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Physics

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Tuesday 29 September

Solar and Stellar Astrophysics

Abundance analysis of three new extremely metal-poor stars, including one CEMP-s star

P. François, T. Suda, S. Wanajo et al. (+5 more)

We report a detailed abundance analysis of three extremely metal-poor (EMP) stars thanks to spectra obtained with the high-dispersion spectrograph (HDS) at the Subaru telescope. The aim is to observe a sample of EMP candidate stars selected from the Sloan Digital Sky Survey (SDSS) and determine their detailed chemical composition. High-resolution spectra of three faint turn-off stars using HDS on the Subaru telescope were acquired.We used standard 1D models to compute the abundances of several elements (Li, C, Mg, Ca, Sr, and Ba). The stars we analysed have a metallicity [Fe/H] of between -3.02 and -3.57 dex. We also measured accurate radial velocities that, coupled with the Gaia astrometric data, allowed us to compute actions and Galactic orbits for the stars. Our analysis confirms that the stars are genuine EMP stars. One of them (SDSS J074238.68 +470537.0) can be classified as a CEMP-s star with the highest [Mg/Fe] ratio ever measured in a turn-off CEMP-s star with [Mg/Fe] = 1.85 dex. For the star SDSS J012630.30+073029.3 ([Fe/H]= -3.02 dex), we have a clear detection of lithium with A(Li) = 2.05. Kinematically, SDSS J214340.08-002835.5 is a thick-disc star, while the other two belong to the halo and are candidate members of the Gaia- Sausage-Enceladus.
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All authors P. François, T. Suda, S. Wanajo, E. Caffau, P. Bonifacio, W. Aoki, S. Yamada, M. Y. Fujimoto

Computational Physics · Cross-listed from cs.LG

PHASE: Multi-Regime Modeling of Incompressible Magnetohydrodynamics

Radhika Achikanath Chirakkara, Rajdeep Haldar, Zezheng Song et al. (+1 more)

Magnetohydrodynamics (MHD) is central to plasma modeling in astrophysics, space science, fusion, and engineering, but resolving multiscale MHD dynamics is computationally expensive. Machine-learning surrogates enable fast inference by learning reusable solution operators, yet existing models require separate training for each physical regime, limiting generalization across varying parameter settings. We introduce PHASE, a PHysics-Adaptive Scalable operator with residual Error correction, designed to model incompressible MHD across varying physical parameters with a single model. PHASE combines transfer learning, regime-aware adaptation, physics-centered learning, and residual refinement to improve both physical fidelity and generalization across MHD regimes. Together, these improvements achieve state-of-the-art prediction accuracy on two-dimensional MHD turbulence by reducing relative $L_2$ errors on physical fields by more than an order of magnitude compared to prior MHD neural-operator baselines. Moreover, PHASE generalizes successfully to unseen parameter values without retraining, demonstrating the cross-regime adaptability expected from operator learning. We evaluate PHASE beyond point-wise prediction errors using derived physical fields, spectral analysis, and distribution statistics, consistently observing improved physical fidelity. We further show that our framework can accurately simulate MHD instabilities by testing it on the Kelvin–Helmholtz instability, demonstrating the robustness of our method.
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All authors Radhika Achikanath Chirakkara, Rajdeep Haldar, Zezheng Song, Jiequn Han

Astrophysics of Galaxies

Fooled by mass? Recovering the $\Gamma-\lambda_{Edd}$ relation of quasars from their X-ray variability

Matilde Signorini, Andrea Sacchi, Bartolomeo Trefoloni et al. (+7 more)

We measure the relation between the X-ray photon index $\Gamma$ and the Eddington ratio $\lambda_{Edd}$ in unobscured type-1 quasars, using as parent sample the cross-match of the SDSS DR16Q catalogue with the 4XMM-DR14 serendipitous catalogue. After cleaning the sample of potential observational biases, we obtain 7835 objects, one order of magnitude larger than most previous analyses in the literature. A single regression of $\Gamma$ against $\log\lambda_{Edd}$, with single-epoch virial black-hole masses, returns slopes that depend on the mass indicator (H$\beta$, MgII, CIV) and on the bolometric correction, and that are generally flat. We interpret this as regression dilution: the systematic uncertainty on virial masses is much larger than the intrinsic spread of $\lambda_{Edd}$ in SDSS quasars. We therefore introduce a different approach, which removes the black-hole mass from the problem. For quasars observed by XMM-Newton at multiple epochs, the mass of each object is fixed, and changes in its X-ray luminosity trace changes in its accretion state. We fit the $\Gamma$-$\log(L_{2keV})$ relation of each object (for a sample of N=893) and combine the per-object posteriors. This recovers the mean response of the population $a_X = 0.35\pm0.03$, which steepens to $\approx0.43$ when only epochs with precisely measured photon indices are used. Translated to the Eddington ratio, this corresponds to $a_\lambda\approx0.20$-0.25, depending on the choice of bolometric correction and on the LX-LUV slope. The $\Gamma$–$\lambda_{Edd}$ relation therefore exists, but it can be uncovered only by exploiting the variability of individual sources, which removes the black-hole mass from the problem. Moreover, its shallowness implies that the differences in Eddington ratio, as currently measured, cannot by themselves account for the variety of photon indices observed among unobscured quasars.
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All authors Matilde Signorini, Andrea Sacchi, Bartolomeo Trefoloni, Matteo Guainazzi, Elisabeta Lusso, Emanuele Nardini, Chiara Niccolai, Federica Ricci, Anastasia Shlentsova, Mateusz Rałowski

Soft Condensed Matter

A Bioinspired Magnetothermally Triggered Capsule for Rapid Microrobot Release

Mengfan Zhang, Zike Chen, Zhihao Lv et al. (+3 more)

Capsules are attractive platforms for microrobot delivery, combining structural simplicity with protected delivery and rapid release remains challenging. Inspired by the latched spring mechanism of Impatiens balsamina seed dispersal, a magnetothermally triggered capsule integrates a phase-change hydrogel latch, a monostable cover that serves as an elastic spring, and a payload-carrying base. Mechanical analysis guides the cover design to avoid bistability after assembly and premature hydrogel latch rupture before triggering. During transport, the hydrogel constrains the inverted cover. Under an alternating magnetic field, Fe3O4-mediated heating softens the hydrogel and induces cohesive failure, releasing stored energy to drive capsule opening and microrobot ejection. The capsule opens within 50 ms after hydrogel softening and ejects microrobots at an estimated initial velocity of 1.0 m/s. Demonstrations on a three-dimensional platform and ex vivo porcine stomach establish protected delivery, target-site opening, and post-release actuation.
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All authors Mengfan Zhang, Zike Chen, Zhihao Lv, Zheng Jia, Rui Xiao, Guoyong Mao

Earth and Planetary Astrophysics

TOI-6981 b: a transiting sub-Neptune at the water ice line

Madison G. Scott, Amaury H.M.J Triaud, Emily K. Pass et al. (+42 more)

We present TOI-6981 b, a cold (Teq= 170.0 +/-4.5 K, assuming an Earth-like albedo) sub-Neptune (Rb=2.40+/-0.10 R_oplus) on a 60.8 day orbit around around its M4-type host star (R*=0.304 +/- 0.012 R_odot, M*=0.296 +/- 0.026 M_odot, Teff = 3215+/-58K), part of the SPECULOOS TEMPOS program. We validate the planetary nature of TOI-6981 b using ground-based follow-up photometry, statistical validation and high-resolution spectroscopy. At such cold temperatures, TOI-6981 b sits roughly at the location of the water ice line (approx 170 K). Given its orbital period and high transmission spectroscopy metric (TSM=51 +/- 9), it is one of the only planets in the sparsely populated cold planet regime amenable for atmospheric studies with JWST. Therefore, TOI-6981 b could. possibly become a crucial benchmark in cold chemistry studies, tests of Hycean world hypotheses, and drawling parallels to the Solar System's ice giants. Additionally, given its current orbit, it may provide insight into planetary formation and migration at or beyond the water ice line.
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All authors Madison G. Scott, Amaury H.M.J Triaud, Emily K. Pass, Aleyna Adamson, Karen A. Collins, Khalid Barkaoui, Allyson Bieryla, Adam J. Burgasser, Mark E. Everett, Steve B. Howell, David W. Latham, Benjamin V. Rackham, Boris S. Safonov, Miquel Serra-Ricart, Abderahmane Soubkiou, Georgina Dransfield, Katharine Hesse, Pipa Fernandez de Diego, Emma Softich, Gregor Srdoc, Mathilde Timmermans, Jeroen Audenaert, Roi Alonso, Artem Y. Burdanov, Yasmin T. Davis, Fatemeh Davoudi, Julien de Wit, Shishir Dholakia, Elsa Ducrot, Michaël Gillon, Yilen Gomez Maqueo Chew, Matthew J. Hooton, Clàudia Janó-Muñoz, Emmanuel Jehin, Akanksha Khandelwal, Thomas R. Marriott, Peter P. Pedersen, Manuel Pichardo Marcano, Francisco J. Pozuelos, Rafael Rebolo-López, Manu Stalport, Alexander Venner, Selçuk Yalçinkaya, Francis Zong Lang, Sebastián Zúñiga-Fernández

Quantum Physics

Semiclassical spin-bath calculation of the nitrogen-isotope effect on NV$^-$ ensemble coherence in diamond

Chikara Shinei

The ratio $T_2$/$T_2^*$ of the Hahn-echo and Ramsey times of nitrogen-vacancy (NV$^-$) ensembles is independent of the nitrogen concentration [N] and is $\approx$ 16 in diamond of natural isotopic abundance ($^{14}$N), yet a recent $^{15}$N-doped ensemble magnetometer gives only 8.05 $\pm$ 0.18 in the single-quantum convention. We ask whether the nitrogen nuclear isotope alone can cause such a reduction. Using a semiclassical spin-bath model with the Jahn-Teller-resolved P1 hyperfine tensor, we show that the fraction of P1 pairs that are hyperfine-degenerate, and hence free to flip-flop, is 1/4 for $^{14}$N (I = 1) but 5/16 for $^{15}$N (I = 1/2). Simulations over [N] = 0.1–100 ppm confirm that this shortens $T_2$ while leaving $T_2^*$ exactly unchanged: $T_2$($^{14}$N)/$T_2$($^{15}$N) = 1.118 $\pm$ 0.011, independent of [N] and 11$\sigma$ above unity. The measured contrast, 2.07 $\pm$ 0.25, is 3.8$\sigma$ larger, identifying resonant-channel counting as a real but partial contribution and setting a quantitative benchmark for many-body calculations.
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Statistical Mechanics

Quantum Statistical Thermal Engine at the BCS-BEC crossover

Santiago Henríquez Lira, Felipe Isaule, Martín HvE Groves et al. (+3 more)

We propose a quantum heat engine based on a two-component Fermi gas with s-wave contact interaction, operating across the BCS-BEC crossover. The work is extracted from the statistical properties of the gas, which are controlled by the interaction, rather than relying solely on compression and expansion stages. Using the functional renormalization group formalism, we obtain the equation of state in a non-perturbative form along the crossover, encompassing the superfluid-normal phase transition. The cycle combines isentropic density strokes, isochoric thermalization, and isothermal interaction sweeps. This construction makes it possible to integrate features of both Otto and Carnot cycles, in which the system simultaneously saturates both efficiency limits without the net work vanishing. In the absence of density variations, the cycle reduces to a statistical Stirling-like engine, in which the work generated arises exclusively from the interaction, achieving efficiencies up to $38\%$. A pronounced asymmetry emerges through the crossover, giving rise to distinct operating regimes depending on the trajectory followed in the phase diagram. Consequently, the same architecture can be tuned to function as an engine, refrigerator, accelerator, or heater. These findings highlight pairing correlations as a versatile thermodynamic resource for quantum heat machines.
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All authors Santiago Henríquez Lira, Felipe Isaule, Martín HvE Groves, Francisco J. Peña, Patricio Vargas, Thomás Fogarty

General Relativity and Quantum Cosmology

Deformation Quantization of Schutz Quantum Cosmology: Relational Time, Constraints, and Physical States

Raphael Fracalossi

A controlled correspondence is established between reduced relational dynamics and extended constrained quantization in an FLRW cosmology coupled to a Schutz perfect fluid. A canonical transformation in the matter sector yields a deparametrized constraint of the form $\mathcal C=p_T+H$, with $T$ serving as an internal time. In the extended Weyl–Wigner formulation, the quantum constraint is imposed bilaterally. Its antisymmetric part gives the exact Moyal evolution generated by the reduced Hamiltonian, while its symmetric part imposes an independent quantum shell condition. For a fixed self-adjoint realization of $\hat H$, every reduced density operator supported on its negative spectral subspace admits an explicit distributional extension. A spectral dyad with energies $E$ and $E'$ is mapped to a clock Wigner distribution supported at $p_T=-(E+E')/2$, with relational phase determined by $E-E'$. The map preserves off-diagonal coherences, satisfies both star constraints, and has the reduced Wigner state as its $p_T$ marginal; it is therefore injective on the admissible positive-density sector. A flat dust model with $q=1/2$ and Dirichlet data provides an explicit example: its reduced spectrum is $(-\infty,0]$, so the admissible sector contains all normalizable reduced states. The correspondence applies to a fixed constraint representative and quantum realization.
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Exactly Solvable and Integrable Systems

Asymptotic behavior analysis of solutions to the Heisenberg ferromagnet equation with the Schwartz initial data

Xumeng Zhou, Xianguo Geng and Bo Xue

This work aims to investigate the long-time asymptotic behavior of solutions to the Cauchy problem for the Heisenberg ferromagnet equation with the Schwartz initial data. Utilizing the gauge transformations, spectral analysis and the inverse scattering method, we prove that the solutions to the Heisenberg ferromagnet equation can be expressed in terms of the solutions to a matrix Riemann-Hilbert problem formulated in the complex $k$-plane. Various Deift-Zhou contour deformations and the motivation behind them are given. By applying the nonlinear steepest descent method to the associated matrix-valued Riemann-Hilbert problem, we obtain the exact leading-order asymptotic formulas and uniform error estimates for solutions to the Cauchy problem of the Heisenberg ferromagnet equation.
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Chemical Physics

What Does a Semilocal Machine-Learning Correction Actually Learn? Size-Dependent Errors across Four Parent Functionals

Abhishek Bhattacharjee, Kishan Kumar Mohanta, Subrata Jana et al. (+1 more)

Machine-learning (ML) corrections to density functional approximations (DFAs) offer a route to improving electronic-structure predictions while retaining the efficiency of semilocal functionals. An important question is whether such corrections learn transferable improvements or instead compensate for errors specific to the parent functional. Here, we address this question by applying the semilocal ML correction of Wang et al. [J.~Chem.~Phys.~158, 154107 (2023)] to PBE, B3LYP, SCAN, and r$^2$SCAN, while keeping the network architecture, loss function, training set, and optimization protocol unchanged. We find that the learned correction develops a systematic size-dependent contribution to atomization energies for all four parents, with $|r|\geq0.9999$ along the $n$-alkane series, where r is the Pearson coefficient of the linear fit. Its magnitude and sign depend systematically on the parent: the correction partially compensates the size-dependent errors of PBE and B3LYP, but introduces substantial size-dependent contributions for SCAN and r$^2$SCAN, whose parent errors show little size dependence. In contrast, ionization potentials, electron affinities, and isomerization energies are largely unaffected. Spatial decomposition further reveals distinct origins of this extensive contribution, with bonding regions dominating for B3LYP, SCAN, and r$^2$SCAN and core regions dominating for PBE. These results show that the global-energy ML correction is strongly dependent on the error structure of its parent DFA, highlighting size-dependent error accumulation as a critical consideration in the assessment and development of ML-enhanced density functionals.
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All authors Abhishek Bhattacharjee, Kishan Kumar Mohanta, Subrata Jana, Prasanjit Samal

Cosmology and Nongalactic Astrophysics

Carving out the Multifield Cosmological Collider Landscape

Denis Werth

We show that inflation with a large number of fields, as predicted by concrete ultraviolet embeddings, generically produces almost-local cosmological collider signals in the bispectrum squeezed limit. We construct the most general boost-breaking mixings between the curvature perturbation and $N_{\rm f}$ additional fields, and extract the late-time scaling dimensions that dictate the soft limits of cosmological correlators. For a handful of fields, an enhanced squeezed limit (with potential oscillations) is a fine-tuned signal. At large $N_{\rm f}\sim100$, however, mixings generically drive the scaling dimensions toward the unitarity boundary. We show that this is a direct consequence of extreme value statistics and random-matrix universality, turning an almost-local bispectrum shape into a generic prediction for almost any masses and mixings.
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High Energy Physics (Phenomenology)

The four-loop quark-to-quark splitting function in QCD

Thomas Gehrmann, Andreas von Manteuffel, Vasily Sotnikov et al. (+1 more)

The scale evolution of parton distributions is governed by splitting functions. We compute the four-loop pure-singlet contribution to the quark-to-quark splitting function in perturbative QCD. Together with the known non-singlet contribution, our result completes the quark-to-quark splitting function at this order. We confirm previous partial results and obtain, for the first time, a fully analytic expression valid for all momentum fractions. We examine its behavior at small momentum fractions and provide precise numerical representations suitable for parton evolution.
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All authors Thomas Gehrmann, Andreas von Manteuffel, Vasily Sotnikov, Tong-Zhi Yang

High Energy Physics (Phenomenology)

Decaying Dark Matter for the Exothermic Recoil at LZ

Yongsoo Jho, Sanghwan Kim and Seong Chan Park

The LUX-ZEPLIN (LZ) experiment has reported a single nuclear-recoil candidate at $248\pm23\,(\mathrm{stat})\pm23\,(\mathrm{sys})$ keV. We suggest that it comes from a GeV-scale dark state $\chi_1$ that downscatters exothermically, $\chi_1A\to\chi_2A$, and is continuously replenished in the halo by the slow decay $\chi_0\to\chi_1\chi_1$ of a long-lived parent. Because the recoil energy is supplied by the mass splitting rather than by the halo velocity, the event is a narrow line with no low-energy tail. Kinematics requires $m_{\chi_1}\gtrsim247$ MeV and fixes the splitting for each $m_{\chi_1}$. The same line should appear at 700$-$810 keV in argon for $m_{\chi_1}=0.3-10$ GeV. Normalizing to one LZ event also fixes the local rate of the radiative decay $\chi_1\to\chi_2\gamma\gamma$, up to the mediator's photon coupling. A rough $\gamma$-ray estimate then requires this coupling to be $\lesssim10^{-2}$ of a proton-loop reference at $m_{\chi_1}=10$ GeV, but $\lesssim10^{-9}$ at 0.3 GeV, which favours daughters near 10 GeV.
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Applied Physics · Cross-listed from eess.SP

Möbius Reparametrization of Multiport-Network Models of PIN-Diode-Programmable Metasurfaces for Accurate Low-Order Neumann Approximations

Philipp del Hougne

Accurate models of programmable metasurfaces based on multiport-network theory (MNT) account for mutual coupling (MC) through a configuration-dependent matrix inversion. The latter's high computational cost during gradient-based optimization (GBO) can be alleviated via a finite-order Neumann approximation. We show that the accuracy of this approximation depends strongly on the (tacitly) chosen MNT parametrization. For 1-bit-programmable meta-elements (e.g., meta-elements based on PIN diodes), we identify a closed-form Möbius reparametrization that depends only on the meta-element's two load states and requires neither training data nor numerical optimization. For an experimentally estimated proxy MNT model of a fabricated 96-element 19-GHz dynamic metasurface antenna with strong MC, a second-order Neumann approximation with our reparametrization achieves forward and control-gradient accuracies of 21.68 and 21.70 dB, respectively. Relative to the full proxy MNT, it reduces the runtime of a combined forward and control-gradient evaluation by a third and the saved-tensor memory by a factor of ten. In a prototypical GBO problem of end-to-end optimization for DMA-based scene classification, it achieves 94.97% test accuracy vs. 95.57% with the full model. We further note that MC-strength metrics and MC-unaware benchmarks should be parametrization-invariant, motivating, for instance, definitions based on the best directly fitted zeroth-order model.
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High Energy Physics (Phenomenology)

Resummation-scale effects in DIS PDF fits with xFitter

Francesco Giuli

Renormalisation-group evolution enters PDF determinations through the running coupling and the splitting functions. At fixed perturbative order, the solution of the evolution equations is not unique beyond the nominal accuracy, and this residual freedom can be probed through resummation-scale variations. This contribution summarises an NNLO study of this effect in inclusive HERA DIS fits performed with the xFitter fitting framework. The induced shifts are sizeable in a low-scale baseline fit, especially for the gluon and sea PDFs, and can affect LHC and FCC top-quark pair predictions at the few-percent level. Raising the PDF starting scale and applying a higher DIS virtuality cut considerably reduces the effect, a conclusion also supported by treating the resummation scale as a free parameter constrained directly by the data.
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Nuclear Experiment

$\pi$-QCD; Proposal for Experiments at the GSI Pion Beam Facility

HADES Collaboration: R. Abou Yassine, J. Adamczewski-Musch, G. Appagere et al. (+126 more)

We propose to investigate the dynamics of hadronic matter in the strong QCD regime using the pion-beam facility at GSI in conjunction with HADES. This program will study hadron physics through elementary pion-nucleon interactions up to $\sqrt{s}\approx$2.35 GeV, bridging cold matter research with detailed analyses of exclusive reactions. Our goals include exploring baryon resonance formation and their electromagnetic structures. This will complement photo-production experiments (e.g., ELSA) and enhance our understanding of emissivity in dense, hot hadronic matter. Key topics include examining baryon couplings to mesons and virtual photons, analyzing hyperon weak decays in exclusive reactions, and using Partial Wave Analyses with differential cross sections and polarization observables to achieve unprecedented precision in baryon-meson coupling data ($\rho$N, $\omega$N). Furthermore, e$^{+}$e$^{-}$ production measurements off nucleons will provide insight into the electromagnetic transition form factors of baryons in the time-like region, revealing the role of vector mesons ($\rho$, $\omega$). Reactions on nuclear targets allow for detailed studies of hadron properties, including vector-meson line shapes and strengths in cold nuclear matter. These measurements provide a critical reference for the interpretation of results from the hot and dense environment created in $A+A$ collisions. This research also has broader implications. It will contribute to the modeling of neutrino-nucleus interactions, facilitate unprecedented investigations into hypernuclei formation, and enhance our understanding of strong interaction dynamics across different energy regimes.
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All authors HADES Collaboration: R. Abou Yassine, J. Adamczewski-Musch, G. Appagere, M. Becker, A. Blanco, C. Blume, M. Bohman, Y. Bondar, L. Chlad, I. Ciepał, S. Deb, M. D. Doncel Monasterio, M. Duerr, W. Esmail, L. Fabbietti, M. Firlej, T. Fiutowski, A. M. Foda, J. Förtsch, P. Fonte, J. Friese, I. Fröhlich, T. Galatyuk, R. Gernhäuser, M. Grunwald, D. Grzonka, M. Gumberidze, S. Harabasz, T. Heinz, C. Höhne, F. Hojeij, R. Holzmann, M. Idzik, B. Kämpfer, K.-H. Kampert, B. Kardan, V. Kedych, S. Kim, V. Kladov, A. Kodym, M. Kohls, J. Kolas, A. Koperwas-Władyszewska, G. Korcyl, G. Kornakov, W. Krueger, A. Kugler, R. Lalik, S. Lebedev, T. Leontiou, S. Linev, F. Linz, L. Lopes, M. Lorenz, A. Malige, P. Marciniewski, J. Markert, T. Matulewicz, S. Mehat, J.G. Messchendorp, V. Metag, J. Michel, A. Molenda, J. Moron, C. Müntz, A. Mukherjee, M. Nabroth, A. Opíchal, J. Orliński, J.-H. Otto, M. Papenbrock, Y. Parpottas, M. Parschau, S. Pattnaik, C. Pauly, D. Pawlowska-Szymanska, V. Pechenov, O. Pechenova, G. Perez Andrade, J. Phan, K. Piasecki, J. Pietraszko, T. Povar, M. Prędota, K. Prościński, A. Prozorov, W. Przygoda, B. Ramstein, N. Rathod, J. T. Rieger, J. Ritman, A. Rost, A. Rustamov, S. Sahu, P. Salabura, J. Saraiva, K. Scharmann, N. Schild, K. Schönning, E. Schwab, F. Seck, I. Selyuzhenkov, J. Smyrski, M. Sobiella, S. Spies, A. Sreejith, A. Strach, H. Ströbele, J. Stroth, P. Subramani, K. Sumara, O. Svoboda, K. Swientek, J. Taylor, P. E. Tegner, P. Tlusty, M. Traxler, S. Treliński, I. C. Udrea, F. Ulrich-Pur, V. Wagner, A.A. Weber, E. Weiler, C. Wendisch, D. Wielanek, P. Wintz, H.P. Zbroszczyk, M. Zieliński, P. Zumbruch

Materials Science

Screening of Coulomb Interactions in MoS2 Nanoribbons: Enhanced Coulomb interactions, Antiscreening, and Edge Magnetism

A. Montaghemi, H. Hadipour, A. Khademi et al. (+1 more)

MoS2 has attracted significant attention for its promising applications in optoelectronics, owing to the remarkable stability of its excitons and trions. These quasiparticles have large binding energies that arise from the MoS2 moderate band gap and the unconventional screening of Coulomb interactions in low dimensions. Here, we investigate the screening of long-range Coulomb interactions in the 1H and 1T' phases of MoS2 across different dimensionalities, with particular emphasis on nanoribbons. Our analysis is based on first-principles calculations combined with the constrained random-phase approximation. This work presents a comparative study of MoS2, h-BN, black phosphorene, and graphene nanoribbons, with emphasis on the role of Coulomb interactions in shaping their electronic and magnetic properties. In one-dimensional nanoribbons, quantum confinement leads to a substantial enhancement of Coulomb interactions relative to 2D MoS2. Calculations show that the Hubbard U increases from 2.6 eV in the 2D system to nearly 3.5 eV in the semiconducting nanoribbons. In these systems, the Coulomb interaction is long-ranged, with its tail extending over more than 100 A, nearly twice of that in the 2D structure. The presence of asymmetric edge states involving d and p orbitals in non-hydrogen-passivated zigzag MoS2 nanoribbons, in contrast to phosphorene, h-BN, and graphene nanoribbons, results in a finite net magnetization.
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All authors A. Montaghemi, H. Hadipour, A. Khademi, A. Yazdani

High Energy Physics (Phenomenology)

Endothermic Dark Matter at LZ from a Decaying Parent

Yongsoo Jho, Sanghwan Kim and Seong Chan Park

The LUX-ZEPLIN experiment has reported a nuclear-recoil candidate near 248 keV. We investigate a decay source for an endothermic interpretation: a long-lived dark parent produces energetic ground-state particles that upscatter on xenon. The parent mass fixes the injection energy, while its lifetime determines the absolute flux through the Galactic dark-matter column density. We include the Doppler broadening from parent and observer motion and use exact scattering kinematics with natural xenon isotopes. For a scalar contact interaction, a benchmark with a 10 MeV incident state and a 506 MeV parent gives an efficiency-weighted recoil spectrum peaked at 248.5 keV. One event in a specified high-energy window requires $\tau_X \simeq 4.4 \times 10^{20}$ s $f_X [\sigma_{\text{ref}}/(10^{-36} \text{cm}^2)]$, with a normalization sensitive to the nuclear response. We quantify the accompanying elastic-scattering requirement and the target-dependent thresholds. The calculation identifies a decay realization of the boosted flux and the portal conditions needed to preserve the recoil signal; a detector-level fit and ultraviolet-specific constraints remain necessary for a complete experimental assessment.
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Chemical Physics

The NewMag crystal-field code for f-element systems: Implementation for extended active spaces, second-order correlated energies, and generalisation to fn configurations

Gwenhaël Duplaix-Rata, Dumitru-Claudiu Sergentu, Boris Le Guennic et al. (+1 more)

We report a massive update of the NewMag program, which enables to extract Stevens crystal-field parameters (CFPs) after relativistic and multiconfigurational calculations are performed. The code can now post-treat ORCA and OpenMolcas outputs that contain state-average complete active space self-consistend field (SA-CASSCF) calculations with minimal or extended active spaces, second-order NEVPT2 or CASPT2 calculations, and spin-orbit configuration interaction (SOCI) calculations. Stevens parameters are extracted following the original Stevens convention with the so-called "extended" parameters. Rotation invariant indicators are also computed, after applying a correction of the parameter values to ensure normalization, following Rudowicz. At the SOCI level, the spin-orbit coupling (SOC) constant is also extracted within a spherical approximation of the SOC operator. For all the reference calculation levels, the model spectrum is reconstructed, allowing a direct assessment of its quality. The reported implementation is successfully applicable to f-element systems with a non-void, non-half-filled/empty or non-full f shell, that is for f^n configurations with n != 0, != 7 and != 14. Similarities and differences with the SINGLE_ANISO and AILFT codes are discussed. With selected examples, we showcase the interest of determining CFPs in f-element systems to understand their magnetic and optical properties in general, and more specifically the added value of NewMag. Finally, application of this approach to d-element systems is discussed, to reveal when it readily and successfully applies and when it may fail in reproducing satisfactorily the ab initio energies.
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All authors Gwenhaël Duplaix-Rata, Dumitru-Claudiu Sergentu, Boris Le Guennic, Rémi Maurice

High Energy Physics (Theory)

The Stieltjes Bootstrap for Feynman Integrals

Hadrien Brochet, Maximilian Haensch, Johannes Henn et al. (+4 more)

We prove that scalar Feynman integrals are Stieltjes functions in each kinematic variable $-p_i\cdot p_j$, as well as in the particle masses, for arbitrary loop order, arbitrary numbers of external legs, and arbitrary internal masses, whenever a certain exponent condition is satisfied. The proof rests on a canonical decomposition of the second Symanzik polynomial with manifestly non-negative coefficients indexed by spanning two-forests. We present a dedicated analysis of the case in which the kinematic variables satisfy relations, as frequently happens in physical applications. We argue that integration-by-parts relations allow the selection of master-integral bases in which every element is a Stieltjes function. The Stieltjes property guarantees the convergence of Padé approximants and provides determinantal (Hankel) constraints on the Taylor coefficients of master integrals that go beyond previously known complete-monotonicity bounds. We develop a numerical strategy that combines these Stieltjes constraints with differential equations to determine the master integrals in the Euclidean region via semidefinite optimization. We demonstrate this approach on the pedagogical example of the six-dimensional massive box integral, and then apply it to the calculation of previously unknown three-loop two-mass integrals needed for three-loop electroweak corrections to the $Z$- and Higgs-boson self-energies.
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All authors Hadrien Brochet, Maximilian Haensch, Johannes Henn, Benjamin Hollering, Prashanth Raman, Qinglin Yang, Simone Zoia

Quantum Physics

Digital quantum state preparation by nucleation

Jean Paul Sadia, Morten Hjorth-Jensen, Dean Lee et al. (+1 more)

Quantum state preparation is crucial for quantum algorithms, and improved state preparation methods can reduce resource requirements by orders of magnitude. In this work, we introduce a state preparation method for lattice Hamiltonians on digital quantum computers inspired by nucleation. In our method, the exact ground state of a small lattice Hamiltonian is prepared in a quantum circuit, then a series of growth stages are performed via Trotterized adiabatic evolution to increase the size of the lattice to the desired model. Using the adiabatic theorem and Trotter error bounds, we provide sufficient conditions on the total evolution time and number of Trotter steps required for nucleation to prepare an initial state with desired fidelity. In addition, we introduce optimized nucleation which considers variational optimization on top of the nucleation structure. For a two-dimensional Ising model, we show that optimized nucleation can outperform a current leading method for state preparation on digital quantum computers.
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All authors Jean Paul Sadia, Morten Hjorth-Jensen, Dean Lee, Ryan LaRose

Quantum Physics

Asymptotic Pseudospectra in Dissipative Floquet Quantum Systems: Geometric Structures and Observable Dynamics

Yuncheng Xie, Haozhe Shi, Zhuocheng Ma et al. (+2 more)

In periodically driven open quantum systems, nonnormality renders the Floquet spectrum insufficient as the system approaches the thermodynamic limit, so that pseudospectra are needed to characterize the dynamics accurately. While conventional approaches mainly focus on the local dynamics of isolated pseudospectra, their global connections and the resulting physical consequences for observables have remained largely unexplored. Here, we uncover this collective behavior by classifying the unit disk into distinct domains of exponential, algebraic, and bounded accuracy according to the asymptotic size-scaling laws of pseudospectral residuals, yielding an underlying geometric structure. We demonstrate the physical implications of this structure through two exactly solvable models. First, in a dissipative shift chain, parameter tuning drives geometric transitions that are detectable via spin-wave observables. Second, in a chiral XY model, we use this geometric structure to explain the origin of a measurable phenomenon: two correlation signals exchange their retention order under continuous parameter tuning. Our findings not only establish a new theoretical paradigm for understanding dissipative Floquet quantum systems, but also predict geometry-driven observables for quantum computing experiments.
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All authors Yuncheng Xie, Haozhe Shi, Zhuocheng Ma, Weibin Chu, Xin-Gao Gong

Physics and Society

Cultural, Structural, and Mediated Routes to Polarization in a Nonlinear Mean-Field Model

Jérôme Michaud and Fredrik Jansson

Collective polarization can arise through mechanisms acting at different stages of social communication, but similar polarized outcomes need not imply dynamically equivalent processes. We introduce a nonlinear two-group mean-field model that distinguishes three routes to polarization: individual content filtering, assortativity, and receiver-side message tailoring. Sender-side reformulation is included as a complementary mediation process that transforms source signals before they are mixed. These message transformations are motivated by AI-mediated cultural transmission, in which intermediaries can reformulate messages or adapt them to receivers. Using common and difference coordinates, we derive general conditions for instabilities toward consensus and balanced polarization and analyze the resulting stationary branches in the full two-dimensional phase plane. Individual filtering can generate polarization through state-dependent updating, assortativity can preserve group differences in the social field, and receiver tailoring can create a polarizing feedback even under complete mixing. By contrast, sender-side reformulation affects the polarization mode only when assortativity preserves differentiated source signals. Although these mechanisms can produce identical local instability conditions or balanced-branch amplitudes, they remain distinguishable through transverse stability, asymmetric equilibria, multistability, and basin geometry. In particular, balanced polarization may emerge as a saddle before becoming a stable attractor, while asymmetric saddles organize the boundary between consensus and polarization basins. These results show that collective polarization depends not only on feedback strength, but also on where feedback enters the communication process.
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Earth and Planetary Astrophysics

The Occurrence Rate of Planets Around Subgiant Stars from TESS Photometric Survey

Arkaprova Dutta and Priyanka Chaturvedi

Subgiant stars represent a critical phase in stellar evolution, offering an opportunity to investigate how planetary systems respond to the early stages of post-main-sequence expansion. Despite their importance, systematic occurrence-rate studies of this population remain sparse compared with those of main-sequence and red-giant hosts. In this work, we present a uniform analysis of planet occurrence around a sample of 282,904 subgiant stars selected from the Gaia DR3 catalogue. We perform an independent reanalysis of TESS light curves for transit-signal detection and refinement, followed by multi-stage vetting including visual inspection and statistical false-positive assessment. We quantify the detection sensitivity of the survey through injection-and-recovery experiments, with 565,808 synthetic transit signals injected across the stellar sample. Over the period range of 1–10 days and the planet-radius range for which the detection completeness is well characterised, we measure a completeness-corrected planet occurrence rate of 0.644^{+0.048}_{-0.041}. The occurrence rate is strongly dependent on planet radius, with the highest occurrence contributed by planets in the 1-4 R_earth range and a secondary enhancement at 12-15 R_earth. These results provide a demographic baseline for studying the population of close-in planets around stars undergoing early post-main-sequence evolution.
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Materials Science

Operando Surface Probe Microscopy Reveals Electrochemical Origins of Reliability Variability in Hafnia Ferroelectrics

Anudeep Tullibilli, Kartick Biswas, Shubham Kumar Parate et al. (+1 more)

Device-to-device and sample-to-sample variability remains a major obstacle to the reliable implementation of hafnia-based ferroelectrics, even in nominally identical structures fabricated under similar processing conditions. This highlights the need for operando diagnostic probes that provide process-relevant feedback beyond conventional structural phase analysis. Here, we demonstrate that operando nanoscale surface measurements serve as sensitive probe of the local electrochemical processes governing reliability in hafnia ferroelectric devices. Using epitaxial rhombohedral Y:HfO2 films grown on La0.67Sr0.33MnO3 (LSMO)-buffered SrTiO3 as a model system, we combine operando atomic force microscopy, conductive AFM, piezoresponse force microscopy, and correlative STEM-EELS to directly link surface evolution with interfacial electrochemistry. Devices exhibiting wake-up show a spatially uniform increase in surface height, arising from homogeneous oxidation of the LSMO electrode followed by oxygen migration into the ferroelectric layer during polarization switching. In contrast, leaky devices display pronounced surface roughening and blister formation, originating from spatially inhomogeneous oxidation states in the pristine LSMO electrode that promote competing oxygen evolution reactions at the LSMO/Y:HfO2 interface. The accompanying electron generation produces leakage which is transient. Guided by these mechanistic insights, we introduce simple modifications to the processing conditions, without altering the optimized ferroelectric phase, that suppress the competing electrochemical pathways and reproducibly yield 100% ferroelectric devices. More broadly, this work establishes operando surface evolution as a powerful nanoscale diagnostic of hidden electrochemical processes and provides a practical route for improving the reliability and reproducibility of hafnia-based ferroelectric devices.
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All authors Anudeep Tullibilli, Kartick Biswas, Shubham Kumar Parate, Pavan Nukala

Optics

Multi-Parameter Error Mitigation in Parametric Down-Conversion via SU(1, 1) Composite Segmentation

Nastaran Ragerdi Kashani and Rouhollah Karimzadeh

Spontaneous parametric down-conversion is a primary resource for generating non-classical light, yet phase mismatch fluctuations from temperature drift, angular misalignment, and domain fabrication errors reduce pair-generation efficiency and phase stability. Here, we analyze error mitigation in spontaneous parametric down-conversion using composite segmentation governed by SU(1, 1) spatial dynamics. We show that odd spatial Fourier harmonics preserve error-cancellation flatness with pair-generation rates scaling asymptotically as $m^{-2}$, while a coordinate-dilation symmetry provides a design prescription for translating configurations across distinct operating wavelengths (405, 532, and 775 nm). Furthermore, an open-loop thermo-optic bias counteracts off-axis angular drift to broaden the 90%-efficiency angular acceptance half-width by 3.46x, and up to two missing poling domains are tolerated with no numerically resolved loss in relative conversion efficiency. Across a 5$^\circ$C thermal window, the generated pairs sustain a relative conversion efficiency of $\eta \ge 0.954$ with the modeled phase-coherence metric remaining above 0.95, providing a structurally robust approach for entangled photon generation without requiring continuous closed-loop feedback stabilization.
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Statistical Mechanics

Exact anomalous current fluctuations in the strong-anisotropy limit of the XXZ chain

Taiki Ishiyama, Taiga Kurose, Kazuya Fujimoto et al. (+1 more)

We study spin-current fluctuations of the folded XXZ chain, which describes the strong-anisotropy limit of the XXZ chain. We obtain an exact expression for the moment-generating function of the time-integrated spin current at infinite temperature. A long-time asymptotic analysis establishes that the rescaled time-integrated current converges to a non-Gaussian distribution described by the M-Wright function. The derivation relies on a nonlocal map to the one-dimensional t-0 model and its exact spin-charge separation. By extending this approach, we also show that the dynamical correlation function of the spins summed over two adjacent sites exhibits a diffusive Gaussian profile at long times.
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All authors Taiki Ishiyama, Taiga Kurose, Kazuya Fujimoto, Tomohiro Sasamoto

General Relativity and Quantum Cosmology

Black objects in a five-dimensional swirling spacetime

Adriano Viganò

We construct a five-dimensional generalization of the swirling universe and embed in it the Myers-Perry black hole and the rotating black ring. We prove that both solutions are free of conical singularities, analyze their geometrical properties, compute their mass and angular momentum, and discuss their uniqueness.
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Astrophysics of Galaxies

Caught in the act: diffuse stellar and Ly$\alpha$ emission around a halo-less quasar in the assembling cluster CARLA J0800+4029 at z=2

Sofia G. Gallego, Simona Mei, Emanuele Daddi et al. (+3 more)

Extended Ly$\alpha$ emission is commonly detected around luminous quasars at $z\sim2$-3 and traces cold gas in the circumgalactic environment of the AGN. Together with the spatial distribution of galaxies, Ly$\alpha$ probes gas and galaxy assembly in high-redshift overdensities. We use deep KCWI wide-field spectroscopy and HST/F140W imaging to investigate the assembling cluster CARLA J0800+4029 at $z=1.986\pm0.014$. No robust extended Ly$\alpha$ emission is detected at the radio-loud quasar position. Instead, the dominant Ly$\alpha$ emission is offset from the AGN and coincides with a disturbed structure composed of galaxies, tidal features, and diffuse intra-halo light (IHL). The detected structure has $L_{\rm Ly\alpha}=1.42\times10^{43}$ erg/s and reaches surface-brightness levels of $\sim10^{-17}$ erg/s/cm$^2$/arcsec$^2$. At the quasar position, a matched $3\sigma$ limit gives $L_{\rm Ly\alpha}<4.20\times10^{42}$ erg/s, a factor of $\sim3.4$ below the detected offset emission and among the most stringent constraints at similar redshift. The Ly$\alpha$ emission is dominated by one extended region near systemic velocity, with FWHM $\sim300$-500 km/s. The associated tidal structure has an IHL fraction of 18.8%, and contains a spatially coherent absorption-like decrement at $\sim+1000$ km/s. The offset and alignment between Ly$\alpha$ emission and IHL suggest that gas and stars have been redistributed together during assembly. The lack of a comparable Ly$\alpha$ halo around the quasar further suggests that gas in the immediate AGN environment is ionized, depleted, or suppressed, while the offset region remains favorable for Ly$\alpha$ emission. CARLA J0800+4029 reveals baryon redistribution during cluster assembly, with the dominant observable Ly$\alpha$ reservoir decoupled from the central AGN and linked to ongoing tidal assembly.
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All authors Sofia G. Gallego, Simona Mei, Emanuele Daddi, Gaël Noirot, Dominika Wylezalek, R. Michael Rich

Quantum Physics

Experimental certification of multipartite Bell correlations using only few-body symmetric correlations

Jiacheng Sun, Mengyao Hu, Paweł Cieśliński et al. (+9 more)

Certifying Bell correlations in increasingly larger multipartite quantum systems is challenging because conventional Bell inequalities rely on many-body correlations, which become experimentally demanding to estimate as system size grows. Here we demonstrate that multipartite Bell correlations can be certified using few-body permutation-invariant (PI) correlations with a fixed maximal correlation order. We experimentally test few-body PI Bell correlation witnesses tailored for six- and eight-photon postselected Dicke states. The addition of a few four-body correlators is found to significantly enhance the noise tolerance compared with previously studied two-body witnesses: for instance, for six qubits, the selected witness tolerates a white-noise fraction of $p_c\approx0.301$, compared with $p_c\approx0.048$ for the best two-body PI inequality with the same two settings per party. For six and eight photons respectively, we observe violations of the witness bounds by $32$ and $8.9$ standard deviations, arising from postselected polarisation states with fidelities of $0.933(4)$ and $0.916(11)$ to the corresponding half-excitation Dicke states. The witnesses for the six- and eight-photon cases use the same symmetric two- and four-body correlators, just with different coefficients. These results demonstrate an experimentally accessible approach for certifying multipartite Bell correlations in larger systems without requiring full-body correlation measurements.
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All authors Jiacheng Sun, Mengyao Hu, Paweł Cieśliński, Jinfu Chen, Fei Shi, Bowen Wang, Hongyu Yang, Jizhou Wu, Jordi Tura, Valerio Scarani, Dian Wu, Jian Wu