A step-by-step approach is followed to study cosmic structures in the context of Brans-Dicke theory with positive cosmological constant $\mathrm{\Lambda }$ and parameter $\omega$. First, it is shown that regular stationary black-hole solutions not only have constant Brans-Dicke field $\varphi$, but can exist only for $\omega =\infty$, which forces the theory to coincide with the general relativity. Generalizations of the theory in order to evade this black-hole no-hair theorem are presented. It is also shown that in the absence of a stationary cosmological event horizon in the asymptotic region, a stationary black-hole horizon can support a nontrivial Brans-Dicke hair. Even more importantly, it is shown next that the presence of a stationary cosmological event horizon rules out any regular stationary solution, appropriate for the description of a star. Thus, to describe a star one has to assume that there is no such stationary horizon in the faraway asymptotic region. Under this implicit assumption generic spherical cosmic structures are studied perturbatively and it is shown that only for $\omega >0$ or $\omega \lesssim -5$ their predicted maximum sizes are consistent with observations. We also point out how, many of the conclusions of this work differ qualitatively from the $\mathrm{\Lambda }=0$ spacetimes.

Light top superpartners play a key role in stabilizing the electroweak scale in supersymmetric theories. For $R$-parity conserved supersymmetric models, traditional searches are not sensitive to the compressed regions. In this Letter, we propose a new method targeting this region, with top squark and neutralino mass splitting ranging from $m_{\tilde{t}}-m_{\chi }\gtrsim m_t$ to about 20 GeV. In particular, we focus on the signal process in which a pair of top squarks are produced in association with a hard jet, and we define a new observable $R_M$ whose distribution has a peak in this compressed region. The position of the peak is closely correlated with $m_{\tilde{t}}$. We show that for the 13 TeV LHC with a luminosity of $3000{\mathrm{fb}}^{-1}$, this analysis can extend the reach of the top squark in the compressed region to $m_{\tilde{t}}$ around 800 GeV.

The monojet search, looking for events involving missing transverse energy (${\cancel{E}}_T$) plus one or two jets, is the most prominent collider dark matter search. We show that multijet searches, which look for ${\cancel{E}}_T$ plus two or more jets, are significantly more sensitive than the monojet search for pseudoscalar- and scalar-mediated interactions. We demonstrate this in the context of a simplified model with a pseudoscalar interaction that explains the excess in GeV energy gamma rays observed by the Fermi Large Area Telescope. We show that multijet searches already constrain a pseudoscalar interpretation of the excess in much of the parameter space where the mass of the mediator $M_A$ is more than twice the dark matter mass $m_{\mathrm{DM}}$. With the forthcoming run of the Large Hadron Collider at higher energies, the remaining regions of the parameter space where $M_A>2m_{\mathrm{DM}}$ will be fully explored. Furthermore, we highlight the importance of complementing the monojet final state with multijet final states to maximize the sensitivity of the search for the production of dark matter at colliders.

We report a study of the process $e^{+}{e}^{-}\to (D^{*}{\overline{D}}^{*}{)}^0{\pi }^0$ using $e^{+}{e}^{-}$ collision data samples with integrated luminosities of $1092{\mathrm{pb}}^{-1}$ at $\sqrt{s}=4.23\mathrm{GeV}$ and $826{\mathrm{pb}}^{-1}$ at $\sqrt{s}=4.26\mathrm{GeV}$ collected with the BESIII detector at the BEPCII storage ring. We observe a new neutral structure near the $(D^{*}{\overline{D}}^{*}{)}^0$ mass threshold in the ${\pi }^0$ recoil mass spectrum, which we denote as $Z_c(4025{)}^0$. Assuming a Breit-Wigner line shape, its pole mass and pole width are determined to be $(4025.5_{-4.7}^{+2.0}\pm 3.1)\mathrm{MeV}/c^2$ and $(23.0\pm 6.0\pm 1.0)\mathrm{MeV}$, respectively. The Born cross sections of $e^{+}{e}^{-}\to Z_c(4025{)}^0{\pi }^0\to (D^{*}{\overline{D}}^{*}{)}^0{\pi }^0$ are measured to be $(61.6\pm 8.2\pm 9.0)\mathrm{pb}$ at $\sqrt{s}=4.23\mathrm{GeV}$ and $(43.4\pm 8.0\pm 5.4)\mathrm{pb}$ at $\sqrt{s}=4.26\mathrm{GeV}$. The first uncertainties are statistical and the second are systematic.

We use a stochastic model and direct numerical simulation to study the impact of turbulence on cloud droplet growth by condensation. We show that the variance of the droplet size distribution increases in time as $t^{1/2}$, with growth rate proportional to the large-to-small turbulent scale separation and to the turbulence integral scales but independent of the mean turbulent dissipation. Direct numerical simulations confirm this result and produce realistically broad droplet size spectra over time intervals of 20 min, comparable with the time of rain formation.

Boron-rich tungsten borides are premier prototypes of a new class of ultrahard compounds. Here, we show by first-principles calculations that their stress-strain relations display surprisingly diverse and anomalous behavior under a variety of loading conditions. Most remarkable is the dramatically changing bonding configurations and deformation modes with rising boron concentration in ${\mathrm{WB}}_n$ ($n=2$, 3, 4), resulting in significantly different stress responses and unexpected indentation strength variations. This novel phenomenon stems from the peculiar structural arrangements in tungsten borides driven by boron’s ability to form unusually versatile bonding states. Our results elucidate the intriguing deformation mechanisms that define a distinct type of ultrahard material. These new insights underscore the need to explore unconventional structure-property relations in a broad range of transition-metal light-element compounds.

The structural and magnetic properties of ultrathin FeO(111) films on Pt(111) with thicknesses from 1 to 16 monolayers (MLs) were studied using the nuclear inelastic scattering of synchrotron radiation. A distinct evolution of vibrational characteristics with thickness, revealed in the phonon density of states (PDOS), shows a textbook transition from 2D to 3D lattice dynamics. For the thinnest films of 1 and 2 ML, the low-energy part of the PDOS followed a linear $\propto E$ dependence in energy that is characteristic for two-dimensional systems. This dependence gradually transforms with thickness to the bulk $\propto E^2$ relationship. Density-functional theory phonon calculations perfectly reproduced the measured 1-ML PDOS within a simple model of a pseudomorphic $\mathrm{Fe}\mathrm{O}/\text{Pt}(111)$ interface. The calculations show that the 2D PDOS character is due to a weak coupling of the FeO film to the Pt(111) substrate. The evolution of the vibrational properties with an increasing thickness is closely related to a transient long-range magnetic order and stabilization of an unusual structural phase.

We show that two-terminal transport can measure the Luttinger liquid (LL) parameter $K$, in helical LLs at the edges of two-dimensional topological insulators (TIs) with Rashba spin-orbit coupling. We consider a Coulomb drag geometry with two coplanar TIs and short-ranged spin-flip interedge scattering. Current injected into one edge loop induces circulation in the second, which floats without leads. In the low-temperature ($T\to 0$) perfect drag regime, the conductance is $(e^2/h)(2K+1)/(K+1)$. At higher $T$, we predict a conductivity $\sim T^{-4K+3}$. The conductivity for a single edge is also computed.

While an ordinary Fermi sea is perturbatively robust to interactions, the paradigmatic composite-fermion (CF) Fermi sea arises as a nonperturbative consequence of emergent gauge fields in a system where there was no Fermi sea to begin with. A mean-field picture suggests two Fermi seas, of composite fermions made from electrons or holes in the lowest Landau level, which occupy different areas away from half filling and thus appear to represent distinct states. Using the microscopic theory of composite fermions, which satisfies particle-hole symmetry in the lowest Landau level to an excellent approximation, we show that the Fermi wave vectors at filling factors $\nu$ and $1-\nu$ are equal when expressed in units of the inverse magnetic length, and are generally consistent with the experimental findings of Kamburov et al. [Phys. Rev. Lett. 113, 196801 (2014)]. Our calculations suggest that the area of the CF Fermi sea may slightly violate the Luttinger area rule.

Dirac semimetals host bulk band-touching Dirac points and a surface Fermi loop. We develop a theory of superconducting Dirac semimetals. Establishing a relation between the Dirac points and the surface Fermi loop, we clarify how the nontrivial topology of Dirac semimetals affects their superconducting state. We note that the unique orbital texture of Dirac points and a structural phase transition of the crystal favor symmetry-protected topological superconductivity with a quartet of surface Majorana fermions. We suggest the possible application of our theory to recently discovered superconducting states in ${\mathrm{Cd}}_3{\mathrm{As}}_2$.

We present a technique to generate relations connecting pure state weights, overlaps, and correlation functions in short-range spin glasses. These are obtained directly from the unperturbed Hamiltonian and hold for general coupling distributions. All are satisfied in phases with simple thermodynamic structure, such as the droplet-scaling and chaotic pairs pictures. If instead nontrivial mixed-state pictures hold, the relations suggest that replica symmetry is broken as described by a Derrida-Ruelle cascade, with pure state weights distributed as a Poisson-Dirichlet process.

We use midinfrared pulses with stable carrier-envelope phase offset to drive molecular vibrations in the charge transfer salt $\mathrm{ET}\text{−}{\mathrm{F}}_2\mathrm{TCNQ}$, a prototypical one-dimensional Mott insulator. We find that the Mott gap, which is probed resonantly with 10 fs laser pulses, oscillates with the pump field. This observation reveals that molecular excitations can coherently perturb the electronic on-site interactions (Hubbard $U$) by changing the local orbital wave function. The gap oscillates at twice the frequency of the vibrational mode, indicating that the molecular distortions couple quadratically to the local charge density.

We have explored isotropically jammed states of semi-2D granular materials through cyclic compression. In each compression cycle, systems of either identical ellipses or bidisperse disks transition between jammed and unjammed states. We determine the evolution of the average pressure $P$ and structure through consecutive jammed states. We observe a transition point ${\varphi }_m$ above which $P$ persists over many cycles; below ${\varphi }_m$, $P$ relaxes slowly. The relaxation time scale associated with $P$ increases with packing fraction, while the relaxation time scale for collective particle motion remains constant. The collective motion of the ellipses is hindered compared to disks because of the rotational constraints on elliptical particles.

We obtain lower and upper bounds on the skewness and kurtosis associated with the cycle completion time of unicyclic enzymatic reaction schemes. Analogous to a well-known lower bound on the randomness parameter, the lower bounds on skewness and kurtosis are related to the number of intermediate states in the underlying chemical reaction network. Our results demonstrate that evaluating these higher order moments with single molecule data can lead to information about the enzymatic scheme that is not contained in the randomness parameter.

We numerically study the dynamics of run-and-tumble particles confined in two chambers connected by thin channels. Two dominant dynamical behaviors emerge: (i) an oscillatory pumping state, in which particles periodically fill the two vessels, and (ii) a circulating flow state, dynamically maintaining a near constant population level in the containers when connected by two channels. We demonstrate that the oscillatory behavior arises from the combination of a narrow channel, preventing bacteria reorientation, and a density-dependent motility inside the chambers.

We theoretically study the self-propulsion of a laser-heated Janus particle in a near-critical water-lutidine mixture, and we relate its velocity $v_p$ and squirmer parameter $\beta$ to the wetting properties of its two hemispheres. For nonionic surface forces, the particle moves the active cap at the front, whereas a charged hydrophilic cap leads to backward motion, in agreement with the experiment. Both $v_p$ and $\beta$ show nonmonotonic dependencies on the heating power, and they may even change sign. The variation of $\beta$ is expected to strongly affect the collective behavior of dense squirmer systems.

Gold-capped Janus particles immersed in a near-critical binary mixture can be propelled using illumination. We employ a nonisothermal diffuse interface approach to investigate the self-propulsion mechanism of a single colloid. We attribute the motion to body forces at the edges of a micronsized droplet that nucleates around the particle. Thus, the often-used concept of a surface velocity cannot account for the self-propulsion. The particle’s swimming velocity is related to the droplet shape and size, which is determined by a so-called critical isotherm. Two distinct swimming regimes exist, depending on whether the droplet partially or completely covers the particle. Interestingly, the dependence of the swimming velocity on temperature is nonmonotonic in both regimes.

The statistical significance of network properties is conditioned on null models which satisfy specified properties but that are otherwise random. Exponential random graph models are a principled theoretical framework to generate such constrained ensembles, but which often fail in practice, either due to model inconsistency or due to the impossibility to sample networks from them. These problems affect the important case of networks with prescribed clustering coefficient or number of small connected subgraphs (motifs). In this Letter we use the Wang-Landau method to obtain a multicanonical sampling that overcomes both these problems. We sample, in polynomial time, networks with arbitrary degree sequences from ensembles with imposed motifs counts. Applying this method to social networks, we investigate the relation between transitivity and homophily, and we quantify the correlation between different types of motifs, finding that single motifs can explain up to 60% of the variation of motif profiles.