We show that the conditions allowing for a spontaneous breaking of the $\mathrm{U}(1{)}_Y$ hypercharge gauge symmetry of the standard model (SM) in the early Universe are generically present in extensions of the SM addressing the generation of light neutrino masses via radiative contributions. In such scenarios, the breaking of (hyper)charge at high temperatures yields new possibilities for explaining the observed matter-antimatter asymmetry of the Universe. Considering for concreteness the Zee-Babu radiative neutrino mass generation model, we show that a period of hypercharge breaking prior to the electroweak phase transition could allow for successful baryogenesis via a nonconventional leptogenesis mechanism, based on the presence of charge-breaking masses for the SM leptons in the early Universe.

Exclusive diffractive meson production represents a golden channel for investigating gluonic saturation inside nucleons and nuclei. In this Letter, we settle a systematic framework to deal with beyond leading power corrections at small $x$, including the saturation regime, and obtain the ${\gamma }^{*}\to M(\rho ,\varphi ,\omega )$ impact factor with both incoming photon and outgoing meson carrying arbitrary polarizations. This is of particular interest since the saturation scale at modern colliders, although entering a perturbative regime, is not large enough to prevent higher-twist effects to be sizable.

Electron imaging has been routinely used for electron spectrometry. It has been ignored, however, that the maximum-intensity circles that surround electric field-produced electron spots do not materialize envelopes of trajectories, but the first interior fringes of a caustic. Neglecting the gap between the fringe and the parent envelope has resulted in spectrometric errors, notably on some reference values of electron affinities. Evidence for the effect is given by photodetachment microscopy of ${\mathrm{O}}^{-}$ and a measurement of the electron affinity of ${}^{75}\mathrm{As}$, which is found to be 0.804 486(3) eV.

Recent scanning tunneling microscopy experiments on graphene at charge neutrality under strong magnetic fields have uncovered a ground state characterized by Kekulé distortion (KD). In contrast, nonlocal spin and charge transport experiments in double-encapsulated graphene, which has a higher dielectric constant, have identified an antiferromagnetic (AF) ground state. We propose a mechanism to reconcile these conflicting observations by showing that Landau-level mixing can drive a transition from AF to KD with the reduction of the dielectric screening. Our conclusion is drawn from studying the effect of Landau-level mixing on the lattice-scale, valley-dependent interactions to leading order in graphene’s fine structure constant $\kappa =e^2/(\hslash v_F\epsilon )$. This analysis provides three key insights: (1) valley-dependent interactions remain predominantly short-range with the $m=0$ Haldane pseudopotential being at least an order of magnitude greater than the others, affirming the validity of delta-function approximation for these interactions. (2) The phase transition between the AF and KD states is driven by the microscopic process in the double-exchange Feynman diagram. (3) The magnitudes of the coupling constants are significantly boosted by remote Landau levels. Our model also provides a theoretical basis for numerical studies of fractional quantum Hall states in graphene.

We use numerical simulations to demonstrate a local rheology for dense granular flows under shear and vibration. Granular temperature has been suggested as a rheological control but has been difficult to isolate. Here, we consider a granular assembly that is subjected to simple shear and harmonic vibration at the boundary, which provides a controlled source of granular temperature. We find that friction is reduced due to local velocity fluctuations of grains. All data obey a local rheology that relates the material friction coefficient, the granular temperature, and the dimensionless shear rate. We also observe that reduction in material friction due to granular temperature is associated with reduction in fabric anisotropy. We demonstrate that the temperature can be modeled by a heat equation with dissipation with appropriate boundary conditions, which provides complete closure of the system and allows a fully local continuum description of sheared, vibrated granular flows. This success suggests local rheology based on temperature combined with a diffusion equation for granular temperature may provide a general strategy to model dense granular flows.

New particles beyond the standard model of particle physics, such as axions, can be effectively searched through their interactions with electrons. We use the large liquid xenon detector PandaX-4T to search for novel electronic recoil signals induced by solar axions, neutrinos with anomalous magnetic moment, axionlike particles, dark photons, and light fermionic dark matter. A detailed background model is established using the latest datasets with $1.54\mathrm{ton}\mathrm{yr}$ exposure. No significant excess above the background has been observed, and we have obtained competitive constraints for axion couplings, neutrino magnetic moment, and fermionic dark matter interactions.

Optomechanical cooling of multiple degenerate mechanical modes is prevented by the mechanical dark mode due to destructive interference. Here, we report the first experimental demonstration of simultaneous cooling of two near-degenerate mechanical modes by breaking the mechanical dark mode in a two-membrane cavity optomechanical system. The dark mode is generated as the system passes the exceptional point of the anti-parity-time symmetric scheme. By introducing a second cavity mode for the additional dissipative channel, the dark mode is broken and the total phonon number is reduced by more than an order of magnitude below the dark mode cooling limit. Owing to the flexible tunability of the optomechanical coupling rates of such a four-mode coupled system, the optimized cooling efficiency can be achieved by investigating different parameter ranges. Our results provide an important step toward the ground state cooling and entanglement among multiple degenerate mechanical resonators.

Optimal path planning and control of microscopic devices navigating in fluid environments is essential for applications ranging from targeted drug delivery to environmental monitoring. These tasks are challenging due to the complexity of microdevice-flow interactions. We introduce a closed-loop control method that optimizes a discrete loss (ODIL) in terms of dynamics and path objectives. In comparison with reinforcement learning, ODIL is more robust, up to 3 orders faster, and excels in high-dimensional action and state spaces, making it a powerful tool for navigating complex flow environments.

We demonstrate that pulsed THz radiation produced in air by a focused ultrashort laser pulse can be steered to large angles or even in the backward direction with respect to the laser propagation axis. The emission angle is adjusted by the flying focus technique, which determines the speed and direction of the ionization front created by the single-color laser pulse. This easily adjustable THz source, being well separated from the intense laser, opens exciting applications for remote THz spectroscopy.

The anomalous valley Hall effect (AVHE) is a pivotal phenomenon that allows for the exploitation of the valley degree of freedom in materials. A general strategy for its realization and manipulation is crucial for valleytronics. Here, by considering all possible symmetries, we propose general rules for the realization and manipulation of AVHE in two-dimensional hexagonal lattices. The realization of AVHE requires breaking the enforced symmetry that is associated with different valleys or reverses the sign of Berry curvature. Further manipulation of AVHE requires asymmetry operators connecting two states with opposite signs of Berry curvature. These rules for realizing and manipulating AVHE are extendable to generic points in momentum space. Combined with first-principles calculations, we realize the controllable AVHE in four representative systems, i.e., monolayer ${\mathrm{AgCrP}}_2{\mathrm{Se}}_6$, CrOBr, ${\mathrm{FeCl}}_2$, and bilayer ${\mathrm{TcGeSe}}_3$. Our work provides symmetry rules for designing valleytronic materials that could facilitate the experimental detection and realistic applications.

Skyrmions are particlelike vortices of magnetization with nontrivial topology, which are usually stabilized by Dzyaloshinskii-Moriya interactions (DMI) in noncentrosymmetric bulk materials. Exceptions are centrosymmetric Gd- and Eu-based skyrmion-lattice (SL) hosts with zero DMI, where both the SL stabilization mechanisms and magnetic ground states remain controversial. We address these here by investigating both the static and dynamical spin properties of the centrosymmetric SL host ${\mathrm{Gd}}_2{\mathrm{PdSi}}_3$ using muon spectroscopy. We find that spin fluctuations in the noncoplanar SL phase are highly anisotropic, implying that spin anisotropy plays a prominent role in stabilizing this phase. We also observe strongly anisotropic spin dynamics in the ground-state (IC-1) incommensurate magnetic phase of the material, indicating that it hosts a meronlike multi-$q$ structure. In contrast, the higher-field, coplanar IC-2 phase is found to be single $q$ with nearly isotropic spin dynamics.

Writing data by electric field (as opposed to electric current) offers promises for energy efficient memory devices. While this data writing scheme is enabled by the magnetoelectric effect, the narrow spectrum of room-temperature magnetoelectrics hinders the design of practical magnetoelectric memories, and the exploration of other mechanisms toward low-power memories is greatly demanding. Here, we propose a mechanism that allows the electric-field writing of data beyond the framework of magnetoelectric effect. By symmetry analysis, we show that electric field can induce longitudinal nonlinear conductivity (LNC) in a wide spectrum of magnetic materials, including ferromagnets, antiferromagnets, magnetoelectrics, and nonmagnetoelectrics. The LNC is electrically switchable by reversing the electric field, where the switched LNC is detectable by transport measurements. Our first-principles simulations combined with transport calculations further predict ${\mathrm{YFeO}}_3$ and ${\mathrm{CuFeS}}_2$ (room-temperature antiferromagnets) to showcase electrically switchable LNC. Our Letter helps enrich the research avenues in nonlinear charge transport, and offers a pathway for designing energy efficient devices based on LNC.

We present a stochastic dynamic model which can explain economic cycles. We show that the macroscopic description yields a complex dynamical landscape consisting of multiple stable fixed points, each corresponding to a split of the population into a large low and a small high income group. The stochastic fluctuations induce switching between the resulting metastable states and excitation oscillations just below a deterministic bifurcation. The shocks are caused by the decisions of a few agents who have a disproportionate influence over the macroscopic state of the economy due to the unequal distribution of wealth among the population. The fluctuations have a long-term effect on the growth of economic output and lead to business cycle oscillations exhibiting coherence resonance, where the correlation time is controlled by the population size which is inversely proportional to the noise intensity.

Gels and attractive glasses—both dynamically arrested states formed through short-range attraction—are commonly found in a range of soft matter systems, including colloids, emulsions, proteins, and wet granular materials. Previous studies have revealed intriguing similarities and distinctions in their structural, dynamic, vibrational, and mechanical properties. However, the microstructural mechanisms underlying the gel-to-glass transition remain elusive. To address this, we investigate uniaxial compression-induced gel collapse using confocal microscopy, which provides experimental access to the relationship between mechanical stress and microstructure. Together with Brownian dynamics simulations, our study reveals two sequential transitions in void structure: from gels with percolating voids to isolated voids, and ultimately to voidless glasses. These transitions are closely linked to a shift from superlinear power-law scaling to explosive divergence toward the packing limit in both normal and deviatoric stresses as a function of volume fraction, particularly at lower temperatures. Understanding these mechanically self-organized transitions and their associated criticality deepens our insight into disordered solids, enabling better control over mechanical properties, interfacial characteristics, and transport behavior in porous materials.

We consider the certification of temporal quantum correlations using the pseudo-density operator (PDO), an extension of the density matrix to the time domain, where negative eigenvalues are key indicators of temporal correlations. Conventional methods for detecting these correlations rely on PDO tomography, which often involves excessive redundant information and requires exponential resources. In this work, we develop an efficient protocol for temporal correlation detection by virtually preparing the PDO within a single time slice and estimating its second-order moments using randomized measurements. Through sample complexity analysis, we demonstrate that our protocol requires only a constant number of measurement bases, making it particularly advantageous for systems utilizing ensemble average measurements, as it maintains constant runtime complexity regardless of the number of qubits. We experimentally validate our protocol on a nuclear magnetic resonance platform, a typical thermodynamic quantum system, where the experimental results closely align with theoretical predictions, confirming the effectiveness of our protocol.

Shell-shaped Bose-Einstein condensate is a typical quantum system in curved geometry. Here, we propose a new type of shell-shaped Bose-Einstein condensate with a self-bound character, thereby liberating it from stringent conditions such as microgravity or a fine-tuned trap. Specifically, we consider a three-component (1, 2, 3) ultracold Bose gas where (1, 2) and (2, 3) both form quantum droplets. The two droplets are mutually immiscible due to strong 1–3 repulsion, while still linked by component-2 to form a globally self-bound object. The outer droplet then naturally develops a shell structure without any trapping potential. It is shown that the shell structure can significantly modify the equilibrium density of the core, and lead to unique collective excitations highlighting the core-shell correlation. All results have been demonstrated in a realistic ${}^{23}\mathrm{Na}\text{−}{}^{39}\mathrm{K}\text{−}{}^{41}\mathrm{K}$ mixture. By extending quantum droplets from flat to curved geometries, this Letter paves the way for future explorations of the interplay of quantum fluctuations and nontrivial real-space topologies in ultracold gases.

Metasurfaces have revolutionized nonlinear and quantum light manipulation in the past decade, enabling the design of materials that can tune polarization, frequency, and direction of light simultaneously. However, tuning of metasurfaces is traditionally achieved by changing their microscopic structure, which does not allow in situ tuning and dynamic optimization of the metasurfaces. In this Letter, we explore the concept of twisted bilayer and tetralayer nonlinear metasurfaces, which offer rich tunability in its effective nonlinear susceptibilities. Using gold-based metasurfaces, we demonstrate that a number of different singularities of nonlinear susceptibilities can exist in the parameter space of twist angle and interlayer gap between different twisted layers. At the singularities, reflected or transmitted light from the nonlinear process (such as second-harmonic generation) can either become circularly polarized (for $C$ points), or entirely vanish (for $V$ points). By further breaking symmetries of the system, we can independently tune all aspects of the reflected and transmitted nonlinear emission, achieving unidirectional emission with full-Poincaré polarization tunability, a dark state ($V\text{−}V$ point), or any other bidirectional output. Our work paves the way for multidimensional control of polarization and directionality in nonlinear light sources, opening new avenues in ultrafast optics, optical communication, sensing, and quantum optics.

Phase change materials (PCMs) serve as useful components in electronics and photonics. Here we demonstrate that various kinds of material properties of a PCM are significantly influenced by the realized mass density. Using ab initio simulations, we investigate supercooled-liquid antimony and the subsequent transition to a glassy phase. We observe a transition in the supercooled-liquid phase from an undistorted high-temperature to an increasingly Peierls-like distorted low-temperature phase. This transition also manifests in both the electronic density of states and optical properties. The strong dependence of these properties on mass density leads the way to explorations of property design for nanoconfined devices beyond the usual compositional modifications.