The detection of GW170817 and the identification of its host galaxy have allowed for the first standard-siren measurement of the Hubble constant, with an uncertainty of $\sim 14\%$. As more detections of binary neutron stars with redshift measurement are made, the uncertainty will shrink. The dominating factors will be the number of joint detections and the uncertainty on the luminosity distance of each event. Neutron star black hole mergers are also promising sources for advanced LIGO and Virgo. If the black hole spin induces precession of the orbital plane, the degeneracy between luminosity distance and the orbital inclination is broken, leading to a much better distance measurement. In addition, neutron star black hole sources are observable to larger distances, owing to their higher mass. Neutron star black holes could also emit electromagnetic radiation: depending on the black hole spin and on the mass ratio, the neutron star can be tidally disrupted, resulting in electromagnetic emission. We quantify the distance uncertainty for a wide range of black hole mass, spin, and orientations and find that the $1\sigma$ statistical uncertainty can be up to a factor of $\sim 10$ better than for a nonspinning binary neutron star merger with the same signal-to-noise ratio. The better distance measurement, the larger gravitational-wave detectable volume, and the potentially bright electromagnetic emission imply that spinning black hole neutron star binaries can be the optimal standard-siren sources as long as their astrophysical rate is larger than $O(10){\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$, a value allowed by current astrophysical constraints.

We search for nuclear recoil signals of dark matter models with a light mediator in PandaX-II, a direct detection experiment in the China Jinping underground laboratory. Using data collected in 2016 and 2017 runs, corresponding to a total exposure of 54 ton day, we set upper limits on the zero-momentum dark matter-nucleon cross section. These limits have a strong dependence on the mediator mass when it is comparable to or below the typical momentum transfer. We apply our results to constrain self-interacting dark matter models with a light mediator mixing with standard model particles, and set strong limits on the model parameter space for the dark matter mass ranging from 5 GeV to 10 TeV.

We compute the leading, strong-interaction contribution to the anomalous magnetic moment of the electron, muon, and tau using lattice quantum chromodynamics (QCD) simulations. Calculations include the effects of $u$, $d$, $s$, and $c$ quarks and are performed directly at the physical values of the quark masses and in volumes of linear extent larger than 6 fm. All connected and disconnected Wick contractions are calculated. Continuum limits are carried out using six lattice spacings. We obtain $a_e^{\mathrm{LO}\text{−}\mathrm{HVP}}=189.3(2.6)(5.6)\times {10}^{-14}$, $a_{\mu }^{\mathrm{LO}\text{−}\mathrm{HVP}}=711.1(7.5)(17.4)\times {10}^{-10}$ and $a_{\tau }^{\mathrm{LO}\text{−}\mathrm{HVP}}=341.0(0.8)(3.2)\times {10}^{-8}$, where the first error is statistical and the second is systematic.

We present a first-principles lattice $\mathrm{QCD}+\mathrm{QED}$ calculation at physical pion mass of the leading-order hadronic vacuum polarization contribution to the muon anomalous magnetic moment. The total contribution of up, down, strange, and charm quarks including QED and strong isospin breaking effects is $a_{\mu }^{\text{HVP LO}}=715.4(18.7)\times {10}^{-10}$. By supplementing lattice data for very short and long distances with $R$-ratio data, we significantly improve the precision to $a_{\mu }^{\text{HVP LO}}=692.5(2.7)\times {10}^{-10}$. This is the currently most precise determination of $a_{\mu }^{\text{HVP LO}}$.

We report the first observation of $a_0^0(980)\text{−}{f}_0(980)$ mixing in the decays of $J/\psi \to \varphi f_0(980)\to \varphi a_0^0(980)\to \varphi \eta {\pi }^0$ and ${\chi }_{c1}\to a_0^0(980){\pi }^0\to f_0(980){\pi }^0\to {\pi }^{+}{\pi }^{-}{\pi }^0$, using data samples of $1.31\times {10}^{9}J/\psi$ events and $4.48\times {10}^8\psi (3686)$ events accumulated with the BESIII detector. The signals of $f_0(980)\to a_0^0(980)$ and $a_0^0(980)\to f_0(980)$ mixing are observed at levels of statistical significance of $7.4\sigma$ and $5.5\sigma$, respectively. The corresponding branching fractions and mixing intensities are measured and the constraint regions on the coupling constants, $g_{a_0{K}^{+}{K}^{-}}$ and $g_{f_0{K}^{+}{K}^{-}}$, are estimated. The results improve the understanding of the nature of $a_0^0(980)$ and $f_0(980)$.

The discovery of the important neutron-rich nucleus ${}_{20}{}^{60}{\mathrm{Ca}}_{40}$ and seven others near the limits of nuclear stability is reported from the fragmentation of a $345\mathrm{MeV}/u$ ${}^{70}\mathrm{Zn}$ projectile beam on ${}^9\mathrm{Be}$ targets at the radioactive ion-beam factory of the RIKEN Nishina Center. The produced fragments were analyzed and unambiguously identified using the BigRIPS two-stage in-flight separator. The eight new neutron-rich nuclei discovered, ${}^{47}\mathrm{P}$, ${}^{49}\mathrm{S}$, ${}^{52}\mathrm{Cl}$, ${}^{54}\mathrm{Ar}$, ${}^{57}\mathrm{K}$, ${}^{59,60}\mathrm{Ca}$, and ${}^{62}\mathrm{Sc}$, are the most neutron-rich isotopes of the respective elements. In addition, one event consistent with ${}^{59}\mathrm{K}$ was registered. The results are compared with the drip lines predicted by a variety of mass models and it is found that the models in best agreement with the observed limits of existence in the explored region tend to predict the even-mass Ca isotopes to be bound out to at least ${}^{70}\mathrm{Ca}$.

Atomic comagnetometers are used in searches for anomalous spin-dependent interactions. Magnetic field gradients are one of the major sources of systematic errors in such experiments. Here we describe a comagnetometer based on the nuclear spins within an ensemble of identical molecules. The dependence of the measured spin-precession frequency ratio on the first-order magnetic field gradient is suppressed by over an order of magnitude compared to a comagnetometer based on overlapping ensembles of different molecules. Our single-species comagnetometer is capable of measuring the hypothetical spin-dependent gravitational energy of nuclei at the ${10}^{-17}\mathrm{eV}$ level, comparable to the most stringent existing constraints. Combined with techniques for enhancing the signal such as parahydrogen-induced polarization, this method of comagnetometry offers the potential to improve constraints on spin-gravity coupling of nucleons by several orders of magnitude.

Chemomechanical effects are known to initiate fluid oscillations in certain liquid metals; however, they typically produce an irregular motion that is difficult to deactivate or control. Here we show that stimulating liquid gallium with electrochemistry can cause a metal drop to exhibit a heart beating effect by shape shifting at a telltale frequency. Unlike the effects reported in the past for mercury, the symmetry-breaking forces generated by using gallium propel the drop several millimeters with velocities of the order of 1 cm per second. We demonstrate pulsating dynamics between 0 and 610 beats per minute for $50–150\mu \mathrm{L}$ droplets in a NaOH electrolyte at $34°\mathrm{C}$. The underlying mechanism is a self-regulating cycle initiated by fast electrochemical oxidation that adjusts the drop’s surface tension and causes a transformation from spherical to pancake form, followed by detachment from the circular electrode. As the beat frequency can be activated and controlled using a dc voltage, the electrochemical mechanism opens the way for fluid-based timers and actuators.

Non-Hermitian systems exhibit striking exceptions from the paradigmatic bulk-boundary correspondence, including the failure of bulk Bloch band invariants in predicting boundary states and the (dis)appearance of boundary states at parameter values far from those corresponding to gap closings in periodic systems without boundaries. Here, we provide a comprehensive framework to unravel this disparity based on the notion of biorthogonal quantum mechanics: While the properties of the left and right eigenstates corresponding to boundary modes are individually decoupled from the bulk physics in non-Hermitian systems, their combined biorthogonal density penetrates the bulk precisely when phase transitions occur. This leads to generalized bulk-boundary correspondence and a quantized biorthogonal polarization that is formulated directly in systems with open boundaries. We illustrate our general insights by deriving the phase diagram for several microscopic open boundary models, including exactly solvable non-Hermitian extensions of the Su-Schrieffer-Heeger model and Chern insulators.

We show that simulations of magnetohydrodynamic turbulence in the multiphase interstellar medium yield an $E/B$ ratio for polarized emission from Galactic dust in broad agreement with recent Planck measurements. In addition, the $B$-mode spectra display a scale dependence that is consistent with observations over the range of scales resolved in the simulations. The simulations present an opportunity to understand the physical origin of the $E/B$ ratio and a starting point for more refined models of Galactic emission of use for both current and future cosmic microwave background experiments.

The thermal Hall conductance in the half-filled first Landau level was recently measured to take the quantized noninteger value ${\kappa }_{xy}=5/2$ (in units of temperature times ${\pi }^2{k}_B^2/3h$), which indicates a non-Abelian phase of matter. Such exotic states have long been predicted to arise at this filling factor, but the measured value disagrees with numerical studies, which predict ${\kappa }_{xy}=3/2$ or $7/2$. We resolve this contradiction by invoking the disorder-induced formation of mesoscopic puddles with locally ${\kappa }_{xy}=3/2$ or $7/2$. Interactions between these puddles generate a coherent macroscopic state that exhibits a plateau with quantized ${\kappa }_{xy}=5/2$. The non-Abelian quasiparticles characterizing this phase are distinct from those of the microscopic puddles and, by the same mechanism, could even emerge from a system comprised of microscopic Abelian puddles.

The unique combination of atomic-scale composition measurements, employing atom probe tomography, atomic structure determination with picometer resolution by aberration-corrected scanning transmission electron microscopy, and atomistic simulations reveals site-specific linear segregation features at grain boundary facet junctions. More specific, an asymmetric line segregation along one particular type of facet junction core, instead of a homogeneous decoration of the facet planes, is observed. Molecular-statics calculations show that this segregation pattern is a consequence of the interplay between the asymmetric core structure and its corresponding local strain state. Our results contrast with the classical view of a homogeneous decoration of the facet planes and evidence a complex segregation patterning.

Transition paths are the most interesting part of folding reactions but remain little studied. We measured the local velocity along transition paths in DNA hairpin folding using optical tweezers. The velocity distribution agreed well with diffusive theories, yielding the diffusion coefficient. We used the average velocity to calculate the transmission factor in transition-state theory (TST), finding observed rates that were $\sim {10}^5$-fold slower than predicted by TST. This work quantifies the importance of barrier recrossing events and highlights the effectiveness of the diffusive model of folding.

We report on the observation of a collective spin mode in a spinor Bose-Einstein condensate. Initially, all spins point perpendicular to the external magnetic field. The lowest energy mode consists of a sinusoidal oscillation of the local spin around its original axis, with an oscillation amplitude that linearly depends on the spatial coordinates. The frequency of the oscillation is set by the zero-point kinetic energy of the BEC. The observations are in excellent agreement with hydrodynamic equations. The observed spin mode has a universal character, independent of the atomic spin and spin-dependent contact interactions.

The ionization energy of ortho-${\mathrm{H}}_2$ has been determined to be $E_{\mathrm{I}}^{\mathrm{o}}({\mathrm{H}}_2)/(hc)=124357.238062(25){\mathrm{cm}}^{-1}$ from measurements of the $GK(1,1)-X(0,1)$ interval by Doppler-free, two-photon spectroscopy using a narrow band 179-nm laser source and the ionization energy of the $GK(1,1)$ state by continuous-wave, near-infrared laser spectroscopy. $E_{\mathrm{I}}^{\mathrm{o}}({\mathrm{H}}_2)$ was used to derive the dissociation energy of ${\mathrm{H}}_2$, $D_0^{N=1}({\mathrm{H}}_2)$, at $35999.582894(25){\mathrm{cm}}^{-1}$ with a precision that is more than one order of magnitude better than all previous results. The new result challenges calculations of this quantity and represents a benchmark value for future relativistic and QED calculations of molecular energies.

The recent detection of an anomalously strong 21-cm signal of neutral hydrogen from cosmic dawn by the EDGES low-band radio experiment can be explained if cold dark matter particles scattered off the baryons draining excess energy from the gas. In this Letter we explore the expanded range of the 21-cm signal that is opened up by this interaction, varying the astrophysical parameters as well as the properties of dark matter particles in the widest possible range. We identify models consistent with current data by comparing to both the detection in the low-band region and the upper limits from the EDGES high-band antenna. We find that consistent models predict a 21-cm fluctuation during cosmic dawn that is between 3 and 30 times larger than the largest previously expected without dark matter scattering. The expected power spectrum exhibits strong baryon acoustic oscillations imprinted by the velocity-dependent cross section. The latter signature is a conclusive evidence of the velocity-dependent scattering and could be used by interferometers to verify the dark matter explanation of the EDGES detection.

The EDGES Collaboration has recently reported the detection of a stronger-than-expected absorption feature in the global 21-cm spectrum, centered at a frequency corresponding to a redshift of $z\simeq 17$. This observation has been interpreted as evidence that the gas was cooled during this era as a result of scattering with dark matter. In this Letter, we explore this possibility, applying constraints from the cosmic microwave background, light element abundances, Supernova 1987A, and a variety of laboratory experiments. After taking these constraints into account, we find that the vast majority of the parameter space capable of generating the observed 21-cm signal is ruled out. The only viable models are those in which a small fraction, $\sim 0.3\%–2\%$, of the dark matter consists of particles with a mass of $\sim 10–80\mathrm{MeV}$ and which couple to the photon through a small electric charge, roughly ${10}^{-6}–{10}^{-4}$ as large as the electron charge. Furthermore, in order to avoid being overproduced in the early Universe, such models must be supplemented with an additional depletion mechanism, such as annihilations through a $L_{\mu }\text{−}{L}_{\tau }$ gauge boson or annihilations to a pair of rapidly decaying hidden sector scalars.

The observation of an absorption feature in the 21-cm spectrum at redshift $z\approx 17$ implies bounds on dark-matter (DM) annihilations for a broad range of masses, given that significant heating of the intergalactic medium would have erased such a feature. The resulting bounds on the DM annihilation cross sections are comparable to the strongest ones from all other observables.

We use a combination of x-ray diffraction, total scattering, and quantum mechanical calculations to determine the mechanism responsible for hydration-driven contraction in ${\mathrm{ZrW}}_2{\mathrm{O}}_8$. The inclusion of ${\mathrm{H}}_2\mathrm{O}$ molecules within the ${\mathrm{ZrW}}_2{\mathrm{O}}_8$ network drives the concerted formation of new $\mathrm{W}─\mathrm{O}$ bonds to give one-dimensional $(─\mathrm{W}─\mathrm{O}─{)}_n$ strings. The topology of the ${\mathrm{ZrW}}_2{\mathrm{O}}_8$ network is such that there is no unique choice for the string trajectories: the same local changes in coordination can propagate with a large number of different periodicities. Consequently, ${\mathrm{ZrW}}_2{\mathrm{O}}_8·{\mathrm{H}}_2\mathrm{O}$ is heavily disordered, with each configuration of strings forming a dense aperiodic “spaghetti.” This new connectivity contracts the unit cell via large shifts in the Zr and W atom positions. Fluctuations of the undistorted parent structure towards this spaghetti phase emerge as the key negative thermal expansion (NTE) phonon modes in ${\mathrm{ZrW}}_2{\mathrm{O}}_8$ itself. The large relative density of NTE phonon modes in ${\mathrm{ZrW}}_2{\mathrm{O}}_8$ actually reflects the degeneracy of volume-contracting spaghetti excitations, itself a function of the particular topology of this remarkable material.

Full control of multiple degrees of freedom of multiple particles represents a fundamental ability for quantum information processing. We experimentally demonstrate an 18-qubit Greenberger-Horne-Zeilinger entanglement by simultaneous exploiting three different degrees of freedom of six photons, including their paths, polarization, and orbital angular momentum. We develop high-stability interferometers for reversible quantum logic operations between the photons’ different degrees of freedom with precision and efficiencies close to unity, enabling simultaneous readout of $2^{18}=262144$ outcome combinations of the 18-qubit state. A state fidelity of $0.708\pm 0.016$ is measured, confirming the genuine entanglement of all 18 qubits.