Dark matter (DM) may belong to a hidden sector (HS) that is only feebly interacting with the standard model (SM) and may have never been in thermal equilibrium in the early Universe. In this case, the observed abundance of dark matter particles could have built up through a process known as freeze-in. We show that, for the first time, direct detection experiments are testing this DM production mechanism. This applies to scenarios where SM and HS communicate through a light mediator of mass less than a few MeV. Through the exchange of such a light mediator, the very same feebly interacting massive particles can have self-interactions that are in the range required to address the small scale structure issues of collisionless cold DM.

Sign problems in path integrals arise when different field configurations contribute with different signs or phases. Phase unwrapping describes a family of signal processing techniques in which phase differences between elements of a time series are integrated to construct noncompact unwrapped phase differences. By combining phase unwrapping with a cumulant expansion, path integrals with sign problems arising from phase fluctuations can be systematically approximated as linear combinations of path integrals without sign problems. This work explores phase unwrapping in zero-plus-one-dimensional complex scalar field theory. Results with improved signal-to-noise ratios for the spectrum of scalar field theory can be obtained from unwrapped phases, but the size of cumulant expansion truncation errors is found to be undesirably sensitive to the parameters of the phase unwrapping algorithm employed. It is argued that this numerical sensitivity arises from discretization artifacts that become large when phases fluctuate close to singularities of a complex logarithm in the definition of the unwrapped; phase.

Parton distribution functions (PDFs) are nonperturbative quantities describing the relation between a hadron and the quarks and gluons within it. We propose to extract PDFs from QCD global analysis of “data” generated by lattice QCD calculations of good “lattice cross sections,” which are basically single-hadron matrix elements that are lattice QCD calculable and perturbative QCD factorizable into the PDFs. To demonstrate the existence of good “lattice cross sections,” we take quasiquark distribution introduced by Ji [Phys. Rev. Lett. 110, 262002 (2013)] as a case study to show that it could be factorized into the PDFs to all orders in perturbation theory if it can be multiplicatively renormalized. We calculate the factorized coefficients at the next-to-leading order in ${\alpha }_s$.

Transversity generalized parton distributions (GPDs) appear as scalar functions in the decomposition of off-forward quark-quark and gluon-gluon correlators with a parton helicity flip. For a spin 1 hadron, we find nine transversity GPDs for both quarks and gluons at leading twist 2. We study these twist-2 chiral odd quark transversity GPDs for the deuteron in a light cone convolution model, based on the impulse approximation, and using the lowest Fock-space state for the deuteron.

Since the dual fermion condensate be used to describe the center symmetry Z, we extend it to thermal ${\mathrm{QED}}_3$ and study the deconfinement phase transition by the truncated Dyson-Schwinger equation for the massive fermion propagator at finite temperature. We show that, for a massive fermion, the system first appears as a deconfinement phase transition with the increase of temperature and then the chiral symmetry is restored and the corresponding temperature of the deconfinement phase transition increases with the enlargement of the fermion mass. It should be pointed out here that the results obtained in this paper are not model independent but are heavily dependent on the truncated Dyson-Schwinger equation we have chosen.

We study the negative modes of gravitational instantons representing vacuum decay in asymptotically flat space-time. We consider two different vacuum decay scenarios: the Coleman-de Luccia O(4)-symmetric bubble, and $\mathrm{O}(3)\times \mathbb{R}$ instantons with a static black hole. In spite of the similarities between the models, we find qualitatively different behaviors. In the O(4)-symmetric case, the number of negative modes is known to be either one or infinite, depending on the sign of the kinetic term in the quadratic action. In contrast, solving the mode equation numerically for the static black hole instanton, we find only one negative mode with the kinetic term always positive outside the event horizon. The absence of additional negative modes supports the interpretation of these solutions as giving the tunneling rate for false vacuum decay seeded by microscopic black holes.

We present a new parametrization for the equation of state (EoS) ${\omega }_X=P_X/{\rho }_X$, which can reproduce a $f(R)$-like evolution with a precision between [0.5%–0.8%] over the numerical solutions. Also, our proposal can render a variety of popular $f(R)$ models that are considered as viable candidates for the cosmic late time acceleration. By using observational data from baryonic acoustic oscillations, supernovae and cosmic chronometers we investigate the constraints on the new EoS parameters. This proposal set an EoS formulation which can be used in an efficient way and makes a good candidate to be implemented in a variety of surveys in order to test the $f(R)$ generic behavior.

Macroscopic evolution of relativistic charged matter with chirality imbalance is described by the chiral magnetohydrodynamics (chiral MHD). One such astrophysical system is high-density lepton matter in core-collapse supernovae where the chirality imbalance of leptons is generated by the parity-violating weak processes. After developing the chiral MHD equations for this system, we perform numerical simulations for the real-time evolutions of magnetic and flow fields and study the properties of the chiral MHD turbulence. In particular, we observe the inverse cascade of the magnetic energy and the fluid kinetic energy. Our results suggest that the chiral effects that have been neglected so far can reverse the turbulent cascade direction from direct to inverse cascade, which would impact the magnetohydrodynamics evolution in the supernova core toward explosion.

We consider the system of relativistic fermions in the presence of rotation. The rotation is set up as an enhancement of the angular momentum. In this approach the angular velocity for the angular momentum plays the same role as the chemical potential for density. We calculate the axial current using the direct solutions of the Dirac equation with the MIT bag boundary conditions. Next, we consider the alternative way of the rotation description, in which the local velocity of the substance multiplied by the chemical potential serves as the effective gauge field. In this approach it is possible to relate the axial current of the chiral vortical effect for the massless fermions to the topological invariant in momentum space, which is robust to the introduction of interactions. We compare the results for the axial current obtained using the two above-mentioned approaches.

If the space of minima of the effective potential of a weakly coupled 2d quantum field theory is not connected, then a mass-gap will be nonperturbatively generated. As examples, we consider two $\sigma$ models compactified on a small circle with twisted boundary conditions. In the compactified ${\mathbb{CP}}^1$ model, the vacuum manifold consists of two points and the mass-gap is nonperturbative. In the case of the compactified SU(2) principal chiral model, the vacuum manifold is a single circle and the mass-gap is perturbative.

We study the expected spin misalignments of merging binary black holes formed in isolation by combining state-of-the-art population-synthesis models with efficient post-Newtonian evolutions, thus tracking sources from stellar formation to gravitational-wave detection. We present extensive predictions of the properties of sources detectable by both current and future interferometers. We account for the fact that detectors are more sensitive to spinning black-hole binaries with suitable spin orientations and find that this significantly impacts the population of sources detectable by LIGO, while this is not the case for third-generation detectors. We find that three formation pathways, differentiated by the order of core collapse and common-envelope phases, dominate the observed population, and that their relative importance critically depends on the recoils imparted to black holes at birth. Our models suggest that measurements of the “effective-spin” parameter ${\chi }_{\mathrm{eff}}$ will allow for powerful constraints. For instance, we find that the role of spin magnitudes and spin directions in ${\chi }_{\mathrm{eff}}$ can be largely disentangled, and that the symmetry of the effective-spin distribution is a robust indicator of the binary’s formation history. Our predictions for individual spin directions and their precessional morphologies confirm and extend early toy models, while exploring substantially more realistic and broader sets of initial conditions. Our main conclusion is that specific subpopulations of black-hole binaries will exhibit distinctive precessional dynamics: these classes include (but are not limited to) sources where stellar tidal interactions act on sufficiently short timescales, and massive binaries produced in pulsational pair-instability supernovae. Measurements of black-hole spin orientations have enormous potential to constrain specific evolutionary processes in the lives of massive binary stars.

Catalogs of stellar-mass compact binary systems detected by ground-based gravitational-wave instruments (such as Advanced LIGO and Advanced Virgo) will offer insights into the demographics of progenitor systems and the physics guiding stellar evolution. Existing techniques approach this through phenomenological modeling, discrete model selection, or model mixtures. Instead, we explore a novel technique that mines gravitational-wave catalogs to directly infer posterior probability distributions of the hyperparameters describing formation and evolutionary scenarios (e.g., progenitor metallicity, kick parameters, and common-envelope efficiency). We use a bank of compact-binary population-synthesis simulations to train a Gaussian-process emulator that acts as a prior on observed parameter distributions (e.g., chirp mass, redshift, rate). This emulator slots into a hierarchical population inference framework to extract the underlying astrophysical origins of systems detected by Advanced LIGO and Advanced Virgo. Our method is fast, easily expanded with additional simulations, and can be adapted for training on arbitrary population-synthesis codes, as well as different detectors like LISA.

We study the $\overline{K}\mathrm{\Xi }$ decay mode of the newly observed $\mathrm{\Omega }(2012)$ assuming that the $\mathrm{\Omega }(2012)$ is a dynamically generated state with spin parity $J^P=3/2^{-}$ from the coupled channel $S$-wave interactions of $\overline{K}\mathrm{\Xi }(1530)$ and $\eta \mathrm{\Omega }$. In addition, we calculate its three-body decay width into $K\pi \mathrm{\Xi }$. It is shown that the so-obtained total decay width is in fair agreement with the experimental data. We compare our results with those of other recent studies and highlight the differences among them.

A dynamical investigation of the nucleon-nucleon ($NN$) interaction by using the resonating group method (RGM) in a chiral SU(3) quark model has been revisited. The considered quark-quark interaction includes, besides the one-gluon exchange (OGE) and the phenomenological confinement potential, the nonet scalar and pseudoscalar meson exchanges derived from the spontaneous SU(3) chiral symmetry breaking. The physical consistency requirement that the wave functions of single baryons satisfy the minimums of the Hamiltonian has been strictly imposed in determination of the model parameters. The calculated masses of the octet and decuplet baryon ground states, the binding energy of the deuteron, and the $NN$ scattering phase shifts up to a total angular momentum $J=6$ are in satisfactory agreement with the experiments.

We discuss the associated production of a top quark with a photon via anomalous $t\text{−}q\text{−}\gamma$ couplings, and present higher-order corrections from soft-gluon emission for the processes $gq\to t\gamma$ at LHC energies. We perform soft-gluon resummation at next-to-leading-logarithm accuracy and derive approximate next-to-next-to-leading-order (aNNLO) double-differential cross sections. We calculate at aNNLO the total $t\gamma$ production cross sections and the top-quark transverse-momentum and rapidity distributions for various LHC energies, and show that the soft-gluon corrections are large and dominant in these processes.

We use the Polyakov-loop extended two-flavor quark-meson model as a low-energy effective model for QCD to study the phase diagram in the ${\mu }_I–T$ plane where ${\mu }_I$ is the isospin chemical potential. In particular, we focus on the Bose condensation of charged pions. At $T=0$, the onset of pion condensation is at ${\mu }_I=\frac{1}{2}{m}_{\pi }$ in accordance with exact results. The phase transition to a Bose-condensed phase is of second order for all values of ${\mu }_I$ and in the $O(2)$ universality class. The chiral critical line joins the critical line for pion condensation at a point whose position depends on the Polyakov-loop potential and the sigma mass. For larger values of ${\mu }_I$ these curves are on top of each other. The deconfinement line enters smoothly the phase with the broken $O(2)$ symmetry. We compare our results with recent lattice simulations and find overall good agreement.

Using $1.31\times {10}^{9}J/\psi$ events collected by the BESIII detector at the BEPCII $e^{+}{e}^{-}$ collider, we report the first observation of the $h_1(1380)$ in $J/\psi \to {\eta }^{\prime }{h}_1(1380)$ with a significance of more than ten standard deviations. The mass and width of the possible axial-vector strangeonium candidate $h_1(1380)$ are measured to be $M=(1423.2\pm 2.1\pm 7.3)\mathrm{MeV}/c^2$ and $\mathrm{\Gamma }=(90.3\pm 9.8\pm 17.5)\mathrm{MeV}$. The product branching fractions, assuming no interference, are determined to be $\mathcal{B}(J/\psi \to {\eta }^{\prime }{h}_1(1380))\times \mathcal{B}(h_1(1380)\to K^{*}(892{)}^{+}{K}^{-}+\mathrm{c}.\mathrm{c}.)=(1.51\pm 0.09\pm 0.21)\times {10}^{-4}$ in ${\eta }^{\prime }{K}^{+}{K}^{-}{\pi }^0$ mode and $\mathcal{B}(J/\psi \to {\eta }^{\prime }{h}_1(1380))\times \mathcal{B}(h_1(1380)\to K^{*}(892)\overline{K}+\mathrm{c}.\mathrm{c}.)=(2.16\pm 0.12\pm 0.29)\times {10}^{-4}$ in ${\eta }^{\prime }{K}_S^0{K}^{\pm }{\pi }^{\mp }$ mode. The first uncertainties are statistical and the second are systematic. Isospin symmetry violation is observed in the decays $h_1(1380)\to K^{*}(892{)}^{+}{K}^{-}+\mathrm{c}.\mathrm{c}.$ and $h_1(1380)\to K^{*}(892{)}^0{\overline{K}}^0+\mathrm{c}.\mathrm{c}.$. Based on the measured $h_1(1380)$ mass, the mixing angle between the states $h_1(1170)$ and $h_1(1380)$ is determined to be $(35.9\pm 2.6)°$, consistent with theoretical expectations.

The Sachdev-Ye-Kitaev (SYK) model attracts attention in the context of information scrambling, which represents delocalization of quantum information and is quantified by the out-of-time-ordered correlators (OTOC). The SYK model contains $N$ fermions with disordered and four-body interactions. Here, we introduce a variant of the SYK model, which we refer to as the Wishart SYK model. We investigate the Wishart SYK model for complex fermions and that for hard-core bosons. We show that the ground state of the Wishart SYK model is massively degenerate and the residual entropy is extensive, and that the Wishart SYK model for complex fermions is integrable. In addition, we numerically investigate the OTOC and level statistics of the SYK models. At late times, the OTOC of the fermionic Wishart SYK model exhibits large temporal fluctuations, in contrast with smooth scrambling in the original SYK model. We argue that the large temporal fluctuations of the OTOC are a consequence of a small effective dimension of the initial state. We also show that the level statistics of the fermionic Wishart SYK model is in agreement with the Poisson distribution, while the bosonic Wishart SYK model obeys the gaussian unitary ensemble (GUE) or the gaussian orthogonal ensemble (GOE) distribution.