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Friday 11 September

General Relativity and Quantum Cosmology

Effects of the Ekpyrotic Mechanism on Inflationary Phase in mLQC-II

Jared Fier, Aqsa Fareed, Reena Danika Bendukuri et al. (+1 more)

Bouncing cosmological models replace the big bang singularity with a regular bounce, but face a well-known obstacle: the anisotropic shear grows as a^(-6) during contraction, where a is the average expansion factor, threatening to dominate before a homogeneous, isotropic universe can emerge from the bounce. A standard remedy is a scalar field with an ekpyrotic-like potential that turns negative near the bounce, pushing its effective equation of state above unity so it outgrows the shear. Here we examine how this mechanism affects the subsequent inflationary phase within mLQC-II, a modified loop quantum cosmology (LQC) model in which inflation is otherwise generic. Taking a potential combining ekpyrotic and inflationary components, we numerically evolve the dynamical equations across the bounce for various parameter choices. We find that while some choices of the free parameters of the theory allow the ekpyrotic potential to dominate near the bounce and resolve the shear problem, it substantially reshapes the post-bounce evolution. In particular, parameter choices that yield sufficient inflation without the ekpyrotic mechanism now often fail to do so. Sufficiently long inflation remains possible but appears to require fine-tuning. As our results are numerical, a more systematic analysis will be needed to establish their generality.
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All authors Jared Fier, Aqsa Fareed, Reena Danika Bendukuri, Anzhong Wang

Astrophysics of Galaxies

Host Galaxy UV Emission and Dust Reddening in Little Red Dots

Emmanuel Durodola, Ryan C. Hickox, Jonathan Cohn et al. (+1 more)

Little Red Dots (LRDs) have been the subject of extensive analysis to place them within the context of galaxy and black hole evolution. Despite several proposed scenarios for the nature of the rest optical emission in LRDs, our understanding of the UV emission remains a matter of debate. Here, we aim to study the origin of the UV emission in LRDs. We conduct emission-line and continuum fitting analysis of thirteen LRDs using a combination of NIRSpec PRISM and medium-resolution G235M and G395M spectroscopy. We isolate and analyze the narrow-line emission arising from larger physical scales in LRDs. We observe that the narrow-line Balmer decrements are typically greater than those predicted for case B recombination and broadly correlated with both the UV slope and the break strength, providing clear evidence that the UV emission originates from galaxy scales and its slope is significantly affected by dust reddening. SED fitting analysis further shows that the UV continuum of LRDs is consistent with a dust attenuated stellar template. Finally, we show through a comparison of the UV slope and the Balmer break strength, that LRDs can be further divided based on break strength, such that the canonical LRD spectral shape (strong break strength ($>$ 3) and flat rest UV continuum) represents the most extreme sub-population. Our results imply that for most LRDs, the UV emission originates primarily from the young host galaxy, and that the characteristic optical emission may be due to a combination of dust reddening and intrinsically red accretion processes.
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All authors Emmanuel Durodola, Ryan C. Hickox, Jonathan Cohn, David M. Alexander

Fluid Dynamics

Large-scale dynamics of equatorial thermal spots

V.P. Goncharov

For a model of a thin spherical layer of an incompressible rotating fluid subjected to the action of Coriolis and buoyancy forces, both analytical solutions in the form of stationary thermal spots moving along the equator and self-similar solutions are found. The influence of the parameters determining the shape of the spots on their propagation speed and direction is studied. It is found that the speed and direction of motion of the spots depend not only on the sign of their thermal contrast with the background flow, but also on the ratio of the semi-axes determining their shape. In particular, if the ratio of the equatorial semi-axis to the meridional one $b/a$ is equal to $\pi/2$, the spots are at rest. If the spots are elongated along the equatorial axis to such an extent that $b/a>\pi/2$, then “cold” spots move westward and “hot” spots move eastward. Under the condition $0.747\leq b/a<\pi/2$, the situation is reversed: “hot” spots move westward and “cold” spots move eastward. Self-similar solutions in the model are realized strictly in the form of circular thermal spots, and their radius varies according to a power law with a scaling exponent $k$, which is determined by the behavior of the cross-frontal buoyancy gradient on the spot contour. We note that the regime $k=1/4$ is realized under the assumption of a constant buoyancy gradient, while the regime $k=1/6$ corresponds to the conservation of total buoyancy.
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High Energy Physics (Phenomenology)

Semi-visible Jets from Sneaky Dark Matter

Deepak Kar, Christiane Scherb, Pedro Schwaller et al. (+1 more)

In this paper, we compare two different ways of generating semi-visible jet signature in non-resonant production mode, and flag the potential advantages of the new generation approach we propose. In addition, we suggest a more efficient matrix element to parton shower matching configuration for this hadronic final state signature. Finally, we perform a reinterpretation study of the ATLAS search for t-channel semi-visible jet production and obtain collider limits on the sneaky DM scenario.
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All authors Deepak Kar, Christiane Scherb, Pedro Schwaller, Sukanya Sinha

Mathematical Physics

Microscopic Parametric Correlations and Spectral Rigidity in the Non-Hermitian Threefold Way

Yan V Fyodorov

We study microscopic spectral correlations between two nearby parameter values in the three non-Hermitian Gaussian bulk classes: $A$ (unconstrained), $AI^\dagger$ (complex symmetric), and $AII^\dagger$ (complex self-dual, with each degenerate doublet counted once). Parameter dependence is modelled by stationary matrix Ornstein–Uhlenbeck evolution, whose microscopic time scale is $N^{-1}$. For every positive integer replica number $n$, we derive exact finite-$N$ auxiliary-field integral representations for joint characteristic-polynomial moments and obtain their bulk asymptotics as $N\to\infty$ with $n$ fixed. With the spectrum normalized to the unit disk, correlations near a bulk point $z_0$, between spectral positions $z_1,z_2$ at times $t_1,t_2$, depend only on $s=N|z_1-z_2|^2+N(1-|z_0|^2)|t_1-t_2|$. Adopting the static Hermitian/non-Hermitian replica continuation yields explicit two-time kernels; for $AI^\dagger$ and $AII^\dagger$ these are replica conjectures and, to our knowledge, the first microscopic two-time kernels proposed for these classes. They determine density correlations, cross-time eigenvalue-count covariances, and equal-time number variances. For a disk of mean eigenvalue count $y$, the latter obey $\mbox{Var}\mathcal N_X(D_y)=\kappa_X\sqrt y+ \beta_X/\sqrt y+o(y^{-1/2})$, with explicitly given constants for each class. Exact perturbation theory further identifies eigenvector nonorthogonality as the mechanism of short-time spectral diffusion and yields a basis-independent condition number for a two-dimensional Kramers eigenspace in class $AII^\dagger$. Direct simulations agree quantitatively with its conjectured inverse-gamma law.
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Solar and Stellar Astrophysics

Sinking Silicates I: Characterizing the benchmark system containing the T0 brown dwarf CWISE J210640.16+250729.0 using JWST

Austin Rothermich, Jacqueline K. Faherty, Ben Burningham et al. (+16 more)

In this study, we present the full (97.3% complete) 0.8–12.5 $\mu$m spectral energy distribution (SED) of an L/T transition object, CWISE J210640.16+250729.0 (CW2106), using the James Webb Space Telescope (JWST). We provide a full characterization of the host star's elemental abundances and age. We empirically derive the bolometric luminosity ($L_{\rm bol}\approx-4.825$ $\textup{L}_\odot$) of CW2106, and obtain estimates of its mass (M$\approx50-62$ M$_{\rm Jup}$), radius (R$\approx0.83-0.87$ R$_{\rm Jup}$), effective temperature ($T_{\rm eff}$$\approx1213$ K), and surface gravity ($\log~g$$\approx5.28$ dex). We find the near-infrared (near-IR) spectrum ($0.8-2.5 ~\mu$m) is best reproduced with cloudy atmospheric models while the mid-infrared (mid-IR) spectrum ($5-12.5 ~\mu$m) is best reproduced with cloudless models. This suggests a cloud layer restricted to only the deepest observable parts of the atmosphere and is qualified by the lack of a 9 $\mu$m silicate feature. Making use of the Mg/Si ratio of the primary, alongside thermochemical models, we predict the clouds in CW2106 to be composed primarily of enstatite (MgSiO$_3$), removing $\sim23\%$ of the bulk oxygen out of the atmosphere. Future retrieval studies will be able to help investigate the existence and full impact of these cloud species.
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All authors Austin Rothermich, Jacqueline K. Faherty, Ben Burningham, Catherine Manea, Emily Calamari, Genaro Suárez, Daniella C. Bardalez Gagliuffi, John M. Brewer, Kelle L. Cruz, Josefine Gaarn, Jonathan Gagné, Eileen C. Gonzales, Marina E. Gemma, Viktória Kecskeméthy, Mark S. Marley, Caprice L. Phillips, Channon Visscher, Johanna M. Vos, Niall Whiteford

Disordered Systems and Neural Networks

Fuzzy Erdos-Renyi random graphs: Spectral statistics

J. A. Mendez-Bermudez

Within a random-matrix-theory (RMT) approach, we perform a detailed numerical study of the spectral statistics of fuzzy Erdos-Renyi (ER) random graphs. Specifically, we consider the membership values of the vertices and edges of a fuzzy ER graph model as random variables. In this way, the corresponding adjacency matrices become sparse matrices with random entries. Then, we apply standard RMT measures to characterize the eigenvalues and eigenvectors of ensembles of Hermitian and non-Hermitian adjacency matrices of both undirected and directed fuzzy graphs. We demonstrate that the average degree of the ER model serves as the scaling parameter of the spectral properties of the corresponding fuzzy setups.
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Materials Science

Precessional modes of phonon angular momentum

Daniel A. Bustamante Lopez and Dominik M. Juraschek

Magnons are collective precessional excitations of electron spins and are ubiquitous in emerging information technologies. Here, we show that the crystal lattice can support an analogous precessional mode of phonon angular momentum. Superposition of a circularly polarized phonon and a linearly polarized phonon normal to the circular-motion plane generates a transverse angular-momentum component that rotates at their difference frequency and decays on a timescale set by the participating phonon linewidths, defining a mode with its own resonance and lifetime. Coupling between spin and phonon angular momentum hybridizes this precessional mode with a magnon near resonance. Our results establish phonon angular momentum precessional modes as lattice analogues of magnons and identify their spectroscopic and time-domain signatures.
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Superconductivity

Spatial instability of a homogeneous superconductor after an interaction quench

Medha Roy Choudhury, Sankha Subhra Bakshi, Pinaki Majumdar et al. (+1 more)

We investigate the quantum dynamics of a conventional superconductor, described by the attrac- tive Hubbard model, driven far from equilibrium by quenching the Hubbard attraction. We evolve the full density matrix of the system in time using the Heisenberg equation of motion, tracking the spatiotemporal dynamics of the pairing and density fields. We use very weakly inhomogeneous initial conditions to probe the stability of the homogeneous dynamics to spatial perturbations. At initial times after the quench the pairing and density fields remain homogeneous in space while fluctuating in time. However, depending on the quench strength the spatially uniform dynamics can become unstable beyond a threshold time, with emergence of spatial textures. The onset time for the instability depends on the strength of the quench and the initial inhomogeneity. At long times the system evolves towards a state with significantly reduced spatial heterogeneity. The time dependence of the global superconducting order parameter suggests two broad categories of re- sponse to a quench. One of these involves strongly inhomogeneous pairing and bond currents in the nonequilibrium superconductor.
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All authors Medha Roy Choudhury, Sankha Subhra Bakshi, Pinaki Majumdar, Amit Ghosal

Earth and Planetary Astrophysics

The core-mantle mode of gravitational oscillation

Mathieu Dumberry

We present the characteristics of a mode of axial oscillation between Earth's mantle, fluid core and solid inner core that has not been previously reported. The mode involves a quasi-rigid rotation of the fluid core outside the tangent cylinder (TC) exchanging its angular momentum with the mantle via a three step process. First, by a magnetic torque with the fluid inside the TC; second by a magnetic torque between the latter and the inner core; and finally by a gravitational torque between the inner core and mantle. Although the gravitational torque is purely between the mantle and inner core, the mode involves an oscillation of the whole of the core, and we refer to it as the core-mantle gravitational (CMG) mode. This form of gravitational oscillation occurs when the magnetic field within the core is sufficiently strong that the propagation time of Alfvén waves is shorter than the mode period, which is the case for Earth. We show how the period, quality factor $Q$ and structure of the CMG mode depends on the strength of the gravitational torque and viscous relaxation time $\tau_i$ of the inner core. For Earth, the CMG mode period should be in the range of 40 to 100 years, but viscous relaxation of the inner core likely implies a small $Q$, below 1 if $\tau_i<10$ years. Our results suggest that the CMG mode may act to amplify resonantly, though only modestly, multi-decadal changes in the length of day driven by zonal accelerations in the fluid core.
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Quantum Physics

High quantum local differential privacy breaks entanglement

Sujeet Bhalerao, Theshani Nuradha and Felix Leditzky

Differential privacy provides a mathematical framework for guaranteeing privacy for sensitive data. In quantum information processing, the interaction of privacy constraints with quantum resources such as entanglement remains a question of interest. Given that the utility of many protocols, and often the presence of a quantum advantage, relies on quantum resources such as entanglement, it is crucial to understand when a privacy requirement for a quantum channel is compatible with the channel's ability to preserve entanglement. We study this question for quantum local differential privacy (QLDP). Our main result shows that every $\varepsilon$-QLDP channel with a $d$-dimensional input is entanglement-breaking whenever $\varepsilon\leq\log\frac{d}{d-1}$. We also prove an approximate version for $(\varepsilon,\delta)$-QLDP, where channels in the same high-privacy regime are close in diamond norm to an entanglement-breaking channel. We further prove a composition result for a collection of private quantum channels having entangled inputs and global measurements in the high-privacy regime. Finally, we apply our results to private quantum learning theory. We prove that any learning protocol using arbitrary quantum memory on copies of the output of an entanglement-breaking channel can be simulated by a protocol that measures the corresponding unprocessed input copies one at a time while storing only classical information. Combining this result with our high-privacy entanglement-breaking theorem, we show that under sufficiently private local noise, a learning protocol with quantum memory for purity testing and bipartite product testing is subject to the sample complexity lower bounds for protocols with single-copy measurements on the noiseless tasks. We also obtain stronger sample complexity lower bounds when a single highly private channel acts on the entire multipartite input.
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Strongly Correlated Electrons

Tripartite entanglement in chaotic eigenstates

Junjia Zhang, Ramanjit Sohal and Shinsei Ryu

It is now well-established that classical statistical mechanics emerges from the entanglement structure of quantum chaotic systems, as quantified by the (subsystem) eigenstate thermalization hypothesis (ETH). While this statement rests on the well-studied bipartite entanglement of the eigenstates of such systems, recent years have shown that many-body states are often characterized by multipartite entanglement, raising the question: what are the universal multipartite entanglement features of chaotic eigenstates? We answer this question in part by studying a tripartite generalization of the ergodic bipartition ansatz through the lens of two tripartite entanglement probes, the Rényi tripartite multi-entropy and the Rényi reflected entropy. We derive leading-order analytical expressions for the ensemble averages of both quantities using a saddle-point analysis. Beyond these measures, we obtain the average of the Rényi-2 reflected density matrix, $\rho_{AA^*}^{(2)}$,which controls the Rényi-2 reflected entropy. We show that $\rho_{AA^*}^{(2)}$ in a chaotic eigenstate is well-described by this ensemble average which, unlike an ordinary reduced density matrix, takes three qualitatively distinct forms across subsystem-size regimes, which may be viewed as a tripartite generalization of subsystem ETH. We benchmark our analytical predictions against exact diagonalization of the mixed-field Ising model.
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Soft Condensed Matter

Biaxial nematics and nematic-nematic demixing in polydisperse mixtures of hard board-like particle fluids

Yuri Martinez-Raton, Daniel de las Heras and Enrique Velasco

We study the bulk phase behavior of a polydisperse liquid crystal fluid made of biaxial boards with restricted orientations using both fundamental measure theory and Monte Carlo computer simulations. The continuous polydispersity is included in the intermediate particle length of the boards via a truncated Schulz distribution. By calculating several phase diagrams across a range of polydispersity coefficients, we find that polydispersity (i) enhances demixing between two uniaxial nematic phases and (ii) expands the stability region of the biaxial phase. Although metastable with respect to non-uniform phases, we identify certain mixtures exhibiting two-phase coexistence paths involving uniaxial-uniaxial and uniaxial-biaxial phase separations. Whether these paths can be completed depends on the precise shape of the parent distribution function. Monte Carlo simulations performed for a representative case exhibit the same phase diagram topology predicted by theory, thereby validating the theoretical approach. The main difference between both approaches lies in quantitative agreement, with simulated phase transitions systematically occurring at higher packing fractions than those predicted theoretically. Our combined theoretical and simulation results may prove relevant to the design and interpretation of sedimentation experiments on colloidal suspensions of polydisperse anisotropic particles.
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Superconductivity

Topological superconductivity in an altermagnet-superconductor heterostructure

Michael Liudeng, Hrishikesh Patel, Marcel Franz et al. (+1 more)

Fully gapped spin-triplet superconductors offer a natural setting for topological edge transport and Majorana excitations. Here we propose a heterostructure that interfaces altermagnetic monolayer V$_2$Se$_2$O with a conventional $s$-wave superconductor. Starting from an ab-initio description of V$_2$Se$_2$O, we construct a low-energy model of its spin-split Fermi surface and study the superconducting instability of the coupled stack. We find that the momentum-dependent exchange splitting of the altermagnet strongly favors equal-spin pairing and converts the proximity-induced order into a fully gapped $p$-wave state. Over a broad range of interface parameters, the resulting Bogoliubov-de Gennes bands carry a nonzero Chern number, and slab spectra exhibit chiral Majorana edge modes traversing the bulk gap. We further quantify the inverse proximity effect and show how the induced gap evolves across a finite multilayer stack. These results establish a route to topological triplet superconductivity by interfacing a conventional superconductor with an experimentally available altermagnetic semiconductor, and provide practical guidance for interface fabrication and experimental detection.
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All authors Michael Liudeng, Hrishikesh Patel, Marcel Franz, Niclas Heinsdorf

Astrophysics of Galaxies

Mapping parameters of idealised hydrodynamic galaxy simulations to bar properties: a case study with the RAMSES code

Srikanth T. Nagesh, Benoit Famaey, Jonathan Freundlich et al. (+4 more)

Cosmological simulations with high spatial resolution often struggle to reproduce the observed fraction of galactic bars across redshift and may produce bars that are too short. To investigate these issues from a purely Newtonian dynamical perspective, we run a grid of idealised hydrodynamic simulations of disc galaxies with stellar masses of $\sim10^{10},{\rm M}_\odot$ using RAMSES. Without cooling, star formation, or feedback, we vary the resolution, gas mass, stellar velocity dispersion, bulge mass, halo mass, and concentration to identify the conditions that inhibit bar formation. We test whether initially axisymmetric discs form bars over the typical time elapsed between $z\sim1$ and $z\sim0.2$. We find that most diagnostics proposed in the literature are too simplistic to reliably predict bar formation. However, a region of parameter space that strongly inhibits bar formation is identified: a high Romeo-Falstad stability parameter, with a threshold that decreases quadratically with bulge mass, combined with a high generalised Efstathiou-Lake-Negroponte (ELN) parameter that accounts for the bulge. Lower gas fractions and larger numbers of dark matter particles also tend to reduce the bar growth rate. We argue that if a bar is destroyed, for example by bulge formation, after the galaxy enters this bar-inhibiting region, re-formation may be difficult. This suggests that a modern version of the angular momentum catastrophe may persist in large-volume cosmological simulations. Finally, we confirm that only baryon-dominated discs lying away from the stellar-to-halo-mass relation expected from abundance matching can form bars sufficiently large relative to their corotation radius.
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All authors Srikanth T. Nagesh, Benoit Famaey, Jonathan Freundlich, Yves Revaz, Giacomo Monari, Arnaud Siebert, Rodrigo Ibata

Superconductivity

Superconducting Diode Effect in Josephson $\varphi_0$ Junction

A. Janalizadeh, Y. M. Shukrinov and M. R. Kolahchi

We investigate the superconducting diode effect in a Josephson junction with a ferromagnetic weak link in the presence of Rashba spin-orbit coupling. While the standard $\varphi_0$ junction model is valid only for weak exchange fields $h \lesssim T_c$, realistic ferromagnetic barriers typically operate in the regime $h \gg T_c$, where the conventional Ginzburg-Landau gradient expansion becomes insufficient and requires the inclusion of higher order gradient terms to ensure stability of the free energy. By extending the free energy with such higher order term, we demonstrate that the linear gradient coupling alone leads to finite momentum Cooper pairing while leaving the critical current symmetry unchanged. The interplay between this linear term and the higher order gradient one leads to the Josephson diode effect.
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Materials Science

Visualizing impurity-driven scattering phase textures in EuCd2As2

Raquel Sánchez-Barquilla, Rafael Pineda Medina, Pablo García Talavera et al. (+11 more)

Understanding how disorder modifies electronic states in magnetic semiconductors is important for controlling spin-dependent transport and topological responses. Here we use scanning tunneling microscopy to visualize scattering phase textures in EuCd2As2. By isolating a single surface wavevector we reconstruct spatial phase maps of the local density of states and identify phase dislocations characterized by 2pi winding around impurity sites. These phase singularities emerge systematically within charge puddles generated by Eu interstitials and their positions evolve with bias voltage. We show that their spatial structure is consistent with interference between multiple scattering channels, including contributions from spin-orbit coupling. We provide a model which reproduces phase dislocations and relates the decay of the phase gradient to the relative strength of spin-orbit and scalar scattering. Our results establish a route to access the phase of electronic scattering in real space and study the role of local disorder and spin-orbit interactions in shaping electronic states in quantum materials.
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All authors Raquel Sánchez-Barquilla, Rafael Pineda Medina, Pablo García Talavera, Adrian Valadkhani, Edwin Herrera, Brinda Kuthanazhi, Lin-Lin Wang, Sergey L. Bud'ko, Paul C. Canfield, Roser Valentí, Isabel Guillamón, William J. Herrera, Alfredo Levy Yeyati, Hermann Suderow

General Relativity and Quantum Cosmology · Cross-listed from math.AP

Nonlinear Phase Mixing in Einstein-Vlasov System near Schwarzschild Spacetime

Saehoon Eo

We study the Einstein-Vlasov system near the Schwarzschild spacetime in spherical symmetry. In particular, we consider the case when the matter is supported on bounded geodesics. In this regime, the decay of the matter is driven by phase mixing rather than dispersion. For the linearized problem, we obtain quantitative phase mixing; the key new ingredient proved here is a monotonicity property of the period function. For the nonlinear coupled problem, we prove phase mixing up to the timescale expected from the nonlinear echo mechanism; this is achieved by analysis on dynamical action angle variables and the integral estimates with the vector field method. This construction is made possible by our gauge choice, an isotropic coordinate system together with a foliation of prescribed mean curvature, in which the Einstein equations gain derivatives over the matter due to its elliptic nature.
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Quantum Physics

Orientation-dependent Pauli noise in one-dimensional discrete-time quantum walks

Alejandro Contreras Reynoso, Adrian Ortega and Thomas Gorin

Discrete-time quantum walks exhibit ballistic spreading that is highly sensitive to decoherence. We study the long-time dynamics of a one-dimensional discrete-time quantum walk under Pauli noise acting on the coin. Choosing the unitary coin such that its invariant Bloch-sphere axis is orthogonal to the axis fixed by the conditional shift, we identify the distinct effects of noise aligned with either dynamical axis or orthogonal to both. Using a Fourier-space Pauli-superoperator formalism, we derive expressions for the first two position moments and long-time asymptotics for X-, Y-, Z-, and depolarizing noise. All channels induce a crossover from ballistic to diffusive spreading, with a second moment growing linearly at long times. The approach to this regime is channel dependent: it is exponentially fast for X-, Z-, and depolarizing noise, but algebraic, with a leading $t^{-1/2}$ correction, for Y-noise. The position distributions retain distinct finite-noise signatures, including a Gaussian-like profile with a central depression for Y-noise. In the maximal-noise limit, depolarizing, Y-, and Z-noise yield the classical binomial distribution for arbitrary initial coin states, whereas X-noise does so only when the initial state has no component along the noise axis. Thus, the quantum-to-classical transition is governed by the relative alignment of the noise, the coherent walk dynamics, and the initial state.
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Strongly Correlated Electrons

Effective theory of the hidden-order pseudogap phase in a doped antiferromagnet

Gaia De Paciani, Gesa Dünnweber, Johannes Poersch et al. (+3 more)

The microscopic origin of the pseudogap phase constitutes a longstanding puzzle related to the emergence of high-temperature superconductivity in cuprate materials. In this work, we develop an effective model for doped antiferromagnets in terms of fluctuating stripes, or string-like domain walls, which obscure the antiferromagnetic order of the spin background. The open ends of such domain walls of the N'eel order are treated as vortices in the resulting lattice gauge theory. We numerically evaluate the phase diagram by classical Monte Carlo simulations, using percolation-based geometric order parameters to diagnose hidden N'eel order. At high temperatures, we identify a BKT-type crossover in which the domain wall ends become deconfined. We interpret this as the $T^*$ crossover from the hidden order regime to the paramagnetic metal above. At low temperatures, we identify stripe instabilities. Predictions of our effective model can be tested in ultracold fermion quantum simulators.
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All authors Gaia De Paciani, Gesa Dünnweber, Johannes Poersch, Simon M. Linsel, Henning Schlömer, Fabian Grusdt

Mesoscale and Nanoscale Physics

Topological classification through knotted graphs: Fermi surface dispersions and Lifshitz transitions

Hakan Akgün, Xianquan Yan and Ching Hua Lee

Knot theory has provided a rich topological taxonomy for band structures, but its reach is fundamentally limited: knot invariants classify only 1D nodal lines at gap closure, and cannot encode the full dispersion or rich Fermi surface structure of realistic materials. Here we show that knotted graphs (knots that admit graph-like intersections in 3D space) - which have so far been elusive in condensed matter literature - provide a unified topological language for classifying the entire band dispersion, and even the eigenstate topology in some contexts. We propose a new framework beyond the existing Yamada polynomials that can topologically characterize the intricacies of realistic Fermi surfaces completely, crucially including how their multiple disconnected pieces are nested. This yields the Yamada set, a boundary-resolved extension which organizes the full topological evolution across energy into a Yamada sequence: a compact dispersion-level fingerprint directly tied to experimental signatures of Lifshitz transitions. Our framework is demonstrated with DFT-based band structures of real materials. Beyond dispersion-level classifications, this framework can be extended to non-Hermitian exceptional surfaces, where Berry-curvature flux further equips the knotted-graph skeleton with a directed Abelian edge flow that also captures the eigenstate topology.
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Quantum Physics

CUDA-Q Logical: Retargetable Compilation for Fault-Tolerant Quantum Computing

Alexander McCaskey, Justin Lietz, Adam Holmes et al. (+8 more)

Realizing fault-tolerant quantum computing requires mapping logical programs to heterogeneous quantum error correction (QEC) codes and diverse fault-tolerant execution models, scheduling physical resources, and coupling to real-time classical control and feedback. Specialized tools exist for each step but rely on manual composition and translation that discard assumptions and provenance, separating resource estimates from the compiler artifacts they describe, and making it difficult to validate correctness, compare architectures, or attribute costs to specific design choices. We present CUDA-Q Logical, an extensible compiler infrastructure for retargetable fault-tolerant compilation, analysis, and execution. Interoperable with CUDA-Q and other mainstream front-ends, CUDA-Q Logical progressively lowers target-independent logical programs through a constrained logical virtual machine, QEC microcode, physical gate schedules, and real-time control plans, with each layer preserving semantics and provenance, while verifying composition and resource constraints. By deriving every resource estimate directly from compiler artifacts, the framework unifies compilation and resource analysis, enabling successively refined estimates and principled cross-architecture comparison while permitting QEC codes, execution models, decoders, and hardware architectures to be introduced as modular extensions. Across workloads ranging from application-architecture studies to qLDPC surgery and detector-error-model composition, we show that schedule-derived estimates reconcile with established independent models. Crucially, this compiler-visible structure exposes cost drivers hidden by aggregate analytical formulas, carries QEC artifacts intact into simulation, and demonstrates a complete compilation pipeline for fault-tolerant quantum computing.
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All authors Alexander McCaskey, Justin Lietz, Adam Holmes, Kohei Nakaji, Vadym Kliuchnikov, Yifan Hong, Amalee Wilson, Andres Paz, Bettina Heim, Bruno Schmitt, Krysta M. Svore

Statistical Mechanics

Quantum Stochastic Walks on the Permutation Group

Feng He, Arthur Hutsalyuk, Giuseppe Mussardo et al. (+1 more)

How rapidly does order give way to randomness, and can quantum coherence accelerate this process? We address these questions through the paradigmatic problem of card shuffling, formulated as a random walk on the symmetric group $S_n$. We first recast the random-transposition walk studied by Diaconis and Shahshahani, as well as more general walks generated by conjugacy classes of $S_n$, in continuous time. We then identify the transition matrix of each classical walk with a permutation Hamiltonian generating a corresponding unitary quantum walk. Purely unitary evolution, however, does not generically converge to the uniform distribution in the classical sense of mixing: coherence preserves information rather than erasing it. We therefore embed the problem into a quantum stochastic walk, where coherent dynamics competes with the dissipative process responsible for classical mixing. In this setting, quantum coherence assists randomization. We prove that it can only decrease the distance from the uniform distribution in the computational basis and can therefore accelerate mixing. An analysis of the slowest mode yields a criterion for the coupling strength required to produce an appreciable speedup. Finally, numerical results reveal a scaling collapse of the ratio between quantum and classical mixing times onto a simple one-parameter form. Our results illustrate how coherence and dissipation can cooperate in the emergence of randomness in walks on permutation groups.
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All authors Feng He, Arthur Hutsalyuk, Giuseppe Mussardo, Andrea Stampiggi

High Energy Physics (Theory)

Matrix Theory from Holography

Shota Komatsu, Eunwoo Lee and Chintan Patel

We propose a setup that embeds Matrix Theory for M-theory into the AdS/CFT correspondence, allowing the former to be tested using the latter. The central claim is a triality among the BMN matrix model of rank $m$, a large-charge monopole sector of ABJM theory with charge $J$, and M-theory on the maximally supersymmetric eleven-dimensional pp-wave with a compact lightlike direction. The relevant ABJM limit sends $N,k,J\to\infty$ while keeping $N/k^2$ and $m=J/k$ fixed. We provide quantitative evidence for this triality by showing that, in this triple-scaling limit, the ABJM superconformal index agrees precisely with a grand-canonical sum of Witten indices of the $U(m)$ BMN matrix model. This relation also yields a compact grand-canonical expression for the BMN index, which we use to revisit its large-$m$ behavior. Our analytic and numerical results reveal strong boson–fermion cancellations and show no evidence for the previously claimed $e^{O(m^2)}$ growth when the BMN charge scales as $Q \sim m^2$. We further study the correspondence between the BPS cohomologies of the two theories by constructing a letter-level dictionary. This leads to a new notion of BPS fortuity in ABJM theory that survives even at strict $N=\infty$: although the usual fortuity associated with finite-$N$ trace relations disappears in the triple-scaling limit, each fixed-monopole sector is governed by the effective rank $m$, and finite-$m$ trace relations generate fortuitous states that map directly to fortuitous states of the BMN matrix model. Finally, we discuss connections to related concepts such as large-charge matrix models, open–closed–open triality, and worldline holography.
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High Energy Astrophysical Phenomena

Gas absorption of soft X-rays strongly impacts the redshift distribution of dark Fast X-ray Transients

Javier Sánchez-Sierras, Peter G. Jonker, Jonathan Quirola-Vásquez et al. (+25 more)

The progenitors of many Fast X-ray Transients (FXTs) and those of $\gamma$-ray bursts (GRBs) are strongly linked. Given that "dark" GRBs are typically found to be events suffering from enhanced extinction in the host galaxy, we investigate the nature of "dark" FXTs. However, unlike $\gamma$-rays, soft X-rays are strongly affected by absorption, implying that dark FXTs discovered by Einstein Probe's Wide-field X-ray Telescope (EP-WXT) have to be emitted at energies $>$2–3 keV restframe hence at a redshift $z\gtrsim2$. To illustrate this we present two dark FXTs, EP241103a and EP260409a, discovered by EP-WXT. For EP241103a, the high extinction precluded the detection of the optical counterpart, while for a probable source redshift of $\sim2.5$, the rest-frame X-ray photons are not severely affected. For EP260409a no counterpart is detected in the optical, but we do detect a near-infrared counterpart. A plausible scenario for EP260409a is that it lies at a redshift $z \gtrsim 4$. Additionally, we conduct simulations of FXTs observed with EP-WXT, showing that the detected counts for absorbed events ($N_{\mathrm{H}}\gtrsim10^{22}$~cm$^{-2}$) strongly decrease at low redshifts, hindering their detection. These results support the theoretical prediction that dark FXTs have an intermediate to high redshift and a different selection function from those of dark GRBs.
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All authors Javier Sánchez-Sierras, Peter G. Jonker, Jonathan Quirola-Vásquez, Agnes P. C. van Hoof, Andrew J. Levan, Maria E. Ravasio, Joyce N. D. van Dalen, Franz E. Bauer, Jia-Ying Cao, Francesco Carotenuto, Jennifer A. Chacón, Ashley A. Chrimes, Laura Cotter, Gregory Corcoran, Rob A. J. Eyles-Ferris, Guoli Huang, Shuai-Qing Jiang, Zexi Li, Yifang Liang, He-Yang Liu, Daniele B. Malesani, Antonio Martin-Carrillo, Daniel Mata Sánchez, Nikhil Sarin, Manuel A. P. Torres, Qinyu Wu, Tong Zhao, Wen-Da Zhang

Solar and Stellar Astrophysics

Classical Cases of Non-solar Mixing Length in Low Mass Stars

Rebecca Woody, Charlie Conroy, Phillip A. Cargile et al. (+1 more)

The treatment of convection is one of the largest remaining uncertainties in models of low mass stars. The Mixing Length Theory (MLT) for super-adiabatic convection has come under particular scrutiny. Evidence is mounting that a single value of the mixing length parameter ($\alpha_\mathrm{MLT}$) should not be applied universally across stellar model grids, although simulations and asteroseismic calibrations disagree on how it should vary with stellar parameters. A variable $\alpha_\mathrm{MLT}$ causes critical systematic changes to the ages of low mass stars, the key age tracers for galactic and exoplanetary studies. In this work we use classical (non-seismic) geometric radii and specialized MIST isochrones with a variable $\alpha_\mathrm{MLT}$ to measure mixing length in detached eclipsing binaries (DEBs) and interferometrically resolved stars, finding plenty of evidence for non-solar $\alpha_\mathrm{MLT}$. In particular we find that standard evolutionary models overpredict the radii of metal-poor interferometric stars and that a sub-solar $\alpha_\mathrm{MLT}$/$\alpha_{\mathrm{MLT},\odot}\sim0.50-0.75$ can neatly explain this discrepancy, consistent with other empirical calibrations and in stark contrast to simulations. We infer low convective efficiency in cool, rapidly rotating lower main-sequence stars, consistent with the known phenomenon of magnetically-induced radius inflation. We also identify several slowly rotating DEBs whose measurements cannot be reproduced by standard isochrones, and we propose these systems as useful case studies of non-solar mixing length in stars outside of the Sun. However, we find no definitive population level correlations between $\alpha_\mathrm{MLT}$ and stellar parameters among the DEBs, calling into question the existence of a ubiquitous mixing length calibration in low mass stars.
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All authors Rebecca Woody, Charlie Conroy, Phillip A. Cargile, Aaron Dotter

Quantum Physics

Noise-resilient sequential circuits for generating quantum order

Konstantin Gattinger, Julian Boesl, Max McGinley et al. (+2 more)

Sequential circuits provide an optimal linear-depth route to unitarily preparing long-range ordered quantum states, but circuit-level noise can be far more damaging than noise applied after preparation: local errors may be propagated by subsequent gates into nonlocal defects that destroy the target order. In this work, we present classes of unitary sequential circuits that prepare certain non-trivial orders in the presence of Pauli noise. Our constructions exploit the spatial structure of the syndromes of the target state, which in certain cases allows us to systematically suppress the propagation of errors using strictly local gates. The strategy can be applied both to symmetry-breaking order, for which we present a 3D example, and to topological order, which we showcase on a 4D version of the toric code. We also highlight how this stability against errors necessitates non-Clifford gates, and how measurement-feedback loops can be used to stabilize lower-dimensional states as well.
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All authors Konstantin Gattinger, Julian Boesl, Max McGinley, Michael Knap, Frank Pollmann

Astrophysics of Galaxies

The GMRT CAT$z$1-COSMOS Survey: HI 21 cm emission from star-forming galaxies at $z\approx1$ in the COSMOS field

Balpreet Kaur, Nissim Kanekar, Aditya Chowdhury et al. (+1 more)

We report a 216-hr upgraded Giant Metrewave Radio Telescope (GMRT) Band-4 $550-850$ MHz observation of the COSMOS field, using 7 GMRT pointings to cover an area of $2.4$ sq. deg., with on-source times of $67$ hrs in the central pointing, and $89$ hrs distributed across the other six pointings. We stacked, at a spatial resolution of 90 kpc, the HI 21 cm emission signals from 8,122 star-forming galaxies with accurate spectroscopic redshifts and lying within the FWHM of the GMRT primary beam at their redshifted HI 21 cm frequencies. We detect the stacked HI 21 cm signal from the 8,122 galaxies at $4.2\sigma$ significance, obtaining an average HI mass of $\langle{M_{\scriptsize{\textrm{HI}}}}\rangle=(15.5\pm3.7)\times10^9 \textrm{M}_\odot$. This is only the second galaxy population at $z\approx1$ with a measurement of the average HI content; the other being the blue star-forming galaxies in the DEEP2 fields. We also detected the median 1.4 GHz radio continuum emission signal from the 8,122 galaxies by stacking the GMRT 680 MHz continuum images, obtaining a weighted-median star-formation rate (SFR) of ${8.90\pm0.92}~M_\odot$ yr$^{-1}$. We measure a characteristic HI-to-stellar mass ratio of $\langle{M_{\scriptsize{{\textrm{HI}}}}}\rangle/\langle{M_\star}\rangle=(1.15\pm0.27)$ and a characteristic HI depletion timescale of $\langle{M_{\scriptsize{{\textrm{HI}}}}}\rangle/\textrm{SFR}=(1.74\pm0.45)$ Gyr for star-forming galaxies at $\langle{z}\rangle=1.081$ in COSMOS, both consistent with earlier measurements for the blue, star-forming DEEP2 galaxies at $z\approx1$. Our results support the evidence from the DEEP2 survey that the observed decline in the SFR density at $z<1$ is due to insufficient accretion of atomic gas from the intergalactic medium to replenish the gas reservoir consumed in the process of star-formation.
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All authors Balpreet Kaur, Nissim Kanekar, Aditya Chowdhury, Jayaram N. Chengalur

High Energy Physics (Theory)

The Conformal $w$-Algebra

Simon Heuveline, Nia Robles Del Pino and Andrew Strominger

Einstein gravity in four asymptotically flat dimensions is governed by a tower of soft theorems obeying an $\mathcal{L}w_{1+\infty}$ commutator algebra. This algebra is deformed to $\mathcal{L}_\Lambda w_{1+\infty}$ in the conformally related AdS$_4$ and dS$_4$ spacetimes. Here we construct the larger “conformal $w$-algebra", denoted $\mathcal{C}w_{1+\infty}$, which acts on conformal gravity in all of these spacetimes. It includes $\mathcal{L}w_{1+\infty}$, $\mathcal{L}_\Lambda w_{1+\infty}$ and the $\mathfrak{so}(4,2)$ 4D conformal algebra as subalgebras. We show that $\mathcal{C}w_{1+\infty}$ is the conformal completion of either $\mathcal{L}w_{1+\infty}$ or $\mathcal{L}_\Lambda w_{1+\infty}$. A derivation of $\mathcal{C}w_{1+\infty}$ is given as the symmetry of the twistor action of self-dual conformal gravity.
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Superconductivity

Strain-Induced Helical Superconductivity and the Zero-Field Diode Effect

Raigo Nagashima and Jörg Schmalian

Motivated by the strain-induced zero-field superconducting diode effect observed in PbTaSe$_2$, we identify a mechanism by which strain generates nonreciprocal superconducting transport without magnetism or an external magnetic field. Uniaxial strain mixes a dominant $s$-wave order parameter with a subdominant two-component pairing channel and enhances their symmetry-allowed Lifshitz coupling. Beyond a critical strain, this coupling drives a transition into a helical state with spontaneously selected finite Cooper-pair momentum and broken time-reversal symmetry. The resulting diode effect is generically non-monotonic in strain and exhibits distinct responses for currents parallel and perpendicular to the residual mirror plane, consistent with experiment. Our theory predicts that reversing the principal strain switches the diode direction by $90^\circ$, while shear strain rotates it continuously. These results establish strain as a symmetry-selective means of creating, controlling, and diagnosing spontaneous helical superconductivity.
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