An analysis of the $B^0\to K^{*0}(\to K^{+}{\pi }^{-}){\mu }^{+}{\mu }^{-}$ decay is presented using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of $8.4{\mathrm{fb}}^{-1}$. The full set of $CP$-averaged and $CP$-asymmetric angular observables is determined in bins of the invariant mass squared of the dimuon system, as well as the branching fraction relative to the $B^0\to J/\psi (\to {\mu }^{+}{\mu }^{-})K^{+}{\pi }^{-}$ decay. For the first time, the full set of observables pertaining to the $K^{+}{\pi }^{-}$ S-wave contribution to the final state are presented and consideration is given to effects arising from the mass of the muons. The extracted $CP$-asymmetry observables show no significant deviations from zero. The measurements of the $CP$-averaged observables and the branching fractions continue to exhibit the pattern of tensions with the standard model predictions that have been seen in previous analyses that use part of the dataset considered in this Letter.

Engineering proximity effects in twisted van der Waals heterostructures offers a powerful platform for designing electronic properties. While theoretical predictions of quantum interference in transition metal dichalcogenide-encapsulated graphene can selectively control the spin-orbit coupling component, experimental realizations have remained elusive. Here, we report pure valley-Zeeman spin-orbit coupling in monolayer graphene achieved by encapsulation between two parallel twisted ${\mathrm{WSe}}_2$ monolayers. We observed a symmetry-enforced reordering of Landau levels, which is driven by the competition between the fixed valley-Zeeman energy and the magnetic-field-dependent cyclotron energy. This reordering is characterized by a transition from symmetry-broken states in the quantum Hall effect to a restored fourfold degeneracy with integer or half-integer quantum Hall sequences. We also demonstrate the ability to completely quench the proximity spin-orbit coupling by tuning the encapsulated geometry.

The final state of a binary black hole merger is predicted with high precision by numerical relativity, but could there be a simple thermodynamic principle within general relativity that governs the selection of the remnant? Using post-Newtonian relations between the mass $M$ (including the binding energy) and angular momentum $J$ of quasicircular, nonspinning binaries, we uncover a puzzling result: When the binary’s instantaneous $M$ and $J$ are mapped to those of a hypothetical Kerr black hole, the corresponding entropy exhibits a maximum during the evolution. This maximum occurs at values of $M$ and $J$, strikingly close to those of the final remnant predicted by numerical relativity. Consistent behavior is observed when using the relation between $M$ and $J$ obtained from numerical relativity evolution. Although this procedure is somewhat ad hoc, the agreement between the masses and spins of the final state obtained from numerical relativity and the results of this maximum entropy procedure is remarkable, with agreement to within a few percent when using either post-Newtonian or numerical relativity results for $M$ and $J$. These findings allow us to propose an entropy maximization conjecture for binary black hole mergers, hinting that thermodynamic principles may govern the selection of the final black hole state.

With the release of the fourth LIGO-Virgo-KAGRA gravitational-wave catalog (GWTC-4), we are starting to gain a detailed view of the population of merging binary black holes. The formation channels of these black holes is not clearly understood, but different formation mechanisms may lead to subpopulations with different properties visible in gravitational-wave data. Adopting a phenomenological approach, we find GWTC-4.0 data supports the presence of at least three subpopulations, each associated with a different range of black hole mass and with sharp transition boundaries between them. Each subpopulation is characterized by different distributions for either the mass ratios, the black-hole spin magnitudes or both. Subpopulation $\mathcal{A}$ with primary mass $m_1\le {27.7}_{-3.4}^{+4.1}{M}_{\odot }$ (90% credibility), is characterized by a nearly flat mass ratio distribution $q=m_2/m_1$, and by small spin magnitudes ($\chi \le {0.5}_{-0.1}^{+0.1}$). Subpopulation $\mathcal{B}$, with ${27.7}_{-3.4}^{+4.1}{M}_{\odot }\le m_1\le {40.2}_{-3.2}^{+4.7}{M}_{\odot }$, has a much sharper preference for mass ratio $q\approx 1$. Subpopulation $\mathcal{C}$, with $m_1\ge {40.2}_{-3.2}^{+4.7}{M}_{\odot }$, has support for large spin magnitudes, and tentative support for mass ratios $q\approx 0.5$. We interpret these transitions as evidence for multiple subpopulations, each potentially associated with a different formation pathways. We suggest putative formation scenarios for each subpopulation, and explore chemically homogeneous evolution, population III stars and dynamical formation channels as an explanation for subpopulation $\mathcal{B}$. Our findings for subpopulation $\mathcal{C}$ are largely consistent with recent claims of hierarchical mergers but with some curious differences in properties.

Repeated black-hole mergers in dense stellar clusters are a plausible mechanism to populate the predicted gap in black hole masses due to the pair-instability supernova process. These hierarchical mergers carry distinct spin characteristics relative to first-generation black holes. We introduce an astrophysically motivated model in the joint space of effective inspiral and precessing spins, which captures the dominant spin dynamics expected for hierarchical mergers. We find decisive evidence for a transition at $m_1={46.2}_{-7.2}^{+12.6}{M}_{\odot }$, above which the population is nearly entirely hierarchical, a location consistent with the anticipated onset of the pair-instability gap. We also infer a global peak in the hierarchical merger rate at $m_1={15.7}_{-1.1}^{+3.2}{M}_{\odot }$. The existence of low- and high-mass subpopulations of higher-generation black holes suggests the contribution of both near-solar-metallicity and metal-poor star clusters to the hierarchical merger population. Our results reinforce the growing evidence for detailed, mass-dependent substructure in the spin distribution of the binary black hole population.

The strong interplay between geometry and electronic structure in clusters consisting of a countable number of atoms critically governs their properties, making precise knowledge of geometry essential. This challenge is particularly acute for transition-metal clusters, where many unpaired electrons lead to multiple low-lying spin and geometric isomers, implying cumbersome and contradicting theoretical predictions of the ground state. In this Letter, we conclusively assign geometries and spin states of iron clusters of 3 to 12 atoms, which significantly reduces uncertainties of spin magnetic moments inferred from x-ray magnetic circular dichroism experiments [Niemeyer et al. Phys. Rev. Lett. 108, 057201 (2012)]. Hereto we use infrared multiple photon dissociation spectroscopy with Ar as messenger atom to measure the vibrational spectra of cationic iron clusters in the $110–400{\mathrm{cm}}^{-1}$ range and compare those with density functional theory calculations. We show that in addition to direct structural information the spectra provide an accurate determination of spin multiplicities. This methodology is broadly applicable to transition-metal clusters of any charge state and provides a general route to benchmark theory.

Unidirectional guided resonances (UGRs)—topological polarization singularities in momentum space with intrinsic unidirectional radiation—have recently garnered widespread attention. However, previous studies have been largely limited to realizing only a few discrete UGRs. We demonstrate an unprecedented continuous ring of UGRs in a hexagonal bilayer cylinder array, whose formation is governed by isotropic interband coupling, ensuring robust and azimuthally continuous unidirectional emission. Furthermore, by leveraging an in-plane inversion symmetry-protected bound state in the continuum at the $\mathrm{\Gamma }$ point, the continuous ring of UGRs acquires its topological properties from the enclosed bound state in the continuum, manifesting as a phase vortex with a nontrivial topological charge. This unique combination of continuous unidirectionality and a global topological charge provides a robust platform for developing novel devices, such as unidirectional vortex lasers.

Self-consistent approaches in many-electron problems typically converge to an unphysical solution in strongly correlated regimes. By deriving the mathematical condition for the stability of the physical solution, we unveil the precise relation between two distinct issues previously considered equivalent: the misleading convergence in self-consistent schemes and the multivaluedness of the Luttinger-Ward functional. Although these problems are fundamentally linked through the divergences of the irreducible vertex function, we show that misleading convergence can occur even in the absence of such divergences. Eventually, a systematic procedure for stabilizing the physical solution is proposed.

Although coupled ion-electron transfer (CIET) has emerged as a powerful framework to rationalize the kinetics of Faradaic reactions, its mechanism has lacked a fully microscopic, first-principles description. Here we show that the coupling of electron transfer to ion transfer can be understood as an extension of Marcus theory in which the ensemble of diabatic nuclear configurations is conditioned on a classical collective variable describing the interfacial anisotropy. This formalism enables direct construction of the CIET free-energy surface from constrained ab initio trajectories, providing a first-principles route to electrochemical current-overpotential relations. We demonstrate this method for ${\mathrm{CO}}_2$ redox on a gold electrode and find that the resulting two-dimensional saddle-point barriers differ substantially from one-dimensional treatments that consider only electron- or ion-transfer coordinates individually.

The symmetry-broken correlated states in twisted double bilayer graphene (TDBG) can be tuned via several external knobs, including twist angle, displacement field, and carrier density. However, a direct, momentum-resolved characterization of how these parameters reshape the flat-band structure remains limited. In this Letter, we employ microfocused angle-resolved photoemission spectroscopy to investigate the flat-band dispersion of TDBG at a twist angle of 1.6°, systematically varying the displacement field and carrier density via electrostatic gating. We directly observe multiple flat moiré minibands near charge neutrality, including a flat remote valence band residing below the low-energy flat-band manifold. Furthermore, the dominant Coulomb repulsive energy over the flat-band bandwidth suggests favorable conditions for the emergence of interaction-driven correlated phenomena in TDBG. These findings establish that the formation and evolution of flat bands in TDBG arises from the interplay between the electron filling and the displacement field.

If the behavior of a system with many degrees of freedom can be captured by a small number of collective variables, then plausibly there is an underlying mean-field theory. We show that simple versions of this idea fail to describe the patterns of activity in networks of real neurons. An extended mean-field theory that matches the distribution of collective variables is at least consistent, though shows signs that these networks are poised near a critical point, in agreement with other observations. These results suggest a path to analysis of emerging data on ever larger numbers of neurons.

In nonequilibrium quantum systems, the quantum Mpemba effect (QME) emerges as a counterintuitive phenomenon: Systems exhibiting greater initial symmetry breaking restore symmetry faster. It has been attracting broad interest in studying QME dynamics and potential applications in quantum information science. While theoretical exploration of QME has surged, experimental studies, specifically on its flexible modulation, remain limited. Here, we report the observation and modulation of QME using a superconducting processor featuring an all-to-all connected, tunable-coupling architecture that enables precise control from short- to long-range interactions. This platform allows independent manipulation of coupling regimes, on-site potentials, and initial states, enabling us to elucidate their roles in QME. To quantify symmetry restoration, we employ entanglement asymmetry (EA), derived from the reconstructed density matrix via quantum state tomography, as a sensitive probe. In strong short-range coupling regimes, EA crossovers during quenches from tilted Néel states confirm the presence of QME. In contrast, in intermediate-coupling regimes, synchronized EA and entanglement entropy dynamics reveal the suppression of QME. Remarkably, QME reemerges with the introduction of on-site linear potentials or quenches from tilted ferromagnetic states, the latter proving robust against on-site disorder. Our study demonstrates flexible QME modulation on a superconducting platform with multiple controllable parameters, shedding light on quantum many-body nonequilibrium dynamics and opening avenues for quantum information applications.

Large- or medium-scale cosmic ray anisotropy at TeV energies has not previously been confirmed to vary with time. Transient anisotropy changes have been observed below 150 GeV, especially near the passage of an interplanetary shock and coronal mass ejection containing a magnetic flux rope ejected by a solar storm, which can trigger a geomagnetic storm with practical consequences. Here, we report the first observation of transient large-scale anisotropy in TeV cosmic ray ions using data from the Large High-Altitude Air Shower Observatory. We analyze hourly skymaps of the transient cosmic ray intensity excess or deficit, the gradient of which indicates the direction and magnitude of transient large-scale anisotropy across the field of view. We observe enhanced anisotropy above typical hourly fluctuations with $>5\sigma$ significance during some hours of November 4, 2021, in separate datasets for four primary cosmic ray energy ranges of median energy from $E=0.6$ to 2.8 TeV. The gradient varies with energy as $E^{\gamma }$, where $\gamma =-0.5$. At a median energy $\le 1.0\mathrm{TeV}$, this gradient corresponds to a dipole anisotropy of at least 0.9%, or possibly a weaker anisotropy of higher order. This new type of observation opens the opportunity to study interplanetary magnetic structures using air shower arrays around the world, complementing existing in situ and remote measurements of plasma properties.

We present a study of the melting dynamics of a two-phase eutectic solid. In situ, thin-sample experiments using a transparent eutectic alloy and two-dimensional phase field simulations calibrated for the very same alloy are combined to assess pattern formation during directional melting in a temperature gradient. Depending on the melting velocity $V_m$ and the spacing $\lambda$ of the presolidified lamellar microstructure, an unexpectedly rich diversity of melting patterns is observed, with good agreement between experiments and simulations. We unravel the different physical mechanisms leading to this diversity, and establish the scaling behaviors of (i) the penetration of the liquid along the solid-solid interface at large $V_m$, (ii) the thickening of the primary-phase fingers at low $V_m$, and (iii) a period-doubling instability for small $\lambda$ values. Our Letter provides a fundamental basis for further investigations of eutectic melting, including additive manufacturing during which melting or solidification cycles take place.

Electron correlation in solids has a major impact on material properties. However, it has been studied mainly by theory, with very limited direct experimental investigations. Here, we demonstrate that dynamic electron correlation function can be experimentally measured using inelastic x-ray scattering on polycrystalline beryllium. The data are expressed as the energy-resolved dynamic pair-distribution function. Our results confirm the size of the exchange-correlation hole as $\sim 2\AA$, consistent with theoretical expectations. However, at the plasmon energy of $\sim 21\mathrm{eV}$, the exchange-correlation hole is extended up to 4–5 Å, suggesting a unique influence of the dynamic plasmon state.

Generating magnon frequency combs with tunable spacing via a single-frequency driving is crucial for practical applications, but it typically relies on complex spin textures like skyrmions or vortices. Here, we theoretically and numerically demonstrate magnon frequency comb generation in geometrically curved ferromagnetic thin films using single-frequency microwave excitation, without topological spin textures. We first show that the curvature transforms the planar ferromagnetic resonance into a localized, redshifted magnon bound state, which, under nonresonant driving, activates sequential three-magnon scattering processes assisted by the curvature-driven effective anisotropy and Dzyaloshinskii-Moriya interaction. It finally produces equally spaced, robust frequency combs with spacing exactly set by the bound mode frequency. Moreover, we find that the curvature gradient at the hybrid interface mimics an analog event horizon, with the bound state’s redshift resembling gravitational effects in black hole physics. Micromagnetic simulations confirm these curvature-driven nonlinear phenomenon, unveiling a novel geometric strategy for controlling magnon interactions and advancing compact magnonic devices.

Gravitational waves from binary black hole mergers provide a glimpse of gravitational dynamics in its most extreme observable regime, potentially enabling precision tests of general relativity (GR) and of the Kerr description of black holes. However, until recently, numerical simulations of black hole mergers have not been possible in theories beyond GR. While recent breakthroughs have overcome that obstacle, simulations covering the full, interesting range of binary parameters remain unfeasible. Here we present a new first-principles approach to this problem. We show how self-force theory can be used to model the merger and ringdown of black holes in a broad class of gravitational theories, assuming one object is much smaller than the other. We calculate self-force effects on the merger waveform for the first time, and we demonstrate how our formulation allows us to modularly compute beyond-GR effects and readily incorporate them into a fast merger-ringdown waveform model.

As in thermodynamics, the celebrated first law of black hole mechanics relates infinitesimal changes in the properties of nearby equilibrium states of black holes (without reference to any physical process that causes the transition). Using dynamical horizon segments (DHSs), we extend the first law to encompass black holes that can be arbitrarily far from equilibrium. It now refers to finite changes that occur due to physical processes. This extension, together with the generalized second law on DHSs [A. Ashtekar and B. Krishnan, Dynamical horizons and their properties, Phys. Rev. D 68, 104030 (2003)], naturally lead one to identify entropy of dynamical black holes with the area of DHSs.

We provide a new formulation of time-dependent density functional theory (TDDFT) based on the geometric structure of the set of states constrained to have a fixed density. Orbital-free TDDFT is formulated using a hydrodynamics equation involving a new density-to-current functional map. In the corresponding Kohn-Sham equation, the density is reproduced using a nonlocal operator. Finally, we present numerical simulations for one-dimensional soft-Coulomb systems.

Strongly disordered superconductors (SDSCs) are widely used in qubits, microwave resonators, photon detectors, and other superconducting quantum devices. In SDSC-based devices, coherence times are limited by low-temperature microwave dissipation in the material. However, the standard Mattis-Bardeen theory fails in SDSCs because their single-particle spectrum exhibits a hard pseudogap ${\mathrm{\Delta }}_P$ both below and above the transition temperature $T_c$. We develop a novel microscopic theory of the dependence of ac dissipation in such systems on temperature $T$ and frequency $\omega$. We analyze the resonator quality factor $Q(\omega ,T)$ in the practically relevant range $\hslash \omega ,T\ll \mathrm{\Delta }\le {\mathrm{\Delta }}_P$, where $\mathrm{\Delta }$ is the typical superconducting order parameter, distinct from ${\mathrm{\Delta }}_P$. We show that low-$\omega$ dissipation is dominated by a new type of bulk localized collective modes arising from spatial inhomogeneity of the superconducting state. Consequently, $Q(\omega )$ decreases strongly with $\omega$ and exhibits two-level-system-like growth with $T$ for $T\ll T_c$. Our theory provides a microscopic understanding of existing and future experiments on thin films of ${\mathrm{InO}}_x$, TiN, NbN, and similar SDSCs, and is phenomenologically relevant to granular aluminum films. The results suggest strategies to mitigate intrinsic microwave losses in SDSC-based quantum devices.