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arXiv2026

Machine Learning Assisted Design of Complex and High Entropy Alloys by Hybrid HiPIMS/Pulsed-DC PVD Process for Low Carbon Energy Applications in Extreme Environments

Complex and high entropy alloys are attracting much attention currently thanks to their mechanical and corrosion resistance properties in harsh environments, in particular needed for carbon-free energy applications. However, their elaboration in bulk and in thin film form in a trial-and-error approach is impractical due to their complexity and the cocktail effect. The recent development of artificial intelligence brings a new possibility for their elaboration and adjustment of their properties. Firstly, we present an overview of Materials and data science research. Then we describe how DIADEM - French initiative for Materials and Data science convergence - tackles the development of innovative coatings for carbon-free energy applications (nuclear, high temperature electrolysis, ...) thanks to the development of a nationwide network of synthesis and characterization platforms - the DIADEM discovery hub. We describe in particular DIADEM-2D, an AI-driven Hybrid HiPIMS/Pulsed-DC PVD process using 4 cathodes in confocal combinatorial configuration. We present the high entropy alloy determination using data from the literature for corrosion resistance in molten salt media and nuclear accidental conditions. An element-independent model gathering deposition parameters and coating properties has been implemented allowing the design of protective coatings with a particular composition. We demonstrate the feasibility of this process and its accuracy.

cond-mat.mtrl-sci↗
arXiv2026

Tuning the magnetic properties of Kitaev materials via the antiferromagnetic proximity effect: Novel phases and application to an $α$-RuCl$_3$/MnPS$_3$ bilayer

In recent years, the increasing level of control over van der Waals (vdW) heterostructures has opened new routes to tune the properties of quantum materials. Motivated by these developments, we examine the potential consequences of interfacing a Kitaev honeycomb magnet, such as $α$-RuCl$_3$, with a nearly lattice-matched vdW antiferromagnet. By combining perturbation theory, exact diagonalization, and a classical energy-minimization method, we show that an effective staggered magnetic field originating from the vdW antiferromagnet can drive a monolayer of a Kitaev material into various novel phases, including an antichiral Kitaev spin liquid, a nonmagnetic nematic phase, and different types of skyrmion crystals. We then apply first-principles simulations to assess the prospect of concretely realizing this setup in a heterobilayer of $α$-RuCl$_3$ and the easy-axis antiferromagnet MnPS$_3$.

cond-mat.str-el↗
arXiv2026

Identification and mitigation of errors in hole spin qubit readout

High-fidelity readout of spin qubits in semiconductor quantum dots can be achieved by combining a radiofrequency charge sensor with spin-to-charge conversion and Pauli spin blockade. However, reaching high readout fidelities with hole spin qubits remains challenging due to site-dependent spin anisotropies and short relaxation times during readout. Here, we analyze the multiple error processes that arise during readout using a double-latched scheme in a germanium double quantum dot hole spin qubit system. We first investigate the spin-to-charge conversion process as a function of magnetic field orientation, and configure the system to adiabatically map the $\lvert \downarrow\downarrow \rangle$ state to the only non-blockaded state. We reveal a strong magnetic field strength dependence of the spin relaxation rates, and minimize it by operating at low fields. We further characterize and mitigate the error processes that arise during the double-latching process. By combining a radiofrequency charge sensor, a double-latching process, and optimized magnetic field parameters, we achieve a single-shot single-qubit state-preparation-and-measurement fidelity of 97.0% while maintaining control of both spins under the readout conditions.

cond-mat.mes-hall↗
arXiv2026

Euclid: Quick Data Release (Q1) -- Ultracool dwarfs in the Euclid Deep Fields

Ultracool dwarfs (UCDs) encompass the lowest-mass stars and brown dwarfs at the substellar boundary. These intrinsically faint objects are challenging to detect, but the wide coverage and deep sensitivity of the Euclid survey increase confirmed UCD counts by orders of magnitude. We carried out a systematic study using Euclid Quick Data Release (Q1) low-resolution near-infrared spectra to identify and characterise UCDs. A sample of previously known UCDs in Q1 validated the analysis, which was then applied to newly identified UCD candidates in Euclid Deep Field North (EDF-N; 22.9 deg^2, down to J_E ~ 24.5 mag). We confirm 33 new UCDs in EDF-N, spanning spectral types M7-T1 (J_E = 17-21 mag) and distances of 50-600 pc. Two objects were followed up with optical and NIR observations using the Gran Telescopio Canarias, providing independent validation of Euclid classifications. We determined spectral types for 33 new UCDs and 167 previously known UCDs by fitting SpeX Prism Library Analysis Toolkit standards. The known sample includes 103 Dark Energy Survey objects (M7-T0, J_E = 17-22 mag), 6 literature sources (M8-T7, J_E = 18-20 mag), and 58 Gaia sources (M7-L1, J_E = 17-24 mag). Independent stellar parameters from atmospheric model fitting agree well with Euclid spectral types. We also investigated Gaia UCDs in Q1 by combining mean XP spectra with Euclid NIR spectra to determine radii. We present a publicly available catalogue including observations, classifications, and stellar parameters. This work demonstrates Euclid's capability to characterise faint stellar populations, establishing a foundation for large-scale UCD studies.

astro-ph.SR↗
arXiv2026

Toward Bayesian photometric cosmic chronometers: Application to VIPERS

The cosmic chronometer (CC) method provides a direct measurement of the expansion history of the universe, $H(z)$, from the differential ages of passively evolving galaxies. However, most CC analyses rely on high-quality spectroscopy to select passive galaxies, measure age-sensitive spectral features, and control stellar-population systematics. We build on existing works that use the D4000 spectral break as a proxy for measuring galaxy ages and apply it to a photometry-selected galaxy sample from VIPERS PDR2 in the range $0.5 \le z \le 0.8$. Our goal is to extend the scope of the standard CC framework to photometric surveys. To achieve this, we first selected a massive and passive galaxy sample using rest-frame colors and mass. Second, we designed a Bayesian framework to infer full galaxy age posteriors in fine redshift bins, using a D4000-age-metallicity grid from stellar population synthesis models. We marginalized over metallicity, using a Gaussian metallicity prior to break the D4000-age-metallicity degeneracy. Subsequently, we derived age-difference posteriors between redshift bins by convolving their age posteriors. Finally, using the median and errors extracted from the differential age posteriors, we calculated the weighted average $H(z)$ over our selected redshift range. We obtain $H(z=0.65)=93.68\pm28.27\,{\rm (stat.)}\pm10.67\,{\rm (syst.)}\ {\rm km\,s^{-1}\,Mpc^{-1}}$, which is consistent with existing spectroscopic CC measurements and with the $Λ$ cold dark matter ($Λ$CDM) model prediction from Planck at the same redshift. This result provides a proof of concept for extending direct $H(z)$ measurements from cosmic chronometers to photometric and spectro-photometric surveys, where larger samples can compensate for lower spectral resolution, provided that passive-galaxy selection, metallicity priors, and stellar-population systematics are carefully controlled.

astro-ph.GA↗
arXiv2026

Estimation Of The Mass And The Spin Of The Neutron Star 4U 1728-34 Using Triples Of X-Ray Quasi-Periodic Oscillations

X-ray quasi-periodic oscillations (QPOs) were reported for 19 different observations of the atoll source 4U 1728- 34. Three of them reveal triplets of QPOs: a lower and a upper kHz QPOs and a low-frequency QPO. Even though they are discernible only after averaging we assume them to be simultaneous. We apply a separate model (formula) for each of the three frequencies of the observed QPOs and compose a system which contains three algebraic equations for the three unknown parameters - the mass and the specific angular momentum of the central neutron star, and the radius of the orbit of orgin of the given triplet of QPOs, which allows us to find the numerical values of the later. Error propagation formulas are applied for the obtaining of interval estimates of the parameters of the star. This is done through implicit function differentiation. The calculations are repeated with several different models for the kHz QPOs.

astro-ph.HE↗
arXiv2026

A comprehensive benchmark of an Ising machine on the Max-Cut problem

QUBO formulations of combinatorial optimization problems allow for solving them using various quantum heuristics. While large-scale quantum computations are currently still out of reach, we can already numerically test such QUBO formulations on a perhaps surprisingly large scale. In this work, we benchmark Fujitsu's Digital Annealer (DA) on the Max-Cut problem, which captures the main complexity of the QUBO problem. We make a comprehensive benchmark against leading other heuristic algorithms on graphs with up to 53,000 variables by focusing on the wall-clock time. Moreover, we compare the DA performance against published performance results of the D-Wave hybrid quantum-classical annealer and the recently proposed QIS3 heuristic. Based on performance statistics for over 2,000 graphs from the MQLib, we find that the DA yields competitive results. We hope that this benchmark demonstrates the extent to which large QUBO instances can be heuristically solved today, yielding consistent results across different solvers.

quant-ph↗
arXiv2026

Kinematic cosmic dipole from a large sample of strong lenses

Measurements of the kinematic cosmic dipole continue to show an intriguing tension between the value inferred from the CMB and that obtained from high-redshift source number counts. While the measured dipole direction appears consistent, the amplitude, set by the observer's peculiar velocity $v_{o}$, remains in significant disagreement. In this paper, we propose using strong gravitational lenses with well-measured Einstein radii to estimate the kinematic cosmic dipole, through the relativistic aberration of the Einstein angle induced by the observer's motion. We show that this effect could be detected solely from measurements of the Einstein radius in wide, high-resolution imaging surveys such as Euclid. However, the precision achievable using Einstein-radius measurements alone, without redshift or lens-galaxy mass information, appears insufficient to discriminate between the CMB value of $v_{o}$ and that derived from source number counts at high statistical significance. Nevertheless, we demonstrate that including a large sample of lenses with available kinematic information, either via the Fundamental Plane relation or, ideally, through spectroscopic velocity-dispersion measurements, drastically reduces the noise and substantially improves the constraining power of this method. We show that, for a realistic sample of strong lenses detected by Euclid and complemented with spectroscopic velocity dispersion measurements from 4MOST or DESI, it is possible to discriminate between the CMB- and source-number-counts-inferred values at the $\sim 5σ$ level using a new, fully independent method. We further demonstrate that this technique is only weakly sensitive to strong-lensing selection effects, with selection biases and threshold effects estimated to be well below the 1% level.

astro-ph.CO↗
arXiv2026

ExoVetter and a TESS Exoplanet Transit Search of Kepler Stars as Ground Truth

We introduce a Python package called exoVetter that produces vetting metrics and visualizations to evaluate transiting exoplanet signals found in high-cadence time-series photometry. exoVetter is open source, modular, and independent of the mission data so that it can be easily expanded and used as part of different transit search pipelines tuned to different science cases and missions. We demonstrate its use in a pipeline as a way to distinguish real events found in a box-least squares exoplanet transit search of 324,530 light curves from the Transiting Exoplanet Survey Satellite mission; we limit our demonstration to stars also observed by the more sensitive Kepler telescope as a way to establish ground truth for the events found in the light curves. Using this ground truth, we provide baseline thresholds for several flux-level vetters and one centroid-offset vetter when using exoVetter metrics on TESS data. Our demonstration also indicates that it is possible to create a planet catalog from the light curves of dim targets (>13.5Tmag) that has a similar fraction of real events to that of the bright targets (<13.5Tmag) for short period events identified in the TESS-Gaia light curves.

astro-ph.EP↗
arXiv2026

Analytical model for the photomultiplier single photoelectron response including the electron back-scattering contribution

Many models exist to describe the single photoelectron response of photomultipliers. Generally to describe the spectral region between the fully amplified primary photoelectron peak and the electronics pedestal an ad hoc function is used (often an exponentially modified gaussian) without a clear physical justification. In this paper, following the physical description of back-scattered primary photoelectrons at the first dynode described in the "The Photomultiplier Handbook" by A.~G. Wright published by Oxford University Press, we derive an analytical function describing these partially amplified primary photoelectrons. This function depends only on intrinsic parameters of the photomultiplier such as the gain at the first dynode and the intrinsic resolution of the dynode chain following the first. Furthermore, analytical descriptions of the fully amplified peak and very low charge signals are derived. The model has been successfully validated with data from two different photomultipliers acquired with a low-noise amplifier.

physics.ins-det↗
arXiv2026

Tracing the Cosmic Origins: Machine Learning Reconstruction of the Primordial Density Field from EoR Observations

Reconstructing the initial conditions of the Universe from late-time tracers would unlock cosmological information buried by non-linear structure formation and astrophysics. We reconstruct the initial density field corresponding to $z=300$, with its linear amplitude extrapolated to $z=0$, from simulated 21-cm and CO(1-0) line-intensity maps at $z=8$ generated with LIMFAST. Using a three-dimensional U-Net, we reconstruct the initial conditions and evaluate their impact on cosmological parameter constraints. The two tracers probe complementary environments: 21-cm emission traces neutral, low-density regions of the IGM, while CO traces overdense, star-forming regions. We also train and evaluate the reconstruction on maps incorporating SKA1-Low- and COMAP-ERA-like instrumental response and thermal noise. In the noiseless case, combining both tracers delivers the most accurate reconstruction across ionisation states, with the cross-correlation coefficient between the reconstructed and true initial density fields, $|C(k)| \gtrsim 0.90$ for $k \lesssim 0.75\,{\rm Mpc}^{-1}$. With observational effects, small-scale information is degraded, but the joint reconstruction retains substantial large-scale coherence, with $|C(k)| \gtrsim 0.70$ for $k \lesssim 0.3\,{\rm Mpc}^{-1}$. We quantify cosmological information gains through simulation-based inference using power-spectrum summaries pre- and post-reconstruction. The largest improvements occur for $σ_8$ and $n_{\rm s}$, with a median aggregate marginal compression of $1.17$ bits in the noiseless case, corresponding to a $56\%$ reduction in the factorised product of prior-normalised $68\%$ marginal widths. With observational effects, the corresponding median compression is $1.29$ bits. These results demonstrate that joint 21-cm-CO reconstruction recovers cosmological information beyond pre-reconstruction summaries.

astro-ph.CO↗
arXiv2026

A Framework for Analysing Nebular-Phase JWST Supernova Spectra with Application to Type Ic SN 2024aecx

We analyse what physical quantities of SN ejecta can be obtained from a single epoch of nebular JWST spectroscopy. We provide an analytical framework, which together with a grid of helium star \texttt{SUMO} spectral synthesis models allows the determination of these quantities for any stripped-envelope SN. Using the framework, we derive critical electron densities for major emission lines, finding values in the range $10^5-10^6$ cm$^{-3}$. This means formation under close to LTE conditions for 200 -- 300 days. We obtain ionisation fractions of Ni and Co, as well as the temperature and filling factor of the Fe/He zone, the $^{56}$Ni and stable nickel masses, the Ni/Fe ratio, and the optical depths $τ_{\mathrm{[Ni\,II]\, 6.636 μm}}$ and $τ_{\mathrm{[Co\,II]\, 10.52 μm}}$. Besides these constraints from iron group elements, one can also obtain the filling factor of the carbon burning (O/Ne/Mg) zone from [Ne II] 12.81 $μ$m, and the masses of Ar II and Cl I. We apply our methodology to a publicly available JWST spectrum of Type Ic SN 2024aecx. We find that this SN produced a chlorine mass of $M_{\mathrm{Cl\, I}} \simeq M_{\mathrm{Cl}} = 5.1^{+2.0}_{-1.6}\times 10^{-4}$ $M_{\odot}$, a factor a few larger than expected from stellar evolution modeling. Furthermore, we find that the SN experienced an unexpectedly small 'Ni-bubble' effect, with $ρ_{\mathrm{FeHe}} = 2.5^{+0.7}_{-0.4} \times 10^{-15}$ g cm$^{-3}$ (or an expansion factor of 1 -- 3 for the Ni-bubble, depending on the adopted model) at 167d for the silicon burning material. We also determine $M_{\mathrm{Ar\, II}} = 4.9^{+2.2}_{-1.5} \times 10^{-4}$ $M_{\odot}$, which from ionisation fractions in our NLTE models yields a best estimate of $M_{\mathrm{Ar}} = 1.1 \pm 0.4 \times 10^{-3}$ $M_{\odot}$.

astro-ph.HE↗
arXiv2026

Chaotic behaviors of particles around the black hole with an anisotropic matter immersed in a magnetic field

We present an exact solution to the Einstein-Maxwell equations that describes a static black hole coexisting with anisotropic matter immersed in an external magnetic field, obtained via the Harrison transformation. Our findings reveal that an increase in the anisotropic matter parameter systematically suppresses the local chaotic behavior, as indicated by a reduction in the Lyapunov exponent. Conversely, variations in the external magnetic field lead to qualitative changes in global chaotic behavior. This is analyzed through Poincaré sections, which demonstrate transitions between regular and chaotic trajectories resulting from the nonlinear gravitational-magnetic interactions. These factors play distinct yet complementary roles in shaping chaotic particle dynamics around black holes. This study would offer a new theoretical framework for exploring nonintegrable particle motion within magnetized black hole spacetimes.

gr-qc↗
arXiv2026

Emergent relativistic symmetry from interacting fermions on the honeycomb bilayer

We study the phase diagram of interacting spinless fermions on the honeycomb bilayer at charge neutrality using large-scale quantum Monte Carlo simulations. In the noninteracting limit, the low-energy spectrum features quadratically dispersing bands that touch at the corners of the hexagonal Brillouin zone. Weak to intermediate interactions induce a splitting of each of the quadratic band touching points into four Dirac points, located along high-symmetry directions of the reciprocal lattice. Strong interactions lead to the formation of a layer-polarized charge density wave, which spontaneously breaks the $\mathbb Z_2$ layer inversion symmetry and opens an insulating gap in the spectrum. We show that the semimetal-to-insulator quantum phase transition as a function of interaction is continuous and characterized by emergent relativistic symmetry. Our results for the values of the correlation-length exponent $ν$, the order-parameter anomalous dimension $η_ϕ$, and the fermion anomalous dimension $η_ψ$ agree with those of the theoretically predicted 2+1D Gross-Neveu-Ising universality class with eight two-component Dirac fermions within less than 5\%\ deviation. We also determine the crossover scale as a function of interaction strength between the nonrelativistic semimetal state at high temperatures, characterized by dynamical critical exponent $z = 2$, and the Dirac semimetal state at intermediates temperatures, characterized by $z=1$. Further reducing the temperature below the crossover scale at a fixed value of the interaction strength above the quantum critical point results in a classical ordering transition in the 2D Ising universality class.

cond-mat.str-el↗
arXiv2026

Intrinsic defects and 4d/5d transition metal defects in Cr$_2$O$_3$: pathways for enhancing the Néel temperature

First-principles calculations are employed to explore avenues to increase the Néel temperature ($T_{\mathrm{N}}$) of the magnetoelectric antiferromagnet Cr$_2$O$_3$ through doping. Employing the hybrid functional method, we calculate the formation energy of intrinsic defects and transition metal dopants (Mo, W, Nb, Ta, Zr, and Hf) to assess their likelihood of formation. Intrinsic defect calculations indicate that Cr interstitials and oxygen vacancies dominate under Cr-rich conditions, whereas Cr vacancies prevail under O-rich conditions. Notably, under Cr-rich conditions, the Fermi level can be pinned slightly above mid-gap due to the formation of Cr interstitials and oxygen vacancies. Additionally, we identify a split Cr vacancy configuration that is more energetically stable than a normal Cr vacancy in corundum Cr$_2$O$_3$. To assess the influence of dopants on $T_{\mathrm{N}}$ of Cr$_2$O$_3$, we calculate the enhancement of the exchange energy for the spin at the dopant site or at an adjacent Cr site using the supercell method.Our study identifies isovalent Mo and W substitutions at Cr sites as the most promising candidates for increasing the Néel temperature because of impurity-mediated enhancement of the exchange interaction for half-filled bands. Formation-energy calculations indicate that Mo and W substitutions at Cr sites form more readily under Cr-rich conditions and that a Fermi level near or slightly above midgap stabilizes the desirable neutral charge states of the Mo and W defects. This is assisted by the formation of intrinsic Cr interstitials and O vacancies under Cr-rich conditions. These findings offer a route to utilize defects for higher $T_{\mathrm{N}}$and enhanced performance of Cr$_2$O$_3$ in magnetoelectric devices and provide useful guidance for future experimental studies.

cond-mat.mtrl-sci↗
arXiv2026

Strain-Tuned Incommensurate Kekulé Spiral Order in Twisted Bilayer Graphene: A Quantum Many-Body Study

The physics of twisted bilayer graphene away from the exactly solvable chiral limit and the quantum Monte Carlo sign-problem-free charge neutrality point is elusive due to the exponential increase in the computational complexity, which has rendered explanations of experimentally observed insulating and superconducting phases restricted largely to the perturbative level. Here we focus on the filling factor $ν=\pm2$ and address the question of the strain dependence of the interacting ground state by approximate quantum Monte Carlo (AQMC), state-of-the-art exact diagonalization (ED) and Hartree-Fock (HF) mean field, in order to investigate the strain-tuned transition from the Kramers intervalley coherent (KIVC) state to the incommensurate Kekulé spiral (IKS) state. While all three methods capture the KIVC order, only ED and HF detect the weaker IKS order that AQMC does not capture adequately. As the AQMC is still capable of capturing stronger orders like the KIVC, our combined protocol may open the door for further understanding of the rich phases of twisted bilayer graphene and other strongly-correlated systems.

cond-mat.str-el↗
arXiv2026

Freezing and Shielding under Global Quenches for Long-Range Interacting Many-Body Systems

We investigate how local perturbations spread on long-range interacting spin chains and show how their nonequilibrium behavior exactly matches the one of a Fermi-Hubbard model with long-range hoppings. We then focus on the thermalization of the fermionic model following a sudden quench of local interactions between two distinct fermionic species. For both models, the quasiparticle spectrum consists of gapped low-energy levels, while the high-energy ones accumulate at a single point. When the low-energy gaps are large enough, turning on the local interactions does not effectively mix high- and low-energy modes, resulting in a freezing of the dynamical evolution. In general, the states within the excited subspace are shielded from the long-range signatures of the model, which are responsible for the low-energy extended states, and the dynamics effectively look as if long-range couplings were absent. This shielding mechanism becomes evident in the presence of disorder. It is shown that shielding and freezing are a universal feature of long-range interacting systems, and their relation to the existence of quasistationary states is conjectured.

quant-ph↗