Solar and Stellar Astrophysics
Magnetic Field Stratification in Active-Region Plage from Ca II K and Ca II 8542 Å Spectropolarimetry
Iñigo Juanikorena Berasategi, Ernest Alsina Ballester, Javier Trujillo Bueno et al. (+31 more)
We investigate the height variation of the line-of-sight (LOS)
magnetic field in
solar active-region (AR) plage from the upper photosphere to the upper chromosphere using co-spatial ultraviolet (UV) and infrared (IR) spectropolarimetric observations from the Sunrise III stratospheric balloon flight. The Ca II K and Ca II 8542 Å lines provide complementary chromospheric diagnostics, while nearby Fe I lines sample photospheric layers. The LOS
magnetic field is inferred from the intensity and circular polarization profiles, applying the weak field approximation for the Ca II lines and the center-of-
gravity method for the Fe I lines. The photospheric Fe I lines reveal strong, finely structured
magnetic fields of the order of a kG. In contrast, the chromospheric Ca II diagnostics yield systematically weaker fields, typically in the $\sim$ 100-400 G range, with a more diffuse spatial distribution.
Magnetic field maps inferred from the Ca II K line, formed higher in the chromosphere, are smoother and more extended than those derived from the Ca II 8542 Å line, which samples lower heights. We find that the magnetized area increases by a factor of $\sim$ 2 from the photosphere to the chromosphere. These results provide direct quantitative evidence that
magnetic fields in AR plage weaken and expand with height, evolving from compact kG photospheric concentrations into weaker and more spatially extended structures in the upper chromosphere.
Read the full abstract ▾
All authors Iñigo Juanikorena Berasategi, Ernest Alsina Ballester, Javier Trujillo Bueno, Francisco A. Iglesias, Yusuke Kawabata, Juan Sebastián Castellanos Durán, Masahito Kubo, Alex Feller, Yukio Katsukawa, Sami K. Solanki, Jose Carlos del Toro Iniesta, Andreas Lagg, Achim Gandorfer, Pietro Bernasconni, Thomas Kerkefeld, Tino L. Riethmüller, Yoshihiro Naito, Alberto Álvarez-Herrero, H. N. Smitha, David Orozco Suárez, Bianca Grauf, Michael Carpenter, Alexander Bell, Valentín Martínez Pillet, Francisco Javier Bailén, Julian Blanco Rodríguez, Edvarda Harnes, Johannes Hölken, Ryohtaroh T. Ishikawa, Takuma Matsumoto, Takayoshi Oba, Azaymi L. Siu-Tapia, Hanna Strecker, Dušan Vukadinović
High Energy Physics (Experiment)
Comment on the preprint: First Limits on Axion Dark Matter from a DALI Prototype arXiv:2603.21951
Erika Garutti, Anton Ivanov and Béla Majorovits
We report on an independent assessment of the sensitivity of the DALI setup to
axion-like particle (ALP) dark matter, as described in [1]. Our analysys is based on the information provided in the preprint and using the formalism developed within the MADMAX collaboration. We do not identify any mode below 12 GHz with significant coupling to the
axion field to account for the reported sensitivity. We provide recommendations for assessing the
axion coupling of electromagnetic modes in dielectric haloscope experiments.
Read the full abstract ▾
Atmospheric and Oceanic Physics
Meteosat Third Generation imagery improves CNN-based SSI retrieval
Gordei Pribõtkin, Piia Post and Velle Toll
Accurate Surface
Solar Irradiance (SSI) estimation is increasingly important for photovoltaic energy monitoring and
forecasting. The recently introduced Meteosat Third Generation (MTG) satellite constellation provides imaging data with higher spatial resolution compared to the Meteosat Second Generation (MSG) satellite constellation, but its benefits for machine-learning-based SSI
retrieval are not well established. We compare multi-resolution convolutional neural network models for 10-minute SSI
retrieval over Northern Europe (Estonia) using either MSG/SEVIRI or MTG/FCI satellite imagery. We evaluate model performance against ground-based pyranometer measurements from eight Estonian meteorological stations using site-based cross-validation with a temporally independent test year and multiple training seeds. Model performance is also compared with the SARAH-3 physics-based satellite SSI product. The FCI-only model significantly outperformed the SEVIRI-only model under overcast and cloudy conditions, reducing RMSE by 5.1 W/m^2 and 6.5 W/m^2, respectively. However, under partly cloudy or clear skies, there was no statistically significant difference in RMSE between the FCI-only and the SEVIRI-only models. In all-sky conditions, the RMSE of the FCI-only model was 5.1 W/m^2 lower on average, but this difference was not statistically significant after Bonferroni correction. Compared with physics-based SARAH-3, the FCI-only model yielded skill scores of 28% under overcast conditions, 19% under cloudy conditions, and 17% overall. Furthermore, both models underperformed SARAH-3 in clear-sky conditions. These results show that higher-resolution MTG/FCI imagery improves CNN-based SSI
retrieval when clouds dominate irradiance variability, but also indicate that higher resolution alone is insufficient to address clear-sky limitations in machine-learning-based SSI
retrieval.
Read the full abstract ▾
Instrumentation and Methods for Astrophysics
Focal-Plane Diagnostics of Atmospheric and Dome-Induced Turbulence: Exploring techniques and applications
Begoña García-Lorenzo, Seifeldin Abouelella, Kabir Baig et al. (+8 more)
Atmospheric
turbulence remains the dominant source of image degradation in ground-based astronomy. Its impact depends not only on the integrated
turbulence strength but also on the wavefront spatial-coherence outer scale (\LO) and on
turbulence generated within the
telescope enclosure (dome seeing). While seeing, coherence time, and related parameters are routinely monitored at major observatories, measurements of \LO\ and dome-induced
turbulence remain sparse, limiting our ability to predict image quality and to construct accurate point-spread function (PSF) models. Building on methodology recently developed for seeing-limited integral-field spectroscopic (IFS) data, we present a series of complementary studies showing how spatial information encoded in standard observations can be used to diagnose both atmospheric and dome
turbulence. We investigate the feasibility of extending these techniques beyond IFS observations to other seeing-limited instruments through the analysis of wavelength-dependent spatial profiles. We also present the development of data-driven three-dimensional PSF models based on atmospheric statistics for the reconstruction of seeing-limited IFS observations. These results show that widely available seeing-limited scientific observations, both from archival data and routine observatory operations, can provide meaningful and operationally useful constraints on key
turbulence parameters and on the spectral behavior of dome seeing, complementing dedicated site-testing instrumentation. The resulting
turbulence diagnostics have direct applications to PSF modelling, image reconstruction, image-quality prediction, and the optimization of future ELT operations.
Read the full abstract ▾
All authors Begoña García-Lorenzo, Seifeldin Abouelella, Kabir Baig, Zenaida García Rodríguez, Kshitij Ghimire, Moisés Pulido Torres, Alejandro Trujillo Ramos, Jose A. Acosta-Pulido, Julio A. Castro-Almazán, Donaji Esparza-Arredondo, Antonio Eff-Darwich
Solar and Stellar Astrophysics
Back Reaction of the Untwisting Solar Corona Scars Sunspots
Chen Xing, Xin Cheng, Guillaume Aulanier et al. (+1 more)
The
evolution of
magnetic fields in the tenuous
solar corona is predominantly governed by the motions of the underlying dense photosphere. Despite, coronal
magnetic restructuring driven by
magnetic reconnection between interacting coronal fields can sometimes react backwards to change photospheric
magnetic fields. However, the mechanism of reactions remains undetermined. Here, we report the discovery of a back-reaction phenomenon: the untwisting of coronal loops that become twisted during reconnection in an eruption results in enhanced currents at the boundary of their footpoint away from the eruption, manifesting as the growth of a sunspot scar. It is revealed to arise from the Alfvenic reverse transfer of
magnetic twist from the corona to the lower atmosphere, thanks to joint space observations and a magnetohydrodynamics simulation. These findings provide a viable and quantitative interpretation for the majority of puzzling photospheric changes associated with coronal mass ejections and/or
flares and warn for unexpected
magnetic field evolutions in sunspots and starspots.
Read the full abstract ▾
All authors Chen Xing, Xin Cheng, Guillaume Aulanier, Mingde Ding
Strongly Correlated Electrons
Thermal spin transport in easy-planar $d$-wave altermagnets controlled by magnetic field
Yuliia I. Gusieva, Kostiantyn V. Yershov, Jeroen van den Brink et al. (+1 more)
Altermagnets constitute a novel class of collinear
spin-compensated materials in which
magnon branches are
spin-split even in the non-relativistic limit. The latter is the result of a more complex
symmetry operation (compared to conventional antiferromagnets) that connects the two sublattices. Altermagnetic splitting strongly affects the
magnon transport properties, leading, in particular, to the thermal
magnon splitter effect in easy-axial $d$-wave altermagnets. Whether this effect also appears in easy-planar systems is not obvious, since the
magnon branches do not carry a constant
magnetic moment in this case. Here, we consider the easy-planar $d$-wave altermagnet of a rutile-type, e.g., NiF$_2$, and demonstrate the emergence of the altermagnetically generated
magnon magnetic moment, which is momentum-dependent and possesses $d$-wave
symmetry. This then leads to the
spin-splitter effect, i.e., the emergence of a
magnon-driven
spin current (the flow of
magnetic moment) in response to the applied temperature gradient. We also demonstrate that the corresponding thermal
spin conductivity can be effectively tuned by an external
magnetic field perpendicular to the easy plane.
Read the full abstract ▾
All authors Yuliia I. Gusieva, Kostiantyn V. Yershov, Jeroen van den Brink, Volodymyr P. Kravchuk
Earth and Planetary Astrophysics
Statistical Constraints on Albedo Structure in Asteroid Families from NEOWISE Measurements
Murat Kaplan
Interpreting asteroid family albedo distributions as compositional signatures requires distinguishing intrinsic structure from measurement artifacts, rarely quantified. We analyze 102 families using NEOWISE data with AKARI cross-validation and SDSS-based photometric checks, establishing detection limits for bimodality and quantifying selection bias in size-albedo correlations. We work primarily in logarithmic albedo space (log10 pV), which more accurately resolves the asymmetric dark/bright mixtures characteristic of compositionally mixed families. NEOWISE albedos are error-dominated: measurement uncertainties rival observed spreads (median sig_obs/sig_err ~ 0.99 in log space). AKARI cross-validation on 1,498 matched asteroids confirms NEOWISE measurements broadly (slope = 1.03, R^2 = 0.76, median |dpV| = 0.015), with a known spectral-type-dependent offset of +11%. Genuine bimodality meeting conservative criteria is found in 6 of 102 families (5.9%); the two most secure detections (Nysa-Polana, Juno) are recovered in both linear and logarithmic albedo, the other four only in log. Monte Carlo simulations show that a dark/bright bimodality at the characteristic separation (dmu ~ 0.64 dex) is recovered with high probability for the intrinsic scatter present in the families, so the low rate reflects genuine compositional homogeneity rather than limited sensitivity. Size-albedo correlations largely reflect magnitude-limited selection bias: only 2 of 63 families survive diameter-limited controls. These results indicate that many apparent compositional trends in family-level NEOWISE analyses are statistically indistinguishable from measurement scatter and selection effects within current uncertainties. Our detection limits and bias tests provide quantitative criteria for deciding when compositional inferences from NEOWISE family albedos are statistically defensible.
Read the full abstract ▾
Optics
Spin-canting-induced Giant Nonlinear Optical Magnetochirality in a 2D Ferrotoroid
Shian Xia, Sheng Liu, Wenhe Jia et al. (+9 more)
Achieving magnetically switchable
chiral light emission is an important goal for 2D opto-spintronics. However, conventional strategies face a fundamental trade-off between dynamic tunability and polarization contrast. Nonlinear optics, particularly the emerging mechanism of
chiral second-harmonic generation (SHG), offers a distinct strategy to bypass this restriction, yet its experimental realization remains elusive due to stringent
symmetry requirements. Here, we report
giant nonlinear optical magnetochirality in a centrosymmetric 2D ferrotoroid,
bilayer (2L) CrSBr. We reveal that a field-induced
spin-canting state breaks the parity-time (PT)
symmetry of the unperturbed
antiferromagnetic (AFM) ground state, activating a
spin-chirality-driven i-type susceptibility. The coherent interference between this emergent i-type and intrinsic c-type SHG susceptibilities generates a macroscopic circularly polarized SHG signal whose helicity is magnetically switchable. Leveraging this sensitive mechanism, we uncover remanent
magnetic states after field saturation that evade conventional linear probes. By exploiting the non-
volatility of these states, we demonstrate magneto-optical
memory and logic operations. Our work establishes a general
symmetry-driven strategy for tailoring nonlinear magnetochirality, while providing a sensitive optical probe for subtle
spin textures in the 2D limit.
Read the full abstract ▾
All authors Shian Xia, Sheng Liu, Wenhe Jia, Fanglu Qin, Xuanji Wang, Haixiang Luo, Yue Sun, Vanessa Li Zhang, Wenduo Chen, Jiazheng Qin, Cheng-Wei Qiu, Ting Yu
Solar and Stellar Astrophysics
Cataclysmic variables from SRG/eROSITA: new systems from eRASS1
A.D. Schwope, J. Brink, D.A.H. Buckley et al. (+12 more)
(abridged) Aims. We aim to generate large samples of CVs selected from the SRG/eROSITA surveys to address fundamental questions about binary
evolution, the role of
magnetic fields in CV
evolution and their contribution to the
Galactic Ridge X-ray Emission (GRXE). Methods. We have trained a Random Forest (RF) classifier based on combined X-ray and optical properties to select CV candidates from the first eROSITA X-ray all-sky survey (eRASS1). Follow-up spectroscopy to securly identify the objects was performed on a subset of the selected candidates using
telescopes at the Northern and the Southern hemisphere. Newly identified CVs were further analyzed to determine their likely subtype with the help of dedicated follow-up photometry, spectroscopy and archival resources. Results. We have identified 156 CVs of almost all subtypes covering a wide range of distances (between 170 pc and several kpc), absolute magnitudes (G= 4.5-12) and X-ray luminosities (log LX (0.2-2.3 keV)= 29.6-33.3 erg/s). For most objects, the nature as a CV is reported here for the first time. For 40 objects periods were determined, which were regarded as their likely orbital periods. These range from 79.2 min, at the CV minimum period, to almost 22 hours. Seven objects were found to be eclipsing, a lower limit to the actual number due to the current lack of dedicated follow-up observations. A further five objects show cyclotron or Zeeman features, that allowed to determine their field strengths. A soft component was found in 14 CVs, all were regarded being
magnetic. The sample comprises X-ray luminous objects, excellent candidates for being new Intermediate Polars, that are thought to be main contributors to the GRXE. The new method of selecting CVs from eRASS1 was found to be superior to other methods described in the literature ...
Read the full abstract ▾
All authors A.D. Schwope, J. Brink, D.A.H. Buckley, V. A. Cúneo, S. Friedrich, S. Hernández-Díaz, K. Knauff, J. Kurpas, G. Lamer, S.B. Potter, K.G. Pradeep, M.R. Schreiber, B. Stelzer, J. R. Thorstensen, D. Tubin-Arenas
Quantum Physics
Deterministic QKD source robust against side-channel attacks
Kiyoshi Tamaki, Marcos Curty, Akihiro Mizutani et al. (+1 more)
Quantum key distribution (QKD) is secure in principle, but practical security can be undermined by discrepancies between real devices and the idealized models assumed in security proofs. Source side channels, including those exploited by Trojan-horse attacks, are particularly detrimental: neglecting them compromises implementation security, whereas accounting for them reduces performance. Here we propose a QKD source that is intrinsically robust against side-channel attacks. Unlike existing passive and modulator-free schemes, it requires neither post-selection of the emitted pulses nor devices with a perfect extinction ratio to suppress side channels, and it does not introduce correlations between the intensity and the encoded bit or basis. Consequently, under idealized source assumptions commonly adopted in proposals for existing schemes, conventional decoy-state security analyses apply directly, yielding substantially higher key rates. Our proposal appears to be within reach of current technology and therefore provides a clear and practical path toward implementation-secure QKD.
Read the full abstract ▾
All authors Kiyoshi Tamaki, Marcos Curty, Akihiro Mizutani, Álvaro Navarrete
Quantum Physics · Cross-listed from math.FA
Poset-refined majorization relations
Alexander E. Guterman and Michael M. Wolf
Several classical majorization relations for sums or products of
matrices involve a majorizing vector of perfectly aligned
eigenvalues or singular values. By relaxing the order of
alignment to a partial order, we show that the majorization can be strengthened, provided the change-of-basis
matrices admit an LU-approximation with respect to this partial order. In this way, we obtain refined versions of Ky Fan's majorization relations, Horn's log-majorization relation, and von Neumann's trace inequality. As an application, we give a short proof of the separable Ky Fan majorization relation for an arbitrary number of tensor factors and extend it to a sum of tensor products of arbitrary
matrices. Further applications concern majorization relations for sums of (anti-)symmetric powers and for products of Kronecker sums.
Read the full abstract ▾
Quantum Physics
Slow-light-enhanced Atomic Frequency Comb Quantum Memory in Stoichiometric EuCl$_3 \cdot$ 6D$_2$O
Zongfeng Li, Wanting Xiao, Mucheng Guo et al. (+3 more)
Rare-earth-doped
crystals are promising candidates for
quantum storage, yet their performance in free-space configurations is fundamentally restricted by low optical depth. Here, we demonstrate high-efficiency
quantum storage in a stoichiometric EuCl$_3 \cdot$ 6D$_2$O
crystal, which intrinsically provides high optical density without the complexity of cavity implementation. We show that in this high-density regime, the system exhibits significant slow-light-like effects, including dispersion-induced echo delays and finesse-dependent echo intensity modulation. We develop a unified theoretical framework showing how absorption and dispersion work in concert to mediate echo generation. We achieve storage efficiencies of 42.9% for classical light and 34.4% for weak coherent pulses, alongside 90% efficiency for slow-light storage. These findings validate EuCl$_3 \cdot$ 6D$_2$O as a robust platform, establishing a viable pathway for scalable solid-state
quantum memory.
Read the full abstract ▾
All authors Zongfeng Li, Wanting Xiao, Mucheng Guo, Shuping Liu, Fudong Wang, Manjin Zhong
Astrophysics of Galaxies
Angular Momentum Evolution from Core to Disk Scales in the Early Phase of Star Formation: Constraints from HH 212, HH 211, and B335
Chin-Fei Lee
I investigate the angular momentum
evolution from core to disk scales in the early phase of
star formation using three protostellar systems: HH 212, HH 211, and B335. Observations show that the specific angular momentum follows a power-law dependence at core scales and transitions to an approximately constant value at smaller radii, indicating dynamical collapse in the inner envelope. I model this behavior using the inside-out collapse solution of Shu (1977) and its rotating extension, the Terebey-Shu-Cassen model, including modest
magnetic effects through a flattened, magnetized core. I find that the observed angular momentum profiles in all three sources are broadly consistent with an inside-out collapse scenario with approximate conservation of specific angular momentum in the collapsing region. The inferred collapse ages and mass infall rates yield total masses accreted onto the center that are broadly consistent with the central masses derived from kinematics, allowing for a fraction of the material to be ejected by jets and winds. The predicted midplane densities at typical radii, including the effect of
magnetic flattening, are also consistent with observational estimates. The three systems exhibit a similar pattern of angular momentum
evolution despite large differences in the magnitude of their specific angular momentum. In particular, the small disk in B335 can be naturally explained by its lower initial specific angular momentum, although alternative explanations, such as
magnetic braking or different initial conditions, cannot be excluded. These results suggest that inside-out collapse, with modest
magnetic modification, provides a plausible first-order description of angular momentum
evolution from core to disk scales in the early phase of
star formation.
Read the full abstract ▾
Physics and Society
Inferring Coupling Strength from the Kuramoto Order Parameter
Gug Young Kim, Hoseok Sul, Jee Woong Choi et al. (+1 more)
Accurately estimating the coupling strength in oscillator networks from macroscopic observations is essential for predicting synchronization transitions. We consider the inverse problem of reconstructing the unknown coupling strength $K$ in the globally coupled Kuramoto model from scalar observations of the macroscopic order parameter $R(t)$, assuming that the natural frequencies and the initial phase configuration are known. After initialization, individual phase trajectories are treated as hidden, and only the scalar order parameter is observed. We employ an extended Kalman filter with an augmented state representation that recursively estimates the coupling strength from observations of $R(t)$. By exploiting the mean-field structure of the globally coupled Kuramoto model, the covariance prediction step can be computed efficiently, substantially reducing the computational cost. Numerical simulations demonstrate that the proposed
estimator accurately reconstructs the coupling strength and remains stable even when $R(t)$ is small and strongly fluctuating.
Read the full abstract ▾
All authors Gug Young Kim, Hoseok Sul, Jee Woong Choi, Seung-Woo Son
General Relativity and Quantum Cosmology
Quartic Scalar Clouds on Fixed Kerr Backgrounds
Hendrik Mennenga
We study stationary nonlinear clouds of a complex scalar field on fixed Kerr and Schwarzschild backgrounds, with an unbounded scalar potential. On Kerr backgrounds we find finite-amplitude Q-clouds satisfying the synchronisation condition $\omega=m\Omega_H$. They occupy two-dimensional regions of the ($\Omega_H,M_K$) plane and reduce to the corresponding linear clouds as the scalar field amplitude tends to zero. The quartic domain can continue to $\Omega_H=0$, where both the synchronised frequency and the Noether charge vanish and the solutions become static nonlinear scalar clouds on a fixed Schwarzschild background. We also compute the existence domain for a normalised,
axion-inspired cosine potential.
Read the full abstract ▾
High Energy Physics (Theory)
Quantum Trigonometric Spin Ruijsenaars-Schneider Models from $K$-theoretic Coulomb Branches
Gleb Arutyunov, Lukas Hardi and Rob Klabbers
We quantize the trigonometric
spin Ruijsenaars-Schneider model of $N$ particles each with $\ell$
spin states using the recently developed description of the classical model in terms of the $K$-theoretic Coulomb branch of the 4d $\mathcal{N}=2$ quiver gauge theory for the necklace quiver with $\ell$ nodes of rank $N$. The main algebraic tool is an
algebra of $L$-operators derived from abelianized monopole operators of minuscule charge, which turns the necklace quiver into an integrable
spin chain by producing a family of commuting
Hamiltonians. We show that the lowest
Hamiltonian coincides with the first mode of the
quantum determinant of the horizontal
quantum loop
algebra living inside the $K$-theoretic Coulomb branch
algebra, whose Bethe subalgebra generates a maximal family of commuting
Hamiltonians. Finally, we derive the commutation relations and
quantum equations of motion of the quantized physical
spin variables.
Read the full abstract ▾
Mathematical Physics · Cross-listed from math.SP
Spectral problems on open-book structures with singularly perturbed density: the limit operator
Yuriy Golovaty, Delfina Gòmez and Maria-Eugenia Pèrez-Martìnez
We investigate the spectral problem arising in the asymptotic analysis of vibrations of open-book structures with a mass density perturbed near the binding. The limiting problem is go\-ver\-ned by a non-self-adjoint block operator
matrix coupling the macroscopic and microscopic components of the model. We describe the spectrum of this operator and completely characterize its eigenspaces and root subspaces. We further prove that generalized eigenvectors form chains of length at most two and derive an explicit criterion for the existence and number of Jordan blocks. This model provides a nontrivial example of a family of self-adjoint operators acting in varying
Hilbert spaces whose limiting spectral behavior is described by a non-self-adjoint operator with a genuine Jordan structure.
Read the full abstract ▾
Quantum Physics
Scaling theory of decoherence in Dicke superradiance
Nico S. Bassler, Julian Lyne and Javier Cuerda
The survival of many-body coherence depends on the competition between correlation buildup and decoherence. In Dicke superradiance, collective emission builds up correlations, producing a peak intensity scaling as $N^2$ for $N$ emitters. We develop a scaling theory including local dephasing and spontaneous emission and obtain fully collective, partially collective, and independent-emitter scaling regimes. The boundary of the fully collective regime defines a continuous phase transition in a transient observable. Local decoherence can prevent $N^2$ scaling despite increasing $N$.
Read the full abstract ▾
Strongly Correlated Electrons
Many-Body Amplification of Ligand Instabilities Driving Verwey-Type Transitions in Altermagnet CsCr$_2$S$_2$O
Xiuhua Chen and Yilin Wang
Altermagnet CsCr$_2$S$_2$O undergoes a Verwey-type metal-to-
insulator transition (MIT), accompanied by a
lattice distortion and stripe charge order on the Cr sublattice. Intriguingly, the atomic distortions occur exclusively at the ligand sites rather than the Cr sites, leaving the origin of the pronounced Cr charge disproportionation unresolved. Using density functional theory plus dynamical mean-field theory (DFT+DMFT) calculations, we identify an orbital-selective Mott state in which the correlated metallic $d_{yz}$ orbital governs the low-energy physics. We show that S-site distortions produces only a small bare charge asymmetry between the Cr sublattices through Cr-$d_{yz}$–S-$p$ hybridization. Dynamical electronic correlations, however, dramatically amplify this asymmetry, producing pronounced differentiation in both the charge occupancy and correlation strength of the $d_{yz}$ orbitals. The resulting site-dependent
spin polarization ultimately drives the MIT. In contrast, replacing S with Te substantially weakens this correlation-amplification effect and preserves a metallic state. Our work reveals a hidden, correlation-amplified feedback loop between ligand instabilities and electronic
symmetry breaking in this altermagnetic family, highlighting ligand engineering as an effective route toward robust metallic altermagnetism.
Read the full abstract ▾
Materials Science
Mapping the influence of symmetry breaking in structure-property relationships of ABO$_3$ perovskites
Panupol Untarabut, Sylvian Cadars, Fabien Pascale et al. (+5 more)
Perovskite
oxides have emerged as an important class of material with promising energy applications owing to their compositional and structural flexibility, which enables stabilization of both low- and high-
symmetry phases and gives rise to diverse physical properties. Under ambient conditions, most perovskites adopt low-
symmetry structures characterized by octahedral tilting and B-site displacements. Despite their importance, computational studies have largely focused on the ideal cubic phase as modeling these distortions remains challenging. The difficulty stems from the absence of a quantitative framework capable of capturing composition-dependent distortions that can occur through multiple non-equivalent atomic displacement modes, often requiring computationally expensive large supercells to explore the structural landscape. Consequently, the influence of distortions on the stability and properties of low-
symmetry perovskites remains insufficiently understood. In this work, we develop an efficient computational framework for the rapid construction and exploration of composition-dependent structural models across both low- and high-
symmetry phases. Using $\textit{symmetry constrained templates}$ and $\textit{unconstrained supercell templates}$, we systematically investigate 15 representative compositions to uncover relationships between composition, supercell size and shape, and distortion patterns. Based on these insights, we propose a robust and computationally inexpensive protocol for rapid structural exploration and assess the influence of different distortion modes on key physical properties.
Read the full abstract ▾
All authors Panupol Untarabut, Sylvian Cadars, Fabien Pascale, Sébastien Lebègue, Olivier Masson, Samuel Bernard, Assil Bouzid, Santanu Saha
Mathematical Physics · Cross-listed from math.OA
Unification of Quantum Graph Properties
Gian Luca Spitzer
Many properties of classical graphs are defined in terms of subsets of the vertex set. Examples include connected components, which are subsets $X \subseteq V(G)$ such that $X \times X^c$ and $E(G)$ are disjoint, or independent sets, for which $X \times X$ and $E(G)$ are disjoint. Direct generalisations of these definitions to
quantum graphs are difficult to achieve, since the natural notion of subsets of a
quantum set is much too rigid. As a consequence, approaches to generalising these classical properties to the
quantum setting have been eclectic. In some cases, multiple inequivalent definitions of the same notion are in use. We introduce a natural and well-motivated alternative definition of subsets of a
quantum set. Building on this, we propose unified definitions of
quantum graph properties as straightforward generalisations of the classical definitions. We recover this way the established notions of colourings and connected components. For independent sets and cliques, our approach suggests variations that diverge from existing definitions, but address some of their counterintuitive properties. We nevertheless show how to recover an important existing definition of independent sets in our framework.
Read the full abstract ▾
Physics and Society
Breathing chimera states from purely triadic interactions
Sudo Yi, Gug Young Kim, Mi Jin Lee et al. (+2 more)
Chimera states, characterized by the coexistence of synchronized and desynchronized dynamics in identical oscillators, are typically studied in systems with pairwise interactions. Recent studies have shown that purely higher-order interactions can support chimera states. Here, we show that breathing chimera states arise in a model governed solely by a triadic phase interaction, whose intrinsic $\pi$-
symmetry permits bimodal phase distributions. We construct a bimodal Ott-Antonsen reduction that incorporates an asymmetry parameter via prescribed asymmetric initial conditions, thereby achieving an exact low-dimensional description of the macroscopic dynamics. This allows us to derive an analytic condition for the emergence of chimera states and identify a bifurcation to a breathing chimera regime characterized by persistent oscillations. Furthermore, the reduced dynamics can be expressed as a Riccati-type equation, providing a
geometric interpretation of the chimera state as a closed periodic orbit in the complex plane. Our results establish purely triadic coupling as a minimal higher-order mechanism for chimera formation and provide a tractable framework for studying
symmetry-broken collective dynamics in systems dominated by many-body interactions.
Read the full abstract ▾
All authors Sudo Yi, Gug Young Kim, Mi Jin Lee, S.-W. Son, B. Kahng
Solar and Stellar Astrophysics
The physical origin of the maximum stellar size
Gautham N. Sabhahit and Jorick S. Vink
One might expect the most massive
stars to also be the largest by size, yet they are not, and this has puzzled astronomers for decades. The Eddington limit sets an upper bound to
stellar mass through the balance between radiation pressure and
gravity, but a second empirical boundary on
stellar radius has equally far-reaching consequences for modern Astrophysics: it affects the black-hole masses and merger rates inferred by LIGO and Virgo, determines whether a
star remains a hot, compact ionising source or inflates into a cool supergiant, and thereby shapes how spectra of distant, unresolved
stellar populations are interpreted. Half a century ago, this radius limit was shown to trace a characteristic kinked shape in the Hertzsprung-Russell diagram known as the Humphreys-Davidson limit, yet a predictive, first-principle physical explanation has remained elusive. Here we show that this kink is the evolutionary manifestation of a transition from classical
stellar outflows to an Eddington-enhanced mass-loss regime implemented self consistently in evolutionary models. With our models accurately reproducing the empirical constraints on the radii of the most massive
stars, we now have a framework that can be incorporated into binary population synthesis, black-hole mass predictions, gravitational-wave event rates, and the interpretation of high-
redshift James Webb spectra.
Read the full abstract ▾
Solar and Stellar Astrophysics
Hydrodynamical mass-loss rates for Very Massive Stars II. New theoretical mass-loss predictions at solar metallicity (Z = 0.02)
Gautham N. Sabhahit, Jorick S. Vink and Andreas A. C. Sander
The evolutionary pathways and ultimate fates of very massive
stars are governed primarily by mass loss through radiatively driven winds. We present a new theoretical mass-loss prescription for (very) massive
stars, capturing the complex dependence on the Eddington parameter $\Gamma_e$, luminosity, temperature, and hydrogen abundance. We calculated an extensive grid of 178 hydrodynamically self-consistent wind-atmosphere models in non-local thermodynamic
equilibrium using the PoWR-HD code, predicting wind properties such as the mass-loss rate and terminal velocity self-consistently. The grid spans masses $M_*$ = 16-500 Msun, luminosities $\log(L_*/L_\odot) = 5.5-6.8$, inner boundary temperatures $T_* = 12-50$ kK, and hydrogen mass fractions X = 0.01-0.9, at a fixed
metallicity Z=0.02. We confirm the presence of a mass-loss kink in the $\dot{M}-\Gamma_e$ relation across the explored parameter space. The kink marks the transition from a shallow scaling ($\sim 2$) at low $\Gamma_\mathrm{e}$ for optically thin O-
star winds to a steeper scaling ($\sim 10$) for optically thick winds at high $\Gamma_e$. We derive comprehensive fitting relations capturing both the kink behaviour and two bistability jumps arising from iron ionisation changes, and provide auxiliary relations for implementation into
stellar evolutionary calculations. Our prescription correctly reproduces the model-independent transition mass-loss rate in the Arches Cluster, confirming the accuracy of our predicted rates at the O-to-WNh transition. Application of our recipe to the zero-age main sequence provides excellent agreement with recent empirical $\dot{M}-\Gamma_e$ relations obtained for a wide range of temperatures and Eddington parameters. We provide a physically motivated, continuous, and empirically anchored mass-loss recipe for (very) massive
stars, suitable for
stellar evolution calculations in the 20-500 Msun range.
Read the full abstract ▾
General Relativity and Quantum Cosmology
High-accuracy drivers to simulate black hole binaries beyond general relativity with the fixing-the-equations approach
Guillermo Lara, Harald P. Pfeiffer, Nils Deppe et al. (+9 more)
We implement the "fixing-the-equations" approach [Phys.Rev.D 96 (2017) 8, 084043] in spectre, an NR code using a pseudo-spectral discontinuous Galerkin scheme, to produce long and accurate NR waveforms in the well-known shift-symmetric version of scalar Gauss-Bonnet (sGB)
gravity. To achieve this, we introduce a new family of comoving driver equations that exploits the approximate
symmetries of quasicircular binary systems and is designed to recover the exact (quasi-)stationary solutions of the fully-coupled theory. We validate our single black hole (BH) solutions against analytic predictions and show that, even for binary BHs in the early inspiral, the intrinsic BH quantities are relatively insensitive to the timescales entering the driver equation.
Attention is given to the prescription of driver equations for tensors, for which we give an example of how treating tensor components as scalars can lead to undesired behaviour over long timescales, including spurious growth of the BH
spins. A more appropriate generalization to the tensor case is given for the comoving driver, which is shown to avoid these issues. Overall, our implementation leverages state-of-the-art methods for eccentricity reduction and wave extraction with Cauchy Characteristic
Evolution to simulate systems with eccentricity $\lesssim 10^{-3}$. We obtain waveforms with phase errors $\lesssim \mathcal{O}(1) \, \mathrm{rad}$ over almost 40 GW-cycles, which naturally incorporate
memory contributions.
Read the full abstract ▾
All authors Guillermo Lara, Harald P. Pfeiffer, Nils Deppe, Lawrence E. Kidder, Geoffrey Lovelace, Sizheng Ma, Alexandra Macedo, Jordan Moxon, Kyle C. Nelli, Mark A. Scheel, William Throwe, Nils L. Vu
Materials Science
PASS: Perturbation augmented space group structure sampling for transferable Fe-O machine learning interatomic potential
Zixiong Wei, Fei Shuang and Poulumi Dey
Iron (Fe) oxidation is a fundamental phenomenon that is scientifically vital and technologically significant. Despite substantial experimental efforts, accurate atomistic modelling of Fe oxidation remains elusive, which requires a reliable interatomic potential, whose development hinges on a representative first-principles training
dataset. However, Fe-oxygen (O) system is known for its structural complexity, rendering the generation of high-quality first-principles
dataset challenging. In this work, we propose the Perturbation Augmented Space group structure Sampling (PASS) method to generate extensive
dataset for Fe-O system consisting of small-
cell structures (no more than 10 atoms). Based on atomic cluster expansion (ACE) framework, we present a systematic approach to developing a transferable machine learning interatomic potential (MLIP). The accuracy and capability of the ACE potential are thoroughly validated across pure Fe and Fe-O systems through bulk, surface, and interface properties. The large-scale Fe oxidation simulations with the ACE potential capture key features of the oxidation process, including the formation of an FeO-like structure consistent with recent experimental observations. This work demonstrates that the PASS method yields an accurate and transferable MLIP that can capture the reactive complexity of
oxide growth while remaining computationally practical for extended systems.
Read the full abstract ▾
Quantum Gases
Observation of Moiré Time Crystal in Floquet-driven Rydberg Atomic Gases
Shuai Shi, Dong-Yang Zhu, Yu Yang et al. (+8 more)
A Moiré time
crystal is a non-
equilibrium quantum phase emerging from the coherent interference of two distinct frequencies, at least one being the intrinsic oscillation of a
symmetry-broken time
crystal. Its hallmark is an ultra-long beat period, reflecting a time-domain mapping of the Moiré fringes that arise from mismatched spatial
lattices. However, to date, no experimental realization of such a Moiré time
crystal has been reported. In this work, by applying a bichromatic driving field with two distinct frequencies, we demonstrate that the interplay between long-range Rydberg interactions and dissipation gives rise to a unique comb-like Moiré pattern characterized by a beat-note comb, which superimposes subharmonic periodicity and fundamental frequencies. This Moiré pattern formed by two mismatched drives is staggered in the spectrum as the frequency of one driver changes. We experimentally map the phase diagram of the system and identify a robust region where the Moiré temporal order persists against perturbations in
laser detuning. The reported Moiré time
crystal not only provides a controllable platform for exploring emergent slow-fast dynamics and synthetic space-time
symmetries but also opens avenues for engineering complex temporal order in driven
quantum many-body systems.
Read the full abstract ▾
All authors Shuai Shi, Dong-Yang Zhu, Yu Yang, Chu-Rong Pan, Jing-Wen Tang, Ya-Peng Zhang, Yan-Li Zhou, Wei-Tao Liu, Li-Hua Zhang, Bang Liu, Dong-Sheng Ding
Statistical Mechanics
Mpemba effect in a chemomechanical model of the Kinesin molecular motor
Karthik Cheruvary and Arnab Pal
The Mpemba effect, wherein a system prepared farther from
equilibrium relaxes faster than one initially closer to
equilibrium, has been extensively investigated in a wide range of physical systems. In contrast, its role in biologically relevant non-
equilibrium processes remains largely unexplored. Here, we investigate anomalous relaxation in the six-state chemomechanical network model of the Kinesin molecular motor under both
equilibrium and non-
equilibrium conditions. We first establish the existence of the Mpemba effect in chemical
equilibrium and show that many of its qualitative features can be understood from the underlying free-energy landscape. We then examine the effects of mechanical and chemical driving, showing that breaking detailed balance primarily reshapes the Mpemba phase diagram without qualitatively altering the relaxation phenomenology over the physically relevant parameter regime. Finally, we demonstrate that the relaxation of the motor velocity also mirrors the anomalous relaxation of the underlying
stochastic dynamics, thereby identifying an experimentally accessible signature of the Mpemba effect. Our results establish molecular motors as a promising baseline for studying anomalous relaxation in living systems and suggest a broader framework for exploring the Mpemba effect in non-
equilibrium biochemical networks.
Read the full abstract ▾
Chemical Physics
Nonclassical condensation pathways revealed by the multivariable theory of nucleation
Yijian Wu and Thomas Philippe
We extend classical nucleation theory (CNT) by explicitly incorporating the multidimensional nature of nucleation and the coupled roles of kinetics and thermodynamics. Specifically, we treat the cluster density as an independent variable, within both sharp-interface and diffuse-interface descriptions. The kinetics are governed by dynamical density functional theory. Applied to
liquid condensation in the Lennard-Jones system, our two-variable (size–density) and three-variable (size–interface width–density) models reveal nonclassical nucleation mechanism. At low supersaturation, both models recover the classical picture, in which clusters nucleate and grow at the
equilibrium liquid density. As supersaturation increases, a nonclassical behavior emerges: the critical cluster density decreases, and the nucleation pathway involves concomitant
evolution in cluster size, density, and, within the diffuse-interface description, interfacial width. Our model with diffuse interface reveals a rapid increase in interfacial diffuseness at high supersaturation. Near the spinodal limit, both models predict the critical cluster with diverging sizes, densities approaching that of the metastable initial phase, and vanishing work of formation, which provides a smooth connection between nucleation and spinodal decomposition. Comparison with molecular dynamics simulations demonstrates that both models substantially outperform CNT. However, the weak non-monotonic dependence of the critical cluster density observed at very low supersaturation is captured only by diffuse-interface models. Overall, our findings indicate that CNT should be applied only in the low-supersaturation regime, and our work provides a robust foundation for its refinement beyond this limit.
Read the full abstract ▾
General Relativity and Quantum Cosmology
Towards long and accurate numerical relativity waveforms of binary black holes beyond general relativity
Guillermo Lara, Harald P. Pfeiffer, Nils Deppe et al. (+9 more)
Numerical relativity (NR) simulations of compact binaries in theories beyond general relativity (GR) will be pivotal for the continued development of future tests of
gravity with gravitational waves (GWs). In this Letter, we show that the combination of spectral methods and the "fixing-the-equations" approach allows us to produce the longest waveforms in the literature for a genuine beyond-GR theory, thus bringing NR methods for alternative theories of
gravity closer to the state-of-the-art in GR. For concreteness, we focus on the well-known shift-symmetric version of scalar Gauss-Bonnet
gravity, a theory postulating the existence of an additional dynamical scalar and describing black holes (BHs) different from the Kerr solution. We extract the gravitational and scalar waveforms at future null infinity for equal-mass, nonspinning, eccentricity-reduced BH binaries, and quantify the phase errors to be $\lesssim$ 1 rad after 40+ GW cycles (20+ orbits). We also show that the GW phase corrections in this alternative theory are distinguishable from Einstein's theory and lead to an earlier coalescence time than in GR. Obtaining such waveforms is a stepping stone to perform precise comparisons with Post-Newtonian theory and to calibrate waveform models beyond GR.
Read the full abstract ▾
All authors Guillermo Lara, Harald P. Pfeiffer, Nils Deppe, Lawrence E. Kidder, Geoffrey Lovelace, Sizheng Ma, Alexandra Macedo, Jordan Moxon, Kyle C. Nelli, Mark A. Scheel, William Throwe, Nils L. Vu