Nuclear Theory
Enhanced hydrodynamic predictions for $v_{02}(p_T)$
Rupam Samanta, Tribhuban Parida and Jean-Yves Ollitrault
We present hydrodynamic predictions for the new observable $v_{02}(p_T)$, which measures the correlation of particle spectra with
elliptic flow. We implement a data-driven correction so as to match hydrodynamic calculations to
elliptic flow ($v_2(p_T)$) data. The corrected results are in fair agreement with $v_0(p_T)$ data up to high $p_T$. We make predictions for $v_{02}(p_T)$ of unidentified charged
hadrons up to $p_T=10$~GeV$/c$, and of pions, kaons and
protons up to $p_T=5-6$~GeV$/c$, in several centrality windows, for Pb+Pb collisions at $\sqrt{s_{NN}}=5.02$~TeV. We predict a decrease of $v_{02}(p_T)$ of charged
hadrons for $p_T>4$~GeV$/c$ and
meson-
baryon splitting for $p_T>3$~GeV$/c$ in mid-central collisions. We also predict a non-monotonic variation of $v_{02}(p_T)$ for
protons at low $p_T$ above $30\%$ centrality. This is a specific feature of this new observable, which is not observed for the usual flow observables $v_2(p_T)$ and $v_0(p_T)$.
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High Energy Astrophysical Phenomena
Spirited Away: Advective Loss of Cosmic Rays into the Milky Way's Circumgalactic Medium Explains the Large Magellanic Cloud's Low Gamma-ray Luminosity
Taaseen Islam, Hilay Shah, Mark R. Krumholz et al. (+1 more)
Models of
galactic-scale
cosmic ray production and transport have successfully reproduced the
radio and $\gamma$-ray spectra of many
galaxies; however, one notable exception is the Large Magellanic Cloud (LMC), where models that successfully fit other
galaxies consistently overestimate its $\gamma$-ray flux. Here we investigate this discrepancy by applying the CRIPTIC
cosmic ray transport code to recent magnetohydrodynamic simulations of the LMC's interactions with the Milky Way circumgalactic medium that accurately reproduce observations of the LMC's
magnetic field structure. We recover a simulated $\gamma$-ray luminosity that is close to the observed luminosity for a wide range of
cosmic ray transport models, while our control simulations of an isolated LMC not interacting with the Milky Way show the same over-prediction problem as previous investigations. Simulations including the CGM interaction yield lower $\gamma$-ray luminosities because in them
cosmic rays escape the
galaxy primarily via advection, significantly decreasing the emission from collisional processes and changing the dominant $\gamma$-ray emission mechanism from pion decay to inverse Compton emission. Comparisons of the detailed spectral shape show that our interacting LMC models match the observed $\gamma$-ray spectrum at
photon energies below $\sim 10$ GeV, but still slightly overestimate the flux at higher energies, suggesting either more strongly energy-dependent transport than the models we have explored, or a
cosmic ray injection spectrum steeper than the $p^{-2.2}$ that we adopt.
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All authors Taaseen Islam, Hilay Shah, Mark R. Krumholz, Roland Crocker
Soft Condensed Matter
A single length scale rules ballistic aggregation: travels of a droplet train
Nathan Vani, Stefan Kooij, Aritro Mukherjee et al. (+3 more)
Ballistic aggregation is a canonical non-
equilibrium process, relevant across scales from granular gases to planetary
accretion. Collisions are driven by differences in velocities, building up persistent correlations between neighbors. Here, we provide the first experimental realization of one-dimensional ballistic aggregation in a train of droplets formed by the breakup of a
liquid jet. Experiments and simulations confirm the analytically predicted scaling, with the global process shown to be governed by a single length scale. While air drag inverts the sign of neighbor velocity correlations, a 1D ordering constraint protects bulk characteristics of ballistic aggregation such as the scaling exponent and the shape of the large mass tail. More broadly, our results show that Smoluchowski-like mean-field descriptions fail when collisions carry directional
memory – as demonstrated here for jet-generated sprays.
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All authors Nathan Vani, Stefan Kooij, Aritro Mukherjee, Antoine Parrenin, Cees J.M. van Rijn, Daniel Bonn
General Relativity and Quantum Cosmology
Octupole moments and the non-universality of free-fall in general relativity
Abraham I. Harte and Paul Ramond
Extended bodies in general relativity do not necessarily fall along geodesics. Instead, a body can experience accelerations that depend on its angular momentum, as well as on its quadrupole, octupole, and higher-order moments. Moreover, due to the fact that one object's multipole moments can evolve differently from those of another, different bodies can fall differently—even with identical initial data. This paper examines how octupole moments contribute to the non-universality of free-fall in general relativity. We begin by showing that in arbitrary
vacuum spacetimes, only the trace-free component of an octupole moment can affect an object's motion. It follows that at least 16 out of 40 octupole components decouple from the laws of motion. We also obtain two decompositions for trace-free octupole moments, one in terms of a timelike frame vector and the other in terms of a null tetrad. These decompositions are applied to motion both in static Newtonian spacetimes and in fully-relativistic
vacuum spacetimes that are of Petrov type D (such as Kerr). In Newtonian spacetimes, the mass moments are shown to have their ordinary Newtonian effects. The momentum moments instead determine a body's hidden momentum—the misalignment between its momentum and its velocity. In Petrov type D spacetimes, we show that some torques that are impossible with quadrupole moments are generically possible with octupole moments. Octupole moments can thus have qualitatively-different effects from quadrupole moments.
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Solar and Stellar Astrophysics
Collisionless stationary states of a stratified plasma in an expanding magnetic tube with stochastic heating
Luca Barbieri, Pascal Démoulin and Daniel Verscharen
We investigate the collisionless kinetic structure of the upper
solar atmosphere in an expanding
magnetic field. Building on established velocity-filtration models, we extend the
stochastic multi-temperature framework developed in previous works by including
magnetic-field expansion and
magnetic-moment conservation.
Stochastic heating generates a non-Maxwellian boundary distribution through the superposition of particle populations associated with different temperatures. We consider a stationary two-component
plasma confined within an expanding
magnetic flux tube and subject to
gravity, self-consistent electrostatic interactions, the Pannekoek–Rosseland electric field, and
magnetic-moment conservation. Starting from the Vlasov equation, we derive fully analytical expressions for the distribution functions, density, and parallel, perpendicular, and total temperature profiles. The combined conservation of energy and
magnetic moment generates a loss-cone distribution, reducing the density relative to the unmagnetized case and producing temperature anisotropy. For a single-temperature boundary, the competition between
gravity and
magnetic-moment conservation produces a maximum in the parallel temperature, for which we derive and numerically validate analytical scaling laws. With
stochastic heating, gravitational filtering enhances the contribution of hotter populations at coronal heights, while
magnetic-moment conservation amplifies the velocity-space anisotropy. Our analytical solution provides a collisionless
benchmark for future kinetic models incorporating more realistic
magnetic-field geometries, Coulomb collisions, and turbulent particle scattering.
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High Energy Physics (Theory)
Diagonally gauged anomaly-free 6D supergravities and their vacua
Xu Guo, Yi Pang, Henning Samtleben et al. (+1 more)
We describe a bounded search for local and global anomaly-free six-dimensional $(1,0)$ models with tensor number $T=1$ and gauge group containing a diagonal abelian factor $U(1)_{R+}$. The abelian factor is the diagonal combination of the usual gauged $U(1)_R$ and a $U(1)\subset Sp(n_H)$ acting on hypermultiplets. We have searched for locally and globally anomaly-free $G_1\times U(1)_{R+}$ and $G_1\times G_2\times U(1)_{R+}$ models, subject to restrictions on the ranks of the simple factors and on the maximal charges carried by matter. We find that, unlike the case of $U(1)_R$ gauged models which are relatively rare, the diagonally gauged ones offer a rich landscape. We also study the 6D
vacua of these models and find that they admit supersymmetric 6D Minkowski
vacua, for which the diagonal nature of the R-
symmetry gauging is necessary.
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All authors Xu Guo, Yi Pang, Henning Samtleben, Ergin Sezgin
General Relativity and Quantum Cosmology
Cosmological initial data without periodic boundary conditions
Károly Csukás
We apply the
parabolic-
hyperbolic formulation of the Einstein constraint equations to generate cosmological initial data. The freely specifiable
geometric data correspond to flat Friedmann–Lemaître–Robertson–Walker background, while the matter sector contains localized anisotropic perturbations of a perfect fluid. Unlike the standard approach, our method evolves the constraints outward from regular data at the origin and therefore requires no boundary conditions. This makes our method well suited as a starting point in investigating systematic biases introduced by commonly adopted boundary conditions, such as periodic boundaries. A second advantage concerns uniqueness: standard
elliptic solvers may fail when multiple solutions exist, whereas solving the constraints as a well-posed evolutionary system always yields a unique solution. To demonstrate our method, we implement it numerically and generate cosmological initial data with localized anisotropic perfect fluid perturbations.
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Instrumentation and Methods for Astrophysics
PROVIDENCE: a ground station for space observation
P.-L. Mayeur, J.-F. Sauvage, T. Fusco et al. (+25 more)
PROVIDENCE is an ONERA-led project to install a new-generation optical ground station at the Haute-Provence Observatory (OHP) in South of France. Built around a 2.5-meter aperture, the station addresses five core science cases: space domain awareness, astronomy,
laser activities and communications, atmospheric characterization, and instrumental prototyping. The project is organized into three parallel subprojects covering the
telescope (Providence T), the building (Providence B), and the instruments (Providence I), the latter including the facility's first-light adaptive optics instrument, INTERSTELLAR. This paper presents the scientific motivation, the project architecture, the
telescope technical specifications, the civil-engineering challenges associated with replacing the existing T152 equatorial
telescope, and the station layout designed to host multiple co-active instrument teams. The project roadmap targets First Light in 2029, timed to track the close-approach flyby of asteroid Apophis.
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All authors P.-L. Mayeur, J.-F. Sauvage, T. Fusco, N. Védrenne, C. Petit, D. Barbon-Dubosc, G. Leplat, G. Guerrin, A. Vincent-Randonnier, V. Michau, F. Dolon, M. Ferrari, F. Huppert, P.-E. Blanc, S. Basa, J. Floriot, B. Neichel, T. Guerini, J. Mingot, T. Jolivet, R. Buchard, N. Robbe, J. Dezeuze, S. Idri, F. Rosso, C. Boyer, S. Thomas, S. Egron
Mesoscale and Nanoscale Physics
Visualization of Defect Electronic States in Layered Semiconductor CrSBr
Jonathan Brunette, Joost Aretz, Kiyoung Jo et al. (+5 more)
Chromium sulfur bromide (CrSBr) is a layered
magnetic semiconducting material combining a rich
magnetic phase diagram with axis-dependent electronic and optical properties. While defects in CrSBr have been shown to affect
magnetic order and excitonic responses, their microscopic nature, atomic structure, and electronic properties are not yet fully understood. In this work, we use scanning tunneling microscopy/spectroscopy (STM/STS) to explore the structure and electronic signatures of two prominent defects in bulk CrSBr. Their structure reflects the
symmetries of the underlying
lattice, with electronic features near the valence band edge. By comparing experimental data with ab initio simulated STM images, we infer that a common defect corresponds to a b-axis-aligned double sulfur vacancy, in line with findings from a recent growth analysis study. This result advances our understanding of the role of intrinsic defects in shaping the electronic structure of CrSBr.
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All authors Jonathan Brunette, Joost Aretz, Kiyoung Jo, Aljoscha Soll, Zdeněk Sofer, Malte Rösner, Nathan Guisinger, Adina Luican-Mayer
Quantum Physics
Classifying Topology via Edge-State Pure Thermalization
Fatih Ozaydin, Haydar Sahin, Armando Perez-Leija et al. (+4 more)
Repeated-interaction machines distinguish heat-like from work-like resources through the steady states they generate, but whether
topology can control this distinction remains unknown. Here we reveal the role of
topology in the process by showing that topological edge states can act as pure-thermalization fuels. For an open Su-Schrieffer-Heeger chain used as the fuel source of a micromaser, edge eigenstates suppress both displacement and squeezing and drive the cavity to a Gibbs state, whereas bulk eigenstates activate coherent channels and yield thermo-mechanical operation. This edge-bulk thermodynamic dichotomy remains robust under realistic decoherence, cavity loss, bond disorder, and moderate onsite disorder. We further design a superconducting implementation in which a sixteen-site SSH eigenstate is deterministically compressed into a four-
qubit fuel register. The resulting cavity response provides a transport-free classifier of
topology and identifies a
topology-thermodynamics link that extends beyond cavity-QED to repeated-interaction settings more generally.
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All authors Fatih Ozaydin, Haydar Sahin, Armando Perez-Leija, Azmi Ali Altintas, Cihan Bayindir, Ozgur E. Mustecaplioglu, Sahin K. Ozdemir
Materials Science
Lifetime effects and satellites in the photoelectron spectrum of platinum metal
Prajna Bhatt, José Julio Gutiérrez Moreno, Laura E. Ratcliff et al. (+9 more)
This work presents a comprehensive investigation of the electronic structure and many-body photoemission effects in metallic platinum using reflection high-energy electron energy-loss spec- troscopy (RHEELS), soft X-ray photoelectron spectroscopy (SXPS), and hard X-ray photoelectron spectroscopy (HAXPES), supported by ab initio calculations. Shallow and deep core state spectra enable the systematic characterisation of intrinsic line-shape asymmetries and satellite structures. Correlation of photoelectron satellites with RHEELS loss features allows the assignment of inter- band transitions, surface and bulk plasmons, plasmonic overtones, and semi-core ionisation losses across the Pt spectrum. Several previously unresolved satellite features and
spin-orbit splittings are identified and discussed. Comparison of experimental valence band spectra with orbital-projected densities of states calculated using ab initio density functional theory (DFT) and G0W0 approaches, with and without
spin-orbit coupling, demonstrates the critical role of relativistic effects in reproducing the Pt valence electronic structure. Together, these results establish a unified, internally consistent spectroscopic reference for metallic platinum, providing a robust framework for interpreting photoelectron spectra of Pt-containing catalysts, electronic materials, and related 5d transition metal systems.
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All authors Prajna Bhatt, José Julio Gutiérrez Moreno, Laura E. Ratcliff, Aysha A. Riaz, Charlotte. M. L. André, Ann S. Y. Lu, Robert G. Palgrave, Andrei Gloskovskii, Christoph Schlueter, Pardeep K. Thakur, Tien-Lin Lee, Anna Regoutz
Quantum Gases
Fluctuation-Induced Bistability in the Dissipative Dynamics of Generic Cavity-Matter Quantum Systems
Luisa Tolle, Simon B. Jäger, Ameneh Sheikhan et al. (+2 more)
We demonstrate that fluctuation-induced bistability is a robust and generic phenomenon in strongly interacting many-body systems with strong light-matter coupling. We identify a common microscopic mechanism based on resonances between photonic transitions and many-body energy scales, unifying the emergence of fluctuation-induced bistability across a broad class of models, including interacting
spins,
fermions, and
bosons coupled to cavity modes. We develop complementary methods to study both the steady-state properties of fluctuation-induced bistability and its dynamical formation at finite times. In particular, we introduce the dressed-state rate equation approach, which reveals rich metastable dynamics and enables the investigation of its system-size dependence. By comparing its predictions with numerically-exact tensor-network simulations, we identify signatures of fluctuation-induced bistability already in small systems on finite timescales. Our results establish fluctuation-induced bistability as a universal feature of dissipative cavity-coupled many-body systems and provide a general framework for the investigation of its non-
equilibrium dynamics across a wide range of hybrid
quantum platforms.
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All authors Luisa Tolle, Simon B. Jäger, Ameneh Sheikhan, Corinna Kollath, Catalin-Mihai Halati
Computational Physics · Cross-listed from math.NA
An unfitted boundary algebraic equation method with Calderón preconditioning for 2D Stokes flow in irregular geometry
Wenjun Ying and Qing Xia
We present an unfitted boundary algebraic equation method for the two-dimensional exterior/interior Stokes equations on a staggered MAC grid. By constructing an explicit free-space pair of velocity and pressure
lattice Green's functions (LGFs) from free-space Laplace LGFs, we represent homogeneous fields using sources supported exclusively on thin staggered boundary layers. This formulation imposes physical Dirichlet data at cut points via local interpolation, while sampled-normal rank updates remove hydrostatic null modes associated with single or multiple obstacles. The workflow parallels that of classical boundary integral formulations and requires no artificial boundary conditions for exterior flows, but follows a discretize-then-represent route and does not require singular/near-singular quadrature. The resulting dense boundary system is solved via GMRES, utilizing a componentwise discrete Calderón preconditioner built from the scalar Laplace kernel and padded FFTs for fast volume convolutions. Extensive numerical validation, including multiply connected domains, narrow gaps, and Moffatt eddies, confirms discrete incompressibility to solver accuracy and recovers the expected Moffatt eddy scaling. We achieve second-order velocity and pressure convergence and bound maximum discrete divergence within numerical accuracy. The discrete Calderón preconditioner reduces the condition number by orders of magnitude and yields nearly mesh-independent conditioning in exterior configurations, while remaining effective—though more demanding—for narrow-gap and fine-grid interior problems.
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Quantum Physics
Device-Independent Self-Testing of the Three-Qubit CCZ Hypergraph State
Yunguang Han, Xin Kuang, Xingyuan Bu et al. (+1 more)
The three-
qubit CCZ state is the smallest rank-three hypergraph state and an elementary entangled magic resource. Its cubic phase is governed by generalized stabilizers that are not Pauli strings, so standard graph-state self-testing arguments do not apply directly. We show that twenty correlators, all obtainable from five of the eight global input triples in the tripartite two-input, two-output scenario, determine this state and the action of the Pauli $X/Z$ measurements up to local isometries. The proof fixes eight equally weighted computational branches and propagates conditional $X$-flip relations across the branch cube, recovering the minus sign of the $111$ amplitude. These five-context correlations are nonlocal, but the canonical Pauli measurements cannot attain the largest
quantum value of any Bell inequality that they violate: whenever they maximize a Bell expression, its local bound has the same value. Introducing an independent third measurement makes self-testing from maximal Bell violation possible. We construct an explicit Bell inequality whose maximal
quantum violation self-tests the CCZ state and all three local measurements. An exact sum-of-squares decomposition proves the
quantum bound, and its equality conditions yield an analytic SWAP extraction. Together, these results give two explicit device-independent self-tests of the CCZ state and demonstrate that determining a state and its measurements from several correlator equalities is distinct from identifying them through the maximal violation of a single Bell inequality.
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All authors Yunguang Han, Xin Kuang, Xingyuan Bu, Yukun Wang
Quantum Physics
QUBO Sampling for Mixed Binary Quadratic Programming without Continuous Variable Binarization
Taisei Takabayashi and Masayuki Ohzeki
Quantum annealing and related combinatorial optimization methods typically accept quadratic unconstrained binary optimization (QUBO) problems as input, whereas many practical models include constraints and continuous variables. Standard QUBO conversions discretize continuous variables, increasing the binary dimension and often making feasible low-energy states harder to sample. We develop a Lagrange-multiplier method for a separable class of mixed-binary quadratic programs (MBQPs) without discretizing continuous variables. The method is based on a finite-temperature free-energy formulation and uses QUBO sampling for the binary sector. At fixed Lagrange multipliers, the continuous sector is integrated out analytically and enters only the multiplier update, leaving a QUBO over the original binary variables. We evaluate the method on the continuous relaxation of the quadratic $p$-median problem. Compared with a penalty-based QUBO formulation, it generates feasible solutions more reliably. At an appropriate inverse temperature, its conditional relative error is comparable to that of local search for small instances and often lower for the larger tested instances. In the time-to-target comparisons, the proposed method maintains high target-reached rates for stringent fixed-accuracy targets. For the larger instances within the tested range, it also reaches the prescribed targets faster than a commercial mixed-integer optimization solver.
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General Relativity and Quantum Cosmology
Zipoy–Voorhees spacetime with Maxwell and dilaton fields: exact solution and equatorial geodesics
Haryanto M. Siahaan
We derive a new exact solution of four-dimensional Kaluza-Klein theory by applying the uplift-boost-reduction procedure to the Zipoy-Voorhees
vacuum seed. The resulting Zipoy-Voorhees-dilaton spacetime is a static, axisymmetric, asymptotically flat configuration parametrised by a seed length scale $M$, the Zipoy-Voorhees deformation parameter $k$, and a boost parameter $\alpha$ that controls the electric charge. For $k=1$ it admits a regular black-hole interpretation; for $k \neq 1$ it inherits the naked
curvature singularity of the seed at $r=2M$. We extract the ADM mass, electric charge, and dilaton charge, finding that the dilaton charge obeys an algebraic constraint independent of the quadrupole deformation. The equatorial geodesics of neutral test particles and
photons are studied in detail. A compact algebraic identity locates the exterior-
photon-ring threshold at $k=1/2$ for all $\alpha$, generalising the known threshold of the
vacuum Zipoy-Voorhees case. The innermost stable circular orbit is mapped over the $(k,\alpha)$ plane, and the comparison with Schwarzschild is shown to depend qualitatively on whether seed-mass or ADM-mass units are used. We further compute the gravitational
redshift, which diverges on the $r=2M$ surface and renders the near-singularity orbits effectively invisible, and the critical impact parameter setting the characteristic shadow size, which in ADM-mass units shrinks below the Schwarzschild value as the charge grows.
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Fluid Dynamics
A general synthetic iterative solver for axisymmetric rarefied gas and electrostatic charged-particle flows
Yifan Wen and Lei Wu
An axisymmetric general synthetic iterative scheme (AxiGSIS) is proposed to simulate rarefied gas flows and charged particle transport under prescribed electrostatic fields. This solver adopts a finite-volume discrete velocity method defined over the two-dimensional axisymmetric meridian plane paired with a three dimensional molecular velocity space. Under the GSIS framework, the kinetic solver computes nonequilibrium stress and heat flux, which are subsequently imported as corrective source terms into the macroscopic synthetic system. Fast iterative updates of low order flow primitive variables are performed on this macroscopic system, whose corrected flow fields are then fed back to the kinetic solver. This bidirectional coupling enables rapid propagation of macroscopic information and substantially accelerates steady state convergence, particularly in near continuum flow regimes. Four
benchmark flows are examined: the Taylor Couette flow, neutral nozzle expansion flow, charged particle flow past an electrostatic sphere, and electrostatically accelerated charged-particle nozzle flow. Results show that AxiGSIS reproduces the reference kinetic solutions and accurately captures axisymmetric flow physics and charged-particle responses to prescribed electrostatic fields. Utilizing fewer spatial
cells and iteration steps, AxiGSIS substantially cuts computational overhead relative to conventional kinetic iterations, particularly for low and moderate Knudsen number flows.
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High Energy Physics (Theory)
Defect entanglement entropy for superconformal RG Interfaces
Evangelos Afxonidis and Christopher Rosen
We study the defect contribution to the
entanglement entropy of a spherical region centred on four-dimensional superconformal RG interfaces. These interfaces are supersymmetric codimension one defects separating the Leigh–Strassler SCFT
vacuum and the $\mathcal{N}=4$ SYM theory deformed by spatially varying mass terms. Exploiting the
holographic dual to these interfaces, we extract a cutoff-independent interface contribution to the
entanglement entropy, $\mathcal{C}^I$. We quantify the non-trivial dependence of $\mathcal{C}^I$ on the supersymmetric mass deformation, and observe a scaling regime for large deformations. We further relate $\mathcal{C}^I$ to the renormalized on-shell action and the stress-tensor one-point function of the interface theory. Our results provide the first fully backreacted
holographic computation of this
entanglement quantity for superconformal RG interfaces in more than two dimensions.
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Soft Condensed Matter
Two-Temperature Induced Phase Separation: Non-equilibrium Phase Behavior, Ordering, and Kinetics
Nayana Venkatareddy, Jaydeep Mandal, Jayeeta Chattopadhyay et al. (+1 more)
Two-temperature induced phase separation (2-TIPS) has emerged as a generic non-
equilibrium mechanism in scalar active systems with heterogeneous activity, where particles coupled to different thermal reservoirs spontaneously demix into dense cold and dilute hot phases. Unlike
equilibrium phase separation or motility-induced phase separation (MIPS), 2-TIPS is driven solely by unequal energy injection and the resulting heat flux between particle species. This review summarizes recent advances in 2-TIPS across diverse soft-matter systems, highlighting both its universal non-
equilibrium mechanisms and the emergent ordered phases arising from particle shape anisotropy, chirality, confinement, and
topology. We further discuss density-dependent phase-separation kinetics and coarse-grained descriptions linking microscopic dynamics to macroscopic behavior, and outline key directions for future research.
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All authors Nayana Venkatareddy, Jaydeep Mandal, Jayeeta Chattopadhyay, Prabal K. Maiti
Mathematical Physics
Representation of the causal logic for the Dirac system and the electron
Domenico P.L. Castrigiano, Carmine De Rosa and Valter Moretti
We construct a covariant representation of the causal logic for the Dirac system and the electron, based on the conserved Dirac probability current and a general current-to-localization procedure for achronal regions. A
polynomial decay estimate, derived by a non-stationary phase argument, verifies the conditions required to define covariant achronal localization for the full Dirac system. Extending this localization to complete spacetime regions yields the corresponding causal-logic representation; restriction to the positive-energy invariant subspace gives the analogous construction for the electron. We establish several structural properties. On Euclidean space, Dirac localization agrees with canonical projection-valued localization, while its position operator differs from the Newton–Wigner operator by an explicitly determined bounded self-adjoint correction. Full Dirac achronal localization is projection valued and represents achronal separateness by orthogonality, thus satisfying microscopic causality. After compression to the electron subspace, it becomes positive-operator valued while preserving causality. We further extend known results from spatial to general achronal regions, prove separation and norm-one criteria, and analyze the high-boost limit, obtaining Lorentz contraction in a precise probabilistic sense. Finally, we discuss the electron–positron decomposition and the state transformation induced by position measurements, showing that measurement-induced positron production is universal and independent of the specific measuring device.
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Instrumentation and Methods for Astrophysics
HARMONI at ELT: optical design of the spectrograph sub-system
Eduard Muslimov, Matthias Teczaa Edgar Castillo-Dominguez, James Kariuki et al. (+4 more)
HARMONI is an adaptive optics assisted, near infrared integral field spectrograph for the European Extremely Large
Telescope. It covers a spectral range from 750 nm to 2450 nm with resolving powers from 3000 to 7000 and spatial sampling of 25 mas and 6 mas. It can operate in two adaptive optics modes, SCAO and MCAO. The spectrograph represents the last optical sub-system of the HARMONI instrument optical train that disperses the light and forms a two-dimensional spectrogram on its scientific detectors. Changes in the top-level goals and specifications have led to a significant revision of the spectrograph optical design. The current baseline design consists of a two-mirror unobscured collimator, a set of six volume-phase
holographic grisms, and a two-mirror unobscured camera. The design is more compact than the previous version, it uses anamorphic freeform mirrors to correct aberrations, and is expected to reach a minimum transmission 57% with improved accessibility of the detector unit and reduced scattered light.
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All authors Eduard Muslimov, Matthias Teczaa Edgar Castillo-Dominguez, James Kariuki, Liam Bolanda, Miriam Cisneros-Gonzalez, Kieran McCall, Sophie Paszynska
Chemical Physics
Determination of fundamental properties of nitrogen from first principles. III. Temperature and frequency dependence of the molecular polarizability and magnetic susceptibility
Jakub Lang, Giovanni Garberoglio, Michał Przybytek et al. (+1 more)
This work is the third part of the series of papers that focus on the theoretical determination of the properties of nitrogen that are relevant in metrology. Here we present first-principles calculations of the temperature and frequency dependence of the molecular polarizability and
magnetic susceptibility of the nitrogen molecule (N$_2$). The purely electronic contributions to the static polarizability, Cauchy coefficients (up to sixth order), and isotropic
magnetic susceptibility are computed over a range of internuclear distances using a robust composite scheme combining several electronic structure methods. The temperature dependence, evaluated from $50$~K to $2000$~K, is determined using two independent methods: rovibrational averaging and path integral Monte Carlo (PIMC). The polarizabilities obtained from theory agree with the recent high-precision thermometry measurements, wherever the latter are available, but are significantly less accurate. However, the main usefulness of the theoretical data revolves around combining it with the available experimental results to generate semi-empirical estimates of various quantities that have never been measured thus far. As an example, we determine highly accurate semi-empirical estimates of the static polarizability at key reference temperatures, $\alpha_0(T)=11.735\,962$~a.u.\ at $T=303$~K and $\alpha_0(T)=11.735\,585$~a.u.\ at $T=273.16$~K. Furthermore, we report theoretical values for the
magnetic susceptibility, highlighting the importance of the paramagnetic contribution, and address a significant discrepancy with the experimental data for this quantity.
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All authors Jakub Lang, Giovanni Garberoglio, Michał Przybytek, Michał Lesiuk
Quantum Physics
Space-division multiplexed quantum key distribution exploiting multi-plane light conversion for few-mode fibers
Qian Zhang, Stefan Krause, Felix Kunzmann et al. (+1 more)
As
quantum key distribution (QKD) progresses from laboratory demonstrations toward practical deployment,
quantum communi- cation networks increasingly require higher key rates and the ability to distribute independent secret keys among multiple users and network nodes. In this paper we present a promsing approach with multi-plane light conversion (MPLC) for demultiplexing entangled
photons, transmitted through a few-mode fiber (FMF). We experimentally demonstrated a spatially multiplexed BBM92 QKD scheme. The modes are selectively excited through separate single-mode-fibers and subsequently separated by MPLC into distinct output ports. Unlike high-dimensional QKD based on coherent modal superpositions, our approach exploits distinguishable guided modes as parallel channels while preserving the
entanglement required for QKD. For the multiplexed links, we obtain
quantum bit error rates of $1.9 \pm 0.4\%$ for the channel 1 and $6.8 \pm 0.8\%$ for the channel 2. These results are relevant for scalable
quantum-secured networks, space-division-multiplexed QKD systems, multi-user
entanglement distribution, and future
quantum internet architectures, where parallel
quantum channels must be implemented without compromising the
quantum correlations required for security.
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All authors Qian Zhang, Stefan Krause, Felix Kunzmann, Juergen W Czarske
Quantum Gases
Thermodynamic Signatures of Phase Separation in Mass Imbalanced Fermi Mixtures: Superfluid Density of States and Quasiparticle Specific Heat in the 163Dy 40K Atomic Mixture
Neda Ebrahimian
Mass imbalance changes not only pairing in a polarized
Fermi gas but also the thermodynamic condition under which normal and superfluid components can remain phase separated. The low-temperature properties of mass imbalanced two component
Fermi gases are investigated within the local density approximation on the BCS side of the BCS BEC crossover, with an unpolarized superfluid spatially separated from a partially polarized normal component. For each interaction strength and mass ratio, the pairing gap, average chemical potential, Hartree Fock potentials, and imbalance chemical potential are obtained self consistently, with the latter determined by the normal superfluid phase separation condition rather than varied independently. The results show that a larger mass ratio requires a larger imbalance chemical potential to maintain phase separation. For the 163Dy 40K mixture, an increase in the absolute value of the interaction strength raises the average and imbalance chemical potentials while reducing the pairing gap. The resulting changes modify the quasiparticle spectrum and the superfluid density of states and are reflected directly in the thermal response, with the quasiparticle specific heat decreasing at a fixed mass ratio. In contrast, increasing the mass ratio enhances the specific heat, which is associated with the larger density of available states near the
Fermi surface of the heavier majority component. The results thus connect the normal superfluid phase separation condition with the quasiparticle spectrum and superfluid density of states, and show that the specific heat provides a clear thermal signature of mass imbalance in the phase separated regime.
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Optics
Laser Remelting for Reduced Porosity on Additively Manufactured Aluminium Mirrors
Joshua West, Valentina Oyarzun, Marcell Westsik et al. (+17 more)
Additively manufactured (AM) AlSi10Mg mirrors are fabricated through
laser powder bed fusion (LPBF), allowing the use of complex geometries such as
lattices and organic structures that enable high mass reduction while maintaining mechanical stiffness. Micron-sized pores that cause optical scatter may form during LPBF as a consequence of deviations from the optimal processing window, particularly from
laser energy input and scan strategy. This work proposes a
laser remelting strategy aimed at reducing porosity; standard LPBF build steps automatically alternate with
laser remelting passes, where previously deposited material is remelted during fabrication.
Laser remelting is evaluated through fabricating 10 mm proof-of-concept cubes. Following single point diamond turning (SPDT), optical measurements characterised surface roughness and identified surface artefacts. The best-performing AlSi10Mg remelted cube exhibited no pores within sampled regions and achieved 6.4 nm average surface roughness, comparable to a conventionally manufactured RSA 6061 control cube (5.8 nm). Driven by these results, AM 52 mm diameter secondary sandwich mirrors were manufactured using LPBF and
laser remelting. These incorporate an optimised diamond TPMS
lattice to achieve a 50% mass reduction while accommodating design for AM considerations. Unlike the cube study, the optical surface of the remelted mirror after SPDT exhibited residual porosity and 11.8 nm average surface roughness. These results show that while the proof-of-concept confirmed the viability of
laser remelting in reducing porosity within simple geometries, optimisation of the LPBF and SPDT processes are required to translate the benefits of
laser remelting to lightweight AlSi10Mg AM mirrors.
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All authors Joshua West, Valentina Oyarzun, Marcell Westsik, Younes Chahid, Magdalena Kraus, Scott McPhee, William Brzozowski, Samuel Tammas-Williams, Nicola Cayzer, Fraser Laidlaw, Sameer Dayanand Meshram, Daniel Ordnung, Berk Baris Celik, Michel Smet, Mirko Sinico, Wenjuan Sun, Brecht Van Hooreweder, Michael Harris, Stephen James, Carolyn Atkins
High Energy Physics (Phenomenology)
Thermal Resummation for Very Strong First-order Phase Transitions
Philipp Klose
Effective potentials are a key ingredient for predicting
stochastic gravitational wave backgrounds from strong first-order phase transitions in the early universe. Established techniques for a robust computation, including dimensional reduction, rely on a high-temperature expansion that is expected to break down for very strong transitions capable of producing observable backgrounds at next-generation gravitational wave detectors such as LISA. We argue that existing 2PI effective action techniques enable consistent resummation for such transitions, and use them to compute the next-to-leading order effective potential of the Abelian
Higgs model for a strong transition in a general covariant gauge. We find that our result can be recovered from a Daisy resummed potential by modifying the power counting, and show explicitly that it satisfies the leading-order Nielsen identity needed for gauge-independent predictions of the bubble nucleation rate and is consistent with prior results for small
Higgs condensates.
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Quantum Physics
Tailoring optical Schrödinger cat states via orientation-dependent high-harmonic generation in $\rm{H}_2^+$
Ziyang Gan, Ahai Chen and Yuhai Jiang
We theoretically demonstrate that the molecular orientation angle $\theta$ provides a structurally intrinsic, continuously tunable control parameter for engineering optical Schrödinger cat states via high-harmonic generation (HHG) in H$_2^+$. Coupling time-dependent Schrödinger equation simulations to the fully quantized HHG framework, we evaluate the Wigner functions of the post-selected harmonic-mode states under two complementary conditioning strategies. Conditioning on resonance-enhanced low-order harmonics exploits the complementary dipole selection rules of the $1\sigma_g\to1\sigma_u$ and $1\sigma_g\to1\pi_u$ transitions, driving a kitten-cat crossover whose direction is opposite in the two channels as $\theta$ is varied. Conditioning on plateau harmonics instead exploits two-center destructive interference, producing a reentrant cat$\to$kitten$\to$cat transition controlled by the order-dependent interference angle $\theta^*(q)$. In both cases the crossover is decoupled from the
laser intensity, focal geometry, and molecular density, offering a degree of control with no counterpart in atomic targets.
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Cosmology and Nongalactic Astrophysics
Contribution to the 2026 Cosmology session of the 60th Rencontres de Moriond: Galactic moments: Understanding polarized foregrounds complexity in the quest for CMB primordial $B$ modes with LiteBIRD
S. Vinzl, J. Aumont, L. Vacher et al. (+4 more)
Accurate modeling of polarized
Galactic emission has become a major challenge for current and next-generation
cosmic microwave background (CMB) $B$-mode experiments. Ignoring the spectral complexity of thermal
dust and
Galactic synchrotron emission when integrating along the line of sight and over large sky fractions inevitably leads to biases in CMB polarization analyses. In this work, we review how the future LiteBIRD satellite, which will benefit from an increased number of bands and sensitivity with respect to past CMB experiments such as Planck, will exploit its broader frequency coverage to characterize the spectral properties of interstellar medium emission across the three-dimensional structure of the Milky Way. We show that the canonical description of foreground spectral behavior will reach its limits for LiteBIRD, and that this challenge can be addressed using the moment expansion formalism.
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All authors S. Vinzl, J. Aumont, L. Vacher, R. T. Génova-Santos, D. Adak, A. Rizzieri, for the LiteBIRD Collaboration
Materials Science
Machine learning based prediction of optical properties in two-dimensional Mo-W-S-Se-Te transition-metal dichalcogenide alloys through physics-informed sampling
Vivek Chowdhury, Tarvir Anjum Aditto, Md. Samrat et al. (+2 more)
Two-dimensional transition-metal dichalcogenide (TMD)
alloys provide a compositionally tunable platform for controlling the optical and electronic properties. However, systematic prediction of their dielectric response across multicomponent
alloy spaces remains challenging owing to the combinatorial cost of first-principles calculations. In this work, we combined ab initio optical-property calculations with a tabular foundation-model regression to predict the real and imaginary components of the frequency-dependent dielectric function for Mo-W-S-Se-Te TMD
alloys. A
dataset of 99
alloy structures spanning binary, ternary, quaternary, and quinary compositions was generated using density functional theory (DFT). The resulting polarization-dependent dielectric spectra were used to train a tabular prior-fitted network (TabPFN) and evaluated against the conventional Extra Trees and XGBoost models. To accommodate the in-context capacity limit of TabPFN, we introduced a non-uniform, physics-informed energy subsampling strategy that concentrates sampling in the optically active region above the band gap, where interband absorption is strongest. Trained solely on quaternary
alloys, our TabPFN reconstructed the dielectric spectra of held-out quaternary compositions with an R2 > 0.98 and a mean absolute error below 0.10 for all four dielectric components, outperforming both baselines while requiring no gradient-based training or hyperparameter tuning. Our model further predicted derived optical quantities, including refractive index, extinction coefficient, and absorption coefficient. Additionally, our model generalized in a zero-shot manner to binary, ternary, and quinary
alloys absent from the training set, with quinary predictions achieving an R2 > 0.97.
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All authors Vivek Chowdhury, Tarvir Anjum Aditto, Md. Samrat, Hafiz Imtiaz, Ahmed Zubair
Nuclear Experiment
Exploring $\alpha$- and $\beta$-decay-induced quenching of the $^{229}$Th nuclear-clock isomer in solid-state hosts
Y. Elskens, M. Athanasakis-Kaklamanakis, S. Arasada Pradeep et al. (+52 more)
The radiative decay dynamics of an ensemble of $^{229\mathrm{m}}$Th
nuclei embedded in CaF$_2$ and MgF$_2$ is investigated. The isomer is populated through $\beta$ decay of $^{229}$Ac following ion implantation, and its radiative decay is detected using
vacuum-ultraviolet spectroscopy and measured as a function of time. This allows to identify and quantify the quenching of the radiative-decay signal induced by $\alpha$ or $\beta$ radiation. The quenching probability density is determined in different CaF$_2$
crystals and in a MgF$_2$
crystal, revealing differences up to two orders of magnitude between the investigated samples and a strong dependence on the host material and defect densities. The results support a microscopic mechanism mediated by charge carriers in which electronic excitations created by the decay radiation are captured near Th defects, thereby favoring non-radiative decay channels.
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All authors Y. Elskens, M. Athanasakis-Kaklamanakis, S. Arasada Pradeep, M. Au, S. Bara, M. Bartokos, K. Beeks, C. Bernerd, B. Biesmans, S. Casci, P. Chhetri, K. Chrysalidis, A. Claessens, T. E. Cocolios, J. G. Correia, A. R. G. Costa, H. De Witte, S. B. Diewald, Ch. E. Düllmann, R. Ferrer, R. Heinke, G. Holthoff, F. Ivandikov, Yu. Kudryavtsev, U. Köster, S. Kraemer, M. Laatiaoui, R. Lica, C. Merckling, J. Moens, I. Morawetz, D. Moritz, L. M. C. Pereira, S. V. Pineda, S. Raeder, S. Rothe, S. Sabrieva, M. Satrazani, F. Schaden, K. Scharl, T. Schumm, S. Stegemann, J. Stricker, T. Teschler, P. G. Thirolf, P. Van den Bergh, P. Van Duppen, A. Vantomme, R. Villarreal, L. von der Wense, U. Wahl, Y. Wang, M. Wiesinger, Z. Yue, F. Zacherl