Materials Science
Reversible Magneto-ionic Modification of Metallic Magnetic Thin Films
Md Golam Hafiz, Hari Babu Vasili, Philippa Shepley et al. (+12 more)
Magnetic multilayers with structural inversion asymmetry, perpendicular
magnetic anisotropy (PMA), and large Dzyaloshinskii-Moriya interaction (DMI) are widely studied for
magnetic domain wall- and skyrmion-based data processing applications. In this work, we report a controlled, nonvolatile, but reversible local modification of such a system by electrically driven oxygen migration through the metallic film structure by using ionic
liquid gating. Our findings provide direct evidence for the modification of the oxidation state at the heavy metal (HM)/ferromagnet (FM) interface. As a result, we observed changes in fundamental
magnetic properties, such as an increase in the effective anisotropy constant (Keff) and coercive field (Hc) with oxidation, and a decrease with the reduction of oxygen ions. Positive gate voltages relative to the thin film extract oxygen ions from the
magnetic layer, significantly reducing the domain nucleation field. In contrast, negative voltages drive oxygen ions into the
magnetic layer, leading to a reversible increase in the extent of domain wall pinning near saturation. We observe a corresponding decrease in the
magnetic moment and DMI, with negative voltage reducing both. This magneto-ionic modulation in fully metallic structures is beneficial for spintronic device applications, particularly in field-programmable domain wall and skyrmion devices.
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All authors Md Golam Hafiz, Hari Babu Vasili, Philippa Shepley, Mannan Ali, Andrew J. Britton, Oscar Cespedes, Weibin Li, Manuel Valvidares, Rohit Pachat, Wilfried Fotso, Mourad Cherif, Shimpei Ono, Yves Roussigne, Mohamed Belmeguenai, Gavin Burnell
Chaotic Dynamics
Beyond RMSE and Granger Gain: Multi-Horizon Forecast-Error Entropy for Nonlinear Predictive Coupling
Andrei Velichko
We investigate whether the past of an auxiliary time series provides predictive information about a target beyond that contained in the target's own history. We compare matched out-of-sample target-only and target-plus-source forecasts and introduce the forecast-error distribution
entropy (FEDE) predictive-causality framework, where predictive causality is understood in the Granger sense: auxiliary history is informative when it improves prediction beyond the target's own past. FEDE quantifies how the full signed forecast-error distribution changes across prediction horizons. Controlled nonlinear
benchmarks hide source-target dependence behind nonlinear transformations not supplied to the predictors. LightGBM recovers these hidden channels, whereas Ridge does not. Across four equal-power nonlinearities and four noise levels, the mean response-sensitivity statistic for FEDE remains 29.00, 27.47, 23.22, and 28.67, compared with 14.09, 10.68, 12.67, and 12.71 for mean log-RMSE gain. Directional and source controls separate the true source-to-target channel from the reverse direction and from independent periodic, quasiperiodic, chaotic, and autoregressive auxiliaries. Chronological Granger-style comparisons show strong model-form dependence: a degree-2
polynomial model is exceptionally sensitive to the matched quadratic channel but becomes weak or oppositely aligned for other nonlinearities, while basic convergent cross mapping is weak or directionally inconsistent in this
stochastic, partly non-invertible setting. FEDE remains positively aligned across all 108 tested combinations of window length, history length, and maximum forecast horizon. Together, these results establish FEDE as a sensitive and robust horizon-resolved tool that extracts predictive information beyond conventional error-magnitude measures when the nonlinear interaction form is unknown. Code available in Zenodo.
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High Energy Astrophysical Phenomena
Reconstruction of Interstellar Cosmic Ray Anisotropy via Heliospheric Propagation Modeling and SVD Inversion
Reilly Tom, Paolo Desiati, Juan Carlos Díaz-Vélez et al. (+1 more)
Ground-based experiments such as the IceCube
Neutrino Observatory and the High-Altitude Water Cherenkov Gamma-Ray Observatory detect
cosmic-ray anisotropy on Earth, but
magnetic deflections within the heliosphere complicate interpretation. Understanding the original spatial distribution of
cosmic rays in the interstellar medium requires modeling particle propagation across the heliospheric boundary. We constructed a simulated transport model that backtracks antiprotons from Earth to the interstellar medium and maps spatial transfer probabilities across energies using HEALPix representations. Because our transfer
matrices are singular, inversion relies on singular value decom- position regularization. Ground-based observations lose the equatorial North-South anisotropy component, severely degrading interstellar map recovery. We developed a
geometric circle-fitting
algorithm to estimate and reintroduce the missing component into the observed signals. Our results show that restoring the North-South anisotropy en- ables more accurate recovery of the interstellar dipole structure. Furthermore, Poisson statistical fluctuations on the detected event counts dominate
matrix-transformation errors when spread over multiple energies.
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All authors Reilly Tom, Paolo Desiati, Juan Carlos Díaz-Vélez, Perri Zilberman
General Relativity and Quantum Cosmology
On the Mathematical Foundations of Gravitational Decoupling in General Relativity
Andrea Giusti
We study the algebraic and
geometric structures of gravitational decoupling within a fixed class of globally static, spherically symmetric spacetimes with non-vanishing areal-radius differential. We show that (minimal and extended)
geometric deformations of the seed metric define a groupoid of partial transformations. We also draw a connection between the
geometric deformation procedures and disformal transformations. It is shown that every admissible minimal
geometric deformation admits a disformal representation using the areal radius as an auxiliary scalar. For extended deformations, we derive a necessary condition and exhibit a global obstruction that persists under diffeomorphisms preserving the areal radius and the static Killing direction up to constant normalization. Finally, we verify that the disformal construction reproduces the standard minimal
geometric deformation source equations and separate conservation law, including anisotropic seeds.
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Atomic Physics
Theory of Sub-Doppler Spectroscopy of Alkali Metal Vapors in the Field of Counterpropagating Bichromatic Laser Beams: Probe Beam Regime
A. M. Mikhailov and D. V. Brazhnikov
Sub-Doppler resonances observed in miniature
cells ($V \ll 1 cm^3$) with Rb or Cs atoms in the field of counterpropagating bichromatic
laser beams are of interest for the creation of a miniature
quantum frequency standard (QFS) of the optical range. However, a theory of these resonances that takes into full account the real structure of energy levels in an atom has not yet been constructed, which would make it possible to obtain explicit analytical expressions for the absorption coefficient of the medium. This paper addresses this gap using the density
matrix formalism and the
algebra of irreducible tensor operators. Namely, we obtained an analytical expression for the absorption coefficient of the probe beam in the presence of a more intense counterpropagating beam (pump-probe regime). Moreover, the calculations were carried out for arbitrary parameters of
laser beam polarization, arbitrary angular momenta of optical dipole transitions in the atom and various relaxation processes. The constructed theory allows us to correctly take into account the simultaneous action of various nonlinear optical effects, in contrast to the simplified three-level model of the atom, and also to investigate the partial contribution of each of them to the overall observed resonant
circuit. The analysis performed, in particular, made it possible to predict an increase in the amplitude of the sub-Doppler resonance when using counterpropagating light beams with opposite circular polarizations in relation to the configuration of counterpropagating beams with orthogonal linear polarizations, which is often used in practice.
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Earth and Planetary Astrophysics
On the Orbital Evolution of Giant Planet Pair Embedded in a Gaseous Disk. III. simultaneous gas accretion and the final mass ratio
Bixuan Zhao, Hui Zhang, Yinhao Wu et al. (+1 more)
Recent
exoplanet surveys reveal a systematic trend in the mass ratios of giant
planet pairs ($> 30 M_\oplus$). Although the $M_{outer}/M_{inner}$ is broadly centered near unity, it exhibits a dependence on orbital separation. Compact pairs tend to have comparable masses, whereas widely separated pairs show outer-heavy configurations. To investigate the origin of this trend, we perform two-dimensional hydrodynamic simulations that couple gas
accretion and orbital migration of two giant
planet embryos with initial masses of $15-30 M_\oplus$. We explore the effects of disk viscosity, surface density slope, and initial mass ratio on the coupled
evolution of planetary growth and migration. We find that convergent migration drives the
planets to open a common gap, restructuring the gas flow. This configuration induces asymmetric
accretion, in which the inner
planet becomes starved as gap clearing suppresses its gas supply, while the outer
planet continues to accrete from the high-density region at the outer gap edge. Consequently, the system naturally evolves toward mass-ratio convergence, and in many cases produces an inversion of the initial core-mass hierarchy. We further show that migration outcomes are highly sensitive to initial conditions. Systems with initially more massive inner cores tend to diverge, whereas steeper surface density profiles and more massive outer cores favor convergent migration and subsequent resonance capture. Overall, our results identify common-gap-driven asymmetric
accretion as a unified mechanism linking orbital architecture, resonant capture, and the observed mass-ratio demographics of giant
planet pairs.
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All authors Bixuan Zhao, Hui Zhang, Yinhao Wu, Ya-Ping Li
Quantum Physics
Beyond Gaussian Entanglement: Practical Criteria for Polynomially Excited Quantum States
Gábor Homa, Richárd Balka, Nikolett Német et al. (+3 more)
Polynomial excitations consisting of creation and annihilation operators are studied. Subsystem
entanglement is proven produced and preserved by such manipulations. NPT
entanglement already present between any two subsystems of a general pure or mixed multipartite Gaussian state is preserved under all
polynomial excitations. Nevertheless, these excitations can create NPT
entanglement between initially separable subsystems, implying that the number of NPT entangled pairs cannot decrease.
Polynomial excitations of a wide class of initially separable pure states are considered. For these states, the method reduces the infinite-dimensional positivity problem to a finite-dimensional one: after partial transposition, NPT
entanglement is equivalent to a corresponding bilinear representation
matrix not being positive semi-definite. Furthermore, using symplectic diagonalization and spectral decomposition, an explicit transformation is constructed between the Fock-space and position representations. It is applied to quadratic excitations of a three-mode mixed Gaussian state. The behavior of the NPT
entanglement is tracked between subsystems as a function of a parameter $\kappa$, which tunes the non-locality of the excitation, and
quantum negativity is evaluated. Under a chosen quadratic
Hamiltonian, the resulting
unitary time
evolution maintains NPT
entanglement for long intervals, interrupted only by short periods of PPT states. Finally, a closed analytical expression is derived for the covariance
matrix of a general quadratic operator for an arbitrary number of degrees of freedom in phase space. Our framework directly connects mathematical foundations, theoretical modeling, and experimentally feasible implementations.
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All authors Gábor Homa, Richárd Balka, Nikolett Német, András Bodor, Tamás Kiss, András Csordás
Quantum Physics
V-type Atomic Variance Squeezing
Chenrui Bi, Hong-Mei Zou, Zhao-Yang Tong et al. (+1 more)
Variance squeezing of a V-type atom interacting with a dissipative cavity is investigated. First, the influence of atomic initial state parameters on the variance squeezing is explored. The results show that the atomic variance squeezing switches alternately between Sx and Sy as the initial state parameter alpha sweeps from -pi to pi. The two squeezing intervals are symmetric about alpha = pi/4, each with a width of pi/2. For alpha = pi/14, only the Sx component can generate variance squeezing and will eventually disappear with time
evolution due to unavoidable environmental noise. Then, the influence of system parameters on the variance squeezing is also studied. It is found that, the optical variance squeezing depth of Sx is determined solely by the atomic initial parameters and is independent of the system parameters. Both weak cavity-environment coupling and atom-cavity detuning can significantly enhance the robustness of the Sx variance squeezing. The SGI parameter has an extremely weak influence on variance squeezing. These results are beneficial for high-precision
quantum communication applications.
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All authors Chenrui Bi, Hong-Mei Zou, Zhao-Yang Tong, Zijin Liang
Soft Condensed Matter
Ionic gradients shape the spatial organization and dynamics of supramolecular polymers
Claudio Perego, Annalisa Cardellini, Andrea Tagliabue et al. (+1 more)
Living supramolecular materials such as microtubules and actin filaments assemble and function in dynamic, heterogeneous environments, subject to chemical concentration gradients. Their rapid and precise response to such gradients—via aggregation, disassembly, or autonomous motion—underlies the fine spatiotemporal control typical of living systems. Reproducing such responsiveness in synthetic materials is a central challenge in materials science and requires a molecular-level understanding of how gradients couple to supramolecular structure and dynamics, which remains difficult to access experimentally. To this end, we combine implicit-solvent coarse-grained molecular dynamics (MD) with the constant chemical potential MD (C${\mu}$MD) technique to investigate, at molecular resolution, the coupling of two prototypical supramolecular
polymer models with externally imposed ionic concentration gradients. Despite their contrasting responses to homogeneous ionic conditions, both systems undergo pronounced spatial reorganization under the gradient, generating regions of locally enhanced supramolecular activity that are inaccessible to homogeneous systems with the same overall content of self-assembling species. Crucially, the local supramolecular dynamics is largely determined by the local concentrations, consistent with the formation of local quasi-
equilibria: this direct connection between spatial composition and supramolecular activity emerges as a common governing principle across the two models. These findings shed light on the spatially complex supramolecular response that can be triggered by chemical gradients, and show how a single gradient simulation can encode this response across a continuous range of local chemical environments, thus providing a general strategy to investigate and design materials operating under spatially heterogeneous conditions.
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All authors Claudio Perego, Annalisa Cardellini, Andrea Tagliabue, Giovanni M. Pavan
Disordered Systems and Neural Networks · Cross-listed from math.PR
Free energy of non-convex multi-species Ising spin glasses with external fields
Jeanne Boursier and Jean-Christophe Mourrat
We identify the limit free energy of mean-field multi-species
spin glasses with +/-1
spins, allowing for the presence of external fields, and without assuming any convexity property of the covariance function of the
Hamiltonian. The limit is given by an "uninverted" variational formula over Brownian martingales. The proof consists in first identifying the limit free energy of configurations with a fixed magnetization. Once the magnetization is fixed, we can show the convergence of the enriched free energy to the solution of a Hamilton-Jacobi equation. The magnetization constraint is also used to show the convexity of the initial condition in this equation, and this yields a variational representation of the solution, as a Hopf formula. Convex duality then turns this formula into an optimization over martingales whose initial values are the prescribed magnetizations.
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Cosmology and Nongalactic Astrophysics
Structure and evolution of cosmic voids within DESI DR1
Óscar Monllor-Berbegal, Susana Planelles and Vicent Quilis
Ongoing stage IV
galaxy surveys such as DESI or Euclid offer an unprecedented amount of information to study the large-scale structure of the Universe by mapping tens of millions of
galaxies. Within the context of
cosmic voids, already released and future catalogues will help better understand the void structure and
evolution as well as the cosmological model constraints derived from their statistics. With the recent DESI Data Release 1, our aim is to obtain a new void catalogue that allows us to study the properties of
cosmic voids at different
redshifts, hence providing insight not only on their structure but also on their
evolution. We select the DESI BGS and LRG samples for this study. Before the void-finding process, the data goes through a preprocessing pipeline tackling
redshift space distortions and reconstructing the mildly non-linear velocity field. After that, the new AVISM void finder is applied to the preprocessed data, obtaining two void catalogues in different
redshift bins (0.1 < z < 0.3 and 0.4 < z < 0.8), both within a 1400^3 cMpc^3 cube. We successfully recover N_BGS = 1114 and N_LRG = 216 clean voids with sizes up to ~ 65 cMpc. The void size function, 3D shape variables, density profiles, and linear bias are obtained and analysed. Both the size function and the density profiles obtained are in agreement with previous theoretical studies. The expected mass depletion in void
evolution is shown by the
evolution of density profiles. We obtain a roughly constant linear bias inside r < Re with mean values of 1.31 +/- 0.02 and 2.14 +/- 0.04 for BGS and LRG, respectively. Both void catalogues are publicly released.
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Atomic Physics
Collision inside an atom: quantum ion-atom dynamics
Arijit Das, Yufeng Wang, Marcin Welter et al. (+6 more)
Rydberg atoms occupy a central role in
quantum science; their loosely bound outer electron gives rise to properties that enable
quantum information processing1 or the formation of exotic molecular bonds2. Beyond these roles, they have been proposed as a neutral platform for the observation of
quantum effects in collisions and reactions of the ionic core with neutral particles3, 4, a long-standing goal of ion-based chemistry and physics. However, all of the experimental results so far could be explained using a classical description of the internuclear motion5. Here we demonstrate cold collisions inside a Rydberg helium atom, achieved by merging helium Rydberg and ground-state helium beams and imaging individual scattering events. We resolve the fully
quantum-coherent motion and observe matter-wave diffraction and tunnelling-driven shape resonances down to collision energies of 90 mK. In the case of identical helium
nuclei, we demonstrate a new regime of identical-particle Mott interference6, where
quantum statistics begin to govern the total scattering cross section. For distinct isotopes, we show the breakdown of the Born-Oppenheimer approximation and
benchmark parameter-free, state-of-the-art theory. We directly measure the helium isotope ionization-energy difference to be 15.0 +/- 0.1 K. Our experiments establish Rydberg atoms as a platform for the direct observation of
quantum dynamics with a general class of ions, atoms and molecules.
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All authors Arijit Das, Yufeng Wang, Marcin Welter, Karl Horn, Dawid Dąbrowski, Michał Przybytek, Julia Narevicius, Michał Tomza, Edvardas Narevicius
High Energy Physics (Theory)
Geometry and holography of $\mathrm{AdS}_2\times\mathrm{S}^2$: towards the field theory dual
Miroslava Mosso Rojas and Anayeli Ramirez
We take a first step in identifying the superconformal
quantum mechanics dual to supersymmetric AdS$_2\times$S$^2$ solutions. We focus on the Type IIB solutions of the form AdS$_2\times$S$^2\times$CY$_2\times\Sigma$ that preserve eight supercharges, with $\Sigma$ a two-dimensional space parametrised by $(x_1,x_2)$, and read off their brane content, a D1-D5-NS5 intersection with D3 and D7 flavour branes. We propose that their dual $\mathcal{N}=4$
quantum mechanics is organised over a two-dimensional
lattice of
cells in $\Sigma$. Namely, it consists of copies of the linear quiver along $x_1$ dual to the U(1)-invariant solutions of the class, one for each interval along $x_2$, with ranks given by the D1 and D5 charges of the corresponding
cell. Its central charge agrees with the holographic one at leading order. We show that the family of SL$(2,\mathbb{R})$ non-Abelian T-duals of the AdS$_3\times$S$^2\times$CY$_2$ solutions of massive Type IIA supergravity, constructed in previous work, belongs to this class, as does the SL$(2,\mathbb{R})\times$SU$(2)$ non-Abelian T-dual of AdS$_3\times$S$^3\times$CY$_2$, and work both out in detail. For both we propose global completions that introduce additional D3 and D7 branes. Along $x_2$ we interpret the fundamental strings stretched between the colour branes and the additional D3 and D7 branes as baryon vertices. Finally, we extend this proposal from the non-Abelian T-duals to the solutions of the class whose defining functions factorise in $x_1$ and $x_2$, including those in which the AdS$_2$ and S$^2$ factors have the same warp factor.
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Solar and Stellar Astrophysics
The EBLM project - XX. Absolute dynamical masses of five low-mass eclipsing binaries, and an evaluation of mass estimation methods
Adam T. Stevenson, Yasmin T. Davis, Daniel Sebastian et al. (+8 more)
Eclipsing binaries consisting of a solar-type primary and an M dwarf secondary are key laboratories to study objects at the bottom of the main sequence. Fundamental parameters of such
stars have a direct impact upon exoplanetary studies, as searches for temperate Earth-sized
planets focus on M dwarf hosts. Eclipsing binaries are essential to measure these parameters. However for stellar masses $<$ 0.35 M$_\odot$ , few double-lined eclipsing systems are known. Thus, stellar
evolution models and empirical relations have had to rely on single-lined eclipsing binaries, for instance those from the EBLM project (Eclipsing Binary - Low Mass). Using high resolution spectroscopy to extract the weak signal of the secondary (flux ratio $<$ 1 per cent in the optical), we transform five more systems from single to double-lined, deriving absolute masses for both
stars. We then compare methods typically employed to estimate stellar masses for field
stars or single-lined binaries with the absolute dynamical masses we obtain, to assess their accuracy. Our results for SB1 and SB2 analyses are mostly consistent within 1-$\sigma$, though we identify a small systematic overestimation of SB1 masses derived from a combination of radial velocities and eclipse photometry. We show that the bias originates from primary radius overestimation during isochronal analysis, wherein the secondary light reduces photometric magnitudes and impacts the recovered radii by modifying the spectral energy distribution. With proper calibration, we can ensure the accuracy of using the full EBLM SB1 sample to constrain mass-radius-luminosity relationships for the smallest, yet most abundant,
stars in the
Galaxy
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All authors Adam T. Stevenson, Yasmin T. Davis, Daniel Sebastian, Amaury H. M. J. Triaud, Pierre F. L. Maxted, Alix V. Freckelton, Thomas A. Baycroft, Neda Heidari, David V. Martin, Nicola J. Miller, Alexandre Santerne
Solar and Stellar Astrophysics
The EBLM Project - XIX. The absence of radius inflation in a homogeneous analysis of 66 Northern low-mass eclipsing binaries
Yasmin T. Davis, Amaury H.M.J. Triaud, David V. Martin et al. (+30 more)
Precise and accurate measurements of host
stars are crucial in the search for Earth-like
exoplanets, and M-dwarfs are favourable targets in this quest. Low-mass eclipsing binaries offer unique opportunities to empirically determine stellar masses and radii for low-mass
stars where stellar models may be systematically biased. We present results from the EBLM-North sample, the largest homogeneous study of low-mass eclipsing binaries with secondary characterisation yet, combining high-resolution and high-precision radial velocities from SOPHIE and TESS photometry. We measure a median precision for stellar companions of 4.2% in radius and 8.6% in mass within a sub-sample of 50 high-quality binaries, all with orbital periods $P_{\rm bin} > 5\,\rm days$. We compare our data to the Baraffe and MIST isochrones, and find our sample is statistically consistent with those models, producing reduced chi-squared values, $\chi^2_\nu\sim 1$. Our measured radius inflation is $0.3\pm 1.6$% indicating no statistically significant trend. We likewise detect no significant trend with
metallicity, despite having the precision to identify such a relationship. As such, our observations do not appear to follow the general
metallicity trend predicted in MIST. A $\chi_\nu^2 \sim 1$ indicates the scatter in our results is commensurate with our uncertainties alone. These results constrain the scope for unmodelled effects on the mass-radius relation that would produce radius deviations greater than 4.2%. However, our secondary effective temperatures do not reproduce this high level of agreement with the models, and we do not recover the predicted trends with
metallicity.
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All authors Yasmin T. Davis, Amaury H.M.J. Triaud, David V. Martin, Alix V. Freckelton, Jenni R. French, Adam T. Stevenson, Annelies Mortier, Karen Collins, Pierre F. L. Maxted, Daniel Sebastian, Aleyna Adamson, Thomas A. Baycroft, Isabelle Boisse, Gavin A. L. Coleman, Georgina Dransfield, Yilen Gómez Maqueo Chew, Leslie Hebb, Neda Heidari, Vedad Kunovac, James McCormac, Nikki J. Miller, Richard Nelson, Martin Nielsen, Alexandre Santerne, Madison G. Scott, Owen Scutt, Alexis M. S. Smith, Matthew R. Standing, Amalie Stokholm, Matthew I. Swayne, Mathilde Timmermans, Peter J. Wheatley, Emma Willett
High Energy Physics (Phenomenology)
Cosmological Consequences of a Highly Decoupled Right-handed Neutrino
Stephen F. King, Rishav Roshan and Sudipta Show
In the minimal type-I seesaw, one right-handed
neutrino (RHN) can decouple from
neutrino mass generation. Such a state is usually neglected, yet its feeble couplings make it long-lived, and it can dominate the energy density of the Universe before decaying. We study this in a minimal $U(1)_{B-L}$ model, where the RHNs are produced through $B-L$ gauge interactions, for the cases of a decoupled lightest RHN $N_1$ and a decoupled heaviest RHN $N_3$. The resulting early matter-dominated era dilutes the baryon asymmetry, and for decoupled $N_3$ it also delays the equilibration of the charged-lepton Yukawa interactions, allowing a lighter $N_1$ to generate the asymmetry in the unflavoured regime. Breaking $U(1)_{B-L}$ forms
cosmic strings whose gravitational-wave background acquires a spectral break from the early matter-dominated era, with a frequency set by the decoupled RHN mass and the lightest
neutrino mass, within reach of future detectors such as SKA, THEIA, LISA, $\mu$ARES, DECIGO and ET.
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High Energy Astrophysical Phenomena
Two sides of the same spin: tracking optical and radio pulsations of SAX J1808.4-3658 from outburst to quiescence
C. Ballocco, A. Miraval Zanon, A. Papitto et al. (+25 more)
High-time-resolution optical and UV observations have revealed bright coherent pulsations from accreting millisecond
pulsars, exceeding the luminosity expected from thermal emission from NS hotspots or X-ray reflection by the
accretion disk. Characterizing optical pulsations over a wide range of
accretion rates through coordinated multi-wavelength observations can shed light on their origin. We present a timing study of the AMSP SAX J1808.4-3658 during its 2022 outburst and quiescence, using optical TNG/SiFAP2 observations, simultaneous NICER X-ray data, LCO optical monitoring, and MeerKAT
radio observations in quiescence. During the outburst, we detect coherent optical pulsations with pulsed luminosities of 1.3x10^(30)erg/s. Combined with previous detections, our results suggest that the optical pulsed amplitude increases as the X-ray flux decreases. The X-ray and optical pulsed luminosities show opposite trends with X-ray luminosity, suggesting different responses to changes in the
accretion rate. We measure X-ray-to-optical delays of 0.88+-0.04ms and 0.51+-0.03 ms in two outburst observations, indicating that the relative timing between the signals is not constant. Together with the spectral energy distribution, these results support different emission mechanisms: non-thermal emission from relativistic particles for optical pulsations and channeled
accretion onto the NS surface for X-ray pulsations. During quiescence, we detect no coherent optical pulsations, obtaining a 95% confidence upper limit of <2.2x10^(29)erg/s on the optical pulsed luminosity, corresponding to an optical efficiency comparable to those of spider
radio millisecond
pulsars. Simultaneous MeerKAT observations reveal no
radio pulsations down to ~10{\mu}Jy, significantly improving previous constraints but not excluding an active rotation-powered
pulsar whose
radio emission may be absorbed by intra-binary material.
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All authors C. Ballocco, A. Miraval Zanon, A. Papitto, M. Burgay, M. C. Baglio, C. Malacaria, F. Ambrosino, A. Possenti, G. Illiano, E. D. Barr, R. P. Breton, L. Burderi, S. Campana, C. J. Clark, F. Coti Zelati, D. de Martino, T. Di Salvo, M. Kramer, R. La Placa, F. Lewis, A. Marino, D. M. Russell, A. Sanna, L. Stella, B. Stappers, J. D. Turner, M. Cecconi, A. Ghedina
Statistical Mechanics
Charge-selective topological locking and ultraslow coarsening in magnetoelastic media
Tirthankar Banerjee and Amaresh Jaiswal
We demonstrate that the
symmetry of magnetoelastic coupling governs the topological organization of composite defects and can qualitatively alter phase-ordering kinetics. In a two-dimensional theory of an in-plane
magnetic vector coupled to elastic strain, we find that integer
magnetic vortices bind pairs of elementary elastic half-defects. Isotropic magnetostriction produces a core-induced elastic winding independent of the
magnetic charge, giving defect binding without charge locking and leaving the
magnetic sector with essentially XY-like coarsening. In contrast, quadrupolar magnetoelastic coupling locks
magnetic and elastic defect charges: continuous rotational
symmetry favors $q_\phi=q_\theta$, whereas crystalline anisotropy can reverse the locking to $q_\phi=-q_\theta$. We reveal that both locking sectors display anomalously slow
vortex annihilation: defect density shows a power-law decay $t^{-2/5}$, while the average defect-velocity scales as $t^{-4/5}$. These results are consistent with a dynamic exponent $z\simeq 5$. We show that this coarsening slowdown is associated with large anisotropic elastic friction. An adiabatic elimination of the elastic field reveals that isotropic magnetostriction merely renormalizes local
magnetic interactions, whereas orientational coupling induces effective nonlocal interactions between
magnetic spins. Our experimentally testable results thus establish magnetoelastic coupling
symmetry as a means of controlling defect
topology and ordering kinetics.
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Materials Science
Accurately Generalizing Deep-Learning Hamiltonian Methods to Plane-Wave Density Functional Theory
Chuntian Wu, Jiaxiang Li, Qiang Xu et al. (+4 more)
Deep neural networks that predict density functional theory (DFT)
Hamiltonians from material structures offer a route to efficient electronic-structure calculations. However, extending localized atomic-orbital (AO)
Hamiltonian learning to plane-wave (PW) calculations with hybrid functionals requires a compact AO representation that preserves the effects of nonlocal operators. Here we propose a projectability-guided construction of nonorthogonal AO
Hamiltonians from a small, selected set of PW eigenstates and
eigenvalues. High-projectability states are retained, and selected higher-energy states complete the AO subspace, avoiding an empirical shift and its arbitrary contribution to the learning targets. Because the construction uses PW eigenstates and
eigenvalues, it incorporates nonlocal contributions present in the reference calculation without explicitly reconstructing their AO
matrix elements.
Benchmarks for MoS2 and sodium phases show accurate reproduction of PW bands with smaller AO bases than real-space reconstruction. The resulting PBE and HSE
Hamiltonians can be learned by equivariant neural networks, connecting PW reference calculations with electronic-structure prediction. This approach broadens the range of PW DFT calculations available for AO
Hamiltonian learning and enables compact, accurate training targets for developing more widely applicable electronic-structure models.
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All authors Chuntian Wu, Jiaxiang Li, Qiang Xu, Xuecheng Shao, Congwei Xie, Yu Xie, Yanming Ma
High Energy Astrophysical Phenomena
Cell-based theoretical criteria on the onset and stability limit of thermonuclear detonation
Kazuya Iwata, Keiichi Maeda and Ken J. Shen
One of the key unresolved problems in thermonuclear explosions of white dwarfs (WDs), including type Ia
supernovae, is the condition for ignition and propagation of thermonuclear flame. Given the limitation of hydrodynamic simulations in resolving the flame front involved in the explosion process, theoretical considerations for these criteria merit accurate prediction of the onset of deflagration and detonation (deflagration-to-detonation transition or direct initiation) and subsequent stable propagation. Application of
cell-based theories, which are originally designed for terrestrial detonation incorporating the size of the cellular structure, to pure-helium detonation in a WD envelope was proven to be powerful. In the present work, we extend this for detonation in helium-carbon and carbon-oxygen mixtures, both of which are associated with the double-detonation model for type Ia
supernovae. Comparing with previous hydrodynamic studies in terms of the minimum initiation energy and critical stellar mass for stable propagation, the agreement is satisfactory. For the helium-carbon detonation, it is theoretically substantiated that even an extremely low-mass WD envelope $\sim 10^{-3}$ M$_{\odot}$ can accommodate stable detonation. For the carbon-oxygen detonation, the oxygen-scale
cell width is shown to be a good diagnosing indicator. In addition, it is indicated that direct initiation of the carbon-oxygen detonation is only available for a WD heavier than 0.6 M$_\odot$. The findings of this study enable first-order calibration of the explosion model by a simple calculation through the analogy between astrophysical and terrestrial burning, the latter of which can be tested and observed in a laboratory-scale experiment.
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Materials Science · Cross-listed from cs.AI
Complex materials engineering via Provenance Action Graphs: potential, structure and demonstration
Yevgeny Rakita, Paul Todd, James R. Neilson et al. (+1 more)
This work discusses and tests the potential of reaction graphs for material synthesis, in which events consist of reaction steps (actions) and their outputs (observations). The importance comes from the requirement to synthesize technologically useful materials, especially those that are kinetically stabilized. Often, it is a science that follows years of trial and error, culminating in (published) successful recipes, but is truly driven by far more (unpublished) failures. The entry into the era of AI provides an opportunity to use learning
algorithms to encode rules from multi-dimensional synthesis pathways, regardless of their technological usefulness, and to decode both forward prediction and inverse learning modes. The main incentive is to accelerate material discovery by generating a global knowledge base that can be shared among data
agents and contributed to by them. We will focus on several scenarios in the common synthesis process during solid-state synthesis, primarily because these reactions are kinetic in nature and require closer monitoring and control of the reaction history.
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All authors Yevgeny Rakita, Paul Todd, James R. Neilson, Simon J. L. Billinge
Materials Science
Transition-Metal-Induced Uniaxial Anisotropy in YFe$_3$
M. Nur Hasan, Bruno L. Fertig, Santa Pile et al. (+13 more)
Achieving uniaxial magnetocrystalline anisotropy while preserving high magnetization and thermal stability remains a central challenge in the development of Fe-rich permanent magnets. YFe$_3$ is a promising candidate owing to its saturation magnetization and Curie temperature, but its intrinsic easy-plane anisotropy limits its potential for permanent-magnet applications. Here, we show that selective transition-metal substitution drives an easy-plane-to-easy-axis transition in YFe$_3$. Systematic first-principles screening identifies V, Nb, and Ta as effective dopants, with YFe$_{2.33}$Ta$_{0.67}$ exhibiting a large uniaxial magnetocrystalline anisotropy energy of 2.3~MJ/m$^{3}$. Calculated exchange interactions and atomistic Monte Carlo simulations show that the enhanced anisotropy is achieved while preserving robust ferromagnetic order and high thermal stability. Micromagnetic simulations further reveal that YFe$_{2.33}$Ta$_{0.67}$ exhibits the highest coercivity and strongest resistance to irreversible demagnetization, whereas YFe$_{2.33}$V$_{0.67}$ achieves a comparable maximum energy product at 300~K. Experimental characterization of V-alloyed YFe$_3$ shows that the YFe$_3$ phase can be retained at low nominal V concentrations (1-3 at.%) under the employed synthesis and heat-treatment conditions, whereas higher V contents lead to increasingly multiphase samples. Concentration-dependent MAE calculations reveal a sign reversal between approximately 11 and 14~at.% V, marking the transition from easy-plane to uniaxial easy-axis anisotropy. Consistent with this concentration dependence, electron backscatter diffraction and Kerr microscopy reveal in-plane
magnetic domain structures in the experimentally accessible low-V regime. Therefore, our work offers a promising approach to tuning the magnetocrystalline anisotropy of YFe$_3$ while retaining high Curie temperatures.
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All authors M. Nur Hasan, Bruno L. Fertig, Santa Pile, Rafael M. Vieira, Alena Vishina, Alexander Kovacs, Gotthard Rieger, Stefan Denneler, Samuel J. R. Holt, Martin Lang, Swapneel Pathak, Andrea Petrocchi, Hans Fangohr, Thomas George Woodcock, Thomas Schrefl, Heike C. Herper
Materials Science
A Topological Spin on Racetrack Memory
Benjamin Zingsem
Magnetic racetrack
memory requires localized carriers that combine rapid motion, resistance to perturbations and a detectable signal. Here we show how a 360{\deg} domain wall in a hollow ferromagnetic tube combines these properties within a single continuous
magnetic shell. Two successive magnetization reversals form a bound object whose surrounding domains point in the same direction. Analytical energetics and micromagnetic simulations establish its finite separation, recovery from tested perturbations and current driven transport without microscopic Dzyaloshinskii-Moriya interaction or a maintaining field. The texture's winding resists unwinding while radial rotation carries an energy cost, providing a specific control over stability. Relative rotation of the constituent
spins accounts quantitatively for additional displacement during current onset. The wall supports motion at hundreds of metres per second, with transient velocities approaching one kilometre per second at stronger drive. A prepared seven-bit pattern retains its carriers and local readout contrast after pulsed transport and recovery. Curved-track and differential-current tests identify radial stiffness and drive uniformity as controls for intact motion. These results establish a physical basis for fast, locally distinguishable tubular
magnetic bits and identify a continuous switching pathway that can be targeted by tailored excitation.
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Mesoscale and Nanoscale Physics
Role of dissipation dilution in achieving high mechanical quality factors in van der Waals resonators
Lukas Schleicher, Leonard Geilen, Alexander Musta et al. (+5 more)
Dissipation dilution has driven a revolution in the quality factors ($Q$) of top-down nanomechanical resonators. Yet it has not been leveraged for van der Waals (vdW) materials. Here we report quality factors up to $372{,}000\pm37{,}000$ in monolayer MoS$_2$ drums at 4 K, nearly an order of magnitude beyond the previous best for any vdW material at this temperature, enabled by a clean,
polymer-free exfoliation technique. We develop a dissipation-dilution model for circular drums and analyze the contributing intrinsic and extrinsic dissipation mechanisms. The MoS$_2$ monolayer exhibits a dilution factor of order $1,000$, establishing sub-nanometer-thin resonators as ultimate dilution materials. The intrinsic quality factor, however, is limited by surface losses at atomic thickness. Conversely, multilayer drums show a lower dilution factor but a high intrinsic quality factor, on par with established top-down materials of similar dimensions, both resulting from the increased thickness. A two-level-system analysis of the temperature-dependent damping confirms this bulk-versus-surface picture and provides first insight into its microscopic origin. Our results identify dissipation dilution as the governing mechanism for high-$Q$ mechanical vdW resonators. Combined with strategies such as soft clamping or stress engineering, they establish atomically thin resonators as a platform for ultrahigh-$Q$
quantum transduction and sensing.
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All authors Lukas Schleicher, Leonard Geilen, Alexander Musta, Niklas Walter, Anne Rodriguez, Philipp Bredol, Alexander W. Holleitner, Eva M. Weig
Superconductivity
Phonon-Mediated Superconductivity near Phase Boundaries in Rhombohedral Multilayer Graphene
Konstantinos Sourounis and Peter M. Oppeneer
The recent observation of superconductivity in untwisted multilayer
graphene has sparked intense interest in its microscopic origin. As the displacement field and carrier density are varied, superconductivity emerges in several distinct regions with different temperature and
magnetic-field responses. This behavior has been attributed to the presence of distinct electronic phases, raising the possibility that different superconducting regions originate from different microscopic mechanisms. While purely electronic pairing mechanisms have been extensively explored, an in-depth examination of
phonon-mediated superconductivity is still missing. Here, we solve the coupled selfconsistent Migdal-Eliashberg equations using input from first-principles calculations and incorporating interaction-driven
symmetry breaking of the electronic ground state. Varying the carrier density and displacement field, we reproduce the experimentally observed superconducting regions with comparable superconducting properties such as gap and $T_c$ and predict additional, as-yet undiscovered superconducting phases. Our findings exemplify that several superconductivity regions in rhombohedral
graphene can be satisfactorily explained by
phonon-mediated pairing.
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Astrophysics of Galaxies
EMU detection of mysterious multiple component radio-continuum emission from nearby spiral Seyfert I type galaxy 'Sand-timer' (NGC 7213)
M. D. Filipović, Z. J. Smeaton, B. S. Koribalski et al. (+24 more)
We present an Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU)
radio-continuum detection of the nearby spiral Seyfert I type
galaxy NGC 7213 which we nickname `Sand-timer' due to its morphological appearance. We find intriguing, peculiar emission extending from the central supermassive black hole (SMBH), which we refer to as
galaxy hyperbubbles and/or active galactic
nucleus (AGN) jets. Finally, we find two previously undetected kiloparsec-scale features in the polarised intensity image, which appear most likely also related to the central SMBH, as restarted bipolar
radio jets, though somewhat obscured in the
radio-continuum total intensity image. They resemble the bow shocks often seen in Fanaroff-Riley Class II (FR-II)
radio galaxies, and so we propose they most likely represent an early episode of the `Sand-timer's' AGN jet activity. An alternative scenario is that the core of NGC 7213 may be a supermassive binary black hole (SMBBH) undergoing a tidal disruption event (TDE), potentially causing the peculiar
radio-continuum emission.
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All authors M. D. Filipović, Z. J. Smeaton, B. S. Koribalski, R. Kothes, A. Ahmad, R. Z. E. Alsaberi, C. Bordiu, A. C. Bradley, E. J. Crawford, A. M. Hopkins, E. Järvelä, S. Lazarević, D. Leahy, J. L. Payne, S. F. ur Rahman, G. P. Rowell, H. Sano, M. Selby, S. S. Shabala, E. J. Stanton, S. Taziaux, K. Tsuge, D. Urosević, N. F. H. Tothill, J. Th. van Loon, V. Velović, G. L. White
General Relativity and Quantum Cosmology
Stable manifolds of heteroclinic chains in Hořava-Lifshitz cosmology
Hauke Sprink and Phillipo Lappicy
We consider
vacuum spatially homogeneous models in Hořava-Lifshitz
gravity, which are expected to describe generic singularities for these modified
gravity theories. These models perturb the well-known Bianchi models in general relativity (GR) by a parameter $v\in (0,1)$, in which GR occurs at $v=1/2$. We show that all periodic heteroclinic chains of Bianchi type II orbits are robust for small perturbations of GR, i.e. they exist for any $v\approx 1/2$. Moreover, we prove the existence of a stable
manifold for each heteroclinic chain within a Cantor set for the supercritical case, $v\in (1/2,1)$. In particular, we discuss the heteroclinic chains of periods three and four in detail.
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Astrophysics of Galaxies
MUSE-DARK IV. Comparing Dark Matter Densities to Star Formation Histories in 375 intermediate-z galaxies
B. I. Ciocan, N. F. Bouché, J. Fensch et al. (+5 more)
(Abridged) Baryonic feedback is expected to transform cuspy dark-matter (DM)
haloes into cores, but direct observational links between inner DM slopes and
galaxy star-formation histories (SFHs) remain limited. We investigate and quantify the connection between
halo inner slopes and baryonic assembly histories in a large sample of intermediate-z
galaxies. We analyse 375
galaxies at 0.1<z<1.43 spanning 7<log(Mstar/Msun)<11.2 using 3D forward modelling of MUSE kinematics and disk-
halo decompositions with mass-dependent (DC14-based) and generalised Navarro-Frenk-White (gNFW)
halo profiles. Stellar population parameters are inferred from multi-band Spectral Energy Distribution fitting of UV-to-MIR photometry using a non-parametric SFH model.
Bayesian model comparison shows that the DC14-based
halo density profiles are statistically preferred over gNFW for a substantial fraction of the sample. The inferred inner slopes from gNFW fits nevertheless follow the DC14 expectation and reproduce the expected dependence on the stellar-to-
halo mass ratio, despite this not being explicitly imposed. Partial correlation coefficient and random forest regression analyses consistently identify stellar mass (or, equivalently, the stellar-to-
halo mass ratio) as the primary driver of the inner density slope, a result that holds robustly even when the analysis is restricted to the gNFW fits. In contrast, SFH-related quantities (e.g. formation time and 'burstiness' indicators) exhibit no independent predictive power on the DM
halo inner slope once the dependence on stellar mass is accounted for. Cored systems preferentially occupy lower-mass, more bursty bins with later assembly times, whereas cuspy systems are associated with higher stellar masses, lower
star formation activity, and earlier assembly epochs, in agreement with theoretical expectations of stellar-feedback-induced cores.
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All authors B. I. Ciocan, N. F. Bouché, J. Fensch, D. Krajnović, J. Freundlich, H. Desmond, A. Jeanneau, B. Famaey
Materials Science
Coherent Phonon Generation from Prethermal Carrier Populations in a Semiconductor
Mingyu Shi, Matteo Savoini, Patrick Friebel et al. (+5 more)
Ultrafast
laser excitation of carriers in
semiconductors often results in the creation of fully symmetric coherent optical
phonons, typically understood in terms of a thermalized transient carrier population. We test this understanding with systematic measurements and first-principles calculations of the
photon-energy dependence of ultrafast-
laser-driven coherent
phonon generation in tellurium, using excitation wavelengths around the electronic band gap. We observe that, contrary to the expectations of models assuming a thermalized carrier population, the coherent amplitude of the fully symmetric $A_1$ mode changes only weakly when tuning wavelength across the band gap. The measured spectral dependence is instead reproduced by a transition-resolved prethermal force weighted by optical
matrix elements and band- and momentum-dependent $A_1$ deformation potentials. Fitting this model to the data yields an excited transition state lifetime of a few femtoseconds. These results identify transition selectivity, rather than a thermalized total carrier density, as a key factor controlling coherent-
phonon generation in
semiconductors excited near a band gap.
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All authors Mingyu Shi, Matteo Savoini, Patrick Friebel, Andrea Annunziata, Thomas Metzger, Yunpei Deng, Laura Cattaneo, Steven L. Johnson
Chemical Physics
Extrapolating Collisional Rate Coefficients for Molecules of Astrophysical Interest Using Neural Networks
Yigit Ergen and Jérôme Loreau
State-to-state rate coefficients for inelastic molecular collisions are essential inputs for non-local thermodynamic
equilibrium radiative transfer models, yet their computation using
quantum scattering methods is prohibitive for large molecules and highly excited rotational states. We investigate the ability of artificial neural networks to extend existing
datasets of collisional excitation rate coefficients without performing additional scattering calculations. A multilayer perceptron model was trained using molecular
quantum numbers, level energies, energy gaps, and kinetic temperature as descriptors, and optimized on logarithmic rate coefficients. The model was tested on diverse collision systems ranging from simple diatomic molecules (CO, SiO) to open-shell species (SO), small asymmetric tops (H$_2$O, SO$_2$), and complex organic molecules (benzonitrile and vinyl cyanide) colliding with H$_2$ molecules or He atoms. Extrapolations were performed toward higher rotational levels, higher temperatures, and combinations of both. For most systems, predictions of rate coefficients involving previously unseen rotational states yielded mean error factors between 1.1 and 1.5, with the dominant rate coefficients generally reproduced more accurately than weaker transitions. Temperature extrapolations proved particularly successful, while combined extrapolations in temperature and rotational levels remained accurate to within a factor of two in most cases. The prediction quality depends on the interplay between
dataset size, temperature range, molecular complexity, and the presence of clear collisional propensity rules. Overall, the approach demonstrates that machine learning can provide a practical route to extending collisional
datasets for astrophysical applications, especially for large molecules for which additional
quantum-scattering calculations are computationally demanding.
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