Mesoscale and Nanoscale Physics
Majorana parity qubit in coupled minimal Kitaev chains
Francesco Zatelli, Bart Roovers, Nick van Loo et al. (+11 more)
Majorana zero modes provide a route to fault-tolerant
qubits by encoding information non-locally in
fermion parity. Their sensitivity to noise is expected to decrease exponentially with increasing separation between the Majoranas, a suppression known as topological protection. Kitaev chains engineered in
quantum dot-
superconductor arrays provide a tunable platform in which separated Majorana zero modes can emerge at the ends of the chain, even in two-site chains. These minimal-chain modes are known as poor man's Majoranas and retain characteristic Majorana properties, including near-zero energy and equal electron-hole character, but have only limited protection. A key outstanding challenge is to move beyond identifying such modes in electrical transport measurements and achieve coherent
qubit control in the time domain. Here, we demonstrate a Majorana parity
qubit by realizing coherent coupling between two-site Kitaev chains. Since total
fermion parity is conserved, the system separates into global even and odd parity
manifolds. We observe coherent parity oscillations in both
manifolds with equal oscillation frequencies at the Majorana sweet spot, as predicted for isolated Majorana zero modes. We further show that the oscillation frequency and coherence depend systematically on inter-chain coupling and
quantum-dot detunings, in close agreement with our model for short, partially protected chains. Our results establish the first coherent control of a Majorana
qubit, encoded in the
fermion parity of Majorana zero modes in minimal Kitaev chains.
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All authors Francesco Zatelli, Bart Roovers, Nick van Loo, Antonio Lombardi, Juan D. Torres Luna, Sebastian Miles, Vincent P.M. Sietses, Florian J. Bennebroek Evertsz', Pablo Cova Fariña, Alberto Bordin, Ghada Badawy, Erik P.A.M. Bakkers, Michael Wimmer, Leo P. Kouwenhoven
Plasma Physics
3D Plasma plume characterization of an electrodeless thruster cluster in magnetic arch configuration
Sacha A. Huot, Marco Riccardo Inchingolo, Jaume Navarro-Cavallé et al. (+1 more)
Clustering electrodeless
plasma thrusters in pairs with opposing
magnetic polarities offers an easy means to scale-up the propulsion system of future missions, and also, to mutually cancel their respective
magnetic dipoles. Their
magnetic nozzles merges to form a new
topology, the `
magnetic arch', which can yield a lower
plasma plume divergence than two separate
magnetic nozzles. This work characterizes the
plasma expansion in the fully-closed
magnetic arch of a cluster of two electron-cyclotron resonance thrusters with electrostatic probes (Langmuir probes, Faraday cups, and a Retarding Potential Analyzer). Electrostatic potential,
plasma density, electron temperature, ion current and energy are measured in the two orthogonal planes of
symmetry of the setup for various operating conditions. Results show that a
plasma jet can be extracted even from this
magnetic configuration, albeit with a reduced ion energy. A slight potential hill and hotter electrons exist in the central part of the arch. Ion current profiles are doubly-peaked in the horizontal plane, likely corresponding to the beamlet of each thruster. Trends with xenon mass flow rate and input power are consistent with the expectations of electrodeless
plasma thrusters. The plume experiences an upward or downward deflection depending on the direction of the applied
magnetic field, which could be attributed to the effect of the lateral electron drifts in the
magnetic arch.
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All authors Sacha A. Huot, Marco Riccardo Inchingolo, Jaume Navarro-Cavallé, Mario Merino
Quantum Physics
Superconducting singlet-triplet qubits
Anatoliy Lotkov, Maria Spethmann and Daniel Loss
Hybrid devices integrating
quantum dots with Josephson junctions are gaining interest because they combine
spin-based
quantum computing with
circuit quantum electrodynamics (
circuit QED) methods. In particular, Andreev
spin qubits have shown significant experimental progress including strong two-
qubit coupling, and are predicted to exhibit all-to-all connectivity. Here we propose superconducting singlet-triplet (SST)
qubits that rely on parallel-aligned double
quantum dots in Josephson junctions. While Andreev
spin qubits require
spin-orbit interaction to unlock the
spin degree-of-freedom, SST
qubits do not require
spin-orbit interaction, making the advantages of hybrid devices available to a wider range of materials. Similar to Andreev
spin qubits, the
qubit states couple to the superconducting phase across the junction, which allows for control and readout using
circuit QED, and supports all-to-all connectivity. Only $N$ flux lines are required to perform any single- and two-
qubit gate among $N$
qubits, and thus the overhead of control lines is small. Finally, linear protection from charge or flux noise makes these
qubits interesting candidates for a future
quantum processor.
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General Relativity and Quantum Cosmology
Causal Space-Time Structure and non-Hausdorff Extension of Schwarzschild Black Hole Interior
Asya Aynbund and V.V. Kiselev
Cones of future and past are rigorously constructed under the horizon of black hole by completions of geodesics continued from causally connected space-time regions outside the black hole interior. Treating the Schwarzschild black hole as a zero charge limit of Reissner–Nordsrøm black hole reforms the Penrose–Carter diagram into the infinite band that excludes the closed proper-time cycles under the geodesic motion. The marginal trajectories between the cones of future and past compose paths common with a compact non-Hausdorff spherical extension of black hole interior forming the thermal bath for particles fallen to the black hole.
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Strongly Correlated Electrons
Macroscopic Zero-Mode Manifold Isolated by Quantum Chaos
Cheryne Jonay, Kun W. Kim, Frank Pollmann et al. (+1 more)
Chaotic many-body spectra are expected to densely fill their energy window. We show that constrained
spin chains with
chiral symmetry evade this expectation by hosting an exponentially large
manifold of
symmetry-protected exact zero modes separated from the surrounding spectrum by a sharp gap at zero energy. The gap is generated by chaotic level repulsion, with width set by the number of zero modes times the mean level spacing. We verify this mechanism in an East-West kinetically constrained chain, develop a minimal random-
matrix description, and show how the gap can be detected through linear-response spectroscopy.
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All authors Cheryne Jonay, Kun W. Kim, Frank Pollmann, Alexander Altland
High Energy Physics (Theory)
Monodromy and geometry of heavy-light Virasoro blocks
Mikhail Belakovskiy and Vladimir Belavin
The AdS/CFT correspondence relates
gravity in anti-de Sitter space to a boundary conformal field theory, and in its AdS$_3$/CFT$_2$ instance the Virasoro
symmetry of the boundary theory organizes correlation functions into conformal blocks. In the semiclassical limit these blocks are computed by lengths of geodesic networks in the bulk, most sharply in the heavy-light regime, where heavy operators source a background probed by light ones. We relate the classical monodromy method to this bulk geometry in
holographic coordinates, showing that the eigenvectors of the monodromy
matrix encode the endpoints of bulk geodesics. This yields the light action and the equations determining the internal geodesic network; crucially, the internal network equations are independent of the heavy background. For two heavy operators we rederive the same equations from elementary Euclidean geometry, which provides an independent
geometric check. As an application we compute the full non-
vacuum 5-point HHLLL block, so far known only in the superlight approximation. More broadly, our construction gives a general framework for computing heavy-light blocks from the bulk, while at the same time fixing its threshold of computability.
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General Relativity and Quantum Cosmology
Head-on Collisions of Boson Stars with Bowen-York Type Initial Data
Jake Doherty and Pablo Laguna
We present a numerical relativity study of head-on collisions involving
boson stars using initial data inspired by the Bowen-York initial data used to model black hole binaries with punctures. The initial data method preserves the simplicity of the Bowen-York approach, thus allowing incorporating information from the early, post-Newtonian inspiral phase in binary coalescences. We test the method on a single
boson star with linear momentum. We present results from head-on collisions of
boson stars as well as encounters of
boson stars with black holes. In general, the results are consistent with previous studies, demonstrating the effectiveness of the initial data method. In particular, we show that
boson star head-on collisions emit more energy in gravitational waves than the equivalent black hole binaries. On the other hand, head-on collisions of a
boson star with a black hole radiate less than their black hole binary counterparts.
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High Energy Physics (Theory)
Factorization Algebras and Quantum Groups from Generalized Poisson Sigma Models
Keyou Zeng
In this work we introduce and study a family of holomorphic–topological field theories, which we call generalized Poisson sigma models. These theories are higher-dimensional analogues of the two-dimensional Poisson sigma model, with target data encoded by shifted
chiral Poisson structures. We investigate their relationship with deformation quantizations of holomorphic–topological factorization
algebras. Along the way, we give a systematic construction of extended objects, including interfaces, enriched boundaries and defects based on relevant notions in derived algebraic geometry. We employ Koszul-duality methods to study boundary
algebras, yielding various versions of
quantum groups. We illustrate the general framework through a range of examples, including twists of supersymmetric gauge theories as well as examples beyond the supersymmetric origin.
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High Energy Physics (Theory)
Unified description of color-electric and color-magnetic strings in hybrid vacua of $\mathcal{N}=2$ supersymmetric QCD
E. Ievlev, D. Vasilev and A. Yung
We study non-Abelian strings supported in $r$-
vacua of 4D $\mathcal{N}=2$ supersymmetric QCD (SQCD) with gauge group $U(N)$ and $N_f$
quark hypermultiplets ($N_f\ge N$), where $r<N$ (scalar)
quarks develop
vacuum expectation values. At the
quantum level, $N-r-1$ monopoles in the orthogonal sector of the gauge group also form a condensate. This leads to the formation of flux tubes (strings) that carry both color-electric and color-
magnetic fluxes and confine
quarks and monopoles, respectively. We present a unified description of the 2D effective theory living on the world sheet of this non-Abelian string. In particular, we derive the exact twisted superpotential of the world sheet theory, which is deformed by the presence of non-perturbative gaugino condensate in 4D hybrid
vacua, using the Gaiotto-Gukov-Seiberg method of resolvents. Next, we extrapolate the 2D-4D correspondence of BPS spectra of the world sheet theory and 4D SQCD (known for
quark vacua) to hybrid
vacua. Namely, our key result is the precise matching between the masses of the two-dimensional kinks and the four-dimensional confined monopoles or
quarks. In addition, we provide a physical picture of the
quark/monopole confinement in hybrid
vacua.
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Cosmology and Nongalactic Astrophysics
Turbulent Transport of Galactic Magnetic Fields into Cosmic Voids: Insights from IllustrisTNG
Yuri Yamashita, Hiroyuki Tashiro and Kiyotomo Ichiki
Astrophysical processes associated with
galaxies may contribute to the magnetization of
cosmic voids. We investigate the
diffusion of
galactic magnetic fields in an expanding universe in the presence of turbulent
magnetic diffusivity. To estimate the turbulent
magnetic diffusivity, we analyze the TNG50-1 data set of the IllustrisTNG simulation and derive its
redshift dependence from the characteristic turbulent velocity and turbulent scale of the intergalactic medium. Using the resulting diffusivity, we find a present-day
magnetic screening length of $\sim 7\,{\rm Mpc}$, roughly twenty times larger than previous estimates based on a constant turbulent diffusivity due to the larger turbulent scale obtained in our analysis. This scale corresponds to a significant fraction of the characteristic size of
cosmic voids and suggests that
galactic magnetic fields can play a more important role in void magnetization than previously estimated.
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Mathematical Physics
Extended group analysis and conservation laws of a class of variable coefficient generalized Kawahara equations
Olena Vaneeva, Alexander Zhalij, Olena Magda et al. (+1 more)
We review and extend the results on the group analysis of a class of generalized Kawahara equations with time-dependent coefficients. First, we provide an overview of the existing literature on Lie
symmetries and Lie-invariant solutions of such equations. We then present a complete description of their transformation properties, including admissible, equivalence, and Lie
symmetry transformations. For practical applications, we further extend these results by presenting a complete Lie
symmetry classification without simplifying the coefficients via equivalence transformations. Lie reductions are then systematically performed, and several exact solutions are constructed. Low-order local conservation laws are exhaustively classified: every equation in this class admits conservation of mass and the squared $L^2$ norm, whereas energy-type conservation laws exist only for specific coefficient branches that align with the cases singled out by the
symmetry classification. Finally, the classification results are enhanced by a study of contractions, which link cases of Lie
symmetry extensions together with the associated reductions and conservation laws.
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All authors Olena Vaneeva, Alexander Zhalij, Olena Magda, Oksana Brahinets
Quantum Physics
Playing Bayesian games better with separable quantum states than with any classical correlation
Yaqing Xy Wang, Giannicola Scarpa and Andreas Winter
Bayesian games, also known as games of incomplete information, are a fruitful arena for exploring the impact of correlations on a set of independent
agents (players) via the game
equilibria to which they give rise. It was realised some time ago that
quantum states shared between the players can lead to new and beneficial
equilibria, compared to classical correlation. While until now examples of this effect required an entangled state, here we show that even separable states can create new, genuinely
quantum equilibria in games, that are advantageous with respect to all classically correlated
equilibria. This shows that non-classical correlations beyond
entanglement are indeed a resource, even in otherwise entirely classical situations. Our result brings
quantum advantage in games significantly closer to possible realisation.
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Quantum Physics
Orthogonal Quantum Krylov Diagonalisation
Hadi Rammal, Alexandre Perrin, Oumaya Ladhari et al. (+3 more)
Quantum subspace-diagonalization methods, particularly
Quantum Krylov Diagonalization (QKD), provide a promising route for computing low-energy spectra of
quantum many-body
Hamiltonians. However, existing
quantum Krylov approaches rely on non-orthogonal Krylov bases, requiring overlap-
matrix regularization that limits numerical stability and accuracy. In this work, we introduce an Orthogonal
Quantum Krylov Diagonalization (OQKD) framework that reformulates the classical Lanczos recursion at the operator level, enabling an orthogonal
quantum implementation of Krylov-subspace diagonalization. By expressing Lanczos vectors as
polynomial transformations of the
Hamiltonian, OQKD reproduces the orthogonality, tridiagonal structure, and convergence behavior of the classical Lanczos
algorithm thus eliminating the need for overlap-
matrix regularization. We further show that the required Lanczos
polynomials can be implemented using block encoding and Generalized
Quantum Signal Processing with the same asymptotic query complexity as Chebyshev-based QKD methods. Numerical simulations of the $J_1$–$J_2$ Heisenberg model confirm the classical Lanczos convergence and numerical stability of the proposed method, while the measurement-complexity scaling is established analytically. Building upon the OQKD framework, we then introduce a restarted state-preparation protocol that replaces a single high-degree
polynomial transformation with a sequence of fixed low-degree transformations, maintaining an affordable block encoding success probability while retaining comparable convergence. These results establish OQKD as an orthogonal
quantum analog of the classical Lanczos
algorithm and identify the restarted protocol as a promising state-preparation strategy for
Quantum Phase Estimation.
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All authors Hadi Rammal, Alexandre Perrin, Oumaya Ladhari, Clément Dutreix, Jérémie Messud, Matthieu Saubanere
Strongly Correlated Electrons
Takumi Fukushima and Han Yan
Classical
spin liquids are correlated paramagnets in which local constraints generate extensive degeneracy and emergent gauge structures, often observable as pinch-point singularities in
spin structure factors. Here we introduce pinch-curve
spin liquids, in which the pinch singularities form one-dimensional algebraic curves in momentum space. Inversion
symmetry protects these curves by reducing the singularity condition to two real algebraic constraints in three dimensions, and the geometry of the pinch locus is algebraically programmable. We identify elementary mechanisms for generating straight and curved pinch loci, construct
lattice spin models that realize them, and test the predicted structure factors using Monte Carlo simulations. We further show that pinch curves can host an infrared Gauss-law transition: the leading local constraint and the associated anisotropic scaling of the structure factor change, even though the singular locus remains one-dimensional.
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Quantum Physics · Cross-listed from cs.DS
A combinatorial framework for clustering graph states: Algorithms and hardness for rank-integrity
Romain Bourneuf, Nathan Claudet, Sang Yoon Kim et al. (+3 more)
We introduce a new notion of distance between two graph states $|G\rangle$ and $|G'\rangle$ on the same set of
qubits. This distance is the minimum number of ancilla
qubits in a graph state $|\widehat{G}\rangle$ from which both $|G\rangle$ and $|G'\rangle$ can be “easily prepared”. (When preparing graph states, we are only allowed to use one-
qubit Clifford gates, one-
qubit Pauli measurements, and classical communication.) We give a graphical description of this distance through the lens of vertex-minors. We then show how this distance yields
quantum network analogs of many graph edit-distance problems. Using this framework, we develop classical
algorithms for identifying the “highly entangled clusters” of a graph state $|G\rangle$. The ancilla integrity problem asks, given a graph $G$ and integer $k$, for the minimum – over all graph states $|G'\rangle$ with distance at most $k$ from $|G\rangle$ – of the maximum component size of $G'$. Up to a factor of $2$ in the number of ancilla
qubits, this problem is equivalent to rank integrity, where the distance between $G$ and $G'$ is instead the minimum rank of the sum of their adjacency
matrices over $\text{GF}(2)$. We prove that rank integrity is XP parameterized by $k$. We also prove the complementary hardness result that rank integrity is W[1]-hard in $k$. Finally, we give an explicit $\mathcal{O}(n^6)$-time
algorithm for ancilla integrity when $G$ has $n$ vertices and $k=1$.
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All authors Romain Bourneuf, Nathan Claudet, Sang Yoon Kim, Rose McCarty, Blair D. Sullivan, Stéphan Thomassé
High Energy Astrophysical Phenomena
Neutron contribution to the force on a proton vortex in superconducting neutron-star matter
Oleg A. Goglichidze and Mikhail E. Gusakov
We investigate the forces acting on a
proton vortex in superconducting
neutron-
star matter composed of
neutrons,
protons, and electrons, accounting for
Fermi-
liquid interactions in the
neutron-
proton subsystem. While the force arising from electron scattering by the
vortex magnetic field is well known, we demonstrate that normal
neutrons also exert a force on
proton vortices due to
Fermi-
liquid coupling with superconducting
protons. Using a kinetic approach based on Landau
Fermi-
liquid theory, we show that
neutron quasiparticles scatter off a
proton vortex through the spatially varying condensate momentum, giving rise to a longitudinal force proportional to the relative
neutron-
vortex velocity. In contrast to the electron contribution, this force has no transverse component and vanishes in the absence of
neutron-
proton Fermi-
liquid interaction. Within a simple model, we analyze the main properties of this force and provide physically motivated estimates of its magnitude.
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Mathematical Physics
Paul Pfeiffer and Wolfgang Spitzer
We study the
entanglement entropy of ground states of a
Hamiltonian defined on a domain with a boundary. Surprisingly, boundary conditions can change the spectrum and the nature of the spectrum drastically but not the leading behaviour of the
entanglement entropy. As is well-known, the Landau
Hamiltonian on the full plane has pure point spectrum (the infinitely degenerate Landau levels) and ground states display a so-called strict area law. On the other hand, the Landau
Hamiltonian on the half-plane has purely absolutely continuous spectrum and yet we prove a strict area law for its ground states. We raise the question of what extra or finer conditions on the absolutely continuous spectrum are necessary to guarantee a logarithmically enhanced area-law as we have for the Laplace operator.
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Materials Science
Unraveling atomic-resolution valence electron energy-loss spectroscopic imaging in a single-crystal CaNb2O6
Sz-Chian Liou, Xiang-Lin Huang, Vladimir P. Oleshko et al. (+4 more)
Despite advancements in electron optics and spectrometer design over the past twenty years, atomic-resolution valence-electron energy-loss spectroscopy imaging remains challenging due to the delocalization of inelastic electron scattering. In this study, we used an energy-filtered spectrometer equipped with a hybrid-pixel direct electron detector and spherical aberration-corrected scanning transmission electron microscopy to analyze many-electron excitations and interband transitions in a single-
crystal calcium niobate, CaNb2O6, with spatial resolution ranging from the nanometers to the atomic scale. In the low-loss region above the bandgap at about 3.8 eV, we observed volume plasmons, around 6 eV and 15 eV energy loss, as well as a mix of strongly correlated plasmons and
excitons, known as plexcitons, at approximately 7.3 eV energy loss. Additionally, we employed an on-axis EELS setup for atomic-resolution zero-loss peak (ZLP) imaging and visualized energy- and atom-resolved images of plexcitons and VPs, which showed contrast reversal relative to high-angle annular dark-field images. To investigate elastic contrast preservation, we also analyzed the effect of the collection angle and minimized its influence to produce delocalized VP images. In fact, the ZLP and VEELS images obtained using the weak-beam setup demonstrate that, in both cases, the contrast resembles Z-contrast. Moreover, we found that [NbO6] octahedra directly contributed to the lateral maps of interband transitions in the range from 3.2 eV to 3.5 eV energy loss. These findings demonstrate that Cs-STEM-EELS, which examines atomic-scale contrast associated with low-energy losses, can be a powerful tool for visualizing the structure, bonding, and electronic properties of complex crystalline nanostructures, including individual atomic sites, interstitial sites, and point defects.
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All authors Sz-Chian Liou, Xiang-Lin Huang, Vladimir P. Oleshko, I-Ching Lin, Yin-Ping Lan, Hsin-An Chen, Guo-Jiun Shu
Strongly Correlated Electrons
Strongly correlated quantum matter: t–J model, real-space pairing, spin-dependent masses, and atomicity in chemical bond and nanosystems
Józef Spałek
I critically overview my research on strongly correlated
fermion systems for almost five decades. It concentrated on: (i) the first derivation of what is now called the t–J model, comprising both the limit of Anderson kinetic exchange of
spin–
spin interaction in the Mott–Hubbard
insulator and taking into account real-space pairing, subsequently applied to high-temperature superconductivity; (ii) the concept of
spin-dependent heavy mass of quasiparticles in heavy-
fermion systems, and (iii) the first nontrivial model of statistical thermodynamics of the Mott–Hubbard transition. Those three features, together with the specific
quantum critical phenomena provide, in my view, fundamental components of the theory of strongly correlated
fermions established in the 1960s. Some related questions such as introduction of atomicity in the chemical bonding (iv), and specific properties of correlated nanosystems within the rigorous EDABI (v) approach are also briefly elaborated at the end.
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Astrophysics of Galaxies
Characterising the Kinematics and Evolution of Young Stellar Groups within 1 kpc of the Sun Using Gaia DR3
Long-Fei Ding, Yun-Qian Li, Bing-Qiu Chen et al. (+2 more)
Star-forming regions are key to understanding the formation and early
evolution of
stars. Young
stellar objects (YSOs) form groups with distinct kinematic and spatial properties, inherited from the turbulent dynamics of their parent molecular clouds. The high-precision astrometry and photometry from
Gaia Data Release 3 (DR3) enable detailed studies of these groups' three-dimensional motions and their evolutionary stability. This study aims to investigate the kinematic properties and evolutionary consistency of YSO associations in the
solar neighbourhood. Here, we show that HDBSCAN clustering of
Gaia DR3 data yields 145 YSO groups comprising 5713
stars within 1 kpc, with a derived Larson's relation of $\sigma_v = (1.10 \pm 0.13) \times r^{0.38 \pm 0.03}$, consistent across age bins up to 20 Myr. This slope aligns with the canonical value of 0.38 and typical ranges of 0.4–0.5. The stable Larson's relation across ages indicates that the inherited turbulent structure from parent clouds persists without significant disruption. These findings establish a
benchmark for studying the kinematic legacy of
star-forming regions.
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All authors Long-Fei Ding, Yun-Qian Li, Bing-Qiu Chen, Guang-Xing Li, Hai-Bo Yuan
General Relativity and Quantum Cosmology
Six-Field Rational Extended Thermodynamics of Polyatomic Gases in Curved Spacetime
Luca Gallerani, Andrea Giusti, Andrea Mentrelli et al. (+1 more)
We formulate a generally covariant six-field Rational Extended Thermodynamics model (RET$_6$) for relativistic polyatomic gases, with the dynamical pressure as the only non-
equilibrium variable. The model is based on a polyatomic extension of the Boltzmann-Chernikov kinetic equation, where the one-particle distribution depends also on an internal-energy variable, and on the Maximum
Entropy closure of the associated relativistic moment hierarchy. The resulting field equations, closure relations, and production term are therefore fixed by the underlying kinetic structure rather than postulated phenomenologically. We extend the RET$_6$ model from Minkowski spacetime to a general curved spacetime by the minimal coupling prescription and couple it to the Einstein equations. As a first structural result, we prove a kinetic-theory no-go
theorem in this polyatomic RET setting stating that any stress-energy tensor induced by a non-negative relativistic one-particle distribution function satisfies the strong energy condition. We then specialize the theory to a homogeneous and isotropic Friedmann-Lemaître-Robertson-Walker (FLRW) spacetime. In this setting the dynamical pressure modifies the expansion dynamics with respect to the perfect-fluid Euler case, but the no-go
theorem excludes acceleration driven by the RET$_6$ gas alone. Finally, we reintroduce a cosmological constant and study the combined $\Lambda$RET$_6$ model. For the diatomic equation of state and a constant positive relaxation time, we prove the existence and local stability of a de Sitter attractor at late times. Numerical integrations show that, for representative post-recombination initial data and constant relaxation times, the expansion history rapidly approaches that of $\Lambda$CDM, with small non-
equilibrium corrections controlled by the relaxation time and by the initial value of the dynamical pressure.
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All authors Luca Gallerani, Andrea Giusti, Andrea Mentrelli, Tommaso Ruggeri
Astrophysics of Galaxies
Project Hephaistos – IV. James Webb Space Telescope Observations of Two Dyson Sphere Candidates
Erik Zackrisson, Arjan Bik, Anita Ali Asgar et al. (+11 more)
We report on JWST/MIRI imaging and spectroscopy of two M-
dwarf stars previously singled out by project Hephaistos as potential Dyson-sphere candidates (their candidates D and E) due to the presence of excess flux at mid-infrared wavelengths. We find that the infrared excess does not originate from Dysonian megastructures, or other radiation mechanisms close to these
stars, but from background
galaxies projected within $\sim 1$ arcsec of the M
dwarfs, thereby confusing previous mid-infrared photometry obtained with the WISE
telescope. The candidate D background
galaxy lies at
redshift $z\approx 0.9$, appears point-source dominated in imaging and has a mid-infrared spectrum consistent with being a Hot
Dust Obscured
Galaxy (Hot DOG). The candidate E background
galaxy lies at $z\approx 0.4$, displays an extended morphology with bright
knots and a spectrum consistent with a dusty starburst.
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All authors Erik Zackrisson, Arjan Bik, Anita Ali Asgar, Olivia Curtis, Jason T. Wright, Tongtian Ren, Roberto J. Assef, Andrew Blain, Alexis Brandeker, Michael A. Garrett, Uma Gorti, Andreas J. Korn, Priyatam K. Mahto, Armin Nabizadeh
High Energy Physics (Phenomenology)
Disentangling short- vs. long-distance dynamics in $B\to K^{*}\mu^+\mu^-$
Marzia Bordone, Gino Isidori and Arianna Tinari
We present an updated data-driven analysis of short- vs. long-distance dynamics in $B\to K^{*}\mu^+\mu^-$. The analysis is based on the recent LHCb measurement of the full angular distribution of this process, taking advantage of the previously published global amplitude fit. Thanks to the precise di-
lepton invariant-mass binning and angular observables directly sensitive to absorptive phases, current data provide novel insights into non-local contributions. We analyze the latter using a dispersive description, whose free parameters are determined via the amplitude fit. The dispersive model provides a satisfactory overall description of current data, without the need to introduce additional ad hoc hadronic parameters. The extracted value of the short-distance coefficient $C_9$ is lower than its Standard Model prediction, but significantly closer to it than in analyses where long-distance contributions are not constrained by data. The overall tension with the SM does not exceed the $2\sigma$ level. We also obtain precise postdictions for the angular observables $S_{7,8,9}$, and envisage novel consistency tests among them. In view of future, more precise data, these could provide valuable tests of the description of non-local effects in this process that, if further validated, would enable an even more robust extraction of short-distance information.
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Accelerator Physics
Report on the Advanced Linear Collider Study Group (ALEGRO) Workshop 2026
L. Verra, P. Muggli, B. Cross et al. (+59 more)
The 7th ALEGRO workshop, hosted by INFN Frascati National Laboratories from 3rd to 5th March 2026, brought together the international Advanced Novel Accelerators (ANA) community to discuss the role of advanced wakefield accelerators (AWA) in particle and high-energy physics. Organized under the ICFA-ANA panel, the workshop highlighted recent progress in
plasma- and structure-based wakefield acceleration and strengthened international collaboration toward future energy-frontier
colliders. A major focus was the ongoing 10 TeV linear
collider design study, launched in 2025 following the US P5 recommendations. A dedicated session covered accelerator concepts, enabling technologies, and the associated physics case, while recognizing that future priorities will depend on the outcome of the European Strategy for Particle Physics Update. The workshop also reviewed nearer-term applications of advanced accelerators, including fixed-target experiments, injectors for future
colliders and light sources,
plasma-based
Higgs factory concepts, and
proton-driven
plasma wakefield acceleration. Beyond high-energy physics, sessions covered free-electron
lasers, synchrotron light sources, and strong-field QED. Recent demonstrations of FEL lasing with
plasma-accelerated electron beams highlighted significant progress in beam quality and accelerator performance. Operational challenges for reliable user facilities, including high-availability
laser and electron-beam systems, were discussed alongside the growing role of artificial intelligence and machine learning for accelerator optimization and control. This report summarizes the workshop discussions and conclusions from the chairs, together with short contributions from the presenters, providing an overview of the current status and future prospects of advanced wakefield accelerators.
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All authors L. Verra, P. Muggli, B. Cross, E. Adli, R. Babjak, T. Barklow, F. Bencivenga, C. Benedetti, C. Benedetti, M. Buscher, S. S. Bulanov, A. Caldwell, G. Chen, O. Chubenko, R. D'Arcy, S. Diederichs, K. Downham, J. Farmer, M. Ferrario, A. Ferran Pousa, A. Formenti, M. Fuchs, S. Gessner, L. Giannessi, Z. Gong, J. Grames, T. Grismayer, H. Jaworska, L. Ji, V. Kain, S. Karkare, A. Knetsch, C. Lindstrom, N. Lopes, N. Lopes, F. Massimo, C. Masciovecchio, P. Oliveira, T. Opferkuch, J. Osterhoff, J. Osterhoff, S. Pagan Griso, G. Penco, J. Power, A. Pukhov, T. P. Rakitzis, A. Rastogi, L. Reichwein, C. B. Schroeder, L.O. Silva, A. Sinn, D. Sofikitis, D. Storey, M. Thévenet, M. Trovò, M. Turner, M. Vranic, F. Willeke, T. Wilson, M. Wing, W. Zhang, Chuan Zheng
Plasma Physics
On the generation of astrophysically-relevant intermittent magnetic turbulence in the laboratory
Itamar Cohen, Weipeng Yao, Archie F. A. Bott et al. (+18 more)
Intermittent
magnetic turbulence, namely the presence of non-ordered and clusterized fields, is a ubiquitous phenomenon in space and astrophysical
plasmas. It is currently understood that it plays a crucial role in the dynamics of astrophysical systems at all scales, from influencing the
evolution of the cosmos as a whole to governing local particle acceleration. While there is direct evidence of
turbulence in the
solar wind, and despite progress obtained through multi-wavelength observations, most of our knowledge of it outside the
solar system derives from indirect evidence, through modeling. Here we show that
magnetic turbulence, that quantitatively matches that measured in space, can be reproduced in the laboratory. Starting from a homogeneous magnetized
plasma, we randomly perturb it using a speckled
laser beam. Using
proton radiography, we can follow the development and quantitatively characterize the produced intermittent
turbulence from its inception.
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All authors Itamar Cohen, Weipeng Yao, Archie F. A. Bott, Sophia N. Chen, Nikola Mirkovic, Jerome Beard, Petrisor Gabriel Bleotu, Georgiana Giubegal, Anda-Maria Talposi, Yoav Heller, Clement Lacoste, Patrizio Antici, Damiano Caprioli, Emmanuel DHumieres, Victor Malka, Alexandre Marcowith, Ovidiu Tesileanu, Mateusz Ruszkowski, Philipp Kempski, Olga Alexandrova, Julien Fuchs
Earth and Planetary Astrophysics
Companion architectures of sub-Saturns: Distinct migration pathways across the Neptunian landscape
Luis Thomas, Louise D. Nielsen, Alex J. Cridland et al. (+2 more)
Close-in sub-Saturns (4.0 - 8.5 R$_\oplus$) are depleted in the Neptunian desert, accumulate in a narrow overdensity near P = 3.2 - 5.7 d (the Neptunian ridge), and thin out into the more moderately populated savanna at longer periods. We test whether sub-Saturns have systematically different companion architectures, as predicted if desert and ridge
planets arrived through high-eccentricity migration while savanna
planets migrated quiescently. We compile 86 systems with both transit and RV data, construct completeness maps and combine them into detection probability surfaces for companions. The combined completeness maps are used to calculate companion occurrence rates across different companion types with a joint Poisson occurrence model. Companion architectures differ significantly across the landscape. $91.1_{-4.3}^{+3.2}\%$ of savanna sub-Saturns have nearby companions (P < 200 d) compared to only $36_{-14}^{+16}\%$ of desert and ridge sub-Saturns. This contrast is driven almost entirely by small ($M_\mathrm{c} < 20\,\mathrm{M}_\oplus$) companions, which accompany $88.2_{-5.5}^{+4.2}\%$ of savanna but only $29_{-14}^{+17}\%$ of desert and ridge sub-Saturns, while medium-mass and
giant companions within 200\,d are rare ($\lesssim 13\%$) everywhere. Savanna sub-Saturns moreover typically reside in compact multi-
planet systems. These contrasts are robust to crosscuts in sub-Saturn radius, bulk density, eccentricity, and host-
star properties. Desert and ridge sub-Saturns reside in dynamically emptied systems whose nearby companion rates match those of hot Jupiters, while savanna sub-Saturns inhabit compact multi-
planet systems resembling those of warm Jupiters. This parallel supports two migration channels operating within a single population: HEM delivering
planets to the desert and ridge, and quiescent disk migration or in-situ formation populating the savanna.
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All authors Luis Thomas, Louise D. Nielsen, Alex J. Cridland, Martin Schlecker, Sydney Vach
Nuclear Theory
Electron-capture rates in the medium-mass nuclei $^{48}$Ti, $^{56}$Ni, $^{60}$Zn, and $^{64}$Ge within deformed quasiparticle random-phase approximation
Eunja Ha, Myung-Ki Cheoun, H. Sagawa et al. (+2 more)
Electron-capture (EC) rates in medium-mass
nuclei are governed by Gamow–Teller (GT) strength distributions and provide important input for
stellar weak-interaction processes. In this work, we investigate the deformation dependence of the GT strengths and
stellar EC rates in selected medium-mass
nuclei in and near the $pf$ shell, namely $^{48}$Ti, $^{56}$Ni, $^{60}$Zn, and $^{64}$Ge. The GT$^{(+/-)}$ strength distributions are calculated in the deformed quasiparticle random-phase approximation (DQRPA) on a single-particle basis obtained by the Skyrme SGII interaction, while the
stellar EC rates are evaluated from the resulting $B(\mathrm{GT}^+)$ strengths using the standard phase-space formalism. The potential-energy curves are used to identify shape softness and possible shape coexistence in the
nuclei under consideration. We find that deformation strongly modifies the GT strength distributions by changing the centroid energies, resonance splitting, and fragmentation patterns. In particular, a pronounced shape dependence of the GT$^{(+/-)}$ strengths is found for $^{56}$Ni and $^{64}$Ge, whereas $^{60}$Zn is characterized by a favoured prolate minimum and $^{48}$Ti exhibits a soft near-spherical/prolate landscape. By contrast, the corresponding EC rates are generally much less sensitive to deformation than the differential GT response itself, except at low temperatures and low densities where the low-lying GT$^+$ strength becomes decisive because of the negative EC $Q$-value in the electron phase space. Available charge-exchange data for $^{48}$Ti and $^{56}$Ni are used as
benchmarks of the model predictions. The present results provide microscopic constraints on the role of deformation and shape coexistence in
stellar weak rates for selected medium-mass
nuclei, including
proton-rich isotopes near the $N = Z$ line.
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All authors Eunja Ha, Myung-Ki Cheoun, H. Sagawa, Gianluca Colò, Toshitaka Kajino
Quantum Physics
Diagnosing quantum reservoirs at scale based on expressivity and coverage
Laia Domingo, Oriol Balló-Gimbernat and Fernando Vilariño
Quantum reservoirs offer a hardware-friendly route to
quantum machine learning, replacing trainable
circuits with fixed random dynamics and a classical readout. Because the reservoir is not optimized, performance depends entirely on the choice of reservoir family, yet existing diagnostics demand resources that grow exponentially with system size. We introduce a scalable, hardware-agnostic framework built on two complementary quantities. The first is a task-independent order-statistics (ORS) expressivity score, which compares only the largest output probabilities of a reservoir ensemble against an analytical Haar baseline. It never reconstructs the full output distribution, is cost-independent of
Hilbert-space dimension, and admits a closed-form depolarizing noise correction, making it directly usable on hardware. The second is the task-dependent effective rank $R_{\mathrm{eff}}$ of the feature
matrix, which measures how much input-dependent information reaches the readout. We validate the ORS score against established complexity diagnostics and confirm it remains informative under simulated noise and on IBM
quantum hardware. Across synthetic and real
quantum extreme learning machine and
quantum reservoir computing
benchmarks, ORS captures the intrinsic expressivity hierarchy of reservoir families while $R_{\mathrm{eff}}$ determines when that expressivity becomes usable predictive information.
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Disordered Systems and Neural Networks
Level statistics in the fractal phase of generalized Rosenzweig–Porter models
Victor Delapalme, Leticia F. Cugliandolo, Alexander K. Hartmann et al. (+2 more)
The Rosenzweig–Porter (RP) random
matrix ensemble has emerged as a minimal model for the integrability-to-chaos crossover in
quantum many-body systems. Its phase diagram features a region with fractal eigenstates, exhibiting intermediate spectral and localization properties between the fully localized and fully delocalized regimes. In this work, we explore several generalizations of the RP model and determine their level statistics at the scale of the Thouless energy $E_T$, which characterizes the crossover. Using tools from free probability theory and the replica method, we compute the full counting statistics in the limit of large system size, and show that it takes a simple, universal scaling form around $E_T$, shared across all variations of the model. We validate our analytical predictions using exact numerical diagonalization of large samples, and large-deviation
algorithms that resolve the full counting statistics down to probabilities as low as $10^{-40}$. We also contrast our predictions with measurements on the
quantum random energy model, which is the simplest model displaying many-body localization.
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All authors Victor Delapalme, Leticia F. Cugliandolo, Alexander K. Hartmann, Marco Tarzia, Davide Venturelli
Superconductivity
Anisotropic Superconductivity with Enhanced Critical Field in Strained RuO2
Younes Ghorbani, Samuel Poage, Xuehsi Gao et al. (+9 more)
The superconductivity in RuO2 emerges under strain. RuO2 is also an altermagnet candidate. The nature of superconductivity and its relation with neighboring orders, however, are not understood. To address this problem, we grew epitaxial RuO2 films on TiO2(100) and TiO2(110) single
crystal substrates and studied the electronic transport and emergent superconductivity along various crystallographic directions. We show that the superconducting transition strongly depends on the growth orientation and the crystallographic direction of the transport in the RuO2 films. We also observe a strong violation of Pauli paramagnetic limit with in-plane applied
magnetic field which we attribute to strong
spin-orbit scattering. These results offer opportunities for epitaxially engineered
superconductors.
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All authors Younes Ghorbani, Samuel Poage, Xuehsi Gao, Luka Mitrovic, Neha Wadehra, Benjamin Gregory, Suchismita Sarker, Betul Pamuk, Andrej Singer, Darrell G. Schlom, Chun Ning Lau, Kaveh Ahadi