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Saturday 25 July

Fluid Dynamics

Characterisation of a multistable turbulent wake: application of an improved regime identification with analytical model training

This article presents the experimental study and the modelling of the multistable jet in the wake of two side by side square bars separated by a distance $G$ at Reynolds number $R=U_\infty H/\nu=10000$ (with $U_\infty$ the velocity of the incoming flow, $H$ the bar side and $\nu$ the kinematic viscosity). The velocity field downstream of the bars is measured by means of two dimensional two components Particle Image Velocimetry (PIV). We use the weighted transverse position of the jet $Y_m$ and the jet width $w$ to characterise the regimes of multistability as the gap ratio $G/H$ is increased. Three main regimes of multistability are possible: tristability, bistability, and monostability. In our wind tunnel, tristability is observed for $G/H\in [1.15,1.25]$, bistability is observed for $G/H\in [1.5,2.65]$ and monostability is observed for $G/H\in [3.0,3.5]$. Within the first two ranges of $G/H$, there exists gap ratios for which multistability is more complex. In order to analyse the simple and complex multistability regimes as well as the transition from bistable to monostable, we construct an analytical stochastic differential equation (SDE) modelling $Y_m$ for each gap ratio. These SDEs are written with polynomial drift and diffusion. For this matter we use a data based method that finds an trade–off between simplicity of the model (smaller number of monomials) and precision. A first key advantage of the use of the data-based model fitting method is that when the flow is tristable, bistable or monostable, we recover the drifts expected from the theory of bifurcations, but we are now able to correct it with the right multiplicative noise expressed by the diffusion. The second key advantage is that we can also fit atypical drift expressions when the multistability regime is complex that help us make sense of the jet behaviour.
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All authors Ariane Barlet, Pierre Bragança, Christophe Cuvier, Joran Rolland

Materials Science

A DFT and Machine Learning-Assisted Study on the Lattice Thermal Conductivity of LiCdSb for Thermoelectric Applications

By using first-principles density functional theory (DFT) and the Boltzmann transport equation, we have calculated the corresponding electronic and thermoelectric properties of LiCdSb. For calculating electron transport properties, accurate band-structure estimation is crucial. Hence, for the precise band gap calculation, we have implemented a hybrid functional HSE06, which is widely known for its high accuracy. To evaluate the thermoelectric performance of a material, the calculation of lattice thermal conductivity (Kl) is a key parameter. However, from a theoretical perspective, the calculation of lattice thermal conductivity is very complex and demands huge computational resources. Therefore, in this work, we have opted for an alternative method of machine-learning interatomic potentials (MLIPs) for the calculation of Kl. Our result of Kl=0.24 Wm^-1K^-1 at room temperature is in qualitative agreement with the available theoretical and experimental data. The figure of merit (ZT) with Kl estimated from Slack+TDEC ZT is 0.18 at 300 K, and machine learning (ML) models ZT is 0.17 at 300K, combining with HSE06-based electronic transport properties agreed well with the available experimentally reported value of ZT is 0.10 at 300K. However, we report the ZT value well above the benchmark value of 1 beyond 600K. The ZT value exceeding 1 at higher temperatures makes LiCdSb a promising material for high-temperature energy conversion.
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All authors R. Zosiamliana, Lalhriat Zuala, N. T. Tien, Vo Khuong Dien, A. Laref, D. P. Rai

High Energy Physics (Phenomenology)

Status of light inflaton: from inflation to laboratory

We investigate the viability of the light inflaton scenario in light of the latest inflationary constraints from the Atacama Cosmology Telescope (ACT), together with bounds from collider and intensity-frontier experiments searching for a feebly coupled light scalar with a sub-GeV mass. Assuming a quartic inflaton potential, we identify the region of parameter space consistent with the ACT observations and derive constraints on the inflaton mass and inflaton-Higgs mixing using results from NA62, KOTO, BaBar, Belle, LHCb, MATHUSLA, FASER2, SHiP, and neutral meson oscillations. We also explore the prospects for dark matter production during reheating within this framework, while remaining consistent with the inflationary observables.
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All authors Niloy Mondal, Shashwat Sharma, Mathew Thomas Arun, Basabendu Barman

High Energy Physics (Phenomenology)

A Chromomagnetic Mechanism for the Rotational Phase Transition of Gluonic Matter

Rotation serves as a pivotal control parameter for QCD matter, yet effective models and lattice QCD yield conflicting predictions regarding its effect on the deconfinement transition. Using a rotation-magnetic correspondence within a holographic framework, we investigate the rotational response of pure gluonic matter. Calibrated against lattice QCD data at imaginary angular velocity, we find real rotation enhances chromomagnetic string tension and raises deconfinement temperature, consistent with lattice QCD analytic-continuation predictions. The temperature dependence of chromomagnetic string tension dominates the system's Barnett response: weak low-temperature tension induces the negative Barnett effect, and slightly above the transition, spin contributions prevail to generate an anomalous negative total moment of inertia. Since growing angular velocity further strengthens chromomagnetic string tension and suppresses spin-dominated inversion, this anomalous regime only survives at weak real rotation and vanishes at large angular velocity. At high temperature, fully restored strong string tension stabilizes conventional Barnett behavior. Stemming from the melting and thermal restoration of nonperturbative chromomagnetic flux tubes, our results establish the chromomagnetic-induced inertia inversion (CII) mechanism as the microscopic origin of this anomalous rotational response.
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Nuclear Theory

Proton Collectivity in Au+Au Collisions at $\sqrt{s_{\rm NN}}=2.4-4.5$~GeV from a Unified Purely Hadronic EOS without QCD Phase Transition

The nuclear equation of state (EOS) is generally considered to soften in the density range of $2-5$ times the saturation density $\rho_0$. Using a purely hadronic transport model, we calculate the proton directed, sideward, and elliptic flows and their excitation functions in heavy-ion collisions (HICs) at $\sqrt{s_{\rm NN}}=2.4-4.5$~GeV and compare with the HADES, E895, and STAR data. We find that a momentum-dependent mean field with a unified incompressibility $K_0=230$~MeV quantitatively reproduces the experimental proton flows up to 4.3 GeV, at which the maximum density reaches approximately $5\rho_0$. At 4.5 GeV, however, the pure hadronic model fails to reproduce the proton directed and elliptic flow data, providing circumstantial evidence for the onset of partonic degrees of freedom in HICs. Our results provide a hadronic baseline to characterize the high-density nuclear matter and to map the region of hadron-quark phase transition.
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All authors Gao-Feng Wei, Shuang-Jie Liu, Yu-Liang Zhao, Qi-Jun Zhi, Zhigang Xiao

Disordered Systems and Neural Networks

Generalized Bloch-like ground states in distinct electron-site configurations derived from the same quasiperiodic structure

Sutherland-Kalugin-Katz (SKK) states have been proposed as generalized Bloch-like states in quasiperiodic systems where the absence of translational symmetry prevents the application of Bloch's theorem. However, previous studies have largely relied on ansatz-based arguments, and a systematic procedure for constructing the SKK state from a specified Hamiltonian has remained unclear. In this work, we develop a constructive approach based on a generalized Fourier transform of creation operators in tight-binding models. We then apply this framework to vertex and dual models on the Ammann-Beenker (AB) tiling that stem from the same quasiperiodicity but differ in their electron-site configurations. Our construction reproduces the previously reported SKK state in the ground state of the vertex model and reveals a corresponding SKK state in the ground state of the dual model with high fidelity. The structural correspondence between the two SKK states indicates that such states are not tied to a particular choice of electron sites and reflect the underlying quasiperiodicity of the AB tiling.
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Quantum Physics

Finite-Time Optomechanical Cooling by Multi-Exceptional-Point Braiding

Cooling a mechanical mode in finite time is a routing problem: excitation must reach a lossy mode before thermal noise rebuilds the population. Exceptional points are non-Hermitian degeneracies at which two hybrid modes and their eigenvectors merge, so a loop around them can exchange connected spectral branches. The main obstacle in testing whether this topology improves cooling is causal. Independently optimized enclosing and non-enclosing protocols normally have different waveforms, so topology and waveform geometry change together. We remove this ambiguity in a three-mode optomechanical system with a strongly damped main cavity and an exactly lossless auxiliary cavity. We keep one power modulation and one detuning shape fixed and change only their relative phase. The shift preserves the matched local control resources but changes the loop from non-enclosing to a braid around both exceptional points. Certified dynamics show that the two-exceptional-point protocol lowers the final mechanical occupation by more than 55 percent. The advantage survives the complete admissible phase family, deliberate waveform changes, a finite neighborhood of nearby smooth controls, and the restoration of counter-rotating heating processes. The auxiliary cavity acts as a coherent buffer, while the main cavity remains the only optical loss channel.
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2607.23179 · 25 Jul · Substantially revised version: introduces a same-waveform topology toggle with an exactly lossless auxiliary cavity, interval-certified cooling advantage, robustness to phase and waveform deformations, microscopic mechanism analysis, and fixed-control beyond-RWA validation

Strongly Correlated Electrons

Field-tuned incommensurate fan phase in an Ising-like triangular antiferromagnet

Using single-crystal neutron diffraction we report the observation of a field-tuned incommensurate phase in a field range just below magnetization saturation in the Ising-like triangular-lattice antiferromagnet Na$_2$BaCo(PO$_4$)$_2$. This phase occurs for magnetic fields applied along the Ising axis and exhibits an in-plane incommensurate propagation vector that moves along the hexagonal Brillouin zone boundary upon varying field, challenging the simple $XXZ$ antiferromagnetic description of the system. Within a semiclassical framework, we successfully identify this pre-saturation phase as a coplanar fan phase and study the role of dipole-dipole interactions and bond-dependent exchange anisotropy in its stabilization mechanism. We additionally present a minimal exchange model including interlayer couplings, which reproduces the complex magnetic phase diagram in field including the observed field-dependence of the incommensurate propagation vector in the fan phase.
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All authors D. Flavián, R. Okuma, P. Manuel, Q. Huang, H. Zhou, R. Coldea

High Energy Physics (Theory)

Horava Stars Revisited: New Phases of Incompressible Stars and Black Holes, and Buchdahl's Theorem

I study a particular exact solution for static stars in four-dimensional non-projectable Horava gravity, which has been proposed as a renormalizable gravity model without the ghost problem by abandoning Einstein's equal-footing treatment of space and time through anisotropic scaling with z > 1. Considering the spherically symmetric static black-hole solutions in z = 3 Horava gravity as the exterior spacetimes of stars, I obtain an exact solution for incompressible (i.e., uniform-density) static stars with an arbitrary cosmological constant and isotropic pressure, and lambda=1, in which Birkhoff's theorem holds. For a vanishing cosmological constant, I obtain a modified Buchdahl bound on the maximum compactness for uniform-density stars, which ranges from 4/9 to 1. By contrast, I find that Ultra-Compact Objects (UCOs) with compactness C > 1 also exist with negative pressure while, surprisingly, satisfying all four standard energy conditions. UCOs include the regular (non-singular) black-hole solutions with masses above the extremal black-hole mass. In these solutions, the matter is localized at the timelike core region bounded by the inner horizon, while their exterior metrics are unaffected by the core matter and identical to the corresponding vacuum Horava black-hole solutions. These long-sought regular black-hole solutions are essential manifestations of Birkhoff's theorem in Horava gravity. I also find negative-mass stars with positive pressure that violate all standard energy conditions. Finally, I prove Buchdahl's theorem in non-projectable Horava gravity. The proof uses a weight-monotonicity condition on the average density and Birkhoff's theorem, together with the usual assumption that average density is non-increasing.
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Mesoscale and Nanoscale Physics

Signatures of Topological Magnon Edge States in THz Spectroscopy and Cavity Response

Topological magnon insulators (TMIs) have emerged as promising platforms for low-energy spin-based information processing, due to their non-trivial bulk magnon topology and robust, chiral edge modes that support dissipationless transport. Although theoretical models predict these edge states, direct experimental detection remains challenging due to their limited sensitivity to conventional probes. In this work, we propose an all-optical pathway to detect topological magnon edge modes in ferromagnetic TMIs. Our approach harnesses parametric amplification of edge magnons via resonant electromagnetic driving, enabled by magnetoelectric coupling mechanisms. We concentrate on two-dimensional van der Waals ferromagnetic materials on the honeycomb lattice with magnonic band gaps in the terahertz (THz) range. We show that a spin-dependent effective electric dipole moment, arising from dynamic charge fluctuations and consistent with the lattice symmetry up to next-nearest-neighbor interactions, gives rise to one-photon-two-magnon processes leading to parametric amplification. On this basis, we propose a THz pump-probe spectroscopy protocol in which edge modes are selectively amplified and subsequently detected in absorption. Furthermore, we discuss the possibility of using THz cavities, enabling selective coupling to edge modes while filtering out bulk contributions. These findings establish a route for probing topological magnets and open new avenues for experimental exploration of exotic topological phenomena in magnetic quantum materials.
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Physics and Society

Individual and collective gains from cooperation and reciprocity in a dynamic-network Prisoner's Dilemma driven by extraversion, openness, and agreeableness

How do stable personality differences shape cooperation when social ties can form and dissolve? We model a repeated Prisoner's Dilemma on an endogenous network in which three continuous Big Five traits map to transparent local mechanisms: Extraversion sets a target number of partners, Openness determines how broadly agents search beyond friends-of-friends, and Agreeableness sets a baseline willingness to cooperate. At each encounter, agents combine this baseline with the partner's directly observed history; there are no trait labels, gossip, or global reputations. Ties form when agents are under-connected and are cut when they become over-connected, with cuts prioritising partners who have defected more often. We vary network size (N=30–200), population composition, and the balance between trait-driven and history-driven behaviour. Three robust patterns emerge. First, cooperate first, then reciprocate—high initial willingness to cooperate combined with history-sensitive response—produces systems that are simultaneously more prosperous, fairer, and safer. Second, personality has predictable conditional effects: Agreeableness helps when history matters but hurts when behaviour is mostly trait-driven; Extraversion amplifies the environment; Openness has little net payoff effect. Third, the network reorganises accordingly: degree assortativity stays near zero, whereas agreeable agents increasingly connect to one another when cooperation takes hold.
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All authors David Abián, Jorge Bernad, Sergio Ilarri, Raquel Trillo-Lado

Cellular Automata and Lattice Gases

Kramers-Wannier Duality at the Heart of Traffic

To model high-risk traffic densities a cellular automaton model is constructed, exhibiting Ising model-like properties. The attraction-repulsion forces between vehicles are evaluated as coupling, and the coupling function $p(1-p)=g/8$, where p is the initial distribution of cells with state 1, and g is the Moore neighbor count, which has roots $\cos^2(\pi/8)$ and $\sin^2(\pi/8)$ for $g=1$. This is achieved without the use of any trigonometric functions in the code. From the roots, the tangent polynomial $\tan^2(x) + \tan(x)$ emerges. Kramers-Wannier duality is recovered and it is conjectured that the $1/\sqrt{2}$ difference between the roots serves as a fixed point for a projection mechanism from the 2-dimensional Ising model onto a 1-dimensional Ising chain through the Gudermannian function. The sigmoid evaluated at the proposed fixed point is substituted into the derivative of the logistic coupling function, $\sigma(1/\sqrt{2})(1-\sigma(1/\sqrt{2}))$, yielding a numerical approximation to the three-dimensional Ising inverse critical coupling. Finally, the results are linked to risk densities in traffic and vehicle types, accounting for the amplification of fatal accidents.
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High Energy Physics (Phenomenology)

Novel Multilepton Signatures from the Fermionic Portal to Vector Dark Matter

We perform a collider study of a novel multilepton signature arising from pair production of heavy vector-like leptons followed by cascade decays through a dark sector. In the muonic realisation of the Fermionic Portal to Vector Dark Matter, this process can lead to final states with four, six, eight, or ten visible muons, depending on the dark-sector spectrum and branching pattern. We identify the six-muon channel as the most powerful target: it remains sizeable over a broad region of parameter space, while being less rate-suppressed than the higher-multiplicity channels and much cleaner and more reconstructable than the four-muon final state. The signal arises from Drell–Yan pair production of vector-like muons, $pp\to\mu'^{+}\mu'^{-}$, followed by decays through the dark vector $V'$ and the dark scalar $H_D$. The six-muon final state receives contributions from symmetric decay topologies in which each $\mu'$ yields three visible muons, and from the asymmetric topology in which one chain yields one muon and the other yields five. The six-lepton signature from vector-like-lepton pair production has not previously been explored at the LHC. We therefore develop a topology-based reconstruction which exploits the repeated dimuon, trimuon, and five-muon resonance structure of the signal. We simulate signal and Standard Model backgrounds at detector level, including a dedicated treatment of rare heavy-flavour muons. The resulting background after the six-muon selection and topology reconstruction is negligible. Existing Run-2 multilepton searches already constrain part of the low-mass parameter space, but they do not exploit the repeated resonance structure of the signal. A dedicated six-muon search can substantially extend the reach. At the HL-LHC, the proposed analysis can probe vector-like muon masses up to about $1.9$ TeV for favourable spectra.
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All authors Alexander Belyaev, Manimala Chakraborti, Claire Shepherd-Themistocleous, Chang-Yuan Yao

Soft Condensed Matter

Active flows drive anchoring of nematics at rigid walls

Although confinement strongly influences flows in active materials, it remains unclear how active particles align at rigid boundaries when no thermodynamic anchoring is imposed. We address this question using continuum simulations of active nematics, together with analytical arguments based on a reduced near-wall description. In the flow-tumbling regime, extensile systems align parallel to the boundary, whereas contractile systems align perpendicular to it, consistent with active anchoring observed at active-passive interfaces. In the flow-aligning regime, the preferred orientation depends on the sign of activity and of the flow aligning parameter: either the shear-like flow generated near the wall selects the Leslie angle, or no unique alignment is established. These results provide a unified framework for activity-induced anchoring at rigid walls, demonstrating that boundary alignment in dense active matter can emerge solely from the interplay between self-generated flows and orientational dynamics.
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All authors Michael Fang, Ioannis Hadjifrangiskou, Sumesh P. Thampi, Julia M. Yeomans, Jan Rozman

High Energy Physics (Phenomenology)

Quasi-two-body decays $B_c^+ \to \chi_{c0,c1} [\rho(K^*) \to] \pi\pi(K\pi)$ in the PQCD approach

We study the quasi-two-body decays $B_c^+ \to \chi_{c0,c1} [\rho(K^*) \to] \pi^+\pi^0(K^0\pi^+)$ in the perturbative QCD framework at leading order. The $\pi\pi$ and $K\pi$ pairs are produced via the P-wave resonances $\rho(770)$, $\rho(1450)$, $\rho(1700)$, and $K^*(892)$, parametrized by the Gounaris-Sakurai and relativistic Breit-Wigner models. The $\rho$ channels, dominated by the $\rho(770)$ resonance, yield $\mathcal{B}(B_c^+ \to \chi_{c0} \pi^+\pi^0) = 7.33 \times 10^{-4}$ and $\mathcal{B}(B_c^+ \to \chi_{c1} \pi^+\pi^0) = 1.02 \times 10^{-3}$, with constructive $\rho$ interference making the coherent total $\sim 26\%$–$30\%$ larger than the $\rho(770)$ contribution alone. The Cabibbo-suppressed $K\pi$ channels yield branching ratios roughly a factor of five below those of the $\pi\pi$ modes, $\mathcal{B}(B_c^+ \to \chi_{c0} K^0\pi^+) = 1.49 \times 10^{-4}$ and $\mathcal{B}(B_c^+ \to \chi_{c1} K^0\pi^+) = 1.94 \times 10^{-4}$, the Cabibbo suppression being only partially compensated by the narrow $K^*(892)$ resonance and the normalization factor $N_{K^*}=1.48$. For $\chi_{c1}$ modes, $f_L \approx 93\%$ dominates and decreases with increasing resonance mass. The ratio $R_{\chi_{c1}/\chi_{c0}}^{\pi\pi} \approx 1.38$ reflects the common resonant $\rho$ production mechanism shared by $\chi_{c0}$ and $\chi_{c1}$, with the charmonium decay-constant hierarchy and phase space determining the relative yield of P-wave charmonia. The analogous ratio in the Cabibbo-suppressed $K\pi$ channel, $R_{\chi_{c1}/\chi_{c0}}^{K\pi} \approx 1.30$, is consistent with this value, confirming that the spin ratio is governed by charmonium-side dynamics.
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Nuclear Theory

Determination of asymptotic normalization coefficients for the $^{7}$Li$\to \alpha + ^{3}$He channel

Asymptotic normalization coefficients (ANCs) $C_{3/2}$ and $C_{1/2}$ for the channels $^7$Li$(3/2^-;0$ MeV)$\to \alpha+^3$H and $^7$Li$(1/2^-;0.478$ MeV)$\to \alpha+^3$H, respectively, were determined by analyzing elastic $\alpha^3$H- scattering data using three different methods. All three methods yield similar results. The ANC values averaged over the three methods are $C_{3/2}=2.08\pm 0.10$ fm$^{-1/2}$ and $C_{1/2}=2.00\pm 0.10$ fm$^{-1/2}$. Comparison of the found ANCs with the previously obtained ANCs for $^7$Be confirms the relationship linking the ANC values for mirror nuclei. This research on determining the ANCs for the $^7$Li nucleus is, to some extent, a continuation of the previously completed study on its mirror nucleus, $^7$Be [ D. A. Savin, L. D. Blokhintsev, B. F. Irgaziev, A. S. Kadyrov, and A. M. Mukhamedzhanov, Phys. Rev. C 112, 065807 (2025)].
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High Energy Physics (Phenomenology)

High-frequency gravitational waves from axion inflation in the weak-backreaction regime

Axion inflation, characterized by a Chern-Simons interaction between the inflaton and a gauge field, provides a powerful mechanism for generating primordial gravitational waves (GWs) through tachyonic enhancement of the gauge field. While recent literature has predominantly focused on the Strong Backreaction (SB) regime to maximize GW signals for future interferometers, this regime suffers from computational complexities as well as the risk of overproducing scalar perturbations. In this work, we investigate gauge field amplification and GW production strictly within the theoretically safer Weak Backreaction (WB) regime, with a particular focus on the largely unexplored non-instantaneous reheating phase. Because the tachyonic enhancement during slow-roll typically increases as inflation approaches its end, it is crucial to investigate how the production of GWs behaves at the very end of inflation and thereafter. By continuously tracking the evolution from slow-roll through reheating to radiation domination, we present a complete picture of inflationary and post-inflationary GW production in this framework. A particularly interesting feature of the post-inflationary phase is that the oscillatory behavior of the inflaton during reheating leads to frequent sign-flips of the instability parameter $\xi$, exciting both helical modes of the gauge field. Our analysis reveals that axion inflation can naturally generate one of the strongest known primordial GW signals at high-frequency bands. The yield is relevant for future precision measurements of the effective number of neutrino species, $N_{{\rm eff}}$, and also strongly motivates the development of novel high-frequency GW detectors.
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Mathematical Physics

Explicit higher order rational rogue waves of the nonlinear Schrödinger equation

The $N$-th order rational rogue wave of the nonlinear Schrödinger equation (NLS), which depends on $2 N-2$ real parameters, has been shown to be impossible to generate by the nonlinear superposition formula. We here generate this sequence by a three-term recurrence relation, each step only requiring the computation of three $N-1$-th order determinants of $2 N-2$ variables, while the previous method requires two determinants of order $2 N$ in $2 N$ variables. This allows us to obtain explicitly the seventh wave with its six arbitrary complex parameters. These very compact expressions open the possibility to investigate the possible existence of new patterns in addition to the already observed ones (concentric rings, polygonal configurations, \dots).
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Fluid Dynamics · Cross-listed from math.NA

Physics-informed token transformer methodology for nonlinear balance laws. I. Schwarzschild–Burgers fluid flows

We introduce a Physics-Informed Token Transformer (PITT) methodology for nonlinear hyperbolic balance laws in one space dimension, using piecewise steady-state profiles for the representation of approximate weak solutions. The method combines symbolic equation tokenization, a Fourier neural operator encoder, an explicit Rankine–Hugoniot law for shock motion, and a learned correction term. For clarity, we present it here for the relativistic Schwarzschild–Burgers equation, a scalar model for spherically symmetric fluid flows on a Schwarzschild background. For this model the steady-state invariant and the generalized Riemann solutions are explicit, and they can therefore be built into the neural evolution. In particular, the leading discontinuities are advanced by the analytical jump condition, while the learned part reconstructs smooth regions, rarefaction fans, geometric dependence, and finite-resolution effects. The method is designed to locate wave fronts accurately and to preserve the relevant steady states. We test our PITT method on moving shocks, stationary shocks, rarefaction waves, and compare it with a standard high-order finite-volume approximation. We also analyze the standard Burgers limit (when the Schwarzschild mass tends to zero). The Rankine–Hugoniot prior plays the dominant role in these tests, while equation tokenization gives a systematic additional gain. The method is relevant for problems involving geometric effects and/or complex shock-wave dynamics, and is used here to study the long-time dynamics of perturbations of steady-state solutions. In particular, we exhibit an asymptotic law of propagation for the shock location of perturbed steady-state flows.
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High Energy Physics (Phenomenology)

Testing selectively enhanced QCD axions couplings as an explanation of the RX J1856.5-3754 hard X-ray excess

We explore the possibility of explaining hard X-ray data obtained from one of the Magnificent Seven (M7) neutron-stars (NSs) employing QCD axion-converted photons. The emission of thermal axions along with neutrinos from the core has been considered. We adopt the nucleon-nucleon bremsstrahlung process as the baseline axion production mechanism and Cooper-pair breaking and formation (PBF) as an additional process. We investigate here whether the selectively enhanced QCD axion coupling model can better explain the hard X-ray excess than the commonly used KSVZ axion model. Our results suggest that meV-mass QCD axions cannot explain the hard X-ray observation within the adopted framework. The enhanced selective model in the micro-eV scale provides closer agreement with the hard X-ray data. We thus conclude that the emission of hard X-rays in the $2-8$ keV range from isolated M7 stars could be explained by QCD axions under an enhanced coupling scenario.
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Mesoscale and Nanoscale Physics

Electrical control of the metal-insulator transition in a one dimensional device

Controlling the low energy spectrum at the nanoscale with an external physical parameter has become an important resource for quantum devices. The emergence of an energy gap is one such key feature, linked to the mitigation of decoherence needed for quantum information processing. Indeed, the detrimental effects of high-energy uncontrolled excitations can only be cured at some specific tuning points in general. Achieving an energy gap is a natural way to extend decoherence countermeasures over a finite region of parameter space. This would be particularly useful in view of the recent efforts to build superconducting topological chains in a top-down approach. In this work, we demonstrate a large energy gap by spatially modulating the local potential of a suspended carbon nanotube, exploiting an analogy with condensed matter systems. This gap is homogeneous on the nanotube and tunable by about two orders of magnitude, bringing the electronic system from an insulating state to a near-metallic state at low temperatures.
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All authors J. Craquelin, L. Jarjat, B. Hue, A. Théry, C. Fruy, N. Struchkov, D. Stefani, M. M. Desjardins, A. Cottet, M. R. Delbecq, T. Kontos

Quantum Physics · Cross-listed from cs.LO

Reasoning about Continuous-Variable Quantum Systems

Continuous-variable quantum computing (CVQC) is a computing paradigm in which measurements yield values over a continuous domain. CVQC is both a convenient computational framework for modeling physical quantum systems, and a good abstraction for hardware platforms based on quantum optics. Yet, the semantic foundations of CVQC remain underdeveloped. To address this gap, we develop a formal semantics for a core CV quantum programming language, and sound verification methods for program correctness. A main contribution of this work is to isolate a well-behaved quantitative predicate domain that achieves sufficient expressiveness to accommodate unbounded values as they arise in the infinite-dimensional, continuous setting. Specifically, we choose closed positive quadratic forms as semantic predicates, representing finite expectations, domains of finiteness, and infinite penalties in one ordered object. We validate our choice by establishing that our semantic predicates satisfy desirable closure properties including the definition of weakest preconditions. We validate our design with two case studies, including an example based on the celebrated GKP error-correcting code, for which we establish a second moment bound.
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All authors Tianshi Yu, Gilles Barthe, Minbo Gao, Mingsheng Ying, Li Zhou

Astrophysics of Galaxies

Correlation between the two-armed $V_R$ spiral in the $Z$–$V_Z$ plane and moving groups

We use a cross-matched sample of 3.7 million stars from Gaia DR3 and LAMOST DR7 to investigate the velocity substructures in the Milky Way disk. The median radial velocity $V_R$ as a function of guiding-center radius $R_g$ exhibits alternating positive and negative stripes, which are strongly correlated with known moving groups. By examining the $V_R$ distribution in the $Z$–$V_Z$ phase space, we find that the D1, P2, D2, and P3 $V_R$ stripes display clear two-armed spirals. Among the moving groups embedded in these $V_R$ stripes, the Coma Berenices moving group in the P3 stripe exhibits the most pronounced two-armed spiral and serves as the primary contributor to the left arm of the overall P3 spiral. The angular momentum, eccentricities, orbital frequencies, and frequency ratios of its stars are consistent with either the corotation resonance of the spiral arms or the $m=4$ inner Lindblad resonance of the bar. Test-particle simulations confirm that a bar with a varying pattern speed, together with static or transient spiral arms, can produce such two-armed spirals.
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All authors Yan Xu, Chao Liu, Chengdong Li, Heidi Neiberg, Hao Tian, Hua Jian Wang, Xiao Dian Chen, Li Cai Deng

Statistical Mechanics

Quantum fluctuation-driven transport crossover between two liquid states in distinguishable helium-4

We show the emergence of a quantum fluctuation-driven transport crossover between two liquid states in distinguishable helium-4 obeying Boltzmann statistics, in the absence of atomic exchange. Using path integral centroid molecular dynamics simulations over 0.1-3.3 K and 1-60 bar, we investigate the transport properties of two distinct liquid states: the low quantum dispersion liquid (LQDL) and the high quantum dispersion liquid (HQDL). While LQDL exhibits conventional liquid behavior consistent with the Stokes-Einstein (SE) relation, HQDL emerges at lower temperatures and displays anomalous gas-like transport characterized by superdiffusion and ultralow viscosity, accompanied by a breakdown of the SE relation. This counterintuitive emergence of gas-like dynamics upon cooling reflects the dominant role of nuclear quantum fluctuations, in contrast to thermal fluctuations at higher temperatures. Across the LQDL-HQDL boundary, we identify a transport crossover marked by a qualitative change in the velocity autocorrelation function (VAF), a transition in the Prandtl number, and the emergence of transport minima in shear and kinematic viscosities, thermal conductivity, and thermal diffusivity. These minima reflect a crossover from liquid-like to gas-like transport upon cooling in the low-temperature subcritical region, in addition to the universal transport minima observed in the supercritical regime. The transition from oscillatory to monotonic VAF defines a second Frenkel line, distinct from the conventional Frenkel line observed in the supercritical region. LQDL is a heat-transport-dominated dissipative fluid, whereas HQDL is a momentum-dominated inertial fluid. These results demonstrate that nuclear quantum fluctuations alone induce gas-like liquid behavior and provide a unified picture of transport phenomena in distinguishable helium-4 without superfluidity.
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General Relativity and Quantum Cosmology

Parameter Estimation on LIGO-Virgo-KAGRA O4a Binary Merger Triggers with Sub-solar Mass Components

The LIGO-Virgo-KAGRA collaboration has reported the results for searches for sub-solar mass components in compact binary coalescence during observing run O4a. No detection candidates were identified, but the most significant seven triggers were reported. We present the results of Bayesian parameter inference on these triggers. Five of the triggers show agreement between the Bayesian parameter estimation and the search pipeline trigger. Our results show that three of the triggers may contain a possible sub-solar mass component. Parameter estimation indicates that the other two events, if real, would be neutron star - black hole binaries. The remaining two triggers do not provide informative parameter estimation. We also study three O4a compact binary coalescence triggers, and one O3 trigger, that have been noted by three other groups, and our parameter estimation indicates that three of these may contain a sub-solar mass component. We study the data quality associated with these triggers. Finally, we discuss the challenges for parameter estimation on compact binary coalescence events containing a sub-solar mass component: long signal duration, possible small chirp masses, possible small mass ratios, and data quality issues over potentially hundreds of seconds of data.
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All authors Nelson Christensen, Neil Cornish, Florian Kühnel, Mairi Sakellariadou, Andres Santiago Villares Guanga

High Energy Astrophysical Phenomena

Diverse Morphologies of GRB X-Ray Plateaus within a Common Magnetar Framework

The origin of the X-ray plateau phase in gamma-ray bursts (GRBs) remains an open problem. In particular, it is unclear whether GRBs with different temporal morphologies (i.e., with a rising, flat, or decaying plateau) arise from a common underlying mechanism. Although magnetar energy injection is a leading explanation, previous studies have primarily inferred magnetar properties on a burst-by-burst basis and have not tested the model at the population level. Here we perform the first hierarchical population inference of magnetar parameters for a uniform sample of 185 long GRBs with X-ray plateaus within a conditional Poisson point-process framework. It is found that the observed plateau population is well reproduced by physically plausible magnetar populations. The inferred parameter distributions show no strong statistical separation among subclasses with different plateau morphologies. Nevertheless, all subclasses show a substantial intrinsic luminosity scatter, $\sigma_{L,\rm int}\sim0.5$–1.0 dex, whereas the intrinsic duration scatter remains considerably smaller. The results provide a population-level test of the magnetar interpretation of GRB X-ray plateaus, showing that the observed diversity of plateau morphologies does not require distinct magnetar populations.
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All authors Xiao-Fei Dong, Yong-Feng Huang, Nurimangul Nurmamat, Chen Deng, Ze-Cheng Zou, Fan Xu, Abdusattar Kurban, Chen Du, Chen-Ran Hu, Jin-Jun Geng

Quantum Physics

Irreducible Architectures of Multipartite Entanglement

Multipartite entanglement is commonly characterized by scalar notions such as separability and entanglement depth, which do not resolve the distribution of entangled cluster sizes. For mixed states, we introduce formation profiles that assign weights to the entanglement architectures appearing in pure-state decompositions. We show that after discarding every profile that admits a strictly weaker feasible replacement, the remaining irreducible structure need not be unique: a four-qubit example exhibits a continuous family of incomparable irreducible profiles. Monotone functions of the architectures recover widely used scalar quantifiers as special cases, whereas the full profile geometry retains additional information, including the minimum weight that every decomposition must assign outside a chosen architectural class. Finally, we derive experimentally accessible bounds on these weights from convex witnesses, including the quantum Fisher information, thereby connecting detailed formation structure with practical entanglement certification.
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Mesoscale and Nanoscale Physics

Janus-induced atomic reconstruction amplifies twist-angle modulation of interlayer thermal transport in moiré bilayers

In two-dimensional moiré bilayers, atomic reconstruction, the spontaneous structural relaxation toward energy-minimizing stacking registries in the near-commensurate regime, can strongly modify local stacking and interlayer coupling, providing a possibility to significantly control phonon-mediated properties. Here we show that the twist-angle dependence of interlayer thermal conductance can be modified by introducing Janus-induced mirror-symmetry breaking into bilayer MoS2. The intrinsic out-of-plane dipole in MoSSe/MoS2 bilayers leads to frictionless interface, and reduces the lattice deformation energy, thereby promoting atomic-reconstruction into locally distorted aperiodic moiré patterns. These features weaken interlayer coupling and suppress phonon transmission across the interface, leading to an anomalously strong twist-angle dependence of thermal conductance, with a pronounced minimum at small twist angles and a reduction rate nearly one order of magnitude larger than that of twisted bilayer MoS2. Our results demonstrate that interlayer thermal transport is modified by atomic reconstruction, highlighting Janus-induced mirror-symmetry breaking as an effective way to promoting phonon engineering in two-dimensional moiré structures.
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All authors Bin Xu, Rulei Guo, Jie Sun, Hiroo Suzuki, Takuma Yoshida, Ichiro Nakaya, Koki Sawasaki, Yasuhiko Hayashi, Shohei Chiashi, Tomoki Machida, Junichiro Shiomi

High Energy Physics (Phenomenology)

Exact Phenomenology of the Neutrino Cuboid: Normal Mass Ordering, the Tribimaximal Limit, and Cosmological Constraints

We investigate the exact phenomenology of a geometric neutrino cuboid defined by $m_1=m_0\sin\xi$, $m_2=m_0\cos\xi\sin\zeta$, and $m_3=m_0\cos\xi\cos\zeta$, whose cubic point corresponds to mass degeneracy and the tribimaximal values of the solar and atmospheric mixing angles. Imposing the mass-mixing alignment $\xi=\theta_{12}$ and $\zeta=\theta_{23}$, we derive closed-form consistency relations without relying on an expansion about the cubic limit. These relations show that the observed condition $\sin^2\theta_{12}<1/3$ selects normal mass ordering and, in the resulting normal-ordering regime, the physical condition $0<\Delta m_{21}^2/\Delta m_{31}^2<1$ requires $\theta_{23}$ to lie in the lower octant. Representative JUNO-based inputs give $\sin^2\theta_{23}\simeq0.440$, $(m_1,m_2,m_3)\simeq(0.0938,0.0942,0.1063)\mathrm{eV}$, and $\sum_i m_i\simeq0.294\mathrm{eV}$. We demonstrate that the first-order expansion around the tribimaximal point is numerically unstable for the solar-to-atmospheric mass-splitting ratio because of a leading-order cancellation. Present atmospheric-angle data yield only mild tension with exact alignment, whereas stringent neutrino-mass bounds in baseline $\Lambda$CDM cosmology strongly disfavor it; its viability under extended cosmological models remains model dependent. We finally formulate geometric alignment residuals as general null-test observables, providing a systematic framework for testing the neutrino cuboid with future oscillation and absolute-mass measurements.
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High Energy Astrophysical Phenomena

Constraining cosmological parameters from very-high-energy $\gamma$-ray attenuation in blazar spectra: Bayesian inference and systematic uncertainties

Very-high-energy $\gamma$ rays from active galactic nuclei are attenuated through pair production on the extragalactic background light (EBL), providing a probe of cosmic expansion. We develop a Bayesian inference analysis framework that uses an observationally driven, redshift-dependent EBL model and anchors intrinsic source spectra to the Fermi-LAT 3FHL catalogue while marginalising spectral-shape departures and dataset normalisations. The method is validated on realistic mock observations and applied to 241 archival H.E.S.S., MAGIC and VERITAS spectra of 50 AGN compiled in STeVECat. Because the leading opacity depends on the ratio of the EBL normalisation to the reduced Hubble constant, the gamma-ray data primarily constrain this ratio rather than $H_0$ alone. We measure $r=1.723^{+0.096}_{-0.095}$. For a fixed EBL scale, this gives $H_0=58.3^{+3.4}_{-3.0},\mathrm{km,s^{-1},Mpc^{-1}}$; allowing an 18% EBL-scale uncertainty gives $H_0=60.5^{+10.8}_{-10.0},\mathrm{km,s^{-1},Mpc^{-1}}$. Matched injections recover the input opacity without appreciable bias, and the tested intrinsic-spectrum and EBL-shape perturbations are subdominant except for large infrared-background mismodelling. The predominantly low-redshift sample leaves $\Omega\mathrm{M}$ weakly constrained. The measurement is therefore limited by the EBL normalisation rather than statistics; reducing its uncertainty to a few per cent would make gamma-ray opacity a competitive, distance-ladder-independent probe of $H_0$.
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