We study the evolution of cosmological perturbations in a nonsingular bouncing cosmology with a bounce phase which has superimposed oscillations of the scale factor. We identify length scales for which the final spectrum of fluctuations obtains imprints of the nontrivial bounce dynamics. These imprints in the spectrum manifest in the form of damped oscillation features at scales smaller than a characteristic value and an increased reddening of the spectrum at all the scales as the number of small bounces increases.

Light (pseudo-)scalar fields are promising candidates to be the dark matter in the Universe. Under certain initial conditions in the early Universe and/or with certain types of self-interactions, they can form compact dark-matter objects such as axion stars or $Q$-balls. Direct encounters with such objects can be searched for by using a global network of atomic magnetometers. It is shown that for a range of masses and radii not ruled out by existing observations, the terrestrial encounter rate with axion stars or $Q$-balls can be sufficiently high (at least once per year) for a detection. Furthermore, it is shown that a global network of atomic magnetometers is sufficiently sensitive to pseudoscalar couplings to atomic spins so that a transit through an axion star or $Q$-ball could be detected over a broad range of unexplored parameter space.

The study of heavy-light meson masses should provide a way to determine renormalized quark masses and other properties of heavy-light mesons. In the context of lattice QCD, for example, it is possible to calculate hadronic quantities for arbitrary values of the quark masses. In this paper, we address two aspects relating heavy-light meson masses to the quark masses. First, we introduce a definition of the renormalized quark mass that is free of both scale dependence and renormalon ambiguities, and discuss its relation to more familiar definitions of the quark mass. We then show how this definition enters a merger of the descriptions of heavy-light masses in heavy-quark effective theory and in chiral perturbation theory ($\chi \mathrm{PT}$). For practical implementations of this merger, we extend the one-loop $\chi \mathrm{PT}$ corrections to lattice gauge theory with heavy-light mesons composed of staggered fermions for both quarks. Putting everything together, we obtain a practical formula to describe all-staggered heavy-light meson masses in terms of quark masses as well as some lattice artifacts related to staggered fermions. In a companion paper, we use this function to analyze lattice-QCD data and extract quark masses and some matrix elements defined in heavy-quark effective theory.

One type of hidden charm pentaquark $P_{cs}$ with quark content $c\overline{c}uds$ in light-flavor singlet state is studied in the quark model. This state is analogous to the $P_c$ with $c\overline{c}uud$ in light-flavor octet, which was observed in LHC in 2015. Considering various combinations of color, spin, and light flavor as internal quantum numbers in $P_{cs}$, we investigate the mass ordering of the $P_{cs}$’s by adopting both the one-gluon exchange interaction and the instanton-induced interaction in the quark model. The most stable configuration of $P_{cs}$ is identified to be total spin $1/2$ in which the $c\overline{c}$ is combined to be color octet and spin 1, while the $uds$ cluster is in a color octet state. The other color octet configurations, the total spin $1/2$ state with the $c\overline{c}$ spin 0, and the state with total spin $3/2$ and $c\overline{c}$ spin 1, are found as excited states. We also discuss possible decay modes of these hidden charm pentaquarks.

The $\mathrm{\Xi }$ baryons are expected to be naturally narrower as compared to their nonstrange and strange counterparts since they have only one light quark and, thus, their decay involves producing either a light meson and doubly strange baryon or both meson and baryon with strangeness which involves, relatively, more energy. In fact, some $\mathrm{\Xi }$’s have full widths of the order of even 10–20 MeV when, in principle, they have a large phase space to decay to some open channels. Such is the case of $\mathrm{\Xi }(1690)$, for which the width has been found to be of the order of 10 MeV in the latest BABAR and BELLE data. In this manuscript we study why some $\mathrm{\Xi }$’s are so narrow. Based on a coupled channel calculation of the pseudoscalar meson-baryon and vector meson-baryon systems with chiral and hidden local symmetry Lagrangians, we find that the answer lies in the intricate hadron dynamics. We find that the known mass, width, spin-parity, and branching ratios of $\mathrm{\Xi }(1690)$ can be naturally explained in terms of coupled channel meson-baryon dynamics. We find another narrow resonance which can be related to $\mathrm{\Xi }(2120)$. We also look for exotic states ${\mathrm{\Xi }}^{+}$ and ${\mathrm{\Xi }}^{--}$ but find none. In addition we provide the cross sections for $\overline{K}\mathrm{\Lambda },\overline{K}\mathrm{\Sigma }\to \pi \mathrm{\Xi }$ which can be useful for understanding the enhanced yield of $\mathrm{\Xi }$ reported in recent studies of heavy ion collisions.

A semi-inclusive measurement of charged hadron multiplicities in deep inelastic muon scattering off an isoscalar target was performed using data collected by the COMPASS Collaboration at CERN. The following kinematic domain is covered by the data: photon virtuality $Q^2>1(\mathrm{GeV}/c{)}^2$, invariant mass of the hadronic system $W>5\mathrm{GeV}/c^2$, Bjorken scaling variable in the range $0.003<x<0.4$, fraction of the virtual photon energy carried by the hadron in the range $0.2<z<0.8$, and square of the hadron transverse momentum with respect to the virtual photon direction in the range $0.02(\mathrm{GeV}/c{)}^2<P_{\mathrm{hT}}^2<3(\mathrm{GeV}/c{)}^2$. The multiplicities are presented as a function of $P_{\mathrm{hT}}^2$ in three-dimensional bins of $x$, $Q^2$, $z$ and compared to previous semi-inclusive measurements. We explore the small-$P_{\mathrm{hT}}^2$ region, i.e. $P_{\mathrm{hT}}^2<1(\mathrm{GeV}/c{)}^2$, where hadron transverse momenta are expected to arise from nonperturbative effects, and also the domain of larger $P_{\mathrm{hT}}^2$, where contributions from higher-order perturbative QCD are expected to dominate. The multiplicities are fitted using a single-exponential function at small $P_{\mathrm{hT}}^2$ to study the dependence of the average transverse momentum $⟨P_{\mathrm{hT}}^2⟩$ on $x$, $Q^2$ and $z$. The power-law behavior of the multiplicities at large $P_{\mathrm{hT}}^2$ is investigated using various functional forms. The fits describe the data reasonably well over the full measured range.

Measurements of $ZZ$ production in the ${\ell }^{+}{\ell }^{-}{\ell }^{\prime +}{\ell }^{\prime -}$ channel in proton–proton collisions at 13 TeV center-of-mass energy at the Large Hadron Collider are presented. The data correspond to $36.1{\mathrm{fb}}^{-1}$ of collisions collected by the ATLAS experiment in 2015 and 2016. Here $\ell$ and ${\ell }^{\prime }$ stand for electrons or muons. Integrated and differential $ZZ\to {\ell }^{+}{\ell }^{-}{\ell }^{\prime +}{\ell }^{\prime -}$ cross sections with $Z\to {\ell }^{+}{\ell }^{-}$ candidate masses in the range of 66 GeV to 116 GeV are measured in a fiducial phase space corresponding to the detector acceptance and corrected for detector effects. The differential cross sections are presented in bins of twenty observables, including several that describe the jet activity. The integrated cross section is also extrapolated to a total phase space and to all standard model decays of $Z$ bosons with mass between 66 GeV and 116 GeV, resulting in a value of $17.3\pm 0.9[\pm 0.6(\mathrm{stat})\pm 0.5(\mathrm{syst})\pm 0.6(\mathrm{lumi})]\mathrm{pb}$. The measurements are found to be in good agreement with the standard model. A search for neutral triple gauge couplings is performed using the transverse momentum distribution of the leading $Z$ boson candidate. No evidence for such couplings is found and exclusion limits are set on their parameters.

We construct a new class of regular soliton solutions of the gauged planar Skyrme model on the target space $S^2$ with fractional topological charges in the scalar sector. These field configurations represent Skyrmed vortices; they have finite energy and carry topologically quantized magnetic flux $\mathrm{\Phi }=2\pi n$, where $n$ is an integer. Using a special version of the product ansatz as a guide, we obtain by numerical relaxation various multimeron solutions and investigate the pattern of interaction between the fractionally charged solitons. We show that, unlike the vortices in the Abelian Higgs model, the gauged merons may combine short-range repulsion and long-range attraction. Considering the strong gauge coupling limit, we demonstrate that the topological quantization of the magnetic flux is determined by the Poincaré index of the planar components ${\varphi }_{\perp }={\varphi }_1+i{\varphi }_2$ of the Skyrme field.

We put forward a new definition of complexity, for static and spherically symmetric self-gravitating systems, based on a quantity, hereafter referred to as complexity factor, that appears in the orthogonal splitting of the Riemann tensor, in the context of general relativity. We start by assuming that the homogeneous (in the energy density) fluid, with isotropic pressure is endowed with minimal complexity. For this kind of fluid distribution, the value of complexity factor is zero. So, the rationale behind our proposal for the definition of complexity factor stems from the fact that it measures the departure, in the value of the active gravitational mass (Tolman mass), with respect to its value for a zero complexity system. Such departure is produced by a specific combination of energy density inhomogeneity and pressure anisotropy. Thus, zero complexity factor may also be found in self-gravitating systems with inhomogeneous energy density and anisotropic pressure, provided the effects of these two factors, on the complexity factor, cancel each other. Some exact interior solutions to the Einstein equations satisfying the zero complexity criterium are found, and prospective applications of this newly defined concept, to the study of the structure and evolution of compact objects, are discussed.

The general form of the action growth for a large class of static black hole solutions in modified gravity which includes $F(R)$-gravity models is computed. The cases of black hole solutions with nonconstant Ricci scalar are also considered, generalizing the results previously found and valid only for black holes with constant Ricci scalar. An argument is put forward to provide a physical interpretation of the results, which seem tightly connected with the generalized second law of black hole thermodynamics.

$f(T)$ gravity theory offers an alternative context in which to consider gravitational interactions where torsion, rather than curvature, is the mechanism by which gravitation is communicated. We investigate the stability of the Kasner solution with several forms of the arbitrary Lagrangian function examined within the $f(T)$ context. This is a Bianchi type–I vacuum solution with anisotropic expansion factors. In the $f(T)$ gravity setting, the solution must conform to a set of conditions in order to continue to be a vacuum solution of the generalized field equations. With this solution in hand, the perturbed field equations are determined for power-law and exponential forms of the $f(T)$ function. We find that the point which describes the Kasner solution is a saddle point which means that the singular solution is unstable. However, we find the de Sitter universe is a late-time attractor. In general relativity, the cosmological constant drives the isotropization of the spacetime while in this setting the extra $f(T)$ contributions now provide this impetus.

We investigate quantum cosmological models in an $n$-dimensional anisotropic universe in the presence of a massless scalar field. Our basic inspiration comes from Chodos and Detweiler’s classical model, which predicts interesting behavior of the extra dimension, shrinking down as time goes by. We work in the framework of a recent geometrical scalar-tensor theory of gravity. Classically, we obtain two distinct types of solutions. One of them has an initial singularity, while the other represents a static universe considered as a whole. By using the canonical approach to quantum cosmology, we investigate how quantum effects could have had an influence in the past history of these universes.

We discuss a class of left-right symmetric theories with a universal seesaw mechanism for fermion masses and mixing and the implications for neutrinoless double beta ($0\nu \beta \beta$) decay where neutrino masses are governed by natural type-II seesaw dominance. The scalar sector consists of left- and right-handed Higgs doublets and triplets, while the conventional Higgs bidoublet is absent in this scenario. We use the Higgs doublets to implement the left-right and the electroweak symmetry breaking. On the other hand, the Higgs triplets with induced vacuum expectation values can give Majorana masses to light and heavy neutrinos and mediate $0\nu \beta \beta$ decay. In the absence of the Dirac mass terms for the neutrinos, this framework can naturally realize type-II seesaw dominance even if the right-handed neutrinos have masses of a few TeV. We study the implications of this framework in the context of $0\nu \beta \beta$ decay.

We have made a detailed study of the phase structure for the lattice Schwinger model with one flavor of Wilson fermion on the $(m,g)$ plane. For numerical investigation, we develop a decorated tensor renormalization method for lattice gauge theories with fermions incorporating the Grassmann tensor renormalization. Our algorithm manifestly preserves rotation and reflection symmetries. We find not only a parity-broken phase but also a Berezinskii-Kosterlitz-Thouless (BKT) transition by evaluating the central charge and an expectation value of a projection operator into the parity-odd subspace. The BKT phase boundaries converge into the degenerated doubler pole $(m,g)=(-2,0)$, while the parity-breaking transition line ends at the physical pole $(m,g)=(0,0)$. In addition, our analysis of scaling dimensions indicates that a conformal field theory with SU(2) symmetry arises on the line of $m=-2$.

A search is presented for the direct pair production of the stop, the supersymmetric partner of the top quark, that decays through an $R$-parity-violating coupling to a final state with two leptons and two jets, at least one of which is identified as a $b$-jet. The data set corresponds to an integrated luminosity of $36.1{\mathrm{fb}}^{-1}$ of proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13\mathrm{TeV}$, collected in 2015 and 2016 by the ATLAS detector at the LHC. No significant excess is observed over the Standard Model background, and exclusion limits are set on stop pair production at a 95% confidence level. Lower limits on the stop mass are set between 600 GeV and 1.5 TeV for branching ratios above 10% for decays to an electron or muon and a $b$-quark.

Recently it has been understood that certain soft factorization theorems for scattering amplitudes can be written as Ward identities of new asymptotic symmetries. This relationship has been established for soft particles with spins $s>0$, most notably for soft gravitons and photons. Here we study the remaining case of soft scalars. We show that a class of Yukawa-type theories, where a massless scalar couples to massive particles, have an infinite number of conserved charges. This raises the question as to whether one can associate asymptotic symmetries to scalars.

A uniformly accelerated (Rindler) observer will detect particles in the Minkowski vacuum, known as the Unruh effect. The spectrum is thermal and the temperature is given by that of the Killing horizon, which is proportional to the acceleration. Considering that these particles are kept in a thermal bath with this temperature, we find that the correlation function of the random force due to radiation acting on the particles, as measured by the accelerated frame, shows the fluctuation-dissipation relation. It is observed that the correlations, in both ($1+1$) spacetime and ($1+3$) dimensional spacetimes, are of the Brownian type. We discuss the implications of this new observation.

It is known that a single quantum harmonic oscillator is characterized by a hidden spectrum generating superconformal symmetry, but its origin has remained rather obscure. We show how this hidden superconformal symmetry can be derived by applying a nonlocal Foldy-Wouthuysen transformation to three extended systems with fermion degrees of freedom. The associated systems have essentially different nature from the point of view of conventional supersymmetric quantum mechanics, and generate the desired hidden symmetry in three different ways. We also trace out how the hidden superconformal symmetry of the quantum free particle system is produced in the limit of zero frequency.

We examine the origin of two opposite results for the growth of perturbations in the Deser-Woodard (DW) nonlocal gravity model. One group previously analyzed the model in its original nonlocal form and showed that the growth of structure in the DW model is enhanced compared to general relativity (GR) and thus concluded that the model was ruled out. Recently, however, another group has reanalyzed it by localizing the model and found that the growth in their localized version is suppressed even compared to the one in GR. The question was whether the discrepancy originates from an intrinsic difference between the nonlocal and localized formulations or is due to their different implementations of the subhorizon limit. We show that the nonlocal and local formulations give the same solutions for the linear perturbations as long as the initial conditions are set the same. The different implementations of the subhorizon limit lead to different transient behaviors of some perturbation variables; however, they do not affect the growth of matter perturbations at the sub-horizon scale much. In the meantime, we also report an error in the numerical calculation code of the former group and verify that after fixing the error the nonlocal version also gives the suppressed growth. Finally, we discuss two alternative definitions of the effective gravitational constant taken by the two groups and some open problems.

We find vacuum solutions such that massive gravitons are confined in a local spacetime region by their gravitational energy in asymptotically flat spacetimes in the context of the bigravity theory. We call such self-gravitating objects massive graviton geons. The basic equations can be reduced to the Schrödinger-Poisson equations with the tensor “wave function” in the Newtonian limit. We obtain a nonspherically symmetric solution with $j=2$, $\ell =0$ as well as a spherically symmetric solution with $j=0$, $\ell =2$ in this system where $j$ is the total angular momentum quantum number and $\ell$ is the orbital angular momentum quantum number, respectively. The energy eigenvalue of the Schrödinger equation in the nonspherical solution is smaller than that in the spherical solution. We then study the perturbative stability of the spherical solution and find that there is an unstable mode in the quadrupole mode perturbations which may be interpreted as the transition mode to the nonspherical solution. The results suggest that the nonspherically symmetric solution is the ground state of the massive graviton geon. The massive graviton geons may decay in time due to emissions of gravitational waves but this timescale can be quite long when the massive gravitons are nonrelativistic and then the geons can be long-lived. We also argue possible prospects of the massive graviton geons: applications to the ultralight dark matter scenario, nonlinear (in)stability of the Minkowski spacetime, and a quantum transition of the spacetime.