Atmospheric and Oceanic Physics
Learning Climate Variability from Scarce Data with Diffusion Models: A Test Case for ENSO
Lluis Palma, Vincent Verjans, Amanda Duarte et al. (+2 more)
Diffusion models are increasingly applied to
climate emulation, but whether they capture the correct modes of variability remains unclear, a concern amplified by data scarcity at longer timescales. We investigate this using synthetic tropical Pacific SST fields from Linear Inverse Models (LIMs), whose known low-order structure bypasses the overlapping and confounding modes of real observations. With sufficient training data, our model recovers the correct structure of both Gaussian and non-Gaussian LIMs, including ENSO's Eastern/Central Pacific asymmetry. Yet an ablation study on the number of monthly training samples reveals that the 700 observations in ERSSTv5 fall an order of magnitude short of the 7,000 samples needed for convergence, and that not all
diffusion parameterisations recover the correct low-order structure. Pre-training on CMIP6 with a learned model
embedding, followed by fine-tuning on scarce observations, closes this gap, reproducing observed statistics more faithfully than both Gaussian and non-Gaussian LIMs.
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All authors Lluis Palma, Vincent Verjans, Amanda Duarte, Albert Soret, Markus Donat
High Energy Physics (Theory)
Index saddle for the D1-D5-P black string and its decoupling limit
Kanhu Kishore Nanda, P Shanmugapriya and Amitabh Virmani
Boruch, Emparan, Iliesiu, and Murthy recently discussed index saddles for 5d black strings, showing that the black string saddle admits a decoupling limit to a complex, finite-temperature BTZ \times S^2 saddle that computes the index of the dual CFT. In this paper, we pursue an analogous construction for the D1-D5-P black string. We construct a four-charge index saddle in the four-dimensional STU model as the BPS limit of the non-extremal four-charge black hole, and show that it exhibits the new form of attraction. We then uplift it successively to five and six dimensions, via the 4D-5D connection and a chain of string dualities, to obtain the gravitational index saddle for the D1-D5-P black string. We take a systematic decoupling limit of this index saddle and obtain the BTZ \times S^3 saddle that computes the index of the D1-D5 CFT.
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Computational Physics
GPU-accelerated superiorization on constrained physical problems with SupPy
Tobias Becher, Yair Censor, Kay Barshad et al. (+1 more)
The superiorization method (SM) is situated between feasibility-seeking and constrained optimization. Instead of aiming at the minimum of a given objective function over a constraint set, it seeks a feasible point at which the objective function value is reduced - though not necessarily minimal - rather than hard targets, or in which a mathematically optimal solution is not strictly required. While the method has been investigated for several applications in physics, its broader use has been limited, in part due to the lack of openly available software for researchers wishing to explore it. In this work we apply superiorization to three problems from applied physics: seismic image reconstruction, low-dose CT reconstruction and intensity-modulated radiotherapy treatment planning. These experiments are conducted with SupPy, an open-source modularized Python toolbox developed for this work, which supports execution of feasibility-seeking
algorithms and their superiorized version on both the CPU and the GPU. In all three cases the superiorized
algorithms achieve favorable results compared to feasibility-seeking alone, with reduced noise in the imaging examples and lowered body dose in the radiotherapy plans. For the radiotherapy case we further observe that superiorization produces clinically viable plans on infeasible constraint sets.
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All authors Tobias Becher, Yair Censor, Kay Barshad, Niklas Wahl
Mathematical Physics · Cross-listed from math.SP
Discrete Space-Time Wave Kernels on Regular Trees
Amar Bašić, Lejla Smajlović and Zenan Šabanac
We study the forward discrete space-time wave equation on the homogeneous $(q+1)$-regular tree $T_{q+1}$ associated with a two-parameter generalized
Laplacian. Under the natural nonnegativity assumption on this operator, we derive explicit formulas for the two fundamental wave kernels. The formulas are given in terms of discrete $I$-Bessel functions and yield convolution representations for solutions with general initial conditions. In the boundary case corresponding to the bottom of the spectrum, we obtain another explicit representation of the wave kernel in terms of discrete $J$-Bessel functions. This representation leads to a discrete analogue of the classical $I\!\leftrightarrow\!J$ relation. We also perform both analytic and numerical studies of the asymptotic behavior of the wave kernels, including large radial distance, large time, and large degree of the tree. An important feature of our analysis is that the wave kernels are expressed as finite sums; hence, the propagation formulas remain finite for every discrete time.
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Quantum Physics · Cross-listed from cs.LG
Finding Stationary Points by Comparisons
Helin Wang, Chenyi Zhang, Xiwen Tao et al. (+2 more)
We study the problem of finding stationary points of non-convex functions when access to the objective is provided only through a comparison oracle that, given two points, outputs which has the larger function value. For a twice differentiable $f\colon\mathbb R^n\to\mathbb R$ with Lipschitz gradient and Hessian, we develop an
algorithm that visits an $\epsilon$-stationary point using $\widetilde O(n^2/\epsilon^{1.5})$ queries. Our approach uses a subroutine that estimates the normalized Hessian to accuracy $\delta$ using $\widetilde O(n^2\log(1/\delta))$ queries. We further study this problem with a
quantum comparison oracle model where queries can be made in superpositions, and develop the first
quantum algorithm that finds an $\epsilon$-stationary point, which takes $\widetilde O(n/\epsilon^{1.5})$ queries.
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All authors Helin Wang, Chenyi Zhang, Xiwen Tao, Yexin Zhang, Tongyang Li
Biological Physics
Efficient Proton Relay Orchestrated by Covalent Bond Switching of Active Amino Acids in Protein Channels
Xiangyu Su, Yuwei Cao, Shuyang Zhao et al. (+1 more)
Through systematic mutational simulations of the key site in a
proton channel, we find that 13 of the 20 canonical amino acid residues are active for
proton transfer through covalent bond switching, whereas the remaining 7 residues, whose side chains terminate in sp3 hybridized carbon-hydrogen covalent bonds, do not undergo such bond switching and are therefore inactive. All active residues have a negative electrostatic potential extremum at the
proton accepting atom and lower energy barriers for
proton relay orchestrated by bond switching, whereas the inactive residues have positive electrostatic potential extremum and significantly higher barriers for bond switching. We further find that the active residues tend to be distributed within the pore to mediate
proton transfer, while the inactive residues are enriched in the periphery to stabilize the structure. This bond switching activity can also be observed in respiratory complex I. These findings establish a new classification criterion for amino acids based on their covalent bond switching activity, providing insights into how life utilizes the 20 types of amino acids.
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All authors Xiangyu Su, Yuwei Cao, Shuyang Zhao, Wanlin Guo
Cosmology and Nongalactic Astrophysics
Spherical Collapse and Halo Formation in a Cosmology with Decaying Dark Matter and a Semi-Cosmographic Dark Energy
Mohit Yadav and Tapomoy Guha Sarkar
We investigate nonlinear structure formation in a cosmological model combining one-body decaying dark matter (DDM) with a semi-cosmographic reconstruction of dark energy. In this scenario, a nonrelativistic dark-matter component decays into relativistic dark radiation with decay rate $\Gamma=\tau_{\rm ddm}^{-1}$, while the dark-energy sector is reconstructed directly from the expansion history rather than being fixed to a cosmological constant. Using DESI DR1 BAO and compressed ShapeFit measurements, we constrain the background
evolution and propagate the resulting posterior into the nonlinear regime through spherical collapse and
halo abundance calculations. This provides a unified framework connecting a reconstructed dark-energy sector and decaying dark matter (DDM) to the nonlinear formation of
cosmic structures. We find that the reconstructed dark-energy equation of state can deviate from the $\Lambda$CDM value, $w=-1$, while the critical density threshold for collapse remains close to its standard prediction. The most pronounced signatures emerge in the abundance of massive
halos, reflecting modifications to the growth of structure driven by both dark-matter decay and dynamical dark energy. By combining DESI DR1 clustering constraints with
halo mass function measurements from the DESI Legacy Imaging Surveys DR9, we obtain joint constraints on the DDM lifetime and dark-energy parameters, demonstrating that
halo abundances provide a powerful complementary probe of non-standard dark-sector physics.
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Lattice Field Theory
Performance of Low Mode Averaging on Twisted-Mass Fermion Ensembles at the physical pion mass point
Constantia Alexandrou, Simone Bacchio, Antonio Evangelista et al. (+4 more)
We study the performance of low-mode averaging (LMA) on twisted-mass
fermion ensembles at near-physical
quark masses, assessing both its theoretical framework and practical cost-effectiveness in modern
lattice QCD. In particular, we present a numerical study of light-
quark meson and
baryon observables. For
mesons, we analyse two-point functions, including the vector-vector correlator relevant for the hadronic
vacuum polarisation contribution to the
muon anomalous
magnetic moment, comparing two implementations of LMA: an exact approach based on explicit low modes and an approximate, high-statistics variant using multigrid techniques. For
baryons, we restrict to the exact approach and study both two- and three-point functions, quantifying the resulting noise and cost reductions at large Euclidean times. In addition, we compute the
eigenvalue density of the massless Wilson operator and determine the renormalised
chiral condensate via the Banks-Casher relation, obtaining $\sqrt[3]{\Sigma_{\mathrm{R}}}=269.5(4.5)~\mathrm{MeV}$ for $N_f{=}2{+}1{+}1$ isospin-symmetric QCD at a scale $2~\mathrm{GeV}$ in the $\overline{\mathrm{MS}}$ scheme, with an uncertainty dominated by the
chiral extrapolation. Additionally, from the pion-mass dependence of $\Sigma_{\mathrm{R}}$, we extract the scale-independent low-energy constant $\bar{h}_1=5.2(1.1)$.
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All authors Constantia Alexandrou, Simone Bacchio, Antonio Evangelista, Roberto Frezzotti, Francesca Margari, Francesco Sanfilippo, Christian Schneider
Nuclear Experiment
Half-Life Measurements of $^{110}$Sn, $^{113}$Sn, $^{117\mathrm{m}}$Sn, and $^{123\mathrm{m}}$Sn Produced via Photon Activation of Natural Tin
O Nusair, D Devries and M Toto-Gonzalez
We report independent determinations of the ground-state half-lives of $^{110}$Sn, $^{113}$Sn, and the isomeric states $^{117\mathrm{m}}$Sn (J$^{\pi} = 11/2^{-}$) and $^{123\mathrm{m}}$Sn (J$^{\pi} = 3/2^{+}$), produced via
photon activation of natural tin using a TT-300HE Rhodotron accelerator. The activated samples were monitored over several months using a high-purity germanium (HPGe) detector. Time-dependent $\gamma$-ray spectra were analyzed using Gaussian peak fitting for the \SI{280.49}{keV}, \SI{391.697}{keV}, \SI{158.56}{keV}, and \SI{160.34}{keV} transitions, yielding half-lives of \SI{4.165(25)}{h} for $^{110}$Sn, \SI{116.08(94)}{d} for $^{113}$Sn, \SI{13.95(1)}{d} for $^{117\mathrm{m}}$Sn, and \SI{39.95(12)}{min} for $^{123\mathrm{m}}$Sn. Agreement with
Nuclear Data Sheets (NDS) recommended values is generally observed for $^{110}$Sn, $^{113}$Sn, and $^{123\mathrm{m}}$Sn, with deviations consistent within combined uncertainties when quantified using standardized differences (z-scores). In contrast, $^{117\mathrm{m}}$Sn exhibits a statistically significant deviation from the evaluated value of \SI{13.76(4)}{d}, with a z-score indicating a discrepancy well beyond expected statistical fluctuations. This result suggests a systematic difference warranting further investigation, with potential implications for applications relying on precise decay data, including calibration, dosimetry, and astrophysical modeling.
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Instrumentation and Methods for Astrophysics
The Line Emission Terahertz Observatory (LETO): Exploring the lifecycle of the ISM and the origins of water
Dimitra Rigopoulou, Peter Roelfsema, William Grainger et al. (+13 more)
The Interstellar Medium (ISM) is the reservoir of baryonic matter from which
stars and planetary systems are formed. It is also the repository of the material that is expelled at the end of the
stellar evolutionary cycle feeding the baryonic matter reservoir. These evolutionary phases in the ISM together form a complex interplay driving
planet and
star formation and thus the
evolution of our own Milky Way as well as
galaxies at low and high
redshifts. The design of the Line Emission Terahertz Observatory (LETO) has been optimized to investigate the impact of the ISM on
star formation on
galactic and extragalactic scales, study the processes that transform gas clouds into
stars and planetary systems, and trace the flow of water in the ISM. To achieve these goals, LETO will carry out deep velocity-resolved wide-area spectroscopic observations of key FIR lines in the ISM covering an area of approximately 900 square degrees of the
Galactic Plane. To complement our local view LETO will map a large sample of about 200 nearby
galaxies in addition to surveys of
Galaxies at
Cosmic Noon. To shed light on the
planet formation process, LETO will study the physical and chemical properties (especially gas mass) of numerous proto-planetary disks and
stellar cores through pointed observations of the HD and H2O lines. LETO is a powerful FIR mission building on rich European heritage. To satisfy the requirements for sensitivity, resolving power and mapping speed, LETO utilizes a 3.5m class mirror and several bands with sensitive state-of-the-art multi-pixel heterodyne arrays. The bands together will cover the wavelength range from 56 to 666 micron and with the heterodyne receivers and backends high resolving power spectroscopy a set of key FIR atomic, ionic, and molecular lines can be studied in great detail. The mission is one of several selected for further study in the context of the ESA M8 call.
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All authors Dimitra Rigopoulou, Peter Roelfsema, William Grainger, Chris Pearson, Boon-Kok Tan, Wouter Laauwen, Andrey Baryshev, Vincent Desmaris, Ismael Garcia-Bernete, Javier R. Goicoechea, Leslie Hunt, Georgios Magdis, Miguel Pereira-Santaella, Kamber Schwarz, Bryan Shaugnessy, Martina Wiedner
Astrophysics of Galaxies
Unveiling a cosmic tango: Integral field spectroscopy and numerical simulations of Arp 143's interaction
Hugo Martel, Carmelle Robert, Laurent Drissen et al. (+6 more)
We present spectral data cubes of the interacting
galaxy system Arp 143, composed of the ring
galaxy NGC 2445 and the lenticular
galaxy NGC 2444, obtained with the imaging
Fourier transform spectrometer SITELLE at the Canada-France-Hawaii
Telescope. Our data allow to probe the kinematics of the interaction and the chemical properties of the ionized gas.
Star-forming regions are almost exclusively found in the ring and
nucleus of NGC 2445 with the exception of a few very faint ones discovered at the base of the long
tidal plume extending north of NGC 2444. Analysis of the H{\alpha} velocity map reveals strong non-circular flows in the ring of NGC 2445, which is expanding. Its
nucleus is off-centered with respect to the ring. Oxygen abundance in the ring is on average slightly sub-
solar whereas it is close to
solar in the
nucleus. Broad-band images obtained with the Dragonfly Telephoto array allow to identify the tenuous
stellar counterpart of the
radio tidal plume. The interaction between the two
galaxies is simulated with a chemodynamical
evolution code; these simulations suggest that Arp 143 has resulted from a head-on collision between a S0 and a Sc spiral
galaxy following a flyby encounter that triggered the formation of the long plume from debris of the disk
galaxy.
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All authors Hugo Martel, Carmelle Robert, Laurent Drissen, Charles-Antoine Parent, Prime Karera, Sébastien Vicens-Mouret, Salvador Duarte Puertas, Jorge Iglesias Páramo, José M. Vilchez
Earth and Planetary Astrophysics
Solarsystem: A Validated Lightweight Python Package for Planetary Positions and Solar-Lunar Event Calculations
Ioannis Nasios
This paper presents solarsystem, a validated lightweight and dependency-free Python package for planetary positions and
solar-lunar event calculations. The package provides heliocentric and geocentric positions for the major
planets, selected
dwarf planets, the Centaur Chiron, and the Moon, together with sunrise, sunset, moonrise, moonset, and lunar illumination calculations. Additional functionality includes coordinate transformations between commonly used astronomical reference systems. The implemented
algorithms employ analytical models that avoid reliance on external ephemeris
datasets, resulting in a portable and computationally efficient solution suitable for a broad range of astronomical applications. An optional precession correction model is included, enabling calculations either in a precession-corrected reference frame or in a fixed epoch framework, depending on user requirements. The numerical performance of solarsystem was evaluated against the JPL DE440 planetary ephemerides using the Skyfield framework as a reference. Validation experiments spanning multiple bodies and extended temporal intervals demonstrate good agreement with the reference ephemerides, with mean planetary longitude and latitude deviations of approximately 0.44 and 0.16 arcminutes, respectively. Additional validation of
solar and lunar event calculations yielded timing differences of only a few minutes relative to the reference solutions, while lunar illumination estimates differed by approximately 0.2%. The package can be installed directly through PyPI while the source code, documentation, validation notebooks and example workflows are publicly available through the project repository in https://github.com/IoannisNasios/solarsystem.
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High Energy Physics (Theory)
Non-topological solitons in biadjoint scalar field theory
Kymani Armstrong-Williams and Chris D. White
Biadjoint scalar theory has been widely studied, due to its being closely related to the double copy correspondence linking gauge,
gravity and related theories. In this paper, we continue a programme of work in elucidating non-linear solutions of this theory, and find a family of new solutions that are richer and more complex than previous cases. Using an ansatz that can be embedded in any choice of non-abelian colour groups, we demonstrate the existence of non-topological
solitons, whose existence is protected by carrying a U(1) charge associated with certain rotations in colour space. The solutions are time-dependent, and closely related to the well-known Q-ball solutions in other scalar field theories. We also show explicitly that our solution set contains those that are stable under small perturbations within a consistent truncation of the theory, and have finite energy in addition to being localised.
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Adaptation and Self-Organizing Systems · Cross-listed from cs.CY
Human–LLM Collaboration Is Transforming Complexity Metrics in Scientific Texts
R. Alexander Bentley, Blai Vidiella, Damian J. Ruck et al. (+3 more)
While human
language has long been studied as a complex system, Large
Language Models (LLMs) are rapidly becoming contributors to its dynamics. Because LLMs are trained on human
language use, their effects on the broader human-AI linguistic ecosystem are likely subtle at first. As their use becomes more widespread, however, LLMs may alter emergent properties of
language, particularly as models increasingly train on mixed human-LLM textual data. Here, we draw on complexity science to look for subtle LLM effects in millions of arXiv abstracts from 2010 to 2025. The year 2023, when LLMs rapidly became widely used, serves as a landmark in a natural experiment. While we find a sharp increase in a composite LLM-associated style index after early 2023, we observe only subtle changes in the exponents of Zipf's law and Heaps' law. More compelling, however, are two subtle changes in complexity metrics that emerge from 2023 onward. First, turnover among top-ranked words increases sharply. Second, the positive relationship between the LLM-associated style index and three complexity metrics–vocabulary size and the exponents of Heaps' and Zipf's laws–becomes flatter after 2022. Together, these patterns are consistent with changes in the emergent properties of scientific text in a mixed human-AI linguistic ecosystem.
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All authors R. Alexander Bentley, Blai Vidiella, Damian J. Ruck, Senjuti Dutta, Kai Li, Sergi Valverde
Cosmology and Nongalactic Astrophysics
Quintom Model Perturbations
L. W. K. Goh and A. N. Taylor
We build upon the work of Goh and Taylor 2025, in which we proposed a two scalar field quintom framework capable of naturally realising a phantom-to-quintessence transition in the dark energy equation of state. In this work, we derive the linear perturbation equations of our model and investigate its implications for large scale structure formation. We show that the quintom model is able to reproduce the phenomenological features of a w0waCDM cosmology with phantom-to-quintessence crossing, including suppressions in the matter power spectrum and enhancements to the late-time Integrated Sachs-Wolfe effect. We then perform a
Bayesian analysis of the quintom framework with BAO, CMB and Type 1a
supernovae data, finding that it is mildly favoured over the standard w0waCDM parametrisation, while successfully reproducing physical trends observed in the data. We further examine the parameter degeneracies inherent to the model and discuss prospective observational strategies for distinguishing quintom cosmologies from conventional dynamical dark energy models given current and future data precision.
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High Energy Astrophysical Phenomena
Optical observations of candidate host galaxies of eight fast X-ray transients
Agnes P. C. van Hoof, Peter G. Jonker, Lieke Tommel et al. (+15 more)
Fast X-ray transients (FXTs) are extragalactic flashes of X-rays with a typical duration of minutes to hours for which a variety of origins has been proposed and observed. To decipher the origin of FXTs, particularly those lacking multi-wavelength counterparts, we aim to understand their energetics and environments. We present deep optical ground-based observations of the positions of eight FXTs in order to try and identify and characterize candidate host
galaxies. We use their properties to discriminate between possible progenitor scenarios. We identify candidate host
galaxies for Swift~J050400.2+673405, XRT140507, XRT040610, XRT151121, XRT191127 and EP240708a. For each candidate, we infer the spectroscopic or photometric
redshift,
stellar mass,
star formation rate,
metallicity and
stellar population age by fitting our data with the spectral energy distribution fitting code BAGPIPES. We re-identify XRT191223 as a
Galactic stellar flare. For several FXTs, there are multiple candidate host
galaxies, which complicates deriving constraints on the origin of the FXT. Assuming association with (one of) those candidates, all are consistent with a (non-)relativistic white
dwarf - intermediate mass black hole
tidal disruption event (WD-IMBH TDE) and a binary
neutron star (BNS) merger. Two are consistent with a
supernova shock breakout and only EP240708a with cocoon emission from a long gamma-ray burst. We also discuss the possibility that the host
galaxies remain undetected in our observations. We conclude that FXTs detected by Chandra and XMM-Newton are likely to arise from a variety of origins, and we discuss that part of this population differs from FXTs detected by Einstein Probe many of which appear consistent with a collapsar scenario.
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All authors Agnes P. C. van Hoof, Peter G. Jonker, Lieke Tommel, Jonathan A. Quirola-Vásquez, Daniel Mata Sánchez, Joyce N. D. van Dalen, Andrew J. Levan, Morgan Fraser, Ann Zabludoff, Manuel A. P. Torres, Javi Sánchez-Sierras, Antonio Martin-Carrillo, Thomas Wevers, Marco Berton, Minghao Yue, Vik S. Dhillon, Franz E. Bauer, Stuart P. Littlefair
Optics
Observation of Non-Hermitian Skin Dynamics in the Liouvillian Regime
Shu Yang, Yeyang Sun, Lingrui Hong et al. (+1 more)
Open
quantum systems generally do not perfectly preserve phase coherence: coupling to uncontrolled environments requires a density-
matrix description based on the Liouvillian framework beyond pure-state wave
evolution. Realizing and probing such dynamics in a programmable platform is therefore essential for connecting coherent physics to realistic dissipative settings. Here we implement a tunable open-system
quantum walk in a photonic mesh
lattice, where controlled phase noise produces adjustable dephasing and non-reciprocal gain-loss imbalance provides an independently tunable non-Hermitian drive. This allows us to continuously interpolate between coherent
quantum walks and incoherent classical walks, and to observe how directional transport evolves in the Liouvillian regime. Using non-Hermitian skin dynamics as a probe, we measure the center-of-mass drift over both the coherence and non-Hermiticity parameters, revealing a crossover from coherence-enhanced to decoherence-enhanced transport in quantitative agreement with
quantum-channel simulations. We further program spatial and temporal interfaces to demonstrate interface accumulation and a long-time drift governed by the instantaneous channel. Our results establish a controllable photonic platform for simulating open
quantum dynamics and show that decoherence can actively reshape non-Hermitian transport.
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All authors Shu Yang, Yeyang Sun, Lingrui Hong, Yi Yang
Optics · Cross-listed from eess.SP
Low Complexity Kolmogorov-Arnold Network-based DPD for Analog RoF Fronthaul
Carlos Daniel Fontes da Silva, Tianyu Jiang, Lu Zhang et al. (+5 more)
This paper proposes and demonstrates experimentally for the first time a Kolmogorov-Arnold Network (KAN)-based digital predistortion (DPD) model, named envelope time-delay KAN (ETDKAN), for mitigating nonlinear distortions in analog
radio-over-fiber (A-RoF) systems. The ETDKAN model incorporates physical constraints of
radio-frequency (RF) nonlinear devices and, through KAN symbolization, achieves a significant reduction in computational complexity while improving interpretability. The proposed model is numerically implemented and optimized alongside multilayer perceptron (MLP) and
memory-
polynomial-based DPDs. Results show that the resulting symbolic ETDKAN (symbETDKAN) attains ACLR and EVM performance comparable to neural network-based models, while maintaining a computational complexity close to that of
memory polynomials. Experimental validation using an A-RoF system confirms the practical feasibility of the proposed approach, which resulted in a 4-5 dB reduction in ACLR in the analyzed scenario.
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All authors Carlos Daniel Fontes da Silva, Tianyu Jiang, Lu Zhang, Vjaceslavs Bobrovs, Xianbin Yu, Xiaodan Pang, Oskars Ozolins, Edson Porto da Silva
Superconductivity
High temperature transitions in Ruddlesden-Popper nickelates La$_{n+1}$Ni$_{n}$O$_{3n+1}$
P. Reiss, A. Shevchenko, P. S. Lizama et al. (+9 more)
The discovery of superconductivity at $15\,\mathrm{K}$ in the infinite-layer nickelate $(\mathrm{Nd},\mathrm{Sr})\mathrm{NiO}_2$, followed by superconductivity at $80\,\mathrm{K}$ in the Ruddlesden–Popper phase $\mathrm{La}_3\mathrm{Ni}_2\mathrm{O}_7$, has ushered in a new era of nickelate research. Despite this progress, large discrepancies between reports exist. Here, we investigate the complete series of bulk-stable $\mathrm{La}_{n+1}\mathrm{Ni}_n\mathrm{O}_{3n+1}$ compounds using a comprehensive set of experimental techniques, including PXRD, single-
crystal XRD, electron microscopy, heat capacity, differential scanning calorimetry,
magnetic susceptibility, and transport measurements, over a broad temperature range from $2$ to $1000\,\mathrm{K}$. By studying high-quality single
crystals, we identify a previously underappreciated high-temperature phase transition in Ruddlesden–Popper nickelates $\mathrm{La}_{n+1}\mathrm{Ni}_n\mathrm{O}_{3n+1}$ distinct from the one going to a tetragonal phase.
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All authors P. Reiss, A. Shevchenko, P. S. Lizama, J. Nuss, R. Dinnebier, P. A. van Aken, M. Hepting, M. Isobe, Y. E. Suyolcu, H. Takagi, B. Keimer, P. Puphal
Pattern Formation and Solitons · Cross-listed from math.DS
On the independence of the slow and fast scales in multiple-scale expansions, with application to Van der Pol's equation
Gregory Kozyreff and John R. King
When implementing the method of multiple scales, one is traditionally instructed to treat the slow and fast time scales as if they were independent. Despite the intuitive motivation and the effectiveness of this perturbation method, one cannot failt to notice that these two scales relate to the same unique variable, so independence can only be formal. How sensible is it, then, to split a variable asymptotically into two (or more) independent ones? In this paper, we elucidate this issue with Van der Pol's equation, one of the simplest weakly nonlinear oscillators, as well as a simple example of a
Hopf bifurcation. The discussion involves carrying the multiple-scale analysis up to arbitrarily large order and dealing with the divergent character of the resulting asymptotic series. Using the technique of optimal truncation, we re-connect the two scales. Specifically, we show that an initial translation of the fast coordinate leads to a non-trivial, exponentially small, phase shift that depends on the slow coordinate. This phase shift breaks the independence of the slow and fast scales and is found to result from the nonlinearity. Numerical simulations confirm its existence, as well as the predicted scaling. The calculation is carried out in sufficient detail to provide confidence in the generality of our result, both in its essence and in its form. In particular, we find strong indications that a
Hopf bifurcation with a quadratic nonlinearity would lead to the same phenomenon, but with a larger magnitude.
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High Energy Astrophysical Phenomena
Gamma-ray Bursts and Kilonovae from Gravitational Wave Events
Alberto Colombo, Marcello Giroletti, Susanna D. Vergani et al. (+1 more)
The detection of gravitational waves (GWs) from binary black holes in 2015 and the joint GW-electromagnetic (EM) observation of the binary
neutron star merger GW170817 set a milestone in the multimessenger era in astrophysics. After four observing runs by the LIGO, Virgo, and KAGRA interferometers, a new cycle is planned for 2028, paving the way for next-generation detectors in the 2030s – such as the Einstein
Telescope,
Cosmic Explorer, and LISA. The prospects for joint GW-EM studies, including kilonova searches in wide optical surveys, are vast but demanding. In the
radio domain, connected interferometers and VLBI arrays have already proven essential in constraining the ejecta properties of GW170817.
Radio emission from gamma-ray burst (GRB) afterglows, whether on- or off-axis, remains detectable for very long time, making
radio observations the most effective method for identifying and tracking GW merger counterparts. These observations enable precise characterization of system
evolution, detailed probing of GRB jet structures, and possible detection of misaligned jets once their velocity becomes non-relativistic. Even in its initial configuration (AA*), the SKAO will provide the sensitivity and field of view needed to complement GW counterpart searches during O5 and beyond, offering unmatched capabilities for long-term monitoring. Furthermore, independent of the GW detections, SKAO will enable population studies of the properties of both long (produced by the collapse of massive
stars) and short (produced by the merger of
neutron stars) GRBs, of their jets and of their environment. We present an overview of this evolving observational landscape and of the key scientific questions SKAO will address.
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All authors Alberto Colombo, Marcello Giroletti, Susanna D. Vergani, Lauren Rhodes
General Relativity and Quantum Cosmology
Terrestrial Sagnac delay in scalar-tensor-vector-gravity
R. Kh. Karimov, R. N. Izmailov and K. K. Nandi
The scalar-tensor-vector-
gravity (STVG), a prototype of modified
gravity developed by Moffat, can correctly explain
galaxy rotation curves, cluster dynamics, Bullet Cluster phenomena and cosmological data without invoking the observationally elusive general relativistic (GR) dark matter. Further, recent observations of
neutron star masses are shown to defy some GR predictions, whereas STVG turns out to be more consistent with those observations. These successes indicate that STVG could be a potential candidate for a new theory of
gravity. However, an important question concerns the possible range of values of the STVG dimensionless parameter $\alpha$ imposed by various physical scenarios. In the literature, the range $0.03<\alpha <2.47$ corresponding to different central source masses has been suggested. We show here that the $\alpha$ can be considerably constrained into the range $0<\alpha<10^{-5}$ assuming that the updated GPS fluctuation does not exceed the $\alpha$-dependent correction to the terrestrial Sagnac delay.
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Optics
In-plane vector-field imaging of propagating surface phonon polaritons
Richarda Niemann, Dorothée S. Mader, Gonzalo Alvarez-Pérez et al. (+9 more)
Polariton interferometry through optical near-field microscopy has become a powerful tool in nanophotonics, enabling direct spatial access to the propagation characteristics of strongly confined, evanescent polariton modes. Scattering-type near-field optical microscopy has matured as the
prime tool for such studies, yet mostly the out-of-plane components of the optical near fields are probed, owing to the elongated geometry of the nanotip. Here, we demonstrate a complementary far-field nonlinear microscopy approach which allows to selectively probe in-plane polariton field components. Accessing the full vector field is interesting when studying complex mode patterns such as
hyperbolic polaritons or skyrmions, where the in-plane field components are typically only inferred from the out-of-plane component but not measured directly. To this end, we use nonlinear infrared-visible wide-field sum-frequency generation microscopy, where the short visible wavelength of the nonlinear signal provides the high spatial resolution to access evanescent modes in the infrared. The
symmetry selection rules of the nonlinear process further enable polarization-selective imaging of both in-plane polariton field components through spatial interferometry. The concept is demonstrated experimentally using surface
phonon polaritons at the AlN-air interface launched by a gold
antenna. A simple, semi-analytical model reproduces the peculiar propagation patterns. Hyperspectral imaging with a tunable narrowband
laser further gives access to the polariton dispersion. The wide-field methodology holds high promise for in-depth and high-throughput studies of infrared nanophotonic structures.
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All authors Richarda Niemann, Dorothée S. Mader, Gonzalo Alvarez-Pérez, Ana I. F. Tresguerres-Mata, Aitana Tarazaga Martín-Luengo, Stefan Partel, Joshua D. Caldwell, Niclas S. Mueller, Martin Wolf, Javier Martín-Sánchez, Pablo Alonso-González, Alexander Paarmann
Astrophysics of Galaxies
Unveiling the roles of thermal and nonthermal processes in the ISM & IGM structure formation and evolution of galaxies with SKAO
Fatemeh S. Tabatabaei, Masoumeh Ghasemi-Nodehi, Mark T. Sargent et al. (+10 more)
Investigating the thermal and nonthermal processes in the interstellar medium (ISM) and intergalactic medium (IGM) is vital to understanding the
evolution of
galaxies over
cosmic time. Resolved observations with SKA pathfinders show that the nonthermal processes, in which
magnetic fields and
cosmic rays are involved, can decelerate the formation of massive
stars in strongly magnetized regions in nearby
galaxies. They can also contribute to the onset of winds and
outflows in
galaxies. The effects of these processes are stronger at higher
redshifts as a result of
star formation activities. The SKA Observatory will allow a major breakthrough by mapping the thermal and nonthermal processes in distant universe
galaxies, shedding light on the role of the ISM and IGM in the
evolution of
galaxies. We demonstrate this by simulating the
radio continuum and HI emission from local
galaxies back to high
redshifts. Our simulations show that the AA4 surveys will make it possible to trace the thermal and nonthermal processes of the ISM in
galaxies that are analogs to M51 and NGC6946, traced in continuum beyond
cosmic noon (z=2-3) and the gas content traced by HI beyond z=1. Both simulations and precursor observations indicate the importance of nonthermal feedback at
cosmic noon.
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All authors Fatemeh S. Tabatabaei, Masoumeh Ghasemi-Nodehi, Mark T. Sargent, Mahdiyar Mousavi-Sadr, Maryam Khademi, Eva Schinnerer, Eric J. Murphy, Elizabeth A. K. Adams, Isabella Prandoni, Cathy Horellou, Volker Heesen, Javier Moldon, Ilsang Yoon
High Energy Physics (Theory)
Dyeing form factors as amplitudes
Xinyue Li, Gang Yang and Guorui Zhu
The double copy of form factors has revealed a striking feature: poles that are spurious from the gauge-theory perspective become physical propagators in
gravity. At the same time, form factors obey hidden factorization relations on the kinematics of these poles. We explain both phenomena by introducing a dyeing procedure, which promotes the color-singlet operator, or the
Higgs particle representing it, to an adjoint massive state. The original form factor is recovered by the inverse bleaching operation, realized as a $U(1)$ decoupling of the dyed leg. In the dyed theory, these apparent spurious poles turn into ordinary physical propagators of colored amplitudes, and the hidden factorization relations follow from standard BCJ relations. Applying this framework to multiple operator insertions gives a systematic double-copy construction for multi-
Higgs amplitudes and, as a byproduct, reveals scalar-ordering sectors. We also discuss higher-length scalar operators and fermionic operators, including the dyed vector construction for $\bar{\psi}\gamma^{\mu}\psi$, as well as a loop-level example.
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Instrumentation and Methods for Astrophysics
SMR: Scheduler with Multi-Channel Map-Encoded Reinforcement Learning for Radio Telescopes
Zhenyang Huang, Na Wang, Zhiyong Liu et al. (+1 more)
Observation scheduling for large single-dish
radio telescopes is a multi-objective optimization problem: schedulers must maximize on-source scientific return under strict mechanical and environmental constraints. Previous dynamic scheduling relies on expert-designed heuristics, while existing reinforcement-learning (RL) approaches often struggle with variable-length target lists and lack an intrinsic representation of sky geometry. We present SMR (Scheduler with Map-encoded Reinforcement Learning), which projects discrete targets onto an azimuth–elevation (Az–El) grid in the local horizon frame. The resulting aligned multi-channel sky maps encode target attributes together with direction-dependent cues such as satellite-interference risk and elevation-dependent receiver gain. This representation provides an explicit spatial inductive bias and enables SMR to learn directly from the sky state. Simulations based on real catalogs and site parameters show that, compared with a tuned look-ahead greedy baseline, SMR achieves about a 10% relative improvement in time utilization by learning non-myopic scheduling strategies. In the full three-channel setting, SMR further achieves joint trade-off among efficiency, interference avoidance, and observation quality, with up to 17% higher LIER and 54% higher HGOR relative to an MLP baseline while maintaining higher utilization across both 12 h and 24 h horizons. Overall, SMR provides a simple and extensible way for data-driven single-dish scheduling.
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All authors Zhenyang Huang, Na Wang, Zhiyong Liu, Chuhao Gao
Quantum Physics
Lattice patch structure for fixed-frequency transmon quantum computer with high-fidelity CNOT gates
Chanpyo Kim, Jeongsoo Kang and Younghun Kwon
Superconducting transmon processors represent a leading platform for large-scale
quantum computing due to their high gate fidelities and scalability. However, conventional
qubit-coupler-
qubit (QCQ) architectures face critical physical and structural bottlenecks, notably frequency crowding [spectator
qubit collisions] during system scaling and inefficient mapping onto the standard surface code.To overcome these limitations, we propose a novel
lattice-patch architecture that couples four fixed-frequency transmons to a single fixed-frequency coupler.This design enhances
qubit connectivity and maps directly onto the surface-code
lattice unit [plaquette], thereby minimizing the compilation overhead associated with logical
qubit implementation. Furthermore, utilizing an entirely fixed-frequency design intrinsically eliminates susceptibility to external flux noise, ensuring robust operational stability.Multi-level numerical simulations demonstrate CNOT gate fidelities exceeding 0.98 across all six connectivity directions within the patch. Nevertheless, the complex interaction network of the four-
qubit architecture induces unintended residual phase accumulation during cross-resonance driving. This parasitic effect necessitates precise calibration, achievable via virtual $R_z$ gates [software phase updates]. Ultimately, our results establish the
lattice-patch architecture as an efficient, robust building block for future fault-tolerant
quantum computers.
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General Relativity and Quantum Cosmology
Time-domain evolution of Lorenz-gauge metric perturbations: taming the $\ell=m=1$ gauge instability
Jonathan Thornburg
Calculating the spacetime metric perturbation (MP) sourced by a small "particle" of mass $\mu M$ (with $0 < \mu \ll 1$) moving in a Schwarzschild or Kerr "background" black hole spacetime of mass $M$ is a longstanding research area in general relativity. This calculation also has an important astrophysical motivation as a major step in calculating the gravitational waves emitted by an extreme-mass-ratio inspiral system. Here I consider the specific problem of the time-domain calculation of the $\mathcal{O}(\mu)$ Lorenz-gauge MP $h_{ab}$ sourced by the particle. Decomposing the Schwarzschild-background MP into $e^{im\phi}$ modes, Dolan and Barack [Phys. Rev. D 87, 084066 (2013), arXiv:1211.4586] found that the $m=1$ time-domain Lorenz-gauge MP generically contains an unstable gauge mode which grows linearly with time. Here I demonstrate a method for computing a Lorenz-gauge time-domain
evolution which is mostly free of this gauge mode. This method computes an "orthogonalized" MP $h_{ab}^\text{ortho}$ as a linear combination of the sourced MP and a homogeneous MP $h_{ab}^\text{hom}$ (evolved in parallel with the sourced MP). The linear combination is updated "occasionally" to make $h_{ab}^\text{ortho}$ orthogonal to $h_{ab}^\text{hom}$ with respect to a chosen inner product on MPs. I show that, for a Schwarzschild-circular-orbit test case, the resulting $h_{ab}^\text{ortho}$ satisfies the $\mathcal{O}(\mu)$ Einstein equations and Lorenz gauge conditions, remains bounded as $t \to \infty$, and at late (finite) times contains only a small component of the unstable gauge mode. These results hold both with the particle modelled via MP jump conditions and with particle modelled by a "effective source". My numerical code for obtaining all of these results is included with this paper, and will be deposited in the Black Hole Perturbation Toolkit.
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Optics
Temporal wave trapping from dynamical pump pulses
T. Torres, R. Terrier, J. Fatome et al. (+3 more)
Temporal reflection in nonlinear optical fibers provides a powerful framework for manipulatinglight. In this work, we theoretically and experimentally demonstrate a novel mechanism for wavetrapping induced by the dynamical
evolution of a single high-order
soliton pulse. Experimentalmeasurements performed in a 5-km-long nonlinear dispersion shifted fiber confirm the coexistence ofreflected, transmitted, and trapped components, in excellent agreement with theoretical predictions.These results establish a simple and versatile route toward dynamic temporal waveguiding using asingle optical pulse, opening new opportunities for all-optical control and manipulation of ultrafastsignals.
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All authors T. Torres, R. Terrier, J. Fatome, B. Kibler, G. Millot, G.P. Agrawal
Mesoscale and Nanoscale Physics
Spin-orbit coupling driven topological superconductivity in twisted bilayer graphene-WSe$_2$ heterostructures
Kamalesh Bera, Arijit Saha and Tanay Nag
Commencing from the low-energy Bistritzer-MacDonald continuum model of twisted bi-layer
graphene (tBLG) with proximity-induced Ising, Rashba, and intrinsic
spin-orbit couplings (SOCs), we construct the corresponding Bogoliubov-de Gennes
Hamiltonian with conventional $s$-wave pairing and theoretically investigate the emergence of topological superconductivity in it. The latter can possibly be experimentally demonstrated in tBLG, Niobium and tungsten diselenide
heterostructures. The topological superconducting phases, bearing an effective $p$-wave pairing profile and exhibiting inverted band dispersion, are protected by a bulk gap and are topologically characterized by Chern numbers. In the absence of intrinsic SOC, variation of the twist angle and other SOC strengths yield extended gapless, trivial, and topological phases, with phase boundaries exactly matching the closing of direct band gaps. The topological regime exhibits clear band inversion in the combined particle-hole and
spin space, along with distinct Bloch localization profiles compared to the trivial phase. Including intrinsic SOC generates additional topological phases and eliminates the gapless phase, indicating the enhanced stability of the gapped topological superconducting regime in tBLG.
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