Papers

Action-based distribution functions $f(\mathbf{J})$ provide a powerful description of stellar systems. Consequently, the construction of physically accurate and dynamically stable $f(\mathbf{J})$ for galactic components has emerged as a key challenge in the field. In this study, we present GroArnold, a computational framework designed to construct analytical $f(\mathbf{J})$ expressions for axisymmetric and triaxial galaxies and dark matter halos. The framework integrates modules for $N$-body initial condition generation, $N$-body simulation, angle–action variable estimation, and distribution-function fitting into a unified workflow. It supports a wide range of density profiles and kinematic properties, and is uniquely designed to generate stable $N$-body models for user-specified galactic systems, with the aim of obtaining an $f(\mathbf{J})$ that approximates a dynamically stable and physically consistent state. To this end, we extend the triaxial Stäckel Fudge method of the TACT code, implemented in our Nbody-TACT module, to enable action estimation directly from $N$-body gravitational potentials. GroArnold provides a robust and flexible tool for deriving numerically empirical, explicitly analytical distribution functions for user-specified galaxies or halos, thereby facilitating a wide range of practical $f(\mathbf{J})$-based modeling applications. In addition, it serves as a powerful tool for investigating the dynamics of realistic triaxial galaxies and halos beyond the scope of traditional spherical or axisymmetric models. We assessed the accuracy of the output $f(\mathbf{J})$ by comparing its predicted spatial and velocity distributions with those of the input $N$-body snapshot, and confirmed that it provides a reasonably accurate representation of the input. The code is modular, publicly available, and designed to support future extensions and adaptations.

We derive the junction conditions for spherically symmetric thin shells in Lovelock and Quasi-topological gravities along two independent routes: from the distributional form of the field equations, and from the boundary term that makes the variational problem well-posed in the non-null case. The former method is ambiguous as it stands, since the equations contain products of Heaviside step functions with a Dirac delta. We show that the singular parts of the field equations are exact differentials in the jumping variables, so that the Vol'pert chain rule for functions of bounded variation fixes these singular combinations uniquely and no products of two deltas survive for a single shell, finding that both routes then agree. The same rule yields the null junction conditions, for which no boundary term is available in Quasi-topological gravities, together with the mass conservation law of the shell. These results clarify recent questions concerning the existence of thin shells in these theories. In particular, we show that previous claims that the junction conditions force the shell mass to vary with radius are incorrect and arise from treating a trapezoidal approximation to the relevant distributional products as exact. Our results also provide a basis for the recent analyses of mass inflation in these theories.

Recent work on the two-Higgs-doublet model (2HDM) has uncovered basis-invariant relations among the parameters in the scalar potential that are stable under renormalization group (RG) evolution but do not coincide with any of the standard Higgs-family or Generalized-$\mathrm{CP}$ symmetry classes of the scalar sector. These relations have subsequently been reformulated in terms of so-called GOOFy transformations. In this paper, we show that the same fixed surface admits a conventional interpretation in terms of spurions. The gauge-covariant kinetic terms of the 2HDM possess a Higgs-family $\mathrm{U}(2)_H$ symmetry, and the couplings in the potential may be organized into irreducible spurions under its nontrivial $\mathrm{SU}(2)_H$ subgroup. We first explain the one-loop closure in the spurion language and then establish stability to all orders in the scalar and gauge couplings in any mass-independent scheme. General Yukawa couplings introduce additional Higgs-family covariants and can spoil the scalar-sector selection rule. We therefore consider the six conventional Higgs-family and Generalized-$\mathrm{CP}$ symmetries of the 2HDM, imposed as exact symmetries of the full Lagrangian, and show that closure is controlled by whether the relevant Higgs-family triplet contains an invariant direction. The spurion formulation thus provides a basis-covariant and conventional group-theoretic explanation of the RG stability of the 2HDM parameter relations.

We propose a post-inflationary first-order phase transition modulated by a light spectator field as the origin of primordial large-scale curvature perturbations. Spectator fluctuations acquired during inflation modulate the bubble nucleation history, generating curvature perturbations together with correlated intrinsic gravitational-wave (GW) anisotropies. We show that this mechanism can reproduce the observed amplitude of curvature perturbations while producing a loud stochastic GW background in the frequency bands of space-based detectors such as LISA, Taiji, and TianQin. A concrete benchmark yields strongly enhanced intrinsic GW anisotropies and a local primordial non-Gaussianity signal within reach of future large-scale-structure surveys.

An excited dark-matter state can produce a high-energy nuclear recoil by releasing its mass splitting in a collision. Motivated by the $248$~keV LUX–ZEPLIN candidate, we study freeze-in of a $45$~GeV pseudo-Dirac particle with a $1$~MeV splitting and a $1$~GeV dark photon during non-instantaneous reheating. We choose a recoil normalization compatible with the published INTEGRAL/SPI three-photon decay limit. It predicts $0.43$ events in the LZ window and retains the reference recoil shape. Including both dark-photon and $Z$ exchange, we calculate production and entropy dilution for backgrounds with $T\propto a^{-\alpha}$ and $\rho_\phi\propto a^{-3(1+\omega)}$. For $\Tmax=m_\chi$, the observed abundance requires $\Trh=1.32$~GeV for matter-like constant-width reheating, $3.09$~GeV for quartic oscillations with scalar decay, and $0.588$~GeV for quartic oscillations with constant width, compared with $4.10$~GeV for instantaneous reheating. These finite-reheating solutions are insensitive to increasing $\Tmax$ above $m_\chi$. For $\Tmax\geq m_\chi$, adiabatic kination has no solution with $\Trh>5.96$~MeV, the BBN-motivated cutoff adopted for our scans. At $\alpha_D=10^{-10}$, the estimated thermal-mediator source is below $0.2\%$ of the Standard Model source, and self-conversion does not appreciably deplete the excited population. The calculation relates an exothermic recoil benchmark to the production and dilution history before radiation domination.

While the spin vectors of binary black holes offer insight into the astrophysical formation channels of these systems, individual spins are less precisely measured through gravitational-wave observations than the effective inspiral spin $\chi_\mathrm{eff}$ and the effective precession spin $\chi_\mathrm{p}$. Reducing to effective parameters discards information in the data, but how much information is lost has yet to be demonstrated. Here we show how to quantify whether individual mergers carry information about component spins beyond the constraints implied by effective parameters (a.k.a. spinformation) and apply the technique to GWTC-5. Thresholding on information loss $\gtrsim 0.25$ bits, over $80\%$ of gravitational-wave events in GWTC-5 have component spin posteriors described by $\chi_\mathrm{eff}$ alone. Only $\sim3\%$ of gravitational-wave events have substantial spin information not explained by $\chi_\mathrm{eff}$ and $\chi_\mathrm{p}$. The catalog's component spin information is effectively two-dimensional in $\chi_\mathrm{eff}$ and $\chi_\mathrm{p}$. Using simulated signals, we find the noise realization can create or destroy over a bit of beyond-$\chi_\mathrm{eff}$ information: the structure in real data may therefore be driven by noise. At current sensitivity, component spins provide interpretive\textemdash rather than informational\textemdash advantage over effective parameters.

We used 14 years of Fermi-Large Area Telescope (LAT) data to derive a catalog of sources detected between 20 MeV and 200 MeV. For each source we provide localization, spectral, and association information. The Second Catalog of Low-Energy Fermi-LAT sources (2FLE) contains 450 sources detected at $TS>25$, with median energy flux of $F_{20-200 \, \text{MeV}} = 1.9\times10^{-11}$ erg cm$^{-2}$ s$^{-1}$. Using a Bayesian and likelihood-ratio method, we associate 377 2FLE sources with a known counterpart. Of the 325 objects associated with extragalactic sources, the dominant source class represented in the 2FLE are flat-spectrum radio quasars (FSRQ). Additionally, 52 sources are associated with Galactic sources. Three associated sources have not been previously detected in any $\gamma$-ray catalog and represent new $\gamma$-ray sources of known origin. We find that 387 2FLE sources have a positional cross-match with the 4FGL-DR4 sources. For the sources with a 4FGL counterpart, we compare the spectrum of the 2FLE source to the 4FGL spectral energy distributions. Of the 73 2FLE sources without multi-wavelength associations, 13 have a 4FGL counterpart that lacks classification, while 60 are newly discovered $\gamma$-ray sources. Among these 60 sources, 51 are found at high latitudes ($|b|>10^{\circ}$), and 38 are detected at $>10\sigma$. Additionally, we find that out of the 450 2FLE sources 45 are TeV emitters, and 6 are spatially coincident with a 1LHAASO source. The 2FLE helps us pave the way for reducing the “MeV gap", and provides the most sensitive catalog between 20-200 MeV to date.

Long-baseline (LBL) accelerator experiments are sensitive not only to the standard neutrino oscillation parameters but also to new physics. Currently, there exists a tension between NOvA and T2K data that can be explained by vector non-standard neutrino interactions (NSI) with complex couplings, which in turn introduce degeneracies in LBL measurements. We demonstrate that dark matter direct detection experiments can use their measurements of solar neutrinos to test the NSI resolution of this tension and to break these degeneracies. Using recent solar neutrino data from LZ, XENONnT, and PandaX-4T, we show that dark matter direct detection experiments already constrain part of the NSI solution of the NOvA-T2K tension. These experiments can also probe parts of the NSI parameter space that even DUNE will be blind to. Our analysis combines nuclear recoils from $^8$B neutrinos and electron recoils from $pp$ neutrinos. A future xenon experiment, such as XLZD or PandaX-xT, will be able to cover a significant fraction of the NSI solution of the NOvA-T2K tension.

Strong coupling between mobile charge carriers or excitons and lattice vibrations gives rise to polarons: quasiparticles formed by charge carriers dressed by a cloud of phonon excitations. Polaron formation determines transport properties of systems ranging from transition-metal oxides and organic semiconductors to light-harvesting complexes. In excitonic systems that admit a hard-core boson description, mapping the excitations to pseudospins provides a natural framework for studying polaron physics, including the nonperturbative regime in which hopping amplitudes, phonon energies, and coupling strengths are comparable. Here, we propose a trapped-ion blueprint for realizing spin-phonon Hamiltonians with programmable spatial coupling between excitation density and phonon displacements, encompassing local Holstein and long-range Fröhlich-type interactions. To access strongly dressed quasiparticles whose bare spectral weight is suppressed, we introduce displaced Green's functions implemented through spin-dependent phonon displacements. Their spectral response reveals the polaron band spectrum, including binding energies and phonon-excitation sidebands, while spatially resolved measurements probe the structure of the phonon dressing cloud, providing a route to polaron tomography. We further complement this spectroscopy with direct and ancilla-assisted measurements of spin-phonon correlations that track the coupled dynamics of the excitation and its environment. These approaches connect the emergent quasiparticle spectrum to the microscopic buildup of its dressing cloud, enabling controlled studies of how the spatial range of coupling shapes polaron formation and mobility.

Wave cold dark matter (wave CDM) is a well-motivated variant within the collisionless CDM paradigm, in which the de~Broglie wavelengths of ultralight bosons become relevant on galactic scales. While many of the previous tests of wave CDM have focused on small-scale tensions involving solitonic cores and certain soliton–halo relations in galaxies, the radial acceleration relation (RAR) provides a complementary test: for a given baryonic mass distribution, it probes whether the DM halo can reproduce the observed total gravitational field. In this work we test wave CDM against the RAR using eight X-ray elliptical galaxies from the compilation of Lelli et al. We perform a suite of 3D Schrödinger–Poisson simulations and evolve the wave-CDM halos to virialized quasi-stationary states. For each galaxy and each adopted boson mass, we select the realization whose final snapshot most closely matches the empirical RAR. We find that the selected wave-CDM realizations for these elliptical galaxies can reproduce the RAR without including baryonic feedback or dark-matter self-interactions. At the boson mass $m_a=10^{-23}$eV, the combined fit to the eight galaxies gives $a_0=1.19\times10^{-10}\,\mathrm{m\,s^{-2}}$, consistent with the canonical value inferred from disk galaxies. When the boson mass is varied over $3\times 10^{-24}$ eV $\le m_a \le 2\times 10^{-23}$ eV, the best-fit value of $a_0$ changes by only $\sim 11\%$, and this variation shows no systematic trend with $m_a$. This insensitivity to boson mass arises because, over the radial range relevant for the RAR, the virialized halos are supported mainly by their velocity field, whereas the boson-mass-dependent quantum-pressure term is dynamically subdominant. These results show that wave CDM can reproduce the RAR in elliptical galaxies, and provide a new galactic-scale test of the model beyond the previous focus on solitonic cores.

The Little Red Dots (LRDs) are compact, red sources, abundant at $4 \lesssim z \lesssim 9$ and likely powered by massive black holes. Photometric studies have found blue companions around them, but none has yet been confirmed spectroscopically. This Letter presents the only two LRD-companion pairs with spectroscopy of both members in the literature: "Waltz" at $z = 3.9$ and "Tango" at $z = 5.5$, with projected separations of $3.6$ and $2.5$ kpc. Both companions lie at the redshift of their LRD, within $132 \, \rm km \, s^{-1}$ and $57 \, \rm km \, s^{-1}$, and are physically identical, but $524$ Myr apart: starbursts $\lesssim 50$ Myr old, metal-poor ($0.2 \, \rm Z_\odot$), dust-free, dynamically cold, and as bright as the LRDs themselves in the rest-frame UV. The LRD in Waltz hosts a $\approx 3 \times 10^{6} \, \rm M_\odot$ black hole accreting at half the Eddington rate, a factor of a few above the birth mass of a direct collapse black hole, and is embedded in gas as metal-poor as its companion. Orbital modeling shows that Tango is bound in $81\%$ of the allowed orbits and that Waltz is bound if its host halo exceeds $5 \times 10^{10} \, \rm M_\odot$. Both blue companions then merge with their respective LRD within a few hundred Myr. We conclude that we are observing what heavy seeding requires: a young black hole beside the metal-poor starburst that the synchronized-pair scenario predicts, in the last steps of a cosmic dance that ends in a merger, and in a galaxy seeded by its black hole.

Non-Abelian anyons, strange particles forming the basis of fault-tolerant topological quantum computing, are predicted to emerge in fractional quantum Hall states at even-denominator filling factors. Identifying which topological order is realized has proven to be a challenging problem that requires an accurate, non-perturbative treatment of realistic Landau level mixing, which has so far been missing from theoretical studies. Here we present the first complete solution of non-Abelian quantum Hall problem that includes all electrons and all Landau levels, for spin-polarized electrons at filling factor $\nu = 3/2$. We develop a momentum-resolved neural-network variational wave function, optimized solely on the microscopic Hamiltonian, which gives direct access to the topologically degenerate ground states. Without any physics input about the expected outcome, it discovers a degenerate ground-state manifold whose entanglement reveals anyons with quantum dimension $\sqrt{2}$, the hallmark of Ising-type non-Abelian order. By directly computing the overlap with trial wave functions, we further show that Landau level mixing favors the anti-Pfaffian over other candidate states. Our results demonstrate the power of neural-network wave functions in finding and characterizing non-Abelian anyons from first principles, in regimes of strong Landau level mixing, relevant to many recent experiments.

Main sequence stars have perceived colours ranging from orange to white to blue with increasing effective temperature. This is because their atmospheric opacities cause only minor deviations from blackbody colours when integrated over the broadband sensitivity curves of the human visual system. White dwarfs can have much denser atmospheres, reaching ~ 1 g/cm3 for the coolest known objects. If metals such as carbon, calcium, or sodium are present in these ultra-dense atmospheres, extreme broadening of atomic and molecular opacities can produce optical spectra that diverge significantly from blackbodies. We investigated how the combination of temperature and chemical composition can affect the perceived colours (chromaticity) of white dwarfs. While we found that most white dwarfs are similar in colour to blackbodies, we also demonstrate examples of known stars that would appear yellow, green, cyan, pink, or purple if viewed close enough for their stellar discs to be resolved. We examined the chromaticity distribution for the volume-limited 20 pc local sample of white dwarfs finding a median correlated colour temperature of ~= 6800 K, establishing that, on average, white dwarfs are indeed white in colour. Finally we show how white dwarf spectral models can be used to generate colour-accurate images of their stellar discs as they would appear from up close.

Non-Abelian anyon chains whose interactions favor a single fusion channel host quantum critical ground states described by minimal-model conformal field theories (CFTs) protected by a topological symmetry. We show that their measurement-only counterpart, where non-commuting fusion charge measurements act locally on the anyons of a chain of $L$ sites, provides a fundamental example of a non-unitary CFT controlling a non-Abelian learning problem. Mapping the monitored dynamics to a random tensor network, we numerically find $1/L$ scaling Lyapunov gaps, logarithmic entanglement scaling with the chord length, and an effective central charge in the Shannon entropy of the measurement record. The conserved topological charge sharpens with dynamical exponent $z= 1$ and is learnable by a decoder on an $O(L)$ time scale. As the topological symmetry is a non-invertible symmetry of the $SU(2)_k$ anyon theories, we establish the monitored golden chain $(k=3)$ as a non-Abelian generalization of the weakly (Kramers-Wannier) self-dual quantum critical point of the toric code $(k=2)$, and the first of a family for $k\geq 3$.

Extreme mass ratio inspirals (EMRIs) are expected to be a major source of gravitational waves (GWs) for the future Laser Interferometer Space Antenna (LISA). An EMRI occurs when a compact object, driven by the emission of gravitational radiation, slowly inspirals into a massive black hole (MBH). The classical formation channel involves repeated two-body interactions within dense nuclear star clusters. However, both EMRI event rates and the expected distribution of their orbital parameters remain highly uncertain. A major source of this uncertainty is the poorly constrained ratio between gradually inspiraling EMRIs and direct plunges, which do not produce detectable GWs. While most studies of astrophysical EMRI production focus on the Schwarzschild limit, previous work examining the Kerr metric found that the spin of the central MBH can significantly affect the EMRI-to-plunge ratio. This enhancement depends sensitively on orbital inclination, yet earlier studies held inclination fixed. In this work, we develop the mathematical framework describing inclination evolution driven by two-body encounters evolving along Kerr geodesics. By implementing 3D diffusion into Monte Carlo simulations, we show that initially prograde orbits may evolve into retrograde states, thereby converting potential EMRIs into plunges or vice versa. We estimate the EMRI-to-plunge ratio and find that substantial MBH spin enhances the EMRI rate by a factor of $\sim 2.5$. Additionally, even for a non-spinning MBH, modeling the orbits as relativistic geodesics rather than Newtonian trajectories increases the number of EMRIs by a similar factor of $\sim 2.5$. The distribution of Kerr EMRI inclinations has a substantial prograde bias that may aid in identifying the subset of loss cone EMRIs within large future EMRI samples.

We study two-point event shapes in planar $\mathcal{N}=4$ super Yang–Mills, with source, sink and detectors given in terms of half-BPS scalars and their light transforms. Akin to local correlation functions, at order by order in perturbation theory, in the large charge limit, this event shape factorizes into the product of two octagons evaluated on the unit circle. Borrowing the octagon results, we study its behavior with respect to the coupling and the angle between the detectors.

Mass distributions of binary black hole mergers inferred from gravitational-wave observations offer clues to how binaries form. These distributions conventionally label the heavier component as the primary, with mass $m_1$, and the lighter as the secondary, with mass $m_2$, such that $m_1 \geq m_2$. This ordering folds the physically labeled mass distribution along the equal-mass line, potentially reshaping the underlying population structure. In this Letter, we determine which population features can arise from mass ordering and which require genuine astrophysical structure. We show that ordering alone can produce (1) an $m_2$ distribution that declines more rapidly than the $m_1$ distribution, without intrinsic differences between the physically labeled components, and (2) an apparent concentration along equal masses, without correlations that preferentially pair black holes of equal mass. Moreover, different physically labeled populations can produce the same ordered mass distribution. Crucially, however, a preferred companion mass that remains constant as $m_1$ increases requires a characteristic mass scale already present in the physically labeled population. Applied to binary black hole mergers in the fifth Gravitational-Wave Transient Catalog, our model recovers such a scale near $m_2 \simeq 50\,\mathrm{M}_\odot$. Around this scale, the merger-rate density declines much more rapidly toward higher $m_2$ than toward lower $m_2$, ruling out an equal or weaker high-$m_2$ decline at 99.45% credibility. This structure therefore requires a characteristic mass scale in at least one physically labeled component, but masses alone cannot determine which component carries it. Any formation model reproducing the observed high-mass binary black hole merger population must contain such a scale.

We study the prospects for an independent determination of $V_{cb}$ from bottom-tagged charged-current deep-inelastic scattering at future electron-proton colliders: the EIC, LHeC, and FCC-eh. The transition $e^- c \to \nu_e b$ probes $|V_{cb}|^2$ through a process with different theoretical and experimental uncertainties from semileptonic $B$ decays. We fit ratios of $b$-tagged charged-current event counts over flavour-inclusive ones in kinematic bins, including correlated parton-distribution and flavour-tag calibration uncertainties, and floating the other CKM parameters. With projected parton distributions and tagging performance motivated by existing studies, we find a potential relative sensitivity in $|V_{cb}|$ of about $0.8\%$ at the LHeC with $1\,\rm{ab}^{-1}$ of integrated luminosity and $0.7\%$ at FCC-eh with $2\,\rm{ab}^{-1}$. The corresponding EIC sensitivity is instead at the level of $20 - 30 \%$, depending on the configuration. The LHeC could thus provide a high-energy determination competitive with low-energy ones, but with substantially different dominant systematic uncertainties, on the timescale of its proposed operation between the HL-LHC and FCC-ee. We identify precise flavour-tag calibration and control of the kinematic response as the main requirements for realising this potential sensitivity.

The James Webb Space Telescope (JWST) has been revolutionizing our understanding of early galaxy formation over its first four years of science operations. With un- precedented sensitivity, spatial resolution, and wavelength coverage from the near- to mid-infrared, JWST has enabled astronomers to identify hundreds of star-forming galaxies at redshifts z>~8 (within ~650 million years of the Big Bang) through strong spectral breaks and characterize these galaxies through sensitive spectroscopy. These capabilities have provided new insights into the stellar populations, neutral gas, nebular continuum emission, chemical enrichment, dust content, and ionization conditions of galaxies during cosmic dawn, revealing more numerous and brighter systems than anticipated from pre-JWST models. We discuss the implications of these discoveries for reionization, the buildup of stellar mass and metals, and the evolution of galaxy populations and luminosity functions. JWST is also revealing a new physical picture of early galaxies, characterized by compact, clumpy star formation, high gas fractions, and intense radiation fields. Despite much progress, many open questions remain, including the efficiency, intermittency, and stellar initial mass function (IMF) of early star formation, conditions in the interstellar medium (ISM), masses, and structure of the earliest galaxies, and the topology of reionization. Resolving these open questions will require lensing magnification, sensitive spectroscopy to > 5 micron, including with the Atacama Large Millimeter Array (ALMA), exploration to higher redshifts, and larger, more complete samples, helping to clarify how the first galaxies formed and evolved.

We study the arithmetic structure of non-invertible duality defects in 4d $U(1)$ Maxwell theory. First, we recast the problem of realizing an elliptic $SL(2,\mathbb{Q})$ transformation as a duality defect in terms of complex multiplication for two-tori. The resulting classification includes well-studied cases in the literature, but extends to infinite Diophantine families of defects at a given gauge coupling. Second, we describe their worldvolume theories explicitly, with the Chern–Simons couplings determined by using continued fractions and tridiagonal continuant matrices. Third, we work out the fusion products of these defects, extracting the condensation defects and decoupled sectors both by lattice arithmetic and from the worldvolume descriptions. Finally, we illustrate our findings with the familiar $N$-ality defects (with $N=2,3$), but also give examples of infinite order.

Compact binaries evolving in the vicinity of massive black holes may be commonplace in the Universe, and their gravitational waves carry signatures of their environment. We study the strong lensing of these signals by the massive companion, a configuration that violates the standard assumptions of the lensing literature: geometric optics and thin lenses. Using a perturbative framework, we compute the full wave optics amplification factors for face-on and edge-on binaries, including spinning lenses. In the edge-on configuration, peak amplification does not occur at perfect source–lens–observer alignment, even for a non-spinning lens. This is a consequence of the anisotropic, coherent quadrupolar emission of the stellar-mass binary breaking the axisymmetry of the system. Restricting to the equatorial plane near the optical axis, we then find that the frequency dependence of the amplification factor is universal across every configuration studied, persisting deep into the wave optics regime. Comparing against a strong-field ray tracing calculation, we find agreement at the $\sim10\%$ level for a face-on binary lensed by a Schwarzschild black hole. In the less symmetric edge-on case only the angular peak shift and fringe spacing is reproduced to this accuracy. For a Kerr lens, the face-on amplification factor is described by its Schwarzschild counterpart to the same $\sim 10 \%$ accuracy once the effect of frame dragging is corrected for. A point mass lens, by contrast, fails to reproduce the features of the system, which may have strong implications for forecasts that adopt it for lensing by massive black holes in the strong field.

Merging galaxy clusters provide an ideal laboratory for testing the self-interacting nature of dark matter. In this paper, we present a pilot study of magnetohydrodynamical cosmological zoom-in simulations of two cluster mergers selected from TNG-Cluster, with $M_{\rm 200c} \sim 9\times10^{14}~M_\odot$ and $M_{\rm 200c}\sim 2\times10^{14}~M_\odot$. The simulations are performed with both standard collisionless cold dark matter (CDM) and self-interacting dark matter (SIDM), assuming an isotropic, velocity-independent cross-section of $\sigma_{\rm T}/m_\chi = 1~\rm cm^2~g^{-1}$, with an additional $0.5~\rm cm^2~g^{-1}$ run for the low-mass system, and the mass resolution and galaxy formation model are unchanged from TNG-Cluster. We show how dark matter self-interactions produce an isothermal core in the dark matter halo, generate unique substructures in the intracluster light, and introduce variation in the multi-wavelength observables of the intracluster plasma. Using these simulations, we test the validity of observational probes for dark matter self-interactions in cluster mergers. We find that the shock-to-shock separation shows similar evolution in the self-interaction models tested here, providing a reference for distinguishing the $\sim100-200~\rm kpc$-scale difference in halo separation induced by self-interactions. Moreover, the dark matter halo centroid of the main cluster in the massive cluster merger is offset from the brightest cluster galaxy by as much as $\sim20~\rm kpc$, larger than the offset in the sub-cluster. This offset persists beyond 4 Gyr after the first pericenter passage. Our results indicate that sample selection plays a key role in testing the possible self-interacting nature of dark matter using cluster mergers, and that double radio relic cluster mergers and massive clusters with evidence of an ancient major merger offer a promising testbed for this purpose.

Gravitational perturbations of rotating black holes in higher dimensions generally obey coupled partial differential equations. We show that scalar gravitational perturbations invariant under rotations of the transverse sphere of a singly spinning Myers-Perry black hole separate, despite the obstruction to a decoupled Teukolsky equation. Two commuting, second-order angular operators organise the three gauge-invariant curvature components into joint eigenfunctions. The physical radial problem is a $2\times2$ first-order system, equivalent to a single second-order equation. This gives a separation of the sector containing both the bar-mode and axisymmetric ultraspinning instabilities. Using only ordinary differential equations, we compute the bar-mode quasinormal spectrum in $d=5,6,7$ and find instability onsets at $a/r_+=0.90498$ and $0.83228$ in $d=6,7$. We also compute the growing axisymmetric modes and their onset rotations in $d=6,\ldots,9$. The construction shows how separability can survive the coupling between gravitational polarisations.

Stabilizer Rényi entropy quantifies magic relative to a complete Pauli frame. In settings such as helicity states of massless particles, unsynchronized qubit registers, energy eigenbases, and systems under superselection rules, the computational basis may be fixed while the transverse Pauli axes remain unspecified. The stabilizer Rényi entropy then depends on the choice of those axes. We define a phase-averaged stabilizer Rényi entropy by averaging the Pauli moments before taking the logarithm. It is exactly invariant under independent local rephasings. For pure states, it vanishes precisely when the state is a stabilizer state in every phase convention. For a broad class of sparse supports, it reduces to a closed-form function of the basis-state probabilities alone. Within this class, the ceiling for $n$ channels is $\ln[n^{3}/(6n-5)]$ for $n\geq3$ and $\ln\frac{7}{5}$ for two channels. We apply the invariant to tree-level gluon scattering at four and five points, where the helicity-basis phases are unspecified. It saturates the two- and three-channel ceilings: $\ln\frac{7}{5}$ at four points and $\ln\frac{27}{13}$ in $3\to2$ scattering. In same-helicity $2\to3$ scattering, it lies between a floor of $\ln\frac{8}{7}$ and a ceiling of $\ln\frac{184}{125}$, reached in the resolved soft limit and particular collinear limits, respectively. In every configuration studied, the invariant is independent of the fixed external colors.

Quantum simulators with disordered spin Hamiltonians offer a natural route to Haar-like unitary ensembles, but face a competition. Disorder enhances randomness, yet strong disorder suppresses dynamics and localizes the system in the computational basis. This suggests an optimal intermediate disorder strength for approximating a unitary $k$-design, which has so far been identified mainly empirically. Here, we develop a perturbative theory for the moment gap $\Delta^{(k)}$, the deviation of the $k$-th moment operator from its Haar value, for the full spectrum of the interacting XXZ chain in a fixed-magnetization sector. We find the non-monotonic asymptotic scalings $\ln \Delta^{(k)}\sim -\sigma^2$ at weak disorder and $\ln \Delta^{(k)}\sim -1/\sigma$ at strong disorder, whose crossover sets an optimal disorder strength $\sigma_c\sim J_{xy}$, where $J_{xy}$ is the energy scale of the non-random interaction. We further show that a multi-quench protocol further suppresses the gap exponentially in the number of quenches. Numerical simulations confirm both scalings and this exponential suppression, and we demonstrate the usefulness of the protocol for classical shadow tomography. This work suggests that strong disorder may block both thermalization and the formation of unitary designs through a common localization mechanism.

Chiral topological order is incompatible with strictly two-dimensional local commuting-projector Hamiltonians on finite-dimensional tensor-product Hilbert spaces. Invertible subalgebras (ISAs) provide an alternative framework. We construct an ISA supporting chiral semions, together with its anti-semion commutant, on a square lattice with one qubit per edge. We give explicit non-Pauli generators for both algebras and prove that together they generate all local operators on the Hilbert space. Starting from the $\mathbb{Z}_4$ toric code, we condense the boson $e^2m^2$ and identify the semion and anti-semion algebras. We then decompose each $\mathbb{Z}_4$ qudit into two qubits and use a finite-depth circuit to disentangle one qubit per edge fixed by the condensation constraints. Pumping the semion ISA along the $z$ direction defines an explicit three-dimensional non-Clifford quantum cellular automaton (QCA). We show that pumping eight times is equivalent to a translation followed by a finite-depth quantum circuit with ancillary qubits. We also give an explicit finite-depth circuit relating this construction to the semion QCA previously obtained from topological quantum field theory. A similar condensation construction yields a $U(1)_4$ ISA on a square lattice. Together with the semion and earlier odd-prime ISAs, finite stacking realizes every pointed Witt class of bosonic Abelian anyon theories. Finally, we extend both constructions to all spatial dimensions $d=4k{-}2$, with one qubit or $\mathbb{Z}_4$ qudit on each $(2k{-}1)$-cell for the semion or $U(1)_4$ ISA, respectively.

We extend the general relativistic Lagrangian perturbation formalism of Friedman and Schutz [Astrophys. J. 200, 204 (1975)] beyond linear order, retaining full time dependence of the perturbations. We provide general formulae to relate the Lagrangian and Eulerian perturbations to any general perturbative order. As a proof of principle, we apply the framework to tidally perturbed relativistic stars in Regge-Wheeler gauge and reduce the second-order field and conservation equations to master equations with a nonlinear source. Projecting the source onto the star's eigenmodes, we obtain a nonlinear equation of motion for the mode amplitudes and the coupling coefficients, which describe the interactions among the eigenmodes and with the external tidal field. Approximating the tidal field and the coupling coefficients, we compute the static quadratic Love number from the quadrupolar fundamental mode alone and find that it reproduces the direct metric-matching value to a reasonable accuracy of $4\%$, up to a further correction arising from the Hamiltonian and momentum constraints of the second-order tidal field.

Despite extensive work on BPS black holes in 4d flat space, there is no direct microstate counting from D-brane quantum mechanics in regimes described by Einstein gravity. We derive an exact formula counting BPS configurations of the D-brane system corresponding to black holes in $N=8$ supergravity obtained from type II strings on $T^6$. As part of the derivation, we relate the BPS equations to a solvable modified Calogero-Moser system. The result agrees with the prediction from the modified elliptic genus of the D1-D5 system, providing a highly nontrivial test of the string dualities relating the two descriptions. We emphasize that this quantum mechanical system is, as a model of quantum black holes, simpler than BFSS and propose some numerical tests to explore this.

Existing machine-learning models for perovskite solar cells struggle to predict devices made from new materials. Most treat device layers as arbitrary categorical labels and represent perovskite absorbers either through featureless composition vectors or through rigid crystal graphs that require a pre-solved unit cell. As a result, they cannot generalize to unrecorded alloys or unfamiliar cell architectures. We present the Virtual-Alloy Physics-Aware Semantic System (V-PaSS), an architecture built around the physical continuity of perovskite solid solutions. V-PaSS represents arbitrary mixed-cation, mixed-halide absorbers by interpolating relaxed crystal graphs of 23 pure $ABX_3$ endpoint compounds via Vegard's law with learned bandgap bowing. For the device stack, it couples layer sequence and cell polarity (n-i-p or p-i-n) with interfacial band offsets and encodes chemical descriptions with a scientific language model. Evaluated under an institution-grouped protocol where test devices come exclusively from unseen laboratories, an untuned default configuration of V-PaSS achieves the lowest error among fourteen tested models (2.861% MAE, a 5.2% relative reduction over a gradient-boosted baseline at 3.017%, and outperforming the best tuned benchmark at 2.912%). V-PaSS pulls furthest ahead where test devices differ most from training: reducing error by 15.7-19.0% on unseen absorber alloys, by 16.1% on mixed absorbers from new laboratories, and widening its lead over the baseline by 3.6$\times$ on devices with unobserved transport layers. Combined with tree ensembles, V-PaSS sets a new state of the art across all five benchmark splits.

Bayesian inversion is widely used in engineering applications, including material characterisation, structural damage identification, and medical diagnostics. These inverse problems are typically ill-posed, because localised variations in material properties must be inferred from noisy observations, and they are computationally intensive, since they often require many evaluations of a high-fidelity forward solver. Quantum computing has recently attracted considerable interest, partly because some near-term algorithms are feasible on NISQ hardware. In particular, PQC combined with classical optimisation enable a hybrid quantum-classical surrogate model. A central obstacle to applying such circuits to inversion is that the discretised parameter and response fields are far too high-dimensional to be embedded in a near-term quantum register. In this work we propose a quantum-assisted latent surrogate model for the Bayesian inversion of inhomogeneous material properties, in which latent compression bridges these high-dimensional fields and the small registers accessible to near-term circuits. The low intrinsic dimensional structure of the spatially varying conductivity and potential fields is exploited by reducing the conductivity through PCA and the response through a convolutional autoencoder. A PQC is then trained to map the latent conductivity to the latent response, and stochastic variational inference is performed entirely in latent space. The methodology is demonstrated on one- and two-dimensional inverse problems under both informative and non-informative priors. We further evaluate the model on IonQ simulator and Rigetti Cepheus-1-108Q, and use a lightweight learned denoising stage that recovers the noiseless accuracy to within a small residual. (The abstract has been shortened to meet arXiv's 1,920-character limit. For the full Abstract, please download the full Article.)