We present a new class of direct detection signals; absorption of fermionic dark matter. We enumerate the operators through dimension six which lead to fermionic absorption, study their direct detection prospects, and summarize additional constraints on their suppression scale. Such dark matter is inherently unstable as there is no symmetry which prevents dark matter decays. Nevertheless, we show that fermionic dark matter absorption can be observed in direct detection and neutrino experiments while ensuring consistency with the observed dark matter abundance and required lifetime. For dark matter masses well below the GeV scale, dedicated searches for these signals at current and future experiments can probe orders of magnitude of unexplored parameter space.

The upper bounds from the ATLAS and CMS experiments on the decay rate of the Higgs boson to two muons provide the strongest constraint on an imaginary part of the muon Yukawa coupling. This bound is more than an order of magnitude stronger than bounds from $CP$-violating observables, specifically the electric dipole moment of the electron. It excludes a scenario—which had been viable prior to these measurements—that a complex muon Yukawa coupling is the dominant source of the baryon asymmetry. Even with this bound, the muon source can still contribute $\mathcal{O}(16\%)$ of the asymmetry.

Topological properties of lattices are typically revealed in momentum space using concepts such as the Chern number. Here, we study unconventional loop states, namely, the noncontractible loop states (NLSs) and robust boundary modes, mediated by nontrivial topology in real space. While such states play a key role in understanding fundamental physics of flatband systems, their experimental observation has been hampered because of the challenge in realizing desired boundary conditions. Using a laser-writing technique, we optically establish photonic kagome lattices with both an open boundary by properly truncating the lattice, and a periodic boundary by shaping the lattice into a Corbino geometry. We thereby demonstrate the robust boundary modes winding around the entire edge of the open lattice and, more directly, the NLSs winding in a closed loop akin to that in a torus. We prove that the NLSs due to real-space topology persist in ideal Corbino-shaped kagome lattices of arbitrary size. Our results could be of great importance for our understanding of the singular flatbands and the intriguing physics phenomenon applicable for strongly interacting systems.

When a drop falls and impacts on a liquid pool, it entraps an air disk below the drop, which then contracts into a central bubble. Here, we use high-speed imaging and high-resolution numerical simulations to characterize the air-disk contraction dynamics for different liquid properties. We show that the air disk can contract into a single central bubble, form a toroidal bubble, or split vertically into two smaller bubbles. We demonstrate that the transitions between the different regimes can be separated by an Ohnesorge number, ${\mathrm{Oh}}_e$, based on the air-disk thickness. For the lowest ${\mathrm{Oh}}_e$, we find a new regime, where vortex shedding from the rim of the contracting air disk breaks the vertical symmetry and prevents the bubble from splitting in two.

We study the dynamics of a contractile active nematic fluid subjected to a Poiseuille flow. In a quasi-1D geometry, we find that the linear rheology of this material is reminiscent of Darcy’s law in complex fluids, with a pluglike flow decaying to zero over a well-defined “permeation” length. As a result, the viscosity increases with size, but never diverges, thereby evading the yield stress predicted by previous theories. We find strong shear thinning controlled by an active Ericksen number quantifying the ratio between external pressure difference and internal active stresses. In 2D, the increase of linear regime viscosity with size only persists up to a critical length beyond which we observe active turbulent patterns, with very low apparent viscosity. The ratio between the critical and permeation length determining the stability of the Darcy regime can be made indefinitely large by varying the flow aligning parameter or magnitude of nematic order.

We investigate the statistics of the work performed during a quench across a quantum phase transition using the adiabatic perturbation theory when the system is characterized by independent quasiparticles and the “single-excitation” approximation is assumed. It is shown that all the cumulants of work exhibit universal scaling behavior analogous to the Kibble-Zurek scaling for the average density of defects. Two kinds of transformations are considered: quenches between two gapped phases in which a critical point is traversed, and quenches that end near the critical point. In contrast to the scaling behavior of the density of defects, the scaling behavior of the cumulants of work are shown to be qualitatively different for these two kinds of quenches. However, in both cases the corresponding exponents are fully determined by the dimension of the system and the critical exponents of the transition, as in the traditional Kibble-Zurek mechanism (KZM). Thus, our study deepens our understanding about the nonequilibrium dynamics of a quantum phase transition by revealing the imprint of the KZM on the work statistics.

A ferromagnetic axion haloscope searches for dark matter in the form of axions by exploiting their interaction with electronic spins. It is composed of an axion-to-electromagnetic field transducer coupled to a sensitive rf detector. The former is a photon-magnon hybrid system, and the latter is based on a quantum-limited Josephson parametric amplifier. The hybrid system consists of ten 2.1 mm diameter yttrium iron garnet spheres coupled to a single microwave cavity mode by means of a static magnetic field. Our setup is the most sensitive rf spin magnetometer ever realized. The minimum detectable field is $5.5\times {10}^{-19}\mathrm{T}$ with 9 h integration time, corresponding to a limit on the axion-electron coupling constant $g_{aee}\le 1.7\times {10}^{-11}$ at 95% C.L. The scientific run of our haloscope resulted in the best limit on dark matter axions to electron coupling constant in a frequency span of about 120 MHz, corresponding to the axion-mass range $42.4–43.1\mu \mathrm{eV}$. This is also the first apparatus to perform a wide axion-mass scanning by only changing the static magnetic field.

The mass hierarchy among the three generations of quarks and charged leptons is one of the greatest mysteries in particle physics. In various flavor models, the origin of this phenomenon is attributed to a series of hierarchical spontaneous symmetry breakings, most of which are beyond the reach of particle colliders. We point out that the observation of a multipeaked stochastic gravitational wave signal from a series of cosmological phase transitions could well be a unique probe of the mechanism behind flavor hierarchies. To illustrate this point, we show how near future ground- and space-based gravitational wave observatories could detect up to three peaks in the recently proposed $P{S}^3$ model.

We report on the first measurement of the charmed baryon ${\mathrm{\Lambda }}_c^{\pm }$ production at midrapidity ($|y|<1$) in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ collected by the STAR experiment at the Relativistic Heavy Ion Collider. The ${\mathrm{\Lambda }}_c/D^0$ [denoting $({\mathrm{\Lambda }}_c^{+}+{\mathrm{\Lambda }}_c^{-})/(D^0+{\overline{D}}^0)$] yield ratio is measured to be $1.08\pm 0.16(\mathrm{stat})\pm 0.26(\mathrm{sys})$ in the 0%–20% most central $\mathrm{Au}+\mathrm{Au}$ collisions for the transverse momentum ($p_T$) range $3<p_T<6\mathrm{GeV}/c$. This is significantly larger than the pythia model calculations for $p+p$ collisions. The measured ${\mathrm{\Lambda }}_c/D^0$ ratio, as a function of $p_T$ and collision centrality, is comparable to the baryon-to-meson ratios for light and strange hadrons in $\mathrm{Au}+\mathrm{Au}$ collisions. Model calculations including coalescence hadronization for charmed baryon and meson formation reproduce the features of our measured ${\mathrm{\Lambda }}_c/D^0$ ratio.

High precision interferometers are the building blocks of precision metrology and the ultimate interferometric sensitivity is limited by the quantum noise. Here, we propose and experimentally demonstrate a compact quantum interferometer involving two optical parametric amplifiers and the squeezed states generated within the interferometer are directly used for the phase-sensing quantum state. By both squeezing shot noise and amplifying phase-sensing intensity the sensitivity improvement of $4.86\pm 0.24\mathrm{dB}$ beyond the standard quantum limit is deterministically realized and a minimum detectable phase smaller than that of all present interferometers under the same phase-sensing intensity is achieved. This interferometric system has significantly potential applications in a variety of measurements for tiny variances of physical quantities.

The secular dynamics of a nonrelativistic charged particle in an electromagnetic wave can be described by the ponderomotive potential. Although ponderomotive electron-laser interactions at relativistic velocities are important for emerging technologies from laser-based particle accelerators to laser-enhanced electron microscopy, the effects of special relativity on the interaction have only been studied theoretically. Here, we use a transmission electron microscope to measure the position-dependent phase shift imparted to a relativistic electron wave function when it traverses a standing laser wave. The kinetic energy of the electrons is varied between 80 and 300 keV, and the laser standing wave has a continuous-wave intensity of $175{\mathrm{GW}/\mathrm{cm}}^2$. In contrast to the nonrelativistic case, we demonstrate that the phase shift depends on both the electron velocity and the wave polarization, confirming the predictions of a quasiclassical theory of the interaction. Remarkably, if the electron’s speed is greater than $1/\sqrt{2}$ of the speed of light, the phase shift at the electric field nodes of the wave can exceed that at the antinodes. In this case there exists a polarization such that the phase shifts at the nodes and antinodes are equal, and the electron does not experience Kapitza-Dirac diffraction. Our results thus provide new capabilities for coherent electron beam manipulation.

We report on measurements of quantized conductance in gate-defined quantum point contacts in bilayer graphene that allow the observation of subband splittings due to spin-orbit coupling. The size of this splitting can be tuned from 40 to $80\mu \mathrm{eV}$ by the displacement field. We assign this gate-tunable subband splitting to a gap induced by spin-orbit coupling of Kane-Mele type, enhanced by proximity effects due to the substrate. We show that this spin-orbit coupling gives rise to a complex pattern in low perpendicular magnetic fields, increasing the Zeeman splitting in one valley and suppressing it in the other one. In addition, we observe a spin polarized channel of $6e^2/h$ at high in-plane magnetic field and signatures of interaction effects at the crossings of spin-split subbands of opposite spins at finite magnetic field.

Polyelectrolytes (PEs) are charged polymers in polar solvents. Classical scaling theories suggest that the viscosity $\eta$ for semidilute unentangled PE solutions in $\theta$ solvents obeys the empirical Fuoss law $\eta \propto n_p^{1/2}$ in the “salt-free” regime, and $\eta \propto n_p^{5/4}$ in the regime affected by added salt, where the polymer concentration $n_p$ is defined as the number of monomers per volume. However, recent experiments have also reported $\eta \propto n_p^{0.68}$ and $\eta \propto n_p^{0.91}$, which are at odds with the classical scaling theories. To rationalize the four distinct scaling laws, we probe the electrostatic energy per monomer under the influence of salt and their contributions to the viscosity of PE solutions. We identify four consecutive regimes dependent on the magnitude of the ratio of the polymer concentration $n_p$ to the salt concentration $n_s$, which capture the unexplained observations, and provide physical insights for the influence of salt contamination and added salt on the properties of both weakly and strongly charged semidilute unentangled PE solutions.

The standard approach to quantum engines is based on equilibrium systems and on thermodynamic transformations between Gibbs states. However, nonequilibrium quantum systems offer enhanced experimental flexibility in the control of their parameters and, if used as engines, a more direct interpretation of the type of work they deliver. Here we introduce an out-of-equilibrium quantum engine inspired by recent experiments with cold atoms. Our system is connected to a single environment and produces mechanical work from many-body interparticle interactions arising between atoms in highly excited Rydberg states. As such, it is not a heat engine but an isothermal one. We perform many-body simulations to show that this system can produce work. The setup we introduce and investigate represents a promising platform for devising new types of microscopic machines and for exploring quantum effects in thermodynamic processes.

With the first detection of gravitational waves from a binary system of neutron stars GW170817, a new window was opened to study the properties of matter at and above nuclear-saturation density. Reaching densities a few times that of nuclear matter and temperatures up to 100 MeV, such mergers also represent potential sites for a phase transition (PT) from confined hadronic matter to deconfined quark matter. While the lack of a postmerger signal in GW170817 has prevented us from assessing experimentally this scenario, two theoretical studies have explored the postmerger gravitational-wave signatures of PTs in mergers of a binary system of neutron stars. We here extend and complete the picture by presenting a novel signature of the occurrence of a PT. More specifically, using fully general-relativistic hydrodynamic simulations and employing a suitably constructed equation of state that includes a PT, we present the occurrence of a “delayed PT,” i.e., a PT that develops only some time after the merger and produces a metastable object with a quark-matter core, i.e., a hypermassive hybrid star. Because in this scenario, the postmerger signal exhibits two distinct fundamental gravitational-wave frequencies—before and after the PT—the associated signature promises to be the strongest and cleanest among those considered so far, and one of the best signatures of the production of quark matter in the present Universe.

In this work we present a precise and model-independent dispersive determination from data of the existence and parameters of the lightest strange resonance $\kappa /K_0^{*}(700)$. We use both subtracted and unsubtracted partial-wave hyperbolic and fixed-$t$ dispersion relations as constraints on combined fits to $\pi K\to \pi K$ and $\pi \pi \to K\overline{K}$ data. We then use the hyperbolic equations for the analytic continuation of the isospin $I=1/2$ scalar partial wave to the complex plane, in order to determine the $\kappa /K_0^{*}(700)$ and $K^{*}(892)$ associated pole parameters and residues.

We report a new oscillatory propagation of cracks in thin films where three cracks interact mediated by two delamination fronts. Experimental observations indicate that delamination fronts joining the middle crack to the lateral crack tips swap contact periodically with the crack tip of the middle crack. A model based on a variational approach analytically predicts the condition of propagation and geometrical features of three parallel cracks. The stability conditions and oscillating propagation are found numerically and the predictions are in favorable agreement with experiments. We found that the physical mechanism selecting the wavelength structure is a relaxation process in which the middle crack produces a regular oscillatory path.

The dimerized quantum magnet ${\mathrm{BaCuSi}}_2{\mathrm{O}}_6$ was proposed as an example of “dimensional reduction” arising near the magnetic-field-induced quantum critical point (QCP) due to perfect geometrical frustration of its interbilayer interactions. We demonstrate by high-resolution neutron spectroscopy experiments that the effective intrabilayer interactions are ferromagnetic, thereby excluding frustration. We explain the apparent dimensional reduction by establishing the presence of three magnetically inequivalent bilayers, with ratios $3:2:1$, whose differing interaction parameters create an extra field-temperature scaling regime near the QCP with a nontrivial but nonuniversal exponent. We demonstrate by detailed quantum Monte Carlo simulations that the magnetic interaction parameters we deduce can account for all the measured properties of ${\mathrm{BaCuSi}}_2{\mathrm{O}}_6$, opening the way to a quantitative understanding of nonuniversal scaling in any modulated layered system.

We investigate the potential for cavity-modified electron transfer in a doped organic semiconductor through the photocurrent that arises from exciting charged molecules (polarons). When the polaron optical transition is strongly coupled to a Fabry-Perot microcavity mode, we observe polaron polaritons in the photoconductivity action spectrum and find that their magnitude depends differently on applied electric field than photocurrent originating from the excitation of uncoupled polarons in the same cavity. Crucially, moving from positive to negative detuning causes the upper and lower polariton photocurrents to swap their field dependence, with the more polaronlike branch resembling that of an uncoupled excitation. These observations are understood on the basis of a phenomenological model in which strong coupling alters the Onsager dissociation of polarons from their dopant counterions by effectively increasing the thermalization length of the photoexcited charge carrier.