Granular gases as dilute ensembles of particles in random motion are at the basis of elementary structure-forming processes in the Universe, involved in many industrial and natural phenomena, and also excellent models to study fundamental statistical dynamics. The essential difference to molecular gases is the energy dissipation in particle collisions. Its most striking manifestation is the so-called granular cooling, the gradual loss of mechanical energy $E(t)$ in the absence of external excitation. We report an experimental study of homogeneous cooling of three-dimensional granular gases in microgravity. The asymptotic scaling $E(t)\propto t^{-2}$ obtained by Haff’s minimal model [J. Fluid Mech. 134, 401 (1983)] proves to be robust, despite the violation of several of its central assumptions. The shape anisotropy of the grains influences the characteristic time of energy loss quantitatively but not qualitatively. We compare kinetic energies in the individual degrees of freedom and find a slight predominance of translational motions. In addition, we observe a preferred rod alignment in the flight direction, as known from active matter or animal flocks.

We report an experimental observation of a flow topology transition via global bifurcation in a turbulent Rayleigh-Bénard convection. This transition corresponds to a spontaneous symmetry breaking with the flow becomes more turbulent. Simultaneous measurements of the large-scale flow (LSF) structure and the heat transport show that the LSF bifurcates from a high heat transport efficiency quadrupole state to a less symmetric dipole state with a lower heat transport efficiency. In the transition zone, the system switches spontaneously and stochastically between the two long-lived metastable states.

Three-dimensional discrete dislocation dynamics (3D-DDD) simulations reveal that, with reduction of sample size in the submicron regime, the mechanism of plastic flow localization in irradiated materials transitions from irradiation-controlled to an intrinsic dislocation source controlled. Furthermore, the spatial correlation of plastic deformation decreases due to weaker dislocation interactions and less frequent cross slip as the system size decreases, thus manifesting itself in thinner dislocation channels. A simple model of discrete dislocation source activation coupled with cross slip channel widening is developed to reproduce and physically explain this transition. In order to quantify the phenomenon of plastic flow localization, we introduce a “deformation localization index,” with implications to the design of radiation-resistant materials.

We find that the reduction in dielectric response (depolarization) of water caused by solvated ions is different for ${\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{D}}_2\mathrm{O}$. This isotope dependence allows us to reliably determine the kinetic contribution to the depolarization, which is found to be significantly smaller than predicted by existing theory. The discrepancy can be explained from a reduced hydrogen-bond cooperativity in the solvation shell: we obtain quantitative agreement between theory and experiment by reducing the Kirkwood correlation factor of the solvating water from 2.7 (the bulk value) to $\sim 1.6$ for NaCl and $\sim 1$ (corresponding to completely uncorrelated motion of water molecules) for CsCl.

The determination of the electronic structure by edge geometry is unique to graphene. In theory, an evanescent nonchiral edge state is predicted at the zigzag edges of graphene. Up to now, the approach used to study zigzag-edged graphene has mostly been limited to scanning tunneling microscopy. The transport properties have not been revealed. Recent advances in hydrogen plasma-assisted “top-down” fabrication of zigzag-edged graphene nanoribbons (Z-GNRs) have allowed us to investigate edge-related transport properties. In this Letter, we report the magnetotransport properties of Z-GNRs down to $\sim 70\mathrm{nm}$ wide on an $h\text{−}\mathrm{BN}$ substrate. In the quantum Hall effect regime, a prominent conductance peak is observed at Landau $\nu =0$, which is absent in GNRs with nonzigzag edges. The conductance peak persists under perpendicular magnetic fields and low temperatures. At a zero magnetic field, a nonlocal voltage signal, evidenced by edge conduction, is detected. These prominent transport features are closely related to the observable density of states at the hydrogen-etched zigzag edge of graphene probed by scanning tunneling spectroscopy, which qualitatively matches the theoretically predicted electronic structure for zigzag-edged graphene. Our study gives important insights for the design of new edge-related electronic devices.

Recent observations of two nodeless gaps in superconducting ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$ have raised intensive debates on its exact gap symmetry, while a satisfactory theoretical basis is still lacking. Here we propose a phenomenological approach to calculate the superconducting gap functions, taking into consideration both the realistic Fermi surface topology and the intra- and interband quantum critical scatterings. Our calculations yield a nodeless $s^{\pm }$-wave solution in the presence of strong interband pairing interaction, in good agreement with experiments. This provides a possible basis for understanding the superconducting gap symmetry of ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$ at ambient pressure and indicates the potential importance of multiple Fermi surfaces and interband pairing interaction in understanding heavy fermion superconductivity.

Envisaged applications of Skyrmions in magnetic memory and logic devices crucially depend on the stability and mobility of these topologically nontrivial magnetic textures in thin films. We present for the first time quantitative maps of the magnetic induction that provide evidence for a 3D modulation of the Skyrmionic spin texture. The projected in-plane magnetic induction maps as determined from in-line and off-axis electron holography carry the clear signature of Bloch Skyrmions. However, the magnitude of this induction is much smaller than the values expected for homogeneous Bloch Skyrmions that extend throughout the thickness of the film. This finding can only be understood if the underlying spin textures are modulated along the out-of-plane $z$ direction. The projection of (the in-plane magnetic induction of) helices is further found to exhibit thickness-dependent lateral shifts, which show that this $z$ modulation is accompanied by an (in-plane) modulation along the $x$ and $y$ directions.

We demonstrate experimentally that a photonic crystal made of ${\mathrm{Al}}_2{\mathrm{O}}_3$ cylinders exhibits topological time-reversal symmetric electromagnetic propagation, similar to the quantum spin Hall effect in electronic systems. A pseudospin degree of freedom in the electromagnetic system representing different states of orbital angular momentum arises due to a deformation of the photonic crystal from the ideal honeycomb lattice. It serves as the photonic analogue to the electronic Kramers pair. We visualized qualitatively and measured quantitatively that microwaves of a specific pseudospin propagate only in one direction along the interface between a topological photonic crystal and a trivial one. As only a conventional dielectric material is used and only local real-space manipulations are required, our scheme can be extended to visible light to inspire many future applications in the field of photonics and beyond.

In this Letter, we investigate stochastic stability in a two-phenotype evolutionary game model for an infinite, well-mixed population undergoing discrete, nonoverlapping generations. We assume that the fitness of a phenotype is an exponential function of its expected payoff following random pairwise interactions whose outcomes randomly fluctuate with time. We show that the stochastic local stability of a constant interior equilibrium can be promoted by the random environmental noise even if the system may display a complicated nonlinear dynamics. This result provides a new perspective for a better understanding of how environmental fluctuations may contribute to the evolution of behavioral diversity.

To identify which principles characterize quantum correlations, it is essential to understand in which sense this set of correlations differs from that of almost-quantum correlations. We solve this problem by invoking the so-called no-restriction hypothesis, an explicit and natural axiom in many reconstructions of quantum theory stating that the set of possible measurements is the dual of the set of states. We prove that, contrary to quantum correlations, no generalized probabilistic theory satisfying the no-restriction hypothesis is able to reproduce the set of almost-quantum correlations. Therefore, any theory whose correlations are exactly, or very close to, the almost-quantum correlations necessarily requires a rule limiting the possible measurements. Our results suggest that the no-restriction hypothesis may play a fundamental role in singling out the set of quantum correlations among other nonsignaling ones.

We developed a novel perturbative expansion based on the replica trick for the Floquet Hamiltonian governing the dynamics of periodically kicked systems where the kick strength is the small parameter. The expansion is formally equivalent to an infinite resummation of the Baker-Campbell-Hausdorff series in the undriven (nonperturbed) Hamiltonian, while considering terms up to a finite order in the kick strength. As an application of the replica expansion, we analyze an Ising spin $1/2$ chain periodically kicked with a magnetic field with a strength $h$, which has both longitudinal and transverse components. We demonstrate that even away from the regime of high frequency driving, if there is heating, its rate is nonperturbative in the kick strength, bounded from above by a stretched exponential: $e^{-\text{const}{h}^{-1/2}}$. This guarantees the existence of a very long prethermal regime, where the dynamics is governed by the Floquet Hamiltonian obtained from the replica expansion.

Detection of the characteristic spectrum of pulsating neutron stars can be a powerful tool not only to probe the nuclear equation of state but also to test modifications to general relativity. However, the shift in the oscillation spectrum induced by modified theories of gravity is often small and degenerate with our ignorance of the equation of state. In this Letter, we show that the coupling to additional degrees of freedom present in modified theories of gravity can give rise to new families of modes, with no counterpart in general relativity, which could be sufficiently well resolved in frequency space to allow for clear detection. We present a realization of this idea by performing a thorough study of radial oscillations of neutron stars in massless scalar-tensor theories of gravity. We anticipate astrophysical scenarios where the presence of this class of quasinormal modes could be probed with electromagnetic and gravitational wave measurements.

Holographic theories with classical gravity duals are maximally chaotic; i.e., they saturate the universal bound on the rate of growth of chaos [J. Maldacena, S. H. Shenker, and D. Stanford, J. High Energy Phys. 08 (2016) 106]. It is interesting to ask whether this property is true only for leading large $N$ correlators or if it can show up elsewhere. In this Letter, we consider the simplest setup to tackle this question: a Brownian particle coupled to a thermal ensemble. We find that the four-point out-of-time-order correlator that diagnoses chaos initially grows at an exponential rate that saturates the chaos bound, i.e., with a Lyapunov exponent ${\lambda }_L=2\pi /\beta$. However, the scrambling time is parametrically smaller than for plasma excitations, $t_{*}\sim \beta \log \sqrt{\lambda }$ instead of $t_{*}\sim \beta \log N^2$. Our result shows that, at least in certain cases, maximal chaos can be attained in the probe sector without the explicit need of gravitational degrees of freedom.

Differential cross sections and photon-beam asymmetries for the $\overrightarrow{\gamma }p\to {\pi }^{-}{\mathrm{\Delta }}^{++}(1232)$ reaction have been measured for $0.7<\cos {\theta }_{\pi }^{\mathrm{c}.\mathrm{m}.}<1$ and $E_{\gamma }=1.5–2.95\mathrm{GeV}$ at SPring-8/LEPS. The first-ever high statistics cross-section data are obtained in this kinematical region, and the asymmetry data for $1.5<E_{\gamma }(\mathrm{GeV})<2.8$ are obtained for the first time. This reaction has a unique feature for studying the production mechanisms of a pure $u\overline{u}$ quark pair in the final state from the proton. Although there is no distinct peak structure in the cross sections, a non-negligible excess over the theoretical predictions is observed at $E_{\gamma }=1.5–1.8\mathrm{GeV}$. The asymmetries are found to be negative in most of the present kinematical regions, suggesting the dominance of $\pi$ exchange in the $t$ channel. The negative asymmetries at forward meson production angles are different from the asymmetries previously measured for the photoproduction reactions producing a $d\overline{d}$ or an $s\overline{s}$ quark pair in the final state. Advanced theoretical models introducing nucleon resonances and additional unnatural-parity exchanges are needed to reproduce the present data.

A search for resonancelike structures in the $B_s^0{\pi }^{\pm }$ invariant mass spectrum is performed using proton-proton collision data collected by the CMS experiment at the LHC at $\sqrt{s}=8\mathrm{TeV}$, corresponding to an integrated luminosity of $19.7{\mathrm{fb}}^{-1}$. The $B_s^0$ mesons are reconstructed in the decay chain $B_s^0\to J/\psi \varphi$, with $J/\psi \to {\mu }^{+}{\mu }^{-}$ and $\varphi \to K^{+}{K}^{-}$. The $B_s^0{\pi }^{\pm }$ invariant mass distribution shows no statistically significant peaks for different selection requirements on the reconstructed $B_s^0$ and ${\pi }^{\pm }$ candidates. Upper limits are set on the relative production rates of the $X(5568)$ and $B_s^0$ states times the branching fraction of the decay $X(5568{)}^{\pm }\to B_s^0{\pi }^{\pm }$. In addition, upper limits are obtained as a function of the mass and the natural width of possible exotic states decaying into $B_s^0{\pi }^{\pm }$.

A search for the exotic meson $X(5568)$ decaying into the $B_s^0{\pi }^{\pm }$ final state is performed using data corresponding to $9.6{\mathrm{fb}}^{-1}$ from $p\overline{p}$ collisions at $\sqrt{s}=1960\mathrm{GeV}$ recorded by the Collider Detector at Fermilab. No evidence for this state is found and an upper limit of 6.7% at the 95% confidence level is set on the fraction of $B_s^0$ produced through the $X(5568)\to B_s^0{\pi }^{\pm }$ process.

A search for the narrow structure, $X(5568)$, reported by the D0 Collaboration in the decay sequence $X\to B_s^0{\pi }^{\pm }$, $B_s^0\to J/\psi \varphi$, is presented. The analysis is based on a data sample recorded with the ATLAS detector at the LHC corresponding to $4.9{\mathrm{fb}}^{-1}$ of $pp$ collisions at 7 TeV and $19.5{\mathrm{fb}}^{-1}$ at 8 TeV. No significant signal was found. Upper limits on the number of signal events, with properties corresponding to those reported by D0, and on the $X$ production rate relative to $B_s^0$ mesons, ${\rho }_X$, were determined at 95% confidence level. The results are $N(X)<382$ and ${\rho }_X<0.015$ for $B_s^0$ mesons with transverse momenta above 10 GeV, and $N(X)<356$ and ${\rho }_X<0.016$ for transverse momenta above 15 GeV. Limits are also set for potential $B_s^0{\pi }^{\pm }$ resonances in the mass range 5550 to 5700 MeV.

We analyze and propose a solution to the apparent inconsistency between our current knowledge of the equation of state of asymmetric nuclear matter, the energy of the isobaric analog state (IAS) in a heavy nucleus such as ${}^{208}\mathrm{Pb}$, and the isospin symmetry breaking forces in the nuclear medium. This is achieved by performing state-of-the-art Hartree-Fock plus random phase approximation calculations of the IAS that include all isospin symmetry breaking contributions. To this aim, we propose a new effective interaction that is successful in reproducing the IAS excitation energy without compromising other properties of finite nuclei.

Efficient nonlinear optical frequency mixing in small volumes is key for future on-chip photonic devices. However, the generally low conversion efficiency severely limits miniaturization to nanoscale dimensions. Here we demonstrate that gradient-field effects can provide for an efficient, conventionally dipole-forbidden nonlinear response. We show that a longitudinal nonlinear source current can dominate the third-order optical nonlinearity of the free electron response in gold in the technologically important near-IR frequency range where the nonlinearities due to other mechanisms are particularly small. Using adiabatic nanofocusing to spatially confine the excitation fields, from measurements of the $2{\omega }_1-{\omega }_2$ four-wave mixing response as a function of detuning ${\omega }_1-{\omega }_2$, we find up to ${10}^{-5}$ conversion efficiency with a gradient-field contribution to ${\chi }_{\mathrm{Au}}^{(3)}$ of up to ${10}^{-19}{\mathrm{m}}^2/{\mathrm{V}}^2$. The results are in good agreement with the theory based on plasma hydrodynamics and underlying electron dynamics. The associated increase in the nonlinear conversion efficiency with a decreasing sample size, which can even overcompensate the volume decrease, offers a new approach for enhanced nonlinear nano-optics. This will enable more efficient nonlinear optical devices and the extension of coherent multidimensional spectroscopies to the nanoscale.