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Wednesday 12 August

Instrumentation and Methods for Astrophysics

LIGO Detector Characterization in the Second and Third Parts of the Fourth Observing Run

J. Glanzer, A. F. Helmling-Cornell, A. Calafat et al. (+244 more)

LIGO detector characterization efforts enabled the confident detection of gravitational waves from hundreds of compact binary coalescences during the fourth observing run. Reliable production of high quality detector data and rapid noise mitigation efforts allow the extraction of the most in-depth knowledge of gravitational wave sources and their progenitors. In this paper we describe LIGO detector characterization activities during the second and third parts of O4-O4b and O4c. We summarize changes in detector configuration and performance at the LIGO Hanford and LIGO Livingston Observatories between the end of the first part of O4a and the end of O4c, including upgrades made during the commissioning break preceding O4b and during repairs performed in O4c. We describe instrumental investigations carried out at both sites designed to understand and subsequently mitigate the effect on detector sensitivity of transient glitches, narrowband spectral lines, and vibration-driven noise, among other data quality concerns. We then review the tools and procedures used to validate gravitational wave candidates and the data quality products thus supplied to searches for gravitational waves from compact binary coalescences and unmodeled transients, continuous gravitational waves, and the stochastic gravitational wave background. The efforts of the detector characterization group are essential for maintaining and improving the sensitivity and reliability of the LIGO detectors especially as observing runs lengthen and more events are detected. We conclude with prospects for LIGO detector characterization activities in future observing runs.
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All authors J. Glanzer, A. F. Helmling-Cornell, A. Calafat, S. R. Callos, E. Capote, A. Effler, T. A. Ferreira, E. Goetz, A. M. Knee, J. R. Mérou, D. Malakar, B. Mannix, D. Nandi, K. Pham, R. M. S. Schofield, P. Sharma, Z. Yarbrough, N. Arnaud, B. K. Berger, K. Burtnyk, C. M. Compton, G. Connolly, D. Davis, F. Di Renzo, G. Grant, J. C. Martins, G. Mo, A. Neunzert, L. K. Nuttall, J. Oberling, J. R. Olson, S. Soni, M. Trevor, R. Abbott, I. Abouelfettouh, R. X. Adhikari, A. Ahuja, S. Álvarez-López, A. Ananyeva, S. Appert, S. K. Apple, K. Arai, J. Areeda, N. Aritomi, S. M. Aston, M. Ball, S. W. Ballmer, D. Barker, L. Barsotti, J. Betzwieser, Z. S. Bhalla, D. Bhattacharjee, G. Billingsley, S. Biscans, C. D. Blair, N. Bode, E. Bonilla, V. Bossilkov, A. Branch, A. F. Brooks, D. D. Brown, R. Bruntz, J. Bryant, C. Cahillane, H. Cao, C. Chatterjee, N. Christensen, F. Clara, J. Collins, R. Cottingham, D. C. Coyne, R. Crouch, J. Csizmazia, A. Cumming, L. P. Dartez, N. Demos, E. Dohmen, K. L. Dooley, J. C. Driggers, S. E. Dwyer, A. Ejlli, T. Etzel, M. Evans, J. Feicht, R. Frey, W. Frischhertz, P. Fritschel, V. V. Frolov, M. Fuentes-Garcia, P. Fulda, M. Fyffe, D. Ganapathy, B. Gateley, T. Gayer, J. A. Giaime, K. D. Giardina, R. Goetz, G. Gonzalez, A. W. Goodwin-Jones, S. Gras, C. Gray, D. Griffith, H. Grote, T. Guidry, J. Gurs, E. D. Hall, J. Hanks, J. Hanson, M. C. Heintze, N. A. Holland, N.-T. Howard, D. Hoyland, H. Y. Huang, B. Hughey, Y. Inoue, A. L. James, A. Jamies, K. Jani, R. Jaume, A. Jennings, W. Jia, D. H. Jones, H. B. Kabagoz, S. Kandhasamy, S. Karat, S. Karki, M. Kasprzack, K. Kawabe, N. Kijbunchoo, P. J. King, J. S. Kissel, K. Komori, A. Kontos, R. Kumar, K. Kuns, M. Landry, B. Lantz, M. Laxen, K. Lee, M. Lesovsky, F. Llamas Villarreal, E. Lofquist-Fabris, M. Lormand, B. R. Lott, H. A. Loughlin, R. Macas, M. MacInnis, C. N. Makarem, G. L. Mansell, R. M. Martin, K. Mason, F. Matichard, N. Mavalvala, N. Maxwell, G. McCarrol, R. McCarthy, D. E. McClelland, S. McCormick, J. McIver, R. McNeil, T. McRae, F. Mera, E. L. Merilh, F. Meylahn, R. Mittleman, S. Mohan S, D. Moraru, G. Moreno, A. Mullavey, M. Nakano, T. J. N. Nelson, S. A. Nichols, J. Notte, T. O'Hanlon, R. Oram, C. Osthelder, D. J. Ottaway, H. Overmier, W. Parker, O. Patane, A. Pele, S. Perry, H. Pham, M. Pirello, J. Pullin, V. Quetschke, K. E. Ramirez, K. Ransom, J. Reyes, J. W. Richardson, K. Riles, M. Robinson, J. G. Rollins, C. L. Romel, J. H. Romie, M. P. Ross, B. I. Rotimi, K. Ryan, T. Sadecki, A. Sanchez, E. J. Sanchez, L. E. Sanchez, R. L. Savage, D. Schaetzl, M. G. Schiworski, R. Schnabel, E. Schwartz, D. Sellers, T. Shaffer, R. W. Short, D. Sigg, B. J. J. Slagmolen, J. R. Smith, C. Soike, V. Srivastava, T. Starkman, L. Sun, D. B. Tanner, J. Tasson, M. Thomas, P. Thomas, K. A. Thorne, E. M. Todd, M. R. Todd, C. I. Torrie, G. Traylor, A. S. Ubhi, R. P. Udall, G. Vajente, J. Vanosky, A. Vecchio, P. J. Veitch, A. M. Vibhute, E. R. G. von Reis, J. Warner, B. Weaver, R. Weiss, C. Whittle, P. Wilcox, B. Willke, C. C. Wipf, J. L. Wright, V. A. Xu, H. Yamamoto, L. Zhang, Z. Zhang, M. E. Zucker

High Energy Physics (Theory) · Cross-listed from math.AG

K3 atoms of the cubic fourfold and the BPS structure of the Painlevé I determinant line

Mark Raugas

The compatibility of the semiorthogonal decomposition of a cubic fourfold with Bridgeland stability beyond a generic point is the missing ingredient in the conjectured dynamical protection of the K3 atom $\AX$. We analyze it in the exactly solvable models of the noncommutative minimal model program. In the uncoupled Fano models ($\PP^1$; $\PP^1 \times \PP^1$ at resonance) the quantum cohomology path exits the geometric chamber at an explicit finite time, enters the selection region of the gluing, and never leaves; perturbing the resonance shows the $\varepsilon$-crossover is not a wall. The $A_2$ quiver provides a coupled counterpart. We examine the deformed cubic oscillator, Painlevé~I, and formulate a tau-JLO dictionary as a determinant identification and establish its perturbative layer, including computing closed-form quantum periods through $Z_4$, all-orders flatness with exact curvature the tau-divisor current, identifying it with the zeta determinant's zero divisor along a Painlevé~I trajectory. We close by conjecturing that the determinant's nonperturbative jumps are automorphisms of the underlying Joyce structure.
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Mesoscale and Nanoscale Physics

Lectures on ultrathin film ferromagnetism

D. Pescia

In these Lecture Notes we review some of the fundamental principles that have emerged from research on the ferromagnetism of ultrathin films consisting of 3d transition-metal overlayers. Their growth is often layer-by-layer. This growth mode produces quantum wells along the vertical direction that profoundly impact any physical property of the materials. In addition, the vertical confinement establishes spin ensembles that extend to macroscopic distances along the in-plane directions and are finite along the vertical (perpendicular) direction, i.e. they are two-dimensional. Accordingly, they display ground state properties that originate from the two-dimensionality, such as “dead” magnetic layers or “enhanced magnetic moments”, an oscillatory interlayer magnetic coupling and an anomalous perpendicular versus in-plane magnetic anisotropy that produces, in some specific situations, a perpendicular collective orientation of the spins. At finite temperatures, ferromagnetic order is observed to persist and an analysis of the magnetic order of ultrathin films in terms of the renormalization group provides a suitable framework for explaining this observation. The ferromagnetic order is lost at a phase transition which follows closely the two-dimensional Ising universality class, as shown by an accurate analysis of data in the vicinity of the critical point. The perpendicular spin orientation is often observed to turn in-plane by a reorientation phase transition which is also properly described by a renormalization group argument. Finally, the perpendicular spin orientation introduces topological excitations of the ferromagnetic order, consisting of stripes of reversed perpendicular spin direction. The stripe order undergoes a phase transition to the paramagnetic state that is not yet completely understood.
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Solar and Stellar Astrophysics

Nascent Embedded-protostar Survey in Taurus (NEST) I: Protostellar Multiplicity

Aislinn C. Plante, John J. Tobin, Patrick D. Sheehan et al. (+5 more)

We present new ALMA 0.9 mm and VLA 9 mm observations in the Taurus Molecular Cloud (TMC) of 25 protostellar systems, containing 40 protostars, observed at 0.3" (~20 au) resolution. Within separations of 18-10,000 au, the ALMA/VLA-observed Taurus sample has a multiplicity fraction (MF), defined as the fraction of systems with at least one companion, of 0.50 +/- 0.07, and a companion fraction (CF), defined as the average number of companions per system, of 0.58 +/- 0.20. To build a more complete census of protostellar multiplicity in this region, we supplement the observed sample with 24 protostars (12 protostellar systems and 5 additional companions associated with systems we observed) previously identified through archival infrared or ALMA observations. Together, these 64 individual protostars (37 systems) define our Taurus+ sample, for which we measure higher values of 0.53 +/- 0.06 and 0.72 +/- 0.19 for the MF and CF, respectively. These multiplicity statistics in the TMC are notably higher than those reported in the more clustered star-forming regions of Orion and Perseus at the ~3-4 sigma level, suggesting that Taurus may preserve a larger fraction of primordial multiples. The separation distributions in our samples show populations of both close and wide multiples, but a deficit at intermediate separations of 200-300 au. This pattern may suggest two distinct formation pathways: close binaries (<200 au) arising primarily from disk fragmentation, and wide multiples (>1000 au) from core fragmentation.
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All authors Aislinn C. Plante, John J. Tobin, Patrick D. Sheehan, Noshin Yesmin, Nicholas P. Ballering, Tyler L. Bourke, Josh Eisner, Zhi-Yun Li

High Energy Physics (Phenomenology)

The $D^*D^*\pi$ and $B^*B^*\pi$ couplings from light-cone sum rules

Chao Wang

We revisit the calculation of the strong couplings $D^{*}D^{*}\pi$ and $B^{*}B^{*}\pi$ from the light-cone sum rules (LCSR) using the pion light-cone distribution amplitudes. The accuracy of the underlying correlation function is upgraded by establishing the hard-collinear factorization formula at the leading power up to the next-to-leading order in $\alpha_s$. Furthermore, the next-to-leading power contributions are systematically incorporated at the leading order by evaluating the two-particle and three-particle higher-twist pion distribution amplitudes up to twist-4 accuracy. By matching the QCD-level spectral representations with the hadronic dispersion relations, we present a solid numerical analysis that accounts for the finite heavy quark masses and carefully evaluates the systematic uncertainty originating from the two-dimensional quark-hadron duality ansatz. We predict $g_{D^{*}D^{*}\pi} = 5.71_{-0.53}^{+0.67} \text{ GeV}^{-1}$ and $g_{B^{*}B^{*}\pi} = 4.90_{-0.44}^{+0.57} \text{ GeV}^{-1}$. Finally, by parameterizing the $1/m_H$ (with $H=D,\,B$) power corrections to extract the universal static coupling $\hat{g} = 0.30 \pm 0.04$, we compare our results with previous theoretical determinations and experimental data, highlighting the significance of heavy quark spin symmetry breaking effects.
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General Relativity and Quantum Cosmology

Robustness of the primordial power spectrum in hybrid loop quantum cosmology to approximations near the bounce

Kristina Giesel, Almudena Guillén, Guillermo A. Mena Marugán et al. (+1 more)

We prove the robustness of the analytic approximation used in (hybrid) loop quantum cosmology to compute the primordial power spectrum of the cosmological perturbations for a recently proposed vacuum state (the non-oscillatory state with asymptotic Hamiltonian diagonalization). To investigate this, we study different approximations to the effective mass of these perturbations near the bounce, showing that the Pöschl-Teller potential employed in previous works leads to indistinguishable power spectra compared to other estimations of the mass, provided that they successfully capture the characteristic scale of the bounce, which translates into a scale of power suppression.
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All authors Kristina Giesel, Almudena Guillén, Guillermo A. Mena Marugán, Leonardo Ricci

Physics and Society

Economic Distance Structures Urban Mobility in 109 U.S. Cities

Wei-Peng Nie, Xiao-Yong Yan, Bin Jia et al. (+4 more)

Urban mobility promises social integration, yet daily movement is systematically constrained by socioeconomic hierarchies. Introducing "economic distance"–the continuous income gap between origin and destination–as a unified lens, we analyze large-scale mobility records across 109 U.S. cities to reveal how urban flows are structured. We identify a universal structural boundary: flows concentrate intensely within a narrow economic distance of 0.25 quantiles, defining the effective "economic radius" of routine mobility. This boundary exhibits profound asymmetry; upward mobility faces a uniform structural ceiling across cities, whereas downward mobility drives cross-city heterogeneity. Mechanistically, the boundary is physically anchored by meso-scale residential clustering but is further tightened by an independent economic-distance friction, validated via gravity modeling. These interactions yield four distinct mobility regimes, with "affluent-confined" systems exhibiting the strongest stratification. These findings establish economic distance as a fundamental, asymmetric, and multi-scale filter shaping urban inequality, offering new theoretical grounds for interventions targeting structural barriers to cross-class interaction.
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All authors Wei-Peng Nie, Xiao-Yong Yan, Bin Jia, Fang Zhou, Er-Jian Liu, Tao Zhou, Zi-You Gao

Quantum Physics

Floquet-Resolved Dissipation Selects Entanglement Beyond Population Spectroscopy

Gianluigi Pacino, Rosario Nicosia and Alessandro Ridolfo

Reliable quantum-state engineering in periodically driven devices requires more than reproducing their excitation spectrum: the environment must resolve the transitions of the driven system. We show that two dissipative descriptions of the same parametrically coupled qubits can yield closely similar period-averaged populations yet qualitatively different asymptotic entanglement. Both retain the complete periodically driven Hamiltonian, the same microscopic bath couplings, and the same physical observables; they differ in the dynamical representation used to resolve the dissipative channels and the corresponding system operators: the static dressed basis in the partial harmonic decomposition approach (PHDA) and the Floquet basis, including all relevant drive sidebands, in Floquet-Born-Markov (FBM) theory. The population maps preserve the same resonance skeleton and remain closely similar over broad low-to-moderate drive regions, while clearer differences emerge as the modulation becomes stronger. Phase-resolved single- and two-qubit coherence observables reveal a substantially stronger redistribution of amplitudes and phases. Concurrence amplifies this hidden state-level discrepancy: Floquet-resolved dissipation selects stronger and more extended Bell-like entangled regions and a larger overlap with a fixed Bell-like reference, while PHDA generally underestimates the entanglement and its thermal persistence. A channel-resolution test verifies the secular, completely positive FBM construction throughout the relevant parameter domain. Our results establish population agreement as an insufficient benchmark for open Floquet quantum-state engineering and identify coherence-sensitive observables as the decisive validation test.
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High Energy Astrophysical Phenomena

Impact of Neutrino Flavour Conversion on the Diffuse Neutrino Background from Neutrino-dominated Accretion Flows

Yun-Feng Wei and Tong Liu

Neutrino-dominated accretion flows (NDAFs) are believed to form during the fallback accretion phase of some core-collapse supernovae (CCSNe). Such systems produce copious neutrino emission, whose cumulative contribution over cosmic history forms the diffuse NDAF neutrino background (DNNB). As neutrinos propagate from the source to Earth, flavour conversion can significantly modify the observed neutrino spectra and consequently the detectability of the DNNB. In this work, based on fallback CCSN simulations, we investigate the effects of progenitor mass, metallicity, and initial explosion energy on neutrino emission from NDAFs. We calculate the heavy-lepton neutrino ($\nu_x$) spectra from NDAFs and incorporate them into DNNB predictions. We find that the unoscillated $\nu_x$ spectra are more than an order of magnitude lower than those of electron antineutrinos $\bar{\nu}_e$. Using the latest neutrino oscillation parameters reported by the Jiangmen Underground Neutrino Observatory (JUNO), we evaluate the impact of flavour conversion on the DNNB and derive the corresponding spectra for both the normal and inverted mass orderings. We further estimate the expected event numbers in JUNO and Hyper-Kamiokande. We find that the predicted DNNB signal is strongly dependent on the neutrino mass ordering. While the DNNB may be detectable in the normal ordering with next-generation neutrino detectors, the signal is significantly suppressed in the inverted ordering, making detection considerably more challenging.
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High Energy Physics (Experiment)

Laboratory constraints on peV-scale mass splitting between ordinary and sterile neutron states

N. J. Ayres, Z. Berezhiani, G. Bison et al. (+19 more)

Sterile states of matter, represented by a parallel “mirror” sector, may contribute to the observed dark matter in the Universe. We investigated the parameter space of neutron $(n)$ to mirror-neutron $(n')$ oscillations, in the case where the two states are not necessarily mass-degenerate, taking into account interactions in the mirror sector. By tuning the magnitude of an applied magnetic-field in the range $5~\mu\mathrm{T} < B < 360~\mu\mathrm{T}$ to corresponding resonance conditions for finite mass splitting, we derive exclusion limits for the $n-n'$ oscillation time constant reaching about $20~\text{s}$ over the mass-difference range $0.3 - 22~\text{peV}$. In parts of this parameter range, our limits exceed the model-dependent neutron-star-cooling bound, providing the first experimental constraints in this scenario that are more stringent than this astrophysical estimate.
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All authors N. J. Ayres, Z. Berezhiani, G. Bison, K. Bodek, V. Bondar, P.-J. Chiu, M. Daum, C. B. Doorenbos, S. Emmenegger, K. Kirch, V. Kletzl, J. Krempel, B. Lauss, D. Pais, I. Rienäcker, D. Ries, D. Rozpędzik, P. Schmidt-Wellenburg, K. S. Tanaka, J. Zejma, N. Ziehl, G. Zsigmond

Medical Physics

Reducing Spectral Oscillations for Robust Reference Frequency-Based Ultrasound Attenuation Estimation in Harmonic Imaging

U-Wai Lok, Jingke Zhang, Chengwu Huang et al. (+14 more)

Ultrasound attenuation coefficient estimation (ACE) has emerged as a quantitative imaging biomarker for noninvasive assessment of hepatic steatosis. A system-independent technique based on spectral normalization, known as the reference frequency method (RFM), was previously proposed to estimate ACE without requiring a well-calibrated reference phantom. Furthermore, incorporating harmonic imaging can significantly suppress reverberation signals. In previous clinical study, RFM has achieved high correlation with MRI-PDFF, demonstrating its potential for clinical application. However, a major challenge of RFM is the presence of oscillations in the frequency power-ratio decay curves (FPDCs), which can distort the linear fitting used to estimate the attenuation coefficient and consequently degrade ACE accuracy. These oscillations arise from constructive and destructive interference among backscattered echoes, resulting in oscillatory fluctuations in the measured power spectrum that propagate into the FPDCs. We propose a transmission scheme combining multiple frequencies and steering angles to mitigate oscillations in the FPDCs. Averaging these FPDCs suppresses the interference-induced oscillations while preserving the attenuation-dependent decay trend, thereby improving linearity and the accuracy of ACE results. In in-vitro experiments using calibrated phantoms (0.5 and 0.76 dB/cm/MHz) demonstrated that the proposed method improved FPDC linearity and ACE accuracy, achieving an R2 of 0.99 and attenuation coefficient estimates of 0.51 and 0.77 dB/cm/MHz, versus an R2 of 0.89 and estimates of 0.56 and 0.70 dB/cm/MHz for conventional RFM. The proposed method also demonstrated superior performance in a pilot patient study (n=15), achieving a stronger correlation with MRI-PDFF (R = 0.89 vs. 0.83) while reducing inter-measurement variability, indicating improved robustness and clinical potential.
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All authors U-Wai Lok, Jingke Zhang, Chengwu Huang, Tao Wu, Jieyang Jin, Ryan M. DeRuiter, Jingyi Yin, Lijie Huang, Yanzhe Zhao, Kaipeng Ji, Kate M. Knoll, Dawn Boynton, Kymberly D. Watt, Kathryn A. Robinson, Joshua D. Trzasko, Matthew Callstrom, Shigao Chen

General Relativity and Quantum Cosmology

Models of a point particle in a three-dimensional AdS universe

Petr Lukeš and Pavel Krtouš

In 2+1-dimensional gravity, a conical deficit is commonly interpreted as a point-like particle. A distributional description of such a source is problematic since the Einstein equations are non- linear. Moreover, the total mass of the spacetime with nontrivial asymptotics is obfuscated by the infinite amount of background energy in the distant regions. In this work, we support the standard claim that the mass of a point particle is given by the angular deficit of the asymptotic geometry. We approximate the singular matter source by a sufficiently regular energy distribution, and we study the limit of negligible size for such a distribution while keeping the asymptotic geometry intact. Comparing spacetimes with equal asymptotics ensures that we correctly identify and remove the cosmological matter. We find that the angular deficit of the resulting conical spacetime is given by a limit of the local mass of the object, where the local mass is a natural concept of additive mass in 2+1 gravity. Surprisingly, the limiting mass is different from the BTZ mass parameter, although both masses are closely related.
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Materials Science · Cross-listed from eess.SP

Effects of Tool Wear on the Surface Texture in Turning: A Feature Characterization Approach Based on ISO 21920-2

Alexander Müller, Maximilian Berndt, Hagen Schmidt et al. (+5 more)

The surface texture of a turned component acts as a fingerprint of both the process parameters and the tool wear condition, imaging the cutting edge. Classical surface parameters such as $R_\mathrm{a}$ or $R_\mathrm{q}$ describe the topography only globally and allow no spatially resolved evaluation of the process-induced deterministic structures. This work investigates how far the feature characterization standardized in ISO 21920-2 makes this wear information accessible and physically interpretable. The database comprises roughness profiles of twelve AlTiN-coated carbide inserts (CNMG120408) machining normalized AISI 1045 steel, measured at nine wear states over the entire tool life, with three replicate profiles per state. The correlation of standardized field and feature parameters with crater wear, flank wear, and cutting time is first examined. Watershed segmentation is then adapted to extract the rotational tool grooves and evaluate their geometry statistically. A newly developed mean-feature approach decomposes the profile into a deterministic and a stochastic component. Wear-induced changes are almost entirely carried by the deterministic component, and within it by the trailing flank of the cutting groove. A comparison with confocal measurements confirms that the mean feature reconstructs the engaged cutting edge geometry, with the trailing-flank steepening attributable to notch wear on the secondary cutting edge. An exhaustive evaluation of more than 920,000 feature characterization combinations and multivariate models reveals that the groove-level mean maximum absolute gradient $\overline{R_\mathrm{dt}}_\mathrm{groove}$ alone explains 83-90% of the variance of the wear indicators, so that a single, physically motivated parameter suffices for robust wear estimation. A follow-up study will investigate inline monitoring using scattered light sensors.
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All authors Alexander Müller, Maximilian Berndt, Hagen Schmidt, Lars Müller, Matthias Eifler, Eberhard Kerscher, Benjamin Kirsch, Jörg Seewig

General Relativity and Quantum Cosmology

Coherent quantum geometry: de Sitter spacetime in different foliations

Tommaso Bambagiotti, Roberto Casadio, Andrea Giusti et al. (+1 more)

In any theory of quantum gravity, an interesting question to address is to what extent known solutions of the Einstein field equations can be obtained as expectation values of metric operators on suitable quantum states. In this work, we consider coherent states (to ensure minimum uncertainty) for different foliations of the de~Sitter spacetime and study temporal evolution and coordinate invariance. A general framework will first be introduced for metrics that can be diagonalised globally. We will then find that the normalisability of coherent states in this framework requires using reference frames without coordinate singularities.
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All authors Tommaso Bambagiotti, Roberto Casadio, Andrea Giusti, Pedro Meert

High Energy Physics (Theory)

Fortuity and fragility in supersymmetric SYK

James Chryssanthacopoulos and David Vegh

In the $\mathcal N=2$ supersymmetric SYK model with $N$ fermions, every BPS state is fortuitous: at fixed charge, it exists only over a finite range of $N$. Allowing the charge to increase, we show that BPS classes may instead be uplifted along lattice walks inside the fortuity window, potentially to arbitrarily large $N$. However, there is no canonical uplift. We therefore introduce a decoder $D$ whose spectrum quantifies exact uplift and its metric cost. We call the failure or increasing cost of uplifting harmonic representatives metric fragility. Chen's single-matrix model and the protected tower of the two-flavor SYK model realize bare and genuinely dressed mechanisms of perfect uplift, respectively. In the generic one-flavor model, exact uplift eventually fails. The Lin-Maldacena-Rozenberg-Shan-type operator $D^\dagger D$ exhibits level statistics consistent with the Gaussian unitary ensemble. Its eigenvalues quantify the metric continuity of BPS states across system size, while their correlations probe chaos within the BPS sector. Metric fragility and BPS chaos are thus encoded in complementary observables of the same operator, distinguishing chaotic BPS sectors from exactly solvable towers.
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Strongly Correlated Electrons

Connecting the tensor-categorical formulation of anyon condensation with operator algebras and entropic order parameters

Hua-Chen Zhang

Anyon condensation that describes the transition between topological quantum field theories can be formulated in the language of tensor categories or that of operator algebras. We deploy the formalism of Doplicher-Haag-Roberts bimodules over quasi-local $\mathrm{C}^{*}$-algebras recently developed in [1] to investigate anyon condensation, which is associated with an extension of a certain operator algebra. The connection between notions in the two formulations is thereby made manifest in an intuitive, diagrammatic manner. An entropic order parameter, as the quantum information-theoretic measure characterising a condensation, is naturally defined, and we give a very simple proof of a bound on it.
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Astrophysics of Galaxies

The Shape of the Vertical Action Distribution Locates the Scatterers that Heat the Galactic Disc

Yuan-Sen Ting and Hans-Walter Rix

The Milky Way's stellar disc is thicker than the cold gas layer from which its stars form. What scatters stars onto orbits with greater vertical motion remains unresolved. Scatterers could fill the disc volume, as bending waves or dark substructure would, or could be confined to the midplane, as giant molecular clouds are. Scattering from a midplane layer occurs only during the fast plane-crossing phase and becomes less effective as that speed increases, whereas a volume-filling perturbation remains effective near the slow turning points. We derive the distribution of vertical action this leaves behind, for any height distribution of scatterers. The geometry turns out to enter only through the logarithmic slope of the diffusivity in action, $D\propto J_z^{b}$, and solving the Fokker-Planck equation gives $p(J_z)\propto\exp[-(J_z/J_0)^{2-b}]$. Scatterers that fill the volume give $b=1$ and an exponential, a thin layer at the midplane gives $b=1/2$ and a sharper cutoff: the shape of $p(J_z)$ records where the scatterers sit, the growth of its scale how strongly they scatter. We fit this model to 7589 low-$\alpha$ red clump stars of Ting & Rix (2019) between 5 and 10 kpc and 2 and 8 Gyr old, leaving the heating history free. This yields $b=0.51^{+0.06}_{-0.07}$, consistent with the thin-layer prediction but not the volume-filling one. Comparing the 2-4 Gyr heating amplitude with the present molecular surface density gives an effective scatterer mass of $2.7\times10^{6}\,M_\odot$. Older stars have experienced more of the Galaxy's gas-richer past; correcting for that history brings all four age bins to $(1.9-2.8)\times10^{6}\,M_\odot$, inside the range cloud catalogues and mass functions give. The Milky Way's disc is heated near the plane, by an evolving population of objects of giant-molecular-cloud mass.
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Statistical Mechanics

Shortcuts to Parameter Sweeps

Chi Xiang, Guodong Cheng and Geng Li

Efficient evaluation of stationary parametric sensitivities over broad parameter ranges is important for identifying influential training data, fitting force fields, and predicting material responses, but standard pointwise approaches require repeated relaxation and sampling. Here we introduce Shortcuts to Parameter Sweeps (STPS), an engineered control strategy that uses an auxiliary control to transport the probability density along a prescribed family of instantaneous stationary states during a finite-time parameter sweep. This enables the continuous response curve over the full parameter interval to be estimated from a single controlled sweep using covariance-based response relations. STPS applies to both equilibrium and nonequilibrium steady-state systems, including those with unknown stationary distributions, and can be implemented directly using stationary samples in high-dimensional settings. Numerical tests on single-particle and interacting many-body systems show that STPS yields response curves in close agreement with reference results. These findings establish STPS as an efficient, sample-based framework for continuous sensitivity analysis in stochastic simulations.
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Materials Science

The electrical transport of intrinsic two-dimensional ferroelectric metal PtBi2

Dan Li, Liu Yang and Lei Li

Breaking the conventional stereotype that ferroelectrics are necessarily insulating, two-dimensional (2D) ferroelectric metals combine seemingly incompatible switchable electric polarization and metallic conductivity, providing a fertile ground for the discovery of novel electrical transport phenomena and the development of innovative electronic devices. Using the semiclassical Boltzmann equation and first-principles calculations, we systematically investigate the linear and nonlinear transport responses of the intrinsic 2D ferroelectric metal \ch{PtBi2} to an applied electric field. Our ab initio molecular dynamics simulations reveal that it possesses a high Curie temperature reaching $800~\text{K}$. We propose that the crystal structure of its high-temperature paraelectric phase can be explicitly distinguished through simple measurements of the in-plane electrical conductivity. Quantitative calculations of the Edelstein effect and the intrinsic spin Hall effect demonstrate a sizable charge-to-spin conversion efficiency, highlighting its potential in spintronics. We also find that a Berry curvature dipole-induced nonlinear Hall effect emerges in uniaxially strained \ch{PtBi2}. Furthermore, we highlight the unique advantages of 2D ferroelectric metals in gate-controlled transport applications. Based on the domain wall scattering mechanism, we conceptually design a novel ferroelectric metal field-effect transistor (FEM-FET) capable of nonvolatile switching between high-resistance and low-resistance states under a gate voltage. Our work not only unveils the rich transport physics in 2D ferroelectric metals but also provides valuable insights into the design of next-generation nonvolatile memory and spintronic devices.
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Physics and Society

Robustness over efficiency in climate coalitions: a bistable model and a map of architectures

Juergen Renn

Designs for international climate cooperation face a trade-off between efficiency and robustness to institutional erosion. We formalize it in a stylized coalition-formation game with two enrolment channels, a membership premium read as the value of club goods and an outsider drain, stabilized with robust control. The free-rider gap is exact within the game, measurable, and separated from the architecture-specific channels. The drain decomposes into a border channel, capped by trade law at the rent it mirrors, and a compensated world-market channel. With sufficiently strong channels the model is bistable, a remnant club and a near-universal coalition separated by a critical mass. For a proposed carbon currency, whose units are reissued each period, extinguished upon use, and enforced at the border, the minimal nucleus is thirty per cent of global emissions, ignition from an EU-China nucleus requires compensating one fifth to three fifths of the outsiders' world-market loss, the established coalition withstands two to four times the erosion admissible at ignition, and the tipping survives heterogeneity to three times the premium. Two robustness coordinates place each architecture on a map with three regimes: the carbon currency is self-igniting, the border adjustment founding-dependent, the export rebate permanent-support-dependent. A third coordinate, the coalition size up to which outsiders' border payments cover joiners' compensation, marks where the full coalition comes to rest on an internal transfer. Architectures without a drain improve efficiency within a coalition but cannot form one. Robustness governs whether cooperation forms and endures; efficiency decides how much an established coalition delivers.
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High Energy Physics (Theory)

Why There is No Memory Burden in Holographic Space-time Models of Black Hole Formation and Evaporation

T. Banks

Recent papers\cite{dvali} have claimed that general quantum information considerations put macroscopic constraints on the properties of large black holes, which can affect their lifetimes in cosmologically and astrophysically interesting ways. We examine black hole evaporation in Holographic Space Time (HST) models\cite{hstbh}, which appear to have the memory burden effect responsible for these deviations from semi-classical expectations, and explain why, in those models, no such effect exists. It is basically a consequence of Fermi's Golden Rule/The Principle of Detailed Balance, but depends crucially on both the definition of energy in HST models and the way in which causality is implemented.
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Instrumentation and Methods for Astrophysics

Voltage-to-temperature calibration of the High Altitude THz Solar telescope acquisition system

Gedeane G.S. Kenshima, Daniel R. Sousa, Tiago Giorgetti et al. (+2 more)

The THz range has been under-explored for solar astronomy, mainly due to technological limitations. Only recently, a few new telescopes, such as the High Altitude Terahertz Solar (HATS) photometer, have been monitoring the solar activity in this range of the spectrum. This paper presents the experimental characterization and voltage-to-temperature calibration of the HATS acquisition system. HATS uses a Golay cell for capturing the incoming radiation, modulated by a 20 Hz fork chopper. The amplitude of the signal is then obtained at predetermined time intervals by applying a windowing function and an FFT to the signal. To characterize this acquisition system, a blackbody calibrator, with temperatures varying from 100 to 500 C (373.15 K to 648.15 K), was used as a THz source, and two signal recovery methodologies were compared: sinusoidal curve fitting and FFT combined with six windowing functions (rectangular, Hamming, Hann, Barlett, Blackman, and Flat Top). Our quantitative results demonstrate high linearity in the system's response over the input source's temperature range, with the Hamming window achieving the highest precision, yielding a Root Mean Square Error (RMSE) of 15.48 and a calibration temperature-to-voltage factor of 10.32 +- 0.13 mV/K. In contrast, the Bartlett window presented the highest error (RMSE 16.02). The choice of windowing function had only a minor effect on the calibration factors, which ranged from 10.32 to 10.43 mV/K, all within the experimental uncertainties. Beyond solar photometry, the signal modulation and windowing concepts established here are highly applicable to other fields requiring high-sensitivity thermal detection, such as industrial pyrometry for high-temperature manufacturing, environmental monitoring of atmospheric water vapor, and the development of medical imaging systems based on Terahertz radiation for non-invasive tissue analysis.
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All authors Gedeane G.S. Kenshima, Daniel R. Sousa, Tiago Giorgetti, Paulo J. A. Simões, C. Guillermo Giménez de Castro

Quantum Physics

The Min-Rains Relative Entropy Is Not Tight for Exact PPT Entanglement Distillation

Chengkai Zhu and Xin Wang

Exact entanglement distillation converts a noisy bipartite state into a maximally entangled state with zero error. Under completely PPT-preserving operations, the additive min-Rains relative entropy provides a single-letter upper bound on the regularized distillation rate. An interesting problem in entanglement theory dating back to 2016 has been whether this bound is always tight. Here we resolve this question in the negative. The key is a tensor-stable rigidity absent from the min-Rains relaxation: every feasible exact-distillation effect must act as the identity on the support of the input state. We convert this constraint into a new single-letter upper bound using a generally non-Hermitian, range-supported witness. For a rank-three subspace, we show this upper bound lies strictly below the min-Rains relative entropy for every state with that support. Thus, the constraint discarded by the min-Rains relaxation remains relevant under arbitrary tensor powers. Our result rules out the min-Rains relative entropy as a closed-form formula for exact PPT distillable entanglement and reveals the subtle asymptotic structure of exact entanglement manipulation under PPT operations.
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Astrophysics of Galaxies

The effect of galaxy interactions on star formation rates in the COLIBRE simulations

Quinten W. E. van Zegveld, Evgenii Chaikin, Joop Schaye et al. (+8 more)

Observations and theory indicate that galaxy interactions enhance star formation rates (SFRs). However, the degree of enhancement and its dependence on the properties of the interacting galaxies vary across different studies. In this work, we use the COLIBRE simulations of galaxy formation to investigate the effect of interactions on the SFRs of star-forming galaxies at redshift $z\approx0$. The COLIBRE simulations capture the multiphase nature of the interstellar medium and have volumes up to $200^3$ and $400^3$ cMpc$^3$ at m6 (gas and dark-matter particle mass $\sim10^6~\mathrm{M_\odot}$) and m7 ($\sim10^7~\mathrm{M_\odot}$) resolutions, respectively. After constructing samples of interacting galaxies (with mass ratios $>0.1$) and isolated controls, matched in stellar mass, large- and small-scale environment, and redshift, we show that the average specific SFR (sSFR) of interacting galaxies is enhanced by up to a factor of $\approx2$ for separations of $\approx10$ kpc. The enhancement decreases with pair separation but remains significant out to $\approx200$ kpc. The enhancement increases with increasing numerical resolution, is more pronounced in the central regions of galaxies, and decreases with increasing stellar mass at fixed separation. Mergers with higher mass ratios induce stronger sSFR enhancement. We compare our results with observational data from the SDSS, finding good agreement in the dependence of the mean sSFR enhancement on separation, but underpredicting its normalisation by a factor of $\approx2$. Finally, we show that the pre-merger sSFR enhancement of resolved interactions accounts for $\approx2$ per cent of the $z\approx0$ cosmic SFR density.
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All authors Quinten W. E. van Zegveld, Evgenii Chaikin, Joop Schaye, David R. Patton, Sara L. Ellison, Alejandro Benítez-Llambay, Filip Huško, Robert J. McGibbon, Sylvia Ploeckinger, Alexander J. Richings, Matthieu Schaller

Mathematical Physics · Cross-listed from math.AP

Sharp instability of planar isotropic–nematic interfaces in the Landau–de Gennes model

Wei Wang and Qin Wu

We study the stability of one-dimensional planar isotropic–nematic interfaces in the Landau–de Gennes model with anisotropic elastic constant $L$. Earlier work proved the instability for $L<0$ only under an extra condition. We remove this condition and prove that any non-negative minimizer of the reduced energy within the diagonal planar class is unstable under general one-dimensional perturbations throughout $-\frac{3}{2}<L<0$. This result shows that $L=0$ is the sharp endpoint of the instability range from the negative-$L$ side: the critical operator is non-negative at $L=0$, while instability holds over the full negative-$L$ range of the reduced problem. We also define the optimal stability index and correct a factor-of-two normalization inconsistency in a previously stated interface profile.
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General Relativity and Quantum Cosmology

Lorentz Symmetry Breaking Traversable Wormhole Models Supported by Einasto Dark Matter

Rana Muhammad Zulqarnain, M. Yousaf, Allah Ditta et al. (+3 more)

We investigate static, spherically symmetric traversable wormholes in Kalb Ramond gravity, where spontaneous Lorentz symmetry breaking arises from a non-vanishing vacuum expectation value of the antisymmetric Kalb Ramond field. The matter sector is modeled by the Einasto dark matter density profile, yielding an analytical shape function expressed via the incomplete Gamma function. The resulting geometry satisfies the throat, flare-out, and asymptotic-flatness requirements, with embedding diagrams providing a geometric visualization of the wormhole structure. The energy density stays positive throughout the considered domain, while the radial null energy condition is violated near the throat, showing that the exotic matter required for traversability can be localized to a restricted region. The internal structure is further characterized through the complexity factor, which is most pronounced near the throat and gradually decays to zero at larger radii. We also examine the total gravitational energy, active gravitational mass, average pressure, and equilibrium behavior via the generalized TOV equation and pressure anisotropy; for the constant-redshift configuration, equilibrium is maintained by a balance between the hydrostatic and anisotropic forces. The optical properties of the spacetime are further explored through the photon sphere, critical impact parameter, light deflection angle, and echo time. Finally, the volume integral quantifier is used to estimate the total amount of null-energy-condition-violating matter, showing that the exotic contribution remains concentrated near the wormhole throat. The analysis highlights the combined role of the Kalb Ramond gravitational parameter and the Einasto matter distribution in shaping the geometric, energetic, and observational characteristics of the resulting wormhole configurations.
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All authors Rana Muhammad Zulqarnain, M. Yousaf, Allah Ditta, Asifa Ashraf, Ahmadjon Abdujabbarov, Farruh Atamurotov

Optics

Twist-Reconfigurable van der Waals Moiré Photonic Crystals

Hugo Quard, Jiyun Kim, Anastasiia Zalogina et al. (+7 more)

Moiré photonics has emerged as a fascinating concept to design and in situ control of the optical bands. Moiré enabled light localisation arises from the relative twist between periodic layers, rather than from fixed, pre-fabricated cavity features. So far, however, the realisation of practical moiré photonic crystals in the visible range has been elusive, due to challenges in engineering nanoscale structures and twisting them dynamically post fabrication. Here, we realise a mechanically reconfigurable moiré photonic crystal, comprising from two patterned van der Waals crystals (tungsten di sulphide, WS$_2$) slabs separated by an optically active hexagonal boron nitride (hBN) spacer. We reconfigured the same pair of WS$_2$ slabs from a twist angle of 3.8{\deg} to 8.4{\deg} and reconstructed their three-dimensional dispersion using momentum-resolved reflectivity spectroscopy. Further, by reducing the twist angle between the slabs, we observe a denser manifold of folded and hybridised resonances that coincides with a 30-fold enhancement of emission from embedded colour centres. Our results open exciting opportunities for in-situ dispersion engineering and programmable light matter interactions employing van der Waals nanostructures.
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All authors Hugo Quard, Jiyun Kim, Anastasiia Zalogina, Xuerong Hu, Evan Williams, Oscar J. Palma Chaundler, Owen R. Wolley, Alexander Tartakovskii, Haoning Tang, Igor Aharonovich

Strongly Correlated Electrons

Two routes to quantum anomalous Hall states in altermagnets

Makoto Naka, Shuntaro Sumita, Yukitoshi Motome et al. (+1 more)

We theoretically propose two possible routes to realizing quantum anomalous Hall states in altermagnetic materials. We consider a minimal square-lattice Hubbard model with antisymmetric spin-orbit coupling associated with an orthorhombic crystal structure, which supports a topologically trivial altermagnetic state. By incorporating Rashba-type spin-orbit coupling and external perturbations, we demonstrate that this trivial state can be turned into topological altermagnetic phases in two distinct ways. The first route is driven by a staggered potential that breaks the symmetry connecting crystallographically equivalent sublattices, leading to a topological altermagnetic ground state characterized by a quantized Hall conductivity $\left| \sigma_{xy} \right|=e^2/h$ and a Chern number $C=1$. The second route is realized by applying a magnetic field perpendicular to the two-dimensional plane. The resulting topological state appears as a metastable state in the magnetic hysteresis loop, exhibiting a quantized Hall conductivity $\left| \sigma_{xy} \right|=2e^2/h$ associated with a Chern number $C=2$. We show that these topological transitions are accompanied by characteristic gap closings at the Brillouin-zone boundary, with the number of gap-closing points determining the Chern number. Ribbon-geometry calculations reveal chiral edge states consistent with the bulk topological invariants and demonstrate distinct spin polarizations between the $C=1$ and $C=2$ states. Our results establish experimentally accessible routes to quantized anomalous Hall responses in altermagnets.
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All authors Makoto Naka, Shuntaro Sumita, Yukitoshi Motome, Hitoshi Seo

Nuclear Theory

Spatial Entanglement Entropy in Nuclear Fission

S.C. Li, J.W. Chen and J.C. Pei

Nuclear fission provides a unique manifestation of spatially nonlocal many-body entanglement. We compute the bipartite spatial entanglement entropy exactly along dynamical fission trajectories, by leveraging the fermionic Gaussian state formulation. Across seven representative fissioning channels, the final entanglement entropy correlates strongly with the intrinsic particle number variance of the fragment, yet exhibits no simple dependence on scission geometries. Most notably the entanglement is significantly suppressed when fragments are magic nuclei, revealing a shell anti-entanglement effect. This work establishes entanglement entropy as a novel lens that extends the conventional conception of nuclear fission.
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Statistical Mechanics

Macroscopic fluctuation theory for the multi-time statistics of current in non-stationary diffusive systems

Sabyasachi Chowdhury, Kapil Sharma, Sandeep Jangid et al. (+1 more)

The statistics of current fluctuations has long been a central object of study in non-equilibrium physics. Most existing work has focused on one-time statistics, while their multi-time generalisation remains comparatively less explored. We address this gap by extending the fluctuating hydrodynamics framework of Macroscopic Fluctuation Theory (MFT) to study multi-time statistics in the non-stationary state of a diffusive system on an infinite line. For the simplest cases of a non-interacting lattice gas and hard-core Brownian point particles, we present explicit solution of the MFT leading to multi-time large-deviation statistics. For generic systems, the MFT is solved perturbatively, yielding explicit results for two-time correlations. These reveal that the connection between current fluctuations and fractional Brownian motion, previously observed for flat initial conditions, does not persist for step initial conditions. We independently verify these hydrodynamic results by solving the corresponding microscopic dynamics for the non-interacting gas and for the symmetric simple exclusion process. Additional confirmation comes from numerical simulations.
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All authors Sabyasachi Chowdhury, Kapil Sharma, Sandeep Jangid, Tridib Sadhu