Gravitational theories differing from general relativity may explain the accelerated expansion of the Universe without a cosmological constant. However, to pass local gravitational tests, a “screening mechanism” is needed to suppress, on small scales, the fifth force driving the cosmological acceleration. We consider the simplest of these theories, i.e., a scalar-tensor theory with first-order derivative self-interactions, and study isolated (static and spherically symmetric) nonrelativistic and relativistic stars. We produce screened solutions and use them as initial data for nonlinear numerical evolutions in spherical symmetry. We find that these solutions are stable under large initial perturbations, as long as they do not cause gravitational collapse. When gravitational collapse is triggered, the characteristic speeds of the scalar evolution equation diverge, even before apparent black-hole or sound horizons form. This casts doubts on whether the dynamical evolution of screened stars may be predicted in these effective field theories.

We introduce a new approach to the Higgs naturalness problem. The Higgs mixes with the dilaton of a conformal field theory (CFT) sector whose true ground state has a large negative vacuum energy. If the Higgs vacuum expectation value is nonzero and below $\mathcal{O}(\mathrm{TeV})$, the CFT admits a second metastable vacuum, where the expansion history of the Universe is conventional. As a result, only Hubble patches with unnaturally small values of the Higgs mass do not immediately crunch. The main experimental prediction of this mechanism is a dilaton in the 0.1–10 GeV range that mixes with the Higgs and can be detected at future colliders and experiments searching for weakly coupled particles.

The topology of the Fermi surface controls the electronic response of a metal, including charge density wave (CDW) formation. A topology conducive for Fermi surface nesting (FSN) allows the electronic susceptibility ${\chi }_0$ to diverge and induce a CDW at wave vector ${\mathbf{q}}_{\mathrm{CDW}}$. Kohn extended the implications of FSN to show that the imaginary part of the lattice dynamical susceptibility ${\chi }_L^{\prime \prime }$ also responds anomalously for all phonon branches at ${\mathbf{q}}_{\mathrm{CDW}}$—a phenomenon referred to as the Kohn anomaly. However, materials exhibiting multiple Kohn anomalies remain rare. Using first-principles simulations of ${\chi }_0$ and ${\chi }_L^{\prime \prime }$, and previous scattering measurements [Crummett et al., Phys. Rev. B 19, 6028 234 (1979)], we show that $\alpha$-uranium harbors multiple Kohn anomalies enabled by the combined effect of FSN and “hidden” nesting, i.e., nesting of electronic states above and below the Fermi surface. FSN and hidden nesting lead to a ridgelike feature in the real part of ${\chi }_0$, allowing interatomic forces to modulate strongly and multiple Kohn anomalies to emerge. These results emphasize the importance of hidden nesting in controlling ${\chi }_0$ and ${\chi }_L^{\prime \prime }$ to exploit electronic and lattice states and enable engineering of advanced materials, including topological Weyl semimetals and superconductors.

The quasi-two-dimensional Mott insulator $\alpha \text{−}{\mathrm{RuCl}}_3$ is proximate to the sought-after Kitaev quantum spin liquid (QSL). In a layer of $\alpha \text{−}{\mathrm{RuCl}}_3$ on graphene, the dominant Kitaev exchange is further enhanced by strain. Recently, quantum oscillation (QO) measurements of such $\alpha \text{−}{\mathrm{RuCl}}_3$ and graphene heterostructures showed an anomalous temperature dependence beyond the standard Lifshitz-Kosevich (LK) description. Here, we develop a theory of anomalous QO in an effective Kitaev-Kondo lattice model in which the itinerant electrons of the graphene layer interact with the correlated magnetic layer via spin interactions. At low temperatures, a heavy Fermi liquid emerges such that the neutral Majorana fermion excitations of the Kitaev QSL acquire charge by hybridizing with the graphene Dirac band. Using ab initio calculations to determine the parameters of our low-energy model, we provide a microscopic theory of anomalous QOs with a non-LK temperature dependence consistent with our measurements. We show how remnants of fractionalized spin excitations can give rise to characteristic signatures in QO experiments.

We investigate, using numerical simulations, the conformations of isolated active ring polymers. We find that their behavior depends crucially on their size: Short rings ($N\lesssim 100$) swell, whereas longer rings ($N\gtrsim 200$) collapse, at sufficiently high activity. By investigating the nonequilibrium process leading to the steady state, we find a universal route driving both outcomes; we highlight the central role of steric interactions, at variance with linear chains, and of topology conservation. We further show that the collapsed rings are arrested by looking at different observables, all underlining the presence of an extremely long timescales at the steady state, associated with the internal dynamics of the collapsed section. Finally, we found that in some circumstances the collapsed state spins about its axis.

Recommendations around epidemics tend to focus on individual behaviors, with much less efforts attempting to guide event cancellations and other collective behaviors since most models lack the higher-order structure necessary to describe large gatherings. Through a higher-order description of contagions on networks, we model the impact of a blanket cancellation of events larger than a critical size and find that epidemics can suddenly collapse when interventions operate over groups of individuals rather than at the level of individuals. We relate this phenomenon to the onset of mesoscopic localization, where contagions concentrate around dominant groups.

Pseudo-entropy is an interesting quantity with a simple gravity dual, which generalizes entanglement entropy such that it depends on both an initial and a final state. Here we reveal the basic properties of pseudo-entropy in quantum field theories by numerically calculating this quantity for a set of two-dimensional free-scalar field theories and the Ising spin chain. We extend the Gaussian method for pseudo-entropy in free-scalar theories with two parameters: mass $m$ and dynamical exponent $z$. This computation finds two novel properties of pseudo-entropy which we conjecture to be universal in field theories, in addition to an area law behavior. One is a saturation behavior and the other one is nonpositivity of the difference between pseudo-entropy and averaged entanglement entropy. Moreover, our numerical results for the Ising chain imply that pseudo-entropy can play a role as a new quantum order parameter which detects whether two states are in the same quantum phase or not.

The first direct experimental observation of an electric quadrupole ($E2$) absorption transition between bound states of an atomic negative ion has been made. The transition was observed in the negative ion of bismuth by resonant ($1+1$) photon detachment from ${\mathrm{Bi}}^{-}$ via ${}^3{P}_2\to {}^3{P}_0$ excitation. The $E2$ transition properties were completely independently calculated using a hybrid theoretical approach to account for the strong multilevel electron interactions and relativistic effects. The experimental and ab initio theoretical results are in excellent agreement, providing valuable new insight into this complex system and forbidden transitions in negative ions more generally.

We study the correlated transport of photons through a chain of three-level emitters that are coupled chirally to a photonic mode of a waveguide. It is found that this system can transfer a weak classical input into a strongly correlated state of light in a unitary manner. Our analysis reveals two-photon scattering eigenstates, that are akin to Fano resonances or shape resonances in particle collisions and facilitate the emergence of antibunched light with long-range correlations upon crossing a critical length of the chain. By operating close to conditions of electromagnetically induced transparency of the three-level medium, a high degree of antibunching and photon transmission can be maintained in the presence of moderate losses. These features suggest a promising mechanism for single-photon generation and may open the door to exploring correlated quantum many-body states of light with repulsively interacting photons.

We report empirical observations of magnetic island heteroclinic bifurcation for the first time. This behavior is observed in interacting coupled $2/1$ tearing modes in the core of a DIII-D tokamak plasma. Poincaré maps constrained by measured magnetic amplitudes and phasing show bifurcation from heteroclinic to homoclinic topology in the $2/1$ island as the $4/2$ relative amplitude ($R_{4/2}$) decreases. Initially, the local electron temperature peak in the $2/1$ island splits, consistent with two $O$ points. As $R_{4/2}$ decreases a single peak forms, consistent with one $O$ point. These call for developing tearing stability theory and control solutions for heteroclinic islands in tokamaks.

Under uniaxial shock compression, the steepness of the plastic shock front usually exhibits power law characteristics with the Hugoniot pressure, also known as the “Swegle-Grady law.” In this Letter, we show that the Swegle-Grady law can be described better by a third power law rather than the classical fourth power law at the strain rate between ${10}^5–{10}^7{\mathrm{s}}^{-1}$. A simple dislocation-based continuum model is developed, which reproduced the third power law and revealed very good agreement with recent experiments of multiple types of metals quantitatively. New insights into this unusual macroscopic phenomenon are presented through quantifying the connection between the macroscopic mechanical response and the collective dynamics of dislocation assembles. It is found that the Swegle-Grady law results from the particular stress dependence of the plasticity behaviors, and that the difference between the third power scaling and the classical fourth power scaling results from different shock dissipative actions.

We characterize metrologically useful multipartite entanglement by representing partitions with Young diagrams. We derive entanglement witnesses that are sensitive to the shape of Young diagrams and show that Dyson’s rank acts as a resource for quantum metrology. Common quantifiers, such as the entanglement depth and $k$-separability are contained in this approach as the diagram’s width and height. Our methods are experimentally accessible in a wide range of atomic systems, as we illustrate by analyzing published data on the quantum Fisher information and spin-squeezing coefficients.

The first observation of the suppressed semileptonic $B_s^0\to K^{-}{\mu }^{+}{\nu }_{\mu }$ decay is reported. Using a data sample recorded in $pp$ collisions in 2012 with the LHCb detector, corresponding to an integrated luminosity of $2{\mathrm{fb}}^{-1}$, the branching fraction $\mathcal{B}(B_s^0\to K^{-}{\mu }^{+}{\nu }_{\mu })$ is measured to be $[1.06\pm 0.05(\mathrm{stat})\pm 0.08(\mathrm{syst})]\times {10}^{-4}$, where the first uncertainty is statistical and the second one represents the combined systematic uncertainties. The decay $B_s^0\to D_s^{-}{\mu }^{+}{\nu }_{\mu }$, where $D_s^{-}$ is reconstructed in the final state $K^{+}{K}^{-}{\pi }^{-}$, is used as a normalization channel to minimize the experimental systematic uncertainty. Theoretical calculations on the form factors of the $B_s^0\to K^{-}$ and $B_s^0\to D_s^{-}$ transitions are employed to determine the ratio of the Cabibbo-Kobayashi-Maskawa matrix elements $|V_{ub}|/|V_{cb}|$ at low and high $B_s^0\to K^{-}$ momentum transfer.

The quark structure of the $f_2(1270)$ meson has, for many years, been assumed to be a pure quark-antiquark ($q\overline{q}$) resonance with quantum numbers $J^{\mathrm{PC}}=2^{++}$. Recently, it was proposed that the $f_2(1270)$ is a molecular state made from the attractive interaction of two $\rho$ mesons. Such a state would be expected to decay strongly to final states with charged pions due to the dominant decay $\rho \to {\pi }^{+}{\pi }^{-}$, whereas decay to two neutral pions would likely be suppressed. Here, we measure for the first time the reaction $\gamma p\to {\pi }^0{\pi }^{0}p$, using the CEBAF Large Acceptance Spectrometer detector at Jefferson Lab for incident beam energies between 3.6 and 5.4 GeV. Differential cross sections, $d\sigma /dt$, for $f_2(1270)$ photoproduction are extracted with good precision due to low backgrounds and are compared to theoretical calculations.

We compute the color-singlet and color-octet nonrelativistic QCD (NRQCD) long-distance matrix elements for inclusive production of $P$-wave quarkonia in the framework of potential NRQCD. In this way, the color-octet NRQCD long-distance matrix element can be determined without relying on measured cross section data, which has not been possible so far. We obtain inclusive cross sections of ${\chi }_{cJ}$ and ${\chi }_{bJ}$ at the LHC, which are in good agreement with data. In principle, the formalism developed in this Letter can be applied to all inclusive production processes of heavy quarkonia.

We investigate the differential ionization probability of chiral molecules in the strong-field regime as a function of the helicity of the incident light. To this end, we analyze the fourfold ionization of bromochlorofluoromethane (CHBrClF) with subsequent fragmentation into four charged fragments and different dissociation channels of the singly ionized methyloxirane. By resolving for the molecular orientation, we show that the photoion circular dichroism signal strength is increased by 2 orders of magnitude.