sharing is a form of secret sharing defined by its unique access structure. One special fixed party, called the helper, can work together with any other party to fully decode the secret. A blind helper is one who can provide this assistance while not holding any local information about the encoded secret. In this work, we analyze the general structure of QSS helper codes and present new code constructions. We fully characterize the structure of blind helper stabilizer codes and show that for the encoding of a single
qubit, recovery is always possible using one-way local operations and classical communication (LOCC) from the helper to the targeted party. Furthermore, we demonstrate how such codes also allow for the helper to target larger subsets of parties by one-way LOCC, enabling them to be authorized to recover the secret. Finally, when each party only holds a
qubit, we identify the general form of all helper codes (including non-stabilizer codes) and find that LOCC recovery is only possible in special cases.
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All authors Eric Chitambar, Sarah Hagen, David W. Kribs, Zhao Ma, Mike I. Nelson, Andrew Nemec
Nuclear Theory
Probing Dense Nuclear Matter at Small-x: A workflow for a global analysis framework
Junaid S. Khan, Rebecca L. Lustberg, Fredrick Olness et al. (+3 more)
The dipole model provides a powerful framework for describing high-energy
nuclear interactions, particularly in the regime of dense gluonic matter. However, accurately evolving the dipole–
nucleus scattering amplitude remains a major computational challenge because it is governed by nonlinear QCD
evolution equations. To address this, we investigate a machine learning (ML) model as an efficient surrogate for the conventional numerical
evolution. These ML-based approximations dramatically reduce the computational cost of global analyses while maintaining the accuracy required to describe a broad range of experimental data. We systematically evaluate the ML results for accuracy, computational efficiency, and ability to capture essential features of dipole
evolution in
nuclear environments. These computational advancements will enable global analyses of diverse
datasets within both the dipole and parton model frameworks, providing a more rigorous probe of
nuclear structure in the dense regime. Comparing both descriptions within a common fitting framework can provide precise constraints on the
gluon distributions and advance our understanding of the
quark and
gluon structure of
nuclei, particularly in the small-x region.
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All authors Junaid S. Khan, Rebecca L. Lustberg, Fredrick Olness, Peter Risse, Bjoern Schenke, Brandon Stevenson
General Relativity and Quantum Cosmology · Cross-listed from math.DG
Dimensional reduction associated with unchanged direction trajectories in flat fiber Robertson Walker spacetimes
D. de la Fuente, R.M. Rubio and J. Torrente-Teruel
In this article, we establish a new dimensional reduction result in (Galilean or Lorentzian) Robertson Walker spacetimes with Euclidean fiber. In this context, we prove that every unchanged direction observer can be embedded into a three dimensional totally geodesic timelike submanifold.
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Solar and Stellar Astrophysics
A Probabilistic Framework for Incorporating Helioseismic Far-Side Active Regions into SFT Models
Bibhuti Kumar Jha, Lisa A. Upton, K. D. Leka et al. (+5 more)
Surface Flux Transport (SFT) models are routinely used to model the Sun's photospheric
magnetic field and provide inner boundary conditions for coronal and heliospheric models, yet they remain fundamentally limited by the lack of direct information about flux emergence on the far side of the Sun. To address this, we develop a framework for incorporating helioseismic images of far-side active regions (HIFAR), into the Advective Flux Transport (AFT) model. Using near-simultaneous
magnetic flux maps (HIFARM) inferred from HIFAR, and STEREO/EUVI 304 A observations from 2010 May 13 to 2014 August 18, we develop a logistic regression model to estimate the probability that a helioseismic detection corresponds to an AR based on descriptors of
magnetic flux, field strength, and location. The model achieves a precision of 0.93 for active region (AR) detections at a probability threshold of 0.73, selected to reject 90% of "ghost" ARs. We also derive an empirical scaling relationship between HIFARM and AFT flux to place HIFARM on the AFT flux scale and demonstrate that the framework reproduces the flux
evolution of ARs consistent with near-side observations over multiple
solar rotations. At the global scale, we find that conventional near-side-driven AFT simulations underestimate the total unsigned
magnetic flux by ~10-20% of the Sun's total
magnetic flux budget. The probabilistic AR detection model and the complete framework developed in this work provide a practical pathway for incorporating helioseismic far-side ARs into SFT models, a step toward realistic modeling of full-Sun
magnetic field.
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All authors Bibhuti Kumar Jha, Lisa A. Upton, K. D. Leka, Ruizhu Chen, Junwei Zhao, Shea Hess Webber, Ignacio Ugarte-Urra, Kiran Jain
Optics
Modeling and Optimization of Cascaded Four-Wave Mixing toward the VUV in Xenon-Filled Negative-Curvature Fibers
Jose Otavio Rosa, Frédéric Gérôme, Fetah Benabid et al. (+2 more)
In this work, we thoroughly characterize third- and fourth-harmonic generation through cascaded four-wave mixing in a xenon-filled negative-
curvature hollow-core fiber operated under a pressure gradient. The experimental results are supported by both a semi-analytical model and numerical simulations, which accurately reproduce the pressure dependence of the harmonic conversion. We identify the optimum pressure conditions for third and fourth-harmonic generation and experimentally observe the cascaded four-wave-mixing process extending into the
vacuum ultraviolet (VUV), up to the sixth harmonic at 172 nm, with the accessible spectral range limited by the available VUV filter.
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All authors Jose Otavio Rosa, Frédéric Gérôme, Fetah Benabid, Jonas H. Osório, Jonathas de Paula Siqueira
High Energy Physics (Phenomenology)
Radiative Corrections and Reheating in Supergravity Models of Inflation
John Ellis, Tony Gherghetta, Kunio Kaneta et al. (+2 more)
We consider the effects of radiative corrections in Starobinsky-like models of inflation, concentrating on models of inflation formulated in N=1 no-scale supergravity. Inflaton couplings to matter fields are necessary for reheating and these have an impact on loop corrections to the inflaton potential. Whilst corrections due to the supergravity couplings of the inflaton to Standard Model (MSSM) fields are negligible, we use Planck data to obtain interesting constraints on GUT bilinear couplings, vevs, and gauge
boson masses that could be sharpened by future CMB measurements.
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All authors John Ellis, Tony Gherghetta, Kunio Kaneta, Wenqi Ke, Keith A. Olive
Quantum Physics
Quantum Secret Sharing with a Helper and Programmable Access Structures
Eric Chitambar, Sarah Hagen, David W. Kribs et al. (+2 more)
Quantum secret sharing (QSS) is a process in which the state of a
quantum system is partitioned into multiple shares, allowing only specific subsets of shareholders to reconstruct the state, while others gain no information about its identity. In this work, we propose a variant of QSS, called “helper QSS,” which designates a special shareholder whose participation with any other group of parties is sufficient for recovering the state. We present different families of helper codes that function for an arbitrary number of parties and system sizes. As an application, we introduce the idea of a programmable access structure in QSS, which allows for a third-party programmer to independently choose the access structure of the code even after the shares are delivered to all the shareholders. This choice is made blindly, meaning that the programmer has no information about the secret being encoded, and it is implemented using the nonlocal process of
quantum steering.
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All authors Eric Chitambar, Sarah Hagen, David W. Kribs, Mike I. Nelson, Andrew Nemec
Computational Physics · Cross-listed from math.NA
Solving the Incompressible Navier-Stokes Equations on Oriented Curved Surfaces Discretized by Point Clouds
Alejandra Foggia and Ivo F. Sbalzarini
We present a meshfree numerical solver for the incompressible Navier-Stokes equations on oriented curved surfaces that are represented by surface point clouds. On curved surfaces, numerical challenges pertaining to stiffness and pressure-velocity coupling are exacerbated. Moreover, vector calculus on curved surfaces differs from its Euclidean counterpart. The presented method operates on surface point clouds in an Eulerian frame of reference without requiring a computational grid or mesh. It achieves consistent approximation in space and time with high order of accuracy; we demonstrate up to order six. The incompressibility constraint is locally imposed as a weak artificial compressibility approximation, avoiding global
matrix inversion. We show that the method provides consistent and convergent approximations of surface vector fields and differential operators. We study the relationship between error, spatial resolution, and artificial Mach number and characterize the frequency spectrum of the artificial oscillations. We provide numerical solutions of the incompressible Navier-Stokes equations on symmetric surfaces, such as the sphere and
torus, and on parametric and non-parametric asymmetric surfaces. Since the proposed method works directly on unstructured surface point clouds, it provides a promising approach for simulations on image-derived geometries, such as in biological morphogenesis from microscopy
videos.
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High Energy Physics (Theory)
Anomaly Matching between Topological Superconductors and $\mathcal{N}=8$ Supergravity
Christopher W. Murphy
The boundary of a $3{+}1$-dimensional topological
superconductor carries a $\mathbb{Z}_{16}$-valued global (Dai-Freed) anomaly, famously matched by the $16$
fermions of a Standard Model generation once a certain $\mathbb{Z}_4$
symmetry is gauged. In a supergravity completion, though, a gravitino contributes $-7/16$ rather than $\pm1/16$, obstructing this $\mathbb{Z}_4$ in the Minimal Supersymmetric Standard Model. We observe that four-dimensional $\mathcal{N}=8$ supergravity evades this fate. Its
fermions, eight gravitini in the $\mathbf 8$ and fifty-six
spin-$\tfrac12$ states in the $\mathbf{56}=\Lambda^3\mathbf 8$ of the $SU(8)$ R-
symmetry, cancel the anomaly. The cancellation holds for every admissible $\mathbb{Z}_4$ structure, is consistent with the vanishing of the continuous $SU(8)$ anomaly, and follows from a Smith homomorphism and the Rarita-Schwinger ghost-subtraction weight identifying the supergravity anomaly with that of the topological
superconductor. In maximal supergravity this $\mathbb{Z}_4$ stays anomaly-free and gaugeable despite its eight gravitini. All numbers are reproduced by an open-source library described in the Supplemental Material.
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Materials Science
Cryogenic Enhancement of Electron Spin Polarization from a Strained GaAs/GaAsP Superlattice Photocathode
Matt Grau, Colin Kirk, Greg Blume et al. (+7 more)
We report electron
spin polarization of 95.0 +/- 0.8 (stat) +/- 2.4 (sys)% from a strained GaAs/GaAsP superlattice photocathode grown by metalorganic chemical vapor deposition (MOCVD) and cooled to dry-ice temperature (195 K). We achieved this polarization with 97.8% circularly polarized excitation light and a
quantum efficiency of 0.7% at the peak polarization wavelength. This measurement exceeds the values of previously reported GaAs-based photocathode polarizations, which have clustered near 92% for two decades. We vary the temperature of the cathode and measure the polarization and
quantum-efficiency spectra at 295 K, 273 K, 195 K, and 77 K. The polarization rises from 91.2(1)% at 295 K to its maximum at 195 K, while the spectral peak shifts from 775 nm to 739 nm (78 meV) over the full temperature range, tracking the widening band gap. The spectra probe two depolarization mechanisms: a thermalized transport channel that is suppressed on cooling, and energy-dependent hot-electron relaxation that persists and sets the low-temperature saturation. The polarization recovers after a full cooling and warmup cycle and is stable while the
quantum efficiency decays, which disfavors surface energy filtering as the origin of the gain. These results indicate that modest cooling to 195 K, for which dry ice suffices, is a practical route to higher-polarization GaAs-based electron sources.
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All authors Matt Grau, Colin Kirk, Greg Blume, John Hill, Sushil Poudel, Alimohammed Kachwala, Marcy Stutzman, Joseph Michael Grames, Sylvain Marsillac, Matt Poelker
Fluid Dynamics
Chordwise micro-jet placement reveals a trade-off between mean hydrodynamic performance and unsteady loading under cloud cavitation
Amirmehran Mahdavi, Soheil Motezakkeri, Yasin Ebrahimi et al. (+1 more)
Prescribed tangential micro-jet injection can modify cloud-cavitation dynamics, but the chordwise location that improves mean hydrodynamic performance may differ from the location that minimizes unsteady loading. This study compares five injection locations (x/c = 0.15, 0.30, 0.45, 0.60, and 0.70) on a Clark-Y hydrofoil at Re = 7 x 10^5 and cavitation number 0.8. Transient large-eddy simulation with a Volume-of-Fluid formulation and the Schnerr-Sauer cavitation model is used in a two-dimensional parametric framework, with one representative three-dimensional case included to illustrate spanwise cavity deformation. The analysis considers vapor
topology, turbulent kinetic energy, velocity and pressure fields, cycle-averaged surface pressure, hydrodynamic forces, force fluctuations, spectra, and cavity-thickness histories. Injection at x/c = 0.15 gives the highest cycle-averaged lift-to-drag ratio among the tested cases: drag decreases from 0.137 to 0.107 and the lift-to-drag ratio increases from 5.693 to 6.261, while lift decreases from 0.78 to 0.67. In contrast, x/c = 0.60 gives the lowest recorded force-fluctuation RMS, with lift- and drag-coefficient RMS values of about 0.112 and 0.0165. The preferred injection location is therefore objective-dependent: the location favored by mean hydrodynamic performance does not coincide with the location favored by unsteady-load reduction under the present conditions.
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All authors Amirmehran Mahdavi, Soheil Motezakkeri, Yasin Ebrahimi, Ali Alavi
Physics and Society
Rock, Paper, Scissors, ... Dynamite - A Model of Disruption from New Technologies
Andrew J. Lohn
We seek to understand the effect of adding disruptive highly-capable new technologies to competitions by assessing the addition of Dynamite to Rock-Paper-Scissors. We find that providing a versatile Dynamite move to only one player provides limited value (win probability increases from 50% to 55.5%) and is played rarely. That value decreases further if the game is expanded beyond just the original three moves. We also observe several mechanisms by which prior moves can become strategically unplayable, or obsolete. We hope that this model illustrates some non-intuitive aspects of developing new versatile technologies. We also hope that it illustrates some pitfalls for developers and integrators to avoid in order to create value rather than merely capability.
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Chemical Physics
Smoothed truncated Coulomb potential for periodic Gaussian-basis Hartree–Fock exchange
Gengzhi Yang, Aamy Bakry and Hong-Zhou Ye
Truncated Coulomb (TC) potentials reduce finite-size errors and accelerate thermodynamic-limit convergence in periodic Hartree–Fock (HF) calculations, but their use with Gaussian basis sets is complicated by the evaluation of electron repulsion integrals (ERIs), particularly for nonspherical truncation domains and all-electron calculations. We introduce the smoothed truncated Coulomb (sTC) potential as a systematically improvable approximation to a parent TC potential. A real-space Gaussian convolution smooths the sharp truncation boundary, and a single dimensionless parameter, $\eta$, controls the width of the smoothing window, which can be tightened to systematically approach the TC reference. The smoothing by sTC enables a dual-space
algorithm for evaluating periodic Gaussian-basis ERIs that requires neither a large plane-wave basis nor new molecular integral kernels and is applicable to both pseudopotential and all-electron calculations, including the important Wigner–Seitz-
cell truncation boundaries.
Benchmarks spanning insulating, semiconducting, layered, metallic, and molecular-
crystal systems show that sTC-based HF closely reproduces TC results in pseudopotential calculations and extends TC-quality calculations to all-electron settings. Across these systems, sTC substantially improves thermodynamic-limit convergence relative to the probe-charge Ewald method while remaining practical for all-electron calculations in which direct TC-based calculations are computationally challenging.
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General Relativity and Quantum Cosmology
Unimodular Gravity with Arbitrary Diffusion Function: A Dynamical System Reconstruction Approach
Gabriel Gómez, Guillermo Palma and Norman Cruz
We investigate cosmological
diffusion models in unimodular
gravity within a dynamical systems reconstruction framework. By treating the logarithmic slope of the
diffusion sector as an invertible dynamical variable, the
diffusion function can be systematically reconstructed from the phase-space structure of the cosmological
evolution. Under these conditions, we determine the physically admissible fixed points of the system, identifying novel matter–
diffusion scaling solutions associated with power-law
diffusion sectors, as well as purely
diffusion-dominated configurations capable of driving late-time accelerated expansion without requiring an explicit cosmological constant term. The local behavior around the fixed points is then extended to the full cosmological
evolution, providing a framework to explore the global implications of
diffusion cosmologies. Beyond the asymptotic fixed-point structure, we further develop a reconstruction formalism based on the dynamical
evolution of the
diffusion slope, allowing for trajectories interpolating between different
diffusion regimes during the
cosmic history. Our results establish a systematic framework for constructing and classifying viable
diffusion cosmologies in unimodular
gravity directly from the phase-space dynamics.
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General Relativity and Quantum Cosmology
Gravitational waves from core collapse of rotating very-massive stars: 3D numerical relativity computation
Alan Tsz-Lok Lam, Masaru Shibata and Sho Fujibayashi
We numerically study the collapse of rotating, very-massive
stellar cores with masses of $\approx 200$, $300$, $500$, and $1100M_\odot$ into black holes using both axisymmetric and three-dimensional (3D) numerical relativity. Our results indicate that when the dimensionless
spin of the resulting black hole exceeds 0.8, a massive disk consistently forms around it. These massive, compact disks, carrying more than about 10% of the black hole's mass, are prone to non-axisymmetric deformations that trigger gravitational-wave bursts with frequencies around 10-50 Hz. Such waves could be detected by the Einstein
Telescope and
Cosmic Explorer, even from sources a few Gpc away. We also summarize the gravitational-wave signals from axisymmetric collapse, which tend to have lower amplitudes and higher frequencies than those caused by non-axisymmetric instabilities.
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Astrophysics of Galaxies
The gradual decline of Ly$\alpha$ visibility in the CANDELS fields: evidence for the combined effects of galaxy evolution and reionization
L. Napolitano, L. Pentericci, A. Ferrara et al. (+35 more)
We investigate the
evolution of Ly$\alpha$ visibility and the physical properties of Ly$\alpha$ emitters (LAEs) across the five CANDELS fields using publicly available JWST/NIRSpec PRISM spectroscopy. Our catalog comprises 3446 spectroscopically confirmed sources at 4 $\leq $ z < 14.2, including 3361
star-forming
galaxies (SFGs), of which 539 are robust (S/N > 3) LAEs. We measure the fraction of LAEs with EW$_0$ > 25A (X$_{\mathrm{Ly\alpha}}$) and trace its
redshift evolution in two UV luminosity bins, namely -20.25 < M$_{\mathrm{UV}}$ < -18.75 and -21.75 < M$_{\mathrm{UV}}$ < -20.25. Within the fainter-UV range, X$_{\mathrm{Ly\alpha}}$ increases from z = 5 to z = 6 at 3$\sigma$ significance and subsequently declines toward higher
redshifts with a significant monotonic trend at z > 6. We also investigate the physical properties of both LAEs and the full SFG population. We find that the
stellar mass, UV slope $\beta$,
stellar reddening, SFR,
metallicity, sSFR, and burstiness of LAEs remain approximately stable with
redshift. The only exception is the mass-weighted age which decreases with increased
redshift. Conversely, the properties of the full SFG population evolve significantly, progressively approaching the region of
galaxy-property space occupied by LAEs as
redshift increases. This suggests that
galaxy evolution may enhance the intrinsic production and escape of Ly$\alpha$
photons toward earlier epochs. We argue that this effect should be accounted when inferring the
evolution of the neutral hydrogen content of the IGM from the observed visibility of Ly$\alpha$ emission. To this end, we employ a physically motivated framework based on the Attenuation-Free Model, jointly accounting for
galaxy evolution and IGM attenuation. Our observations favor reionization histories that proceed gradually over scenarios characterized by a rapid increase in the
cosmic neutral hydrogen fraction.
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All authors L. Napolitano, L. Pentericci, A. Ferrara, M. Llerena, M. Dickinson, A. Calabrò, S. L. Finkelstein, R. Begley, P. Arrabal Haro, A. Arroyo-Polonio, B. E. Backhaus, D. Bevacqua, A. Bhagwat, M. Bischetti, M. Castellano, S.-J. Chang, E. R. Cueto, V. D'Odorico, C. T. Donnan, M. Galbiati, G. Gandolfi, M. Giavalisco, M. Hirschmann, J. Kartaltepe, A. M. Koekemoer, K. K. Knudsen, R. A. Lucas, S. Mascia, L. Paquereau, B. Pérez-Díaz, C. Piscitelli, R. Rana, P. Santini, A. J. Taylor, E. Taylor, R. Tripodi, S. M. Wilkins, L. Y. A. Yung
Fluid Dynamics · Cross-listed from cs.CV
A Lagrangian View of Flow Matching
Peyman Milanfar
Modern explicit-time generative models, such as Flow Matching [Lipman et al., 2023] and Rectified Flow [Liu et al., 2023], are typically derived top-down via Optimal Transport and the continuity equation. This standard Eulerian approach focuses on the macroscopic transport of probability mass. In this paper, we present an alternative, bottom-up mechanical derivation grounded in a Lagrangian (particle-centric) perspective. By analyzing the local Taylor expansion of a continuous denoiser, we motivate a strict invariance condition required for optimal, singlestep generation: the conservation of target identity. Enforcing this condition yields a governing quasi-linear advection Partial Differential Equation (PDE). We demonstrate that solving this PDE via the Method of Characteristics analytically yields the straight-line trajectories of Flow Matching. This
geometric perspective isolates the Jacobian of the denoiser as the primary source of trajectory
curvature, providing a direct mathematical explanation for why straight-line flows enable massive step sizes, and why empirical models require
distillation to flatten intersecting characteristics.
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High Energy Astrophysical Phenomena
GRMHD Simulations of Accreting Proto-Magnetars II. Implications for r-process Nucleosynthesis
Tejas Prasanna, Kyle Parfrey, Brian D. Metzger et al. (+3 more)
Newly formed, rapidly spinning, strongly magnetized
neutron stars ("millisecond proto-magnetars") can arise in collapsars,
neutron star mergers, or white-
dwarf accretion-induced collapse, and are often surrounded by compact
accretion disks. At
accretion rates of ~0.1 Msun/s, these disks can become
neutron rich and power
outflows capable of rapid
neutron-capture (r-process) nucleosynthesis. In Paper I, we presented axisymmetric GRMHD simulations of
accretion onto such proto-magnetars and showed how the disk-magnetosphere interaction regulates jet power, variability, and
neutron star torques. Here we use the same simulations to study how this interaction regulates the mass, composition, and velocity of the
baryon-rich ejecta, comparing proto-magnetar models to otherwise similar black hole
accretion. A magnetized
neutron star qualitatively changes both the amount and composition of the ejecta. Stronger
neutron star magnetic fields suppress
accretion and redirect more inflowing material into unbound
outflows, even when the magnetosphere remains strongly compressed by the disk. Once the field produces
magnetic channeling or centrifugal acceleration, mass loss is enhanced further. Reaction-network calculations show that these magnetically driven
outflows can synthesize the full range of r-process
nuclei, including the heaviest elements. Moderate
neutrino irradiation substantially reduces the third-peak yield, but magnetically accelerated
neutron star outflows retain a heavy component more effectively than black hole disk winds; sufficiently strong early-time irradiation suppresses it altogether. Accreting proto-magnetars may therefore be important heavy r-process sources once their
neutrino emission has sufficiently declined.
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All authors Tejas Prasanna, Kyle Parfrey, Brian D. Metzger, Ore Gottlieb, Andrei Beloborodov, Koushik Chatterjee
Astrophysics of Galaxies
Local Heavily Obscured Active Galaxies Observed With Chandra (I): Spectral Properties of the Nuclear and Extended X-ray Emission
R. Middei, G. Fabbiano, A. Trindade Falcão et al. (+3 more)
The Chandra X-ray Observatory has revealed that kiloparsec-scale extended X-ray emission is commonly associated with heavily absorbed ($\log (N_{H}$/cm$^{-2})\,>\, 23$) Active
Galactic Nuclei (AGN) in the local Universe. We present a homogeneous spatially resolved spectral analysis of a sample of nearby obscured AGN observed with deep ($>100$~ks) Chandra/ACIS exposures and all associated with extra-
nuclear extended emission. Exploiting the sub-arcsecond resolution of Chandra, we separate unresolved
nuclear emission from physically distinct extended regions and model their spectra using photoionized and thermal
plasma components. The extended emission is spectrally complex, requiring a combination of photoionized and collisionally ionized components in most regions. The spectral parameters exhibit systematic radial variations, with
nuclear regions typically hosting higher-column and higher-ionization components, while extended regions span similarly broad but overlapping ranges without a simple monotonic radial progression. Hard ($>3$ keV) X-ray emission in excess of
nuclear PSF spillover is detected in 19/20 sources, while extended Fe~K$\alpha$ emission is observed in 12/20 systems. These results establish a uniform baseline for the X-ray properties of heavily obscured AGN and provide constraints on the geometry and physical conditions of AGN-driven feedback in the local Universe.
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All authors R. Middei, G. Fabbiano, A. Trindade Falcão, D. Ł. Król, W. P. Maksym, M. Elvis
Cosmology and Nongalactic Astrophysics
TDCOSMO XXVIII. The Hubble constant from the quadruply lensed quasar J1537$-$3010 with precise time delays
A. Galan, A. G. Schweinfurth, S. H. Suyu et al. (+21 more)
We present the first measurement of the Hubble constant ($H_0$) from the quadruply-lensed
quasar J1537$-$3010, which has optically-measured time delays at $\sim2 \%$ precision. We combine these delays with multi-band imaging data from the Hubble Space
Telescope (HST) and model the system with two independent software and teams. We adopt a mass profile that is maximally degenerate with $H_0$ to fully incorporate the mass-sheet degeneracy in the error budget, with nuisance parameters constrained by spatially resolved
stellar kinematics from the Multi Unit Spectroscopic Explorer (MUSE) and a line-of-sight (LoS) analysis using the Euclid Flagship simulation. The entire analysis is performed blindly to $H_0$, distances and mass density slope of the main deflector. After unblinding, we measure $H_0 = 75.5^{+9.3}_{-5.8}\ {\rm km\,s^{-1}\,Mpc^{-1}}$, corresponding to a $10\%$ precision measurement from a single system. This precision is driven by conservative lens modeling assumptions including differences between lens modeling methods and the limited
stellar kinematics constraints, from which we infer a total mass-sheet parameter $\lambda\equiv(1-\kappa_{\rm ext})\lambda_{\rm int} = 0.89^{+0.11}_{-0.06}$ ($\lambda_{\rm int}=0.89^{+0.09}_{-0.07}$) that is consistent with current results for elliptical
galaxies ($\lambda \approx 1$). Our
lensing constraints,
stellar kinematic measurements and LoS characterization will be included in subsequent population-level measurements of $H_0$. Moreover, our lens models combined with future near-infrared spectroscopy and imaging from the James Webb Space
Telescope will further reduce the uncertainties on $H_0$ from J1537$-$3010 alone, bringing it closer to the few percents precision of the time delays.
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All authors A. Galan, A. G. Schweinfurth, S. H. Suyu, D. P. Johnson, A. Chawla, D. Sluse, G. V. Kharchilava, E. Buckley-Geer, H. Lin, S. Knabel, W. Sheu, S. Ertl, T. Anguita, S. Birrer, F. Courbin, F. Dux, M. Millon, V. Motta, S. Schuldt, T. Treu, D. M. Williams, M. Cappellari, K. C. Wong, D. Eckert
Soft Condensed Matter
Polarisation-mediated underscreening from weakly bonded ion clusters
David Ribar, Jake W. Felber, Clifford E. Woodward et al. (+1 more)
We explore the hypothesis that ions form loosely connected clusters at high ionic strength in aqueous solutions, and that these clusters have relevance to the experimentally observed phenomenon usually referred to as "anomalous underscreening". Cluster formation lowers the ionic strength below its nominal value, slowing the decay of the screening length but not reversing it. Here we focus on an additional contribution, cluster polarisation. We demonstrate that this effect produces longer-ranged repulsive interactions between like-charged surfaces or particles in concentrated salt solutions. We derive an analytical bulk relation in which the entire architecture of a cluster enters through a single quantity, the charge-weighted second moment of its intramolecular charge structure factor, which quantifies the polarisation response of an arbitrary cluster
topology. We also make numerical calculations using classical
polymer Density Functional Theory, cDFT, for a model based on
star-like clusters in which satellite ions are weakly bonded by a harmonic spring to a common central ion. The corona of satellite ions is assumed to be net neutral, since the formation of highly charged clusters would be accompanied by a significant self-energy cost. Using this model, we calculate surface interactions and screening lengths at various overall salt concentrations. We show that, under the assumption that the fraction of ions belonging to clusters increases with salt concentration, one may qualitatively arrive at "anomalous underscreening", i.e., an effective screening length that displays a minimum at an overall (monovalent) salt concentration of about 1 M. Quantitatively, we note that the predicted growth of the screening length beyond this threshold value is weaker than typically found by experimental surface force measurements.
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All authors David Ribar, Jake W. Felber, Clifford E. Woodward, Jan Forsman
High Energy Astrophysical Phenomena
Portraits of the young and old in X-ray: New millisecond pulsar detections and updated characterization of young neutron stars
Wynn C. G. Ho, Patrick H. Wang and Sebastien Guillot
We present analyses of new and archival Chandra and NuSTAR data on two old millisecond
pulsars, a young highly-energetic
pulsar, and a young
neutron star. PSR J1810-0623 is a recently-discovered 4.55 ms
radio pulsar in a binary with a possible carbon-oxygen white
dwarf companion. We tentatively detect the
pulsar for the first time in X-ray using a new short Chandra HRC-I observation. Its faintness suggests a distance more in accord with the further (~1 kpc) of its dispersion measure-inferred distances. PSR J1933-6211 is a 3.54 ms
radio pulsar also with a carbon-oxygen white
dwarf companion. Our first-time X-ray detection in an archival HRC-S image indicates its X-ray luminosity is similar to that of the 1.9 Msun
pulsar PSR J1614-2230. Next, PSR J1813-1749 is a 1-2 kyr
pulsar with one of the highest known
spin-down luminosities. We measure its
spin period of 44.7 ms using 2025 NuSTAR and 2026 Chandra ACIS-S data and update its
spin evolution model. We show for the first time the pulse profile of PSR J1813-1749 at 3-79 keV, and we find that the spectra of the
pulsar and
pulsar wind nebula at these energies did not change significantly between observations in 2018 and 2025. Finally, for the 5-10 kyr
neutron star CXOU J182913.1-125113 in the
supernova remnant G18.95-1.1, we combine ACIS-I observations from 2009 and 2024 to better measure the
neutron star's spectrum.
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High Energy Astrophysical Phenomena
Evidence for a luminosity-class dichotomy in the supergiant donors of persistent high-mass X-ray binaries and supergiant fast X-ray transients
Lara Sidoli and Vito Sguera
We have investigated the properties of the supergiant donors in two types of high-mass X-ray binaries (HMXBs, i.e. the so-called supergiant fast X-ray transients (SFXTs) and the classical X-ray sources), by collecting all available information from the literature. A prevalence of O-type versus B-type supergiant donors in SFXTs was previously suggested in the literature, possibly indicative of faster winds in SFXTs than in classical, persistent sources. Our aim is to investigate whether there is evidence for a dichotomy in the
stellar luminosity class, since B-type supergiants are also known to be hosted in SFXTs. Our collection of the relevant literature allowed us to build a robust sample of both types of HMXBs with a secure
stellar classification. We have found that the SFXTs showing the most extreme, transient X-ray emission host only O-type or B-type
stars with a Ib and Iab luminosity class, whereas classical sources have mostly Ia donors. This is robust evidence that might explain the two different behaviours of HMXBs at X-rays since the
stellar luminosity class appears to be linked to the wind properties (the supergiant wind terminal velocity, the mass-loss rate, and the wind strength Q parameter), indicative of faster and less dense winds in SFXTs than in classical sources.
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High Energy Astrophysical Phenomena
GRMHD Simulations of Accreting Proto-Magnetars I. Implications for Gamma-Ray Burst Jets and Energetic Explosions
Tejas Prasanna, Kyle Parfrey, Brian D. Metzger et al. (+3 more)
Newly formed, rapidly rotating, strongly magnetized
neutron stars ("millisecond proto-magnetars") are promising central engines for gamma-ray bursts (GRBs) and luminous
supernovae. Although often modeled in isolation, they can be born surrounded by
accretion disks in
stellar collapse,
neutron-
star mergers, or
accretion-induced collapse. We present axisymmetric GRMHD simulations of hyperaccretion onto such objects, including a physical equation of state and charged-current weak interactions. Holding the weakly magnetized
accretion torus fixed, we vary the
stellar dipole field strength to span crushed-magnetosphere, magnetically channeled
accretion, and centrifugal-propeller regimes, and compare with an otherwise similar accreting black hole.
Accretion compresses the
stellar magnetosphere and opens additional
magnetic flux, producing relativistic jet powers that exceed isolated-dipole
spin-down estimates by factors of a few to ~10. Even while the magnetosphere remains compressed against the
stellar surface, stronger fields increasingly impede
accretion and enhance
outflows. Channeled-
accretion models show strong jet variability driven by plasmoid eruptions and intermittent magnetospheric
accretion, whereas the propeller model produces a steadier, more powerful jet and rapid
spin-down. The disk-magnetosphere interaction also regulates how efficiently the
neutron star grows and whether it
spins up or down; near
spin equilibrium, inefficient
accretion can delay collapse to a black hole relative to estimates based on the external mass-supply rate. Accreting proto-magnetars can therefore power relativistic jets and
baryon-rich
outflows with energetics comparable to those inferred for long GRBs and GRB-
supernovae. A companion paper explores implications for
neutron-rich ejecta and r-process nucleosynthesis.
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All authors Tejas Prasanna, Kyle Parfrey, Brian D. Metzger, Ore Gottlieb, Andrei Beloborodov, Koushik Chatterjee
High Energy Astrophysical Phenomena
Equation of state and neutron star properties with new mass-radius constraints from PSR~J1614–2230, PSR~J2124–3358, and 47~Tuc~X7
Melissa Mendes, Isak Svensson, Hannah Gottling et al. (+9 more)
We study the impact of new mass-radius information from PSR J1614-2230, PSR J2124-3358, and 47 Tuc X7 in a combined equation of state inference based on
chiral effective field theory constraints at
nuclear densities and using different high-density extensions, including perturbative QCD constraints. The largest impact stems from the heavy-mass PSR J1614-2230
star, which shifts heavy
neutron stars to smaller radii by around 0.4 km. Moreover, the combined astrophysical NICER, LIGO/Virgo, and X-ray information drives the radius posterior to a more data-driven distribution, which is less sensitive to the high-density extension. For the equation of state, the new mass-radius information significantly tightens the pressure and speed-of-sound posterior distributions, especially around three times saturation density. Finally, we make predictions for the poorly constrained masses of PSR J2124-3358 and 47 Tuc X7 based on the combined equation of state analysis and the other astrophysical sources.
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All authors Melissa Mendes, Isak Svensson, Hannah Gottling, Kai Hebeler, Achim Schwenk, Nathan Rutherford, Lucien Mauviard, Christine Kazantsev, Yves Kini, Denis Gonzalez-Caniulef, Sebastien Guillot, Anna Watts
High Energy Astrophysical Phenomena
A NICER view of PSR J1614$-$2230: a massive and compact millisecond pulsar
Lucien Mauviard, Sebastien Guillot, Lami Suleiman et al. (+17 more)
Using pulse profile modeling, we obtain the mass-radius measurement of a millisecond
pulsar (MSP) with data from the
Neutron Star Interior Composition ExploreR, XMM-Newton and the Chandra X-ray Observatory. We report here the radius of PSR J1614$-$2230, the second most massive MSP confirmed by
radio timing. All of the data sets are well described by a simple model composed of two circular hot spots. The final result yields an equatorial radius of $R_{\rm eq}=10.06 ^{+1.25}_{-0.87}\,$km, and a gravitational mass of $M=1.937^{+0.012}_{-0.013}\,M_{\odot}$ (equally tailed 68% credible intervals). Although a non-thermal component was previously reported at higher energies, we find no sign of it in either our phase-averaged or phase-resolved spectral analyses. Using new relations linking the compactness to oblateness or surface
gravity, and tailored to the
spin frequency of PSR J1614$-$2230, we infer a configuration with one hot spot near the pole, and another near the equator. The tight mass posterior is essentially informed by
radio timing, while the radius constraint is not as tight due to the low source signal (8.5$\sigma$ X-ray pulse significance). However, over all geometries and atmosphere models tested, the radius posterior tends toward low values ($\lesssim12.08\,$km, 90th percentile in all cases).
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All authors Lucien Mauviard, Sebastien Guillot, Lami Suleiman, Yves Kini, Denis González-Caniulef, Christine Kazantsev, Pierre Stammler, Devarshi Choudhury, Bas Dorsman, Mariska Hoogkamer, Daniela Huppenkothen, Tuomo Salmi, Anna L. Watts, Jérôme Novak, Natalie A. Webb, Jean-Francois Olive, Matthew Kerr, Lucas Guillemot, Ismaël Cognard, Gilles Theureau