In this work, we investigate the decays of the fully open-flavor tetraquark state $X_0(2900)$ which was observed by the LHCb collaboration very recently. By using an effective Lagrangian approach, the partial widths of $X_0(2900)$ are estimated, where $X_0(2900)$ is assumed to be an $S$-wave ${\overline{D}}^{*}{K}^{*}$ hadronic molecule with $I=0$. It is found that the estimated results are in agreement with the experimental observations. Moreover, we also predict the decay behaviors of the other unobserved ${\tilde{X}}_{J(J=1,2)}$, which are the spin partners of the $X_0(2900)$ in the $S$-wave ${\overline{D}}^{*}{K}^{*}$ picture. It is pointed out that the ${\tilde{X}}_1$ state with $I=0$ is a broad state with the width more than 100 MeV, while another ${\tilde{X}}_2$ state with $I=0$ is a narrow state with the width approaching half of that for the $X_0(2900)$. In addition, our results also show that the ${\overline{D}}^{*}K$ mode is expected to be the dominant decay mode for both ${\tilde{X}}_1$ and ${\tilde{X}}_2$. Searching for those unobserved ${\tilde{X}}_{J(J=1,2)}$ in the future experiments might be helpful to understand the nature of $X_0(2900)$.

We measure the time-dependent $CP$ violation parameters in $B^0\to K_S^0{K}_S^0{K}_S^0$ decays using $772\times {10}^{6}B\overline{B}$ pairs collected at the $\mathrm{\Upsilon }(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. The obtained mixing-induced and direct $CP$ asymmetries are $-0.71\pm 0.23(\mathrm{stat})\pm 0.05(\mathrm{syst})$ and $0.12\pm 0.16(\mathrm{stat})\pm 0.05(\mathrm{syst})$, respectively. These values are consistent with the Standard Model predictions. The significance of $CP$ violation differs from zero by 2.5 standard deviations.

Searching for axion dark matter, the ADMX Collaboration acquired data from January to October 2018, over the mass range $2.81–3.31\mathrm{\mu }\mathrm{eV}$, corresponding to the frequency range 680–790 MHz. Using an axion haloscope consisting of a microwave cavity in a strong magnetic field, the ADMX experiment excluded Dine-Fischler-Srednicki-Zhitnisky (DFSZ) axions at 90% confidence level and 100% dark matter density over this entire frequency range, except for a few gaps due to mode crossings. This paper explains the full ADMX analysis for run 1B, motivating analysis choices informed by details specific to this run.

The curvature parameter tension between Planck 2018, cosmic microwave background (CMB) lensing, and baryon acoustic oscillation (BAO) data is measured using the suspiciousness statistic to be $2.5–3\sigma$. Conclusions regarding the spatial curvature of the Universe which stem from the combination of these data should therefore be viewed with suspicion. Without CMB lensing or BAO, Planck 2018 has a moderate preference for closed universes, with Bayesian betting odds of over $50:1$ against a flat universe and over $2000:1$ against an open universe.

We present concrete construction of interior operators for a black hole which is perturbed by an infalling observer. The construction is independent from the initial states of the black hole while dependent only on the quantum state of the infalling observer. The construction has a natural interpretation from the perspective of the boundary operator’s growth, resulting from the collision between operators accounting for the infalling and outgoing modes. The interior partner modes are created once the infalling observer measures the outgoing mode, suggesting that the black hole interior is observer dependent. Implications of our results on various conceptual puzzles, including the firewall puzzle, the Marolf-Wall puzzle, and the information problem, are discussed. Explicit counterarguments against the $\mathrm{ER}=\mathrm{EPR}$ approach by Maldacena and Susskind are also presented.

We discuss particle production associated with vacuum decay, which changes the mass of a scalar field coupled to a background field which induces the decay. By utilizing the Stokes phenomenon, we can optimally track the time evolution of the mode function and hence calculate particle production properly. In particular, we use real time formalisms for vacuum decay in Minkowski and de Sitter spacetime together with the Stokes phenomenon method. For each case, we consider the flyover vacuum decay model and stochastic inflation, respectively. Within the real time formalism, the particle production can be viewed as that caused by nontrivial external fields. This gives us a novel perspective of the real time formalism of vacuum decay.

We study the vacuum interaction of a scalar field and two concentric spheres defined by a singular potential on their surfaces. The potential is a linear combination of the Dirac $\delta$ and its derivative. The presence of the delta prime term in the potential causes that it behaves differently when it is seen from the inside or from the outside of the sphere. We study different cases for positive and negative values of the delta prime coupling, keeping positive the coupling of the delta. As a consequence, we find regions in the space of couplings, where the energy is positive, negative or zero. Moreover, the sign of the ${\delta }^{\prime }$ couplings cause different behavior on the value of the Casimir energy for different values of the radii. This potential gives rise to general boundary conditions with limiting cases defining Dirichlet and Robin boundary conditions what allows us to simulate purely electric or purely magnetic spheres.

We present a $3+1$ formulation of the effective field theory framework called the standard model extension in the gravitational sector. The explicit local Lorentz and diffeomorphism symmetry breaking assumption is adopted, and we perform a Dirac-Hamiltonian analysis. We show that the structure of the dynamics presents significant differences from general relativity and other modified gravity models. We explore Hamilton’s equations for some special choices of the coefficients. Our main application is cosmology, and we present the modified Friedmann equations for this case. The results show some intriguing modifications to standard cosmology. In addition, we compare our results to existing frameworks and models, and we comment on the potential impact to other areas of gravitational theory and phenomenology.

Recent work on the Szekeres inhomogeneous cosmological models uncovered a surprising rotation effect. Hellaby showed that the angular $(\theta ,\varphi )$ coordinates do not have a constant orientation, while Buckley and Schlegel provided explicit expressions for the rate of rotation from shell to shell, as well as the rate of tilt when the 3-space is embedded in a flat 4-d Euclidean space. We here investigate some properties of this embedding, for the quasispherical recollapsing case, and use it to show that the two sets of results are in complete agreement. We also show how to construct Szekeres models that are closed in the “radial” direction, and hence have a “natural” embedded torus topology. Several explicit models illustrate the embedding as well as the shell rotation and tilt effects.

We investigate the possibility that axionlike particles (ALPs) with various potentials account for the isotropic birefringence recently reported by analyzing the Planck 2018 polarization data. For the quadratic and cosine potentials, we obtain lower bounds on the mass, coupling constant to photon $g$, abundance and equation of state of the ALP to produce the observed birefringence. Especially when the ALP is responsible for dark energy, it is possible to probe the tiny deviation of dark energy equation of state from $-1$ through the cosmic birefringence. We also explore ALPs working as early dark energy (EDE), which alleviates the Hubble tension problem. Since the other parameters are limited by the EDE requirements, we narrow down the ALP-photon coupling to ${10}^{-19}{\mathrm{GeV}}^{-1}\lesssim g\lesssim {10}^{-16}{\mathrm{GeV}}^{-1}$ for the decay constant $f=M_{\mathrm{pl}}$. Therefore, the Hubble tension and the isotropic birefringence imply that $g$ is typically the order of $f^{-1}$, which is a nontrivial coincidence.

When transient events are observed with multiple sensors, it is often necessary to establish the significance of coincident events. We derive a universal null test for an arbitrary number of sensors motivated by the archetypal detection problem for independent Poisson-distributed events in gravitational-wave detectors such as LIGO and Virgo. In these detectors, transient events may be witnessed by myriad channels that record interferometric signals and the surrounding physical environment. We apply our null test to a broad set of simulated gravitational-wave events as well as to a real gravitational-wave detection to determine which auxiliary channels do and do not witness real gravitational waves, and therefore which are safe to use when constructing vetoes. We also describe how our approach can be used to study detector artifacts and their origin, as well as to quantify the statistical independence of candidate gravitational-wave signals from noise artifacts observed in auxiliary channels.

We investigate unpolarized and polarized gluon distributions and their applications to the Ioffe-time distributions, which are related to lattice QCD calculations of parton distribution functions. Guided by the counting rules based on the perturbative QCD at large momentum fraction $x$ and the color coherence of gluon couplings at small $x$, we parametrize gluon distributions in the helicity basis. By fitting the unpolarized gluon distribution, the inferred polarized gluon distribution from our parametrization agrees with the one from global analysis. A simultaneous fit to both unpolarized and polarized gluon distributions is also performed to explore the model uncertainty. The agreement with the global analysis supports the ($1-x$) power suppression of the helicity-antialigned distribution relative to the helicity-aligned distribution. The corresponding Ioffe-time distributions and their asymptotic expansions are calculated from the gluon distributions. Our results of the Ioffe-time distributions can provide guidance to the extrapolation of lattice QCD data to the region lacking precise gluonic matrix elements. Therefore, they can help regulate the ill-posed inverse problem associated with extracting the gluon distributions from discrete data from first-principle calculations, which are available in a limited range of the nucleon momentum and the spatial separation between the gluonic currents. Given various limitations in obtaining lattice QCD data at large Ioffe time, phenomenological approaches can provide important complementary information to extract the gluon distributions in the entire momentum fraction region, especially at small $x$. The possibility of investigating higher-twist effects and other systematic uncertainties in the contemporary first-principle calculations of parton distributions from phenomenologically well-determined Ioffe-time distributions in the large Ioffe-time region is also discussed.

Many particle physics models for dark matter self-interactions—motivated to address long-standing challenges to the collisionless cold dark matter paradigm—fall within the semiclassical regime, with interaction potentials that are long range compared to the de Broglie wavelength for dark matter particles. In this work, we present a quantum-mechanical derivation and new analytic formulas for the semiclassical momentum transfer and viscosity cross sections for self-interactions mediated by a Yukawa potential. Our results include the leading quantum corrections beyond the classical limit and allow for both distinguishable and identical dark matter particles. Our formulas supersede the well-known formulas for the momentum transfer cross section obtained from the classical scattering problem, which are often used in phenomenological studies of self-interacting dark matter. Together with previous approximation formulas for the cross section in the quantum regime, our new results allow for nearly complete analytic coverage of the parameter space for self-interactions with a Yukawa potential. We also discuss the phenomenological implications of our results and provide a new velocity-averaging procedure for constraining velocity-dependent self-interactions. Our results have been implemented in the newly released code CLASSICS.

We present a testable mechanism of low-scale baryogenesis and dark matter production in which neither the baryon nor lepton number are violated. Charged $D$ mesons are produced out of equilibrium at tens of MeV temperatures. The $D$ mesons quickly undergo $CP$-violating decays to charged pions, which then decay into dark-sector leptons without violating the lepton number. To transfer this lepton asymmetry to the baryon asymmetry, the dark leptons scatter on additional dark-sector states charged under the lepton and baryon number. Amusingly, this transfer proceeds without electroweak sphalerons, which are no longer active at such low scales. We present two example models which can achieve this transfer while remaining consistent with current limits. The required amount of $CP$ violation in charged $D$ meson decays, while currently allowed, will be probed by colliders. Additionally, the relevant decays of charged pions to dark-sector leptons have been constrained by the PIENU and Paul Scherrer Institute experiments and will be further explored in upcoming experiments.

The phase diagram of the Gross-Neveu model in $2+1$ space-time dimensions at nonzero temperature and chemical potential is studied in the limit of infinitely many flavors, focusing on the possible existence of inhomogeneous phases, where the order parameter $\sigma$ is nonuniform in space. To this end, we analyze the stability of the energetically favored homogeneous configuration $\sigma (\mathbf{x})=\overline{\sigma }=\text{const}$ with respect to small inhomogeneous fluctuations, employing lattice field theory with two different lattice discretizations as well as a continuum approach with Pauli-Villars regularization. Within lattice field theory, we also perform a full minimization of the effective action, allowing for arbitrary 1-dimensional modulations of the order parameter. For all methods special attention is paid to the role of cutoff effects. For one of the two lattice discretizations, no inhomogeneous phase was found. For the other lattice discretization and within the continuum approach with a finite Pauli-Villars cutoff parameter $\mathrm{\Lambda }$, we find a region in the phase diagram where an inhomogeneous order parameter is favored. This inhomogeneous region shrinks, however, when the lattice spacing is decreased or $\mathrm{\Lambda }$ is increased, and finally disappears for all nonzero temperatures when the cutoff is removed completely. For vanishing temperature, we find hints for a degeneracy of homogeneous and inhomogeneous solutions, in agreement with earlier findings.

The pentaquark states $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$ could be nicely arranged into a multiplet of seven molecules of ${\overline{D}}^{(*)}{\mathrm{\Sigma }}_c^{(*)}$ dictated by heavy quark spin symmetry. However, the spins of $P_c(4440)$ and $P_c(4457)$ are not yet fully determined. We employ the contact-range effective field theory to investigate the SU(3)-flavor counterparts of ${\overline{D}}^{(*)}{\mathrm{\Sigma }}_c^{(*)}$ and study the possibility of whether their discovery could help determine the spins of $P_c(4457)$ and $P_c(4440)$. We find the existence of a complete hidden charm strange multiplet of ${\overline{D}}^{(*)}{\mathrm{\Xi }}_c^{(\prime )*}$ molecules, irrespective of the spins of $P_c(4440)$ and $P_c(4457)$. On the other hand, we find that although molecules of ${\overline{D}}^{(*)}{\mathrm{\Xi }}_c$ are also likely, depending on the realization of the underlying dynamics, their discovery could be more useful for determining the spins of $P_c(4440)$ and $P_c(4457)$ and for telling us how heavy quark and light quark interactions depend on the spin of the light quark pair.

We investigate roads for evaluating model-independent cross-section-distribution functions for the sequential-hyperon decay ${\mathrm{\Sigma }}^0\to \mathrm{\Lambda }\gamma$; $\mathrm{\Lambda }\to p{\pi }^{-}$ and its corresponding antihyperon decay. The ${\mathrm{\Sigma }}^0$ and ${\overline{\mathrm{\Sigma }}}^0$ hyperons are produced in the reaction $e^{+}{e}^{-}\to J/\psi \to {\overline{\mathrm{\Sigma }}}^0{\mathrm{\Sigma }}^0$. Cross-section-distribution functions are calculated using the folding technique, but a comparison with results using the helicity technique is also made.

Massive bosonic fields in the background of a Kerr black hole can either trigger superradiant instabilities (black-hole bombs) or form equilibrium configurations corresponding to pure bound states, known as stationary scalar clouds. Here, similar phenomena are shown to emerge in the fluctuation dynamics of a rotating photon-fluid model. In the presence of suitable vortex flows, the density fluctuations are governed by the massive Klein-Gordon equation on a ($2+1$) curved spacetime, possessing an ergoregion and an event horizon. We report on superradiant instabilities originating from quasibound phonon states trapped by the vortex background and, remarkably, on the existence of stationary modes in synchronous rotation with the horizon. These represent the acoustic counterpart of astrophysical scalar clouds. Our system offers a promising platform for analogue gravity experiments on superradiant instabilities of massive bosons and black-hole-field equilibrium configurations.

In this paper the scattering between a wobbling kink and a wobbling antikink in the standard ${\varphi }^4$ model is numerically investigated. The dependence of the final velocities, wobbling amplitudes and frequencies of the scattered kinks on the collision velocity and on the initial wobbling amplitude is discussed. The fractal structure becomes more intricate due to the emergence of new resonance windows and the splitting of those arising in the nonexcited kink scattering. Outside this phase the final wobbling amplitude exhibits a linear dependence of the collision velocity, which is almost independent of the initial wobbling amplitude.