Lepton number violation (LNV) mediated by short-range operators can manifest itself in both neutrinoless double beta decay ($0\nu \beta \beta$) and in processes with same-sign dilepton final states at the LHC. We derive limits from existing LHC data at $\sqrt{s}=8\mathrm{TeV}$ and compare the discovery potential of the forthcoming $\sqrt{s}=14\mathrm{TeV}$ phase of the LHC with the sensitivity of current and future $0\nu \beta \beta$ decay experiments, assuming the short-range part of the $0\nu \beta \beta$ decay amplitude dominates. We focus on the first of two possible topologies triggered by one fermion and two bosons in the intermediate state. In all cases, except for the pure leptoquark mechanism, the LHC will be more sensitive than $0\nu \beta \beta$ decay in the future. In addition, we propose to search for a charge asymmetry in the final state leptons and to use different invariant mass peaks as a possible tool to discriminate the various possible mechanisms for LNV signals at the LHC.

We extend the density-of-states approach to gauge systems (LLR method [K. Langfeld, B. Lucini, and A. Rago, Phys. Rev. Lett. 109, 111601 (2012)]) to QCD at finite temperature and density with heavy quarks. The approach features an exponential error suppression and yields the Polyakov loop probability distribution function over a range of hundreds of orders of magnitude. $SU(2)$ gauge theory is considered in the confinement and the high-temperature phase, and at finite densities of heavy quarks. In the latter case, a smooth rise of the density with the chemical potential is observed, and no critical phenomenon associated with deconfinement due to finite densities is found.

We revisit the spherically symmetric third order Lovelock black hole solution in seven dimensions. We show that the general solution for the metric function does not admit the Gauss-Bonnet (GB) limit. This is not expected due to the linear superposition of the second (GB) and third order Lovelock Lagrangians in the general action. It is found that the two branches of the GB solutions are indeed the limit of the other two complex solutions of the field equations in the third order Lovelock gravity. These two complex solutions could not be accepted as the solutions of Einstein’s field equations which are supposed to be real value functions on the entire real $r$ axis. A new solution, which is valid only if the third order Lovelock parameter is small, is introduced which can be considered as the natural extension of general relativity to the third order Lovelock modified theory of gravity. We also generalize the discussion to the higher dimensional third order Lovelock gravity coupled to matter sources with a cosmological constant.

We study the thermalization of a class of four-dimensional strongly coupled theories dual to a five-dimensional AdS-Vaidya spacetime with Gauss-Bonnet curvature corrections. We probe the thermalization using the two-point functions, the expectation values of circular Wilson loops, and entanglement entropy. When boundary separation is small, we observe that the thermalization times of these observables have weak dependence on the Gauss-Bonnet coupling constant $\alpha$. In addition, the growth rate of entanglement entropy density is nearly volume independent. We also show that a new kind of swallowtail behavior may appear in the thermalization of the two-point function when $\alpha$ is negative and $\ell$ is large enough. At large negative $\alpha$ ($\alpha \lesssim -0.1$) the relationship between the critical thermalization time of entanglement entropy and the boundary separation encounters a certain “phase transition.”

We revisit the photon polarization tensor in a homogeneous external magnetic or electric field. The starting point of our considerations is the momentum space representation of the one-loop photon polarization tensor in the presence of a homogeneous electromagnetic field, known in terms of a double parameter integral. Our focus is on explicit analytical insights for both on- and off-the-light-cone dynamics in a wide range of well-specified physical parameter regimes, ranging from the perturbative to the manifestly nonperturbative strong field regime. The basic ideas underlying well-established approximations to the photon polarization tensor are carefully examined and critically reviewed. In particular, we systematically keep track of all contributions, both the ones to be neglected and those to be taken into account explicitly, to all orders. This allows us to study their ranges of applicability in a much more systematic and rigorous way. We point out the limitations of such approximations and manage to go beyond at several instances.

We study a model of $n$ coupled scalar fields in Minkowski spacetime in which all masses degenerate, which is considered as a toy model of polycritical gravity on anti-de Sitter spacetime. We quantize this model within the Becchi–Rouet–Stora–Tyutin scheme by introducing $n$ Faddeev–Popov (FP) ghost fields. Extending a Becchi–Rouet–Stora–Tyutin quartet generated by two scalars and two FP ghosts to $n$ scalars and $n$ FP ghosts, there remains a physical subspace with positive norm for odd $n$, but there exists only the vacuum for even $n$. This clearly shows a nontriviality of odd higher-order derivative scalar field theories. This is helpful to understand the truncation mechanism, which is used to obtain a unitary conformal field theory dual to linearized polycritical gravity. It turns out that the truncation mechanism is nothing but a general quartet mechanism that appears when introducing the FP ghost action.

We consider the decay of vortices trapped in the false vacuum of a theory of scalar electrodynamics in $2+1$ dimensions. The potential is inspired by models with intermediate symmetry breaking to a metastable vacuum that completely breaks a $U(1)$ symmetry, while in the true vacuum, the symmetry is unbroken. The false vacuum is unstable through the formation of true vacuum bubbles; however, the rate of decay can be extremely long. On the other hand, the false vacuum can contain metastable vortex solutions. These vortices contain the true vacuum inside in addition to a unit of magnetic flux and the appropriate topologically nontrivial false vacuum outside. We numerically establish the existence of vortex solutions which are classically stable; however, they can decay via tunneling. In general terms, they tunnel to a configuration which is a large, thin-walled vortex configuration that is now classically unstable to the expansion of its radius. We compute an estimate for the tunneling amplitude in the semiclassical approximation. We believe our analysis would be relevant to superconducting thin films or superfluids.

We study the second-order quantum phase transition of massive real scalar field theory with a quartic interaction in ($1+1$) dimensions on an infinite spatial lattice using matrix product states. We introduce and apply a naive variational conjugate gradient method, based on the time-dependent variational principle for imaginary time, to obtain approximate ground states, using a related ansatz for excitations to calculate the particle and soliton masses and to obtain the spectral density. We also estimate the central charge using finite-entanglement scaling. Our value for the critical parameter agrees well with recent Monte Carlo results, improving on an earlier study which used the related density matrix normalization group method, verifying that these techniques are well-suited to studying critical field systems. We also obtain critical exponents that agree, as expected, with those of the transverse Ising model. Additionally, we treat the special case of uniform product states (mean field theory) separately, showing that they may be used to investigate noncritical quantum field theories under certain conditions.

We apply an effective field theory method for the gravitational interaction of compact stars, developed within the context of general relativity, to Newtonian gravity. In this effective theory, a compact object is represented by a point particle possessing generic gravitational multipole moments. The time evolution of the multipoles depends on excitations due to external fields. This can formally be described by a response function of the multipoles to applied fields. The poles of this response correspond to the normal oscillation modes of the star. This gives rise to resonances between modes and tidal forces in binary systems. The connection to the standard formalism for tidal interactions and resonances in Newtonian gravity is worked out. Our approach can be applied to more complicated situation. In particular, a generalization to general relativity is possible.

We present dynamical properties of linear waves and null geodesics valid for Kerr and Kerr–de Sitter black holes and their stationary perturbations. The two are intimately linked by the geometric optics approximation. For the null geodesic flow the key property is the $r$-normal hyperbolicity of the trapped set and for linear waves it is the distribution of quasinormal modes: the exact quantization conditions do not hold for perturbations but the bounds on decay rates and the statistics of frequencies are still valid.

On the lines of the four-dimensional Kerr black hole we consider the particle acceleration near a five-dimensional Kerr black hole which has the two rotation parameters. It turns out that the center of mass energy of the two equal mass colliding particles as expected diverges for the extremal black hole and there is a symmetry in the results for $\theta =0$, $\pi /2$. Because of the two rotation parameters, $r=0$ can be a horizon without being a curvature singularity. It is shown that the acceleration of particles to high energies near the 5D extreme rotating black hole avoids fine-tuning of the angular momentum of particles.

We characterize the radial and angular variance of the Hubble flow in the composite sample of 4534 galaxies, on scales in which much of the flow is in the nonlinear regime. With no cosmological assumptions other than the existence of a suitably averaged linear Hubble law, we find with decisive Bayesian evidence ($\ln B\gg 5$) that the Hubble constant, when averaged in independent spherical shells, is closer to its asymptotic value when referred to the rest frame of the Local Group (LG), rather than the standard rest frame of the cosmic microwave background (CMB). An exception occurs for radial shells in the range $40h^{-1}–60h^{-1}\mathrm{Mpc}$. Angular averages reveal a dipole structure in the Hubble flow, whose amplitude changes markedly over the range $32h^{-1}–62h^{-1}\mathrm{Mpc}$. Whereas the LG frame dipole is initially constant and then decreases significantly, the CMB frame dipole initially decreases but then increases. The map of angular Hubble flow variation in the LG rest frame is found to coincide with that of the residual CMB temperature dipole, with correlation coefficient $-0.92$. These results are difficult to reconcile with the standard kinematic interpretation of the motion of the Local Group in response to the clustering dipole, but are consistent with a foreground nonkinematic anisotropy in the distance-redshift relation of 0.5% on scales up to $65h^{-1}\mathrm{Mpc}$. Effectively, the differential expansion of space produced by nearby nonlinear structures of local voids and denser walls and filaments cannot be reduced to a local boost. This hypothesis suggests a reinterpretation of bulk flows, which may potentially impact on calibration of supernova distances, anomalies associated with large angles in the CMB anisotropy spectrum, and the dark flow inferred from the kinematic Sunyaev-Zel’dovich effect. It is consistent with recent studies that find evidence for a nonkinematic dipole in the distribution of distant radio sources.

We propose a model for the dust matter in the cosmological context. The model contains a scalar field with a kinetic term nonminimally coupled to gravity. By investigating the background and perturbative equations, it is demonstrated that the scalar field has the same dynamics as the dust matter. We have also considered the cosmological constant in the model. It turns out that the model has not exotic behavior. Thus, a universe including the scalar field and the cosmological constant evolves just as our Universe. Moreover, we have added the quadratic term in the action. It is shown that the quadratic term can be ruled out by its consequences.

In this paper we provide a consistency relation between the amplitude of the hemispherical bipolar asymmetry, $A$, and the amplitude of the primordial non-Gaussianity in the squeezed limit, $f_{NL}$, as $|A|\lesssim {10}^{-1}{f}_{NL}$. We demonstrate that this consistency condition is at work for any model of inflation in which the curvature perturbations are sourced by a single light field with the Bunch–Davies initial condition, irrespective of the number of inflation fields that contribute to the background inflationary expansion. As a nontrivial example, we show that observable hemispherical asymmetry can be generated in single-field nonattractor inflationary models. We also study hemispherical asymmetry generated in the models of multiple fields inflation. We show that $A$ is controlled by the weighted sum of non-Gaussianity contribution from each field. In particular, we show that observable hemispherical asymmetry can be generated in models in which inhomogeneities are generated from a light scalar field modulating the surface of the end of inflation.

Typically, cold inflation with positive vacuum energy density dilutes all matter except the quantum fluctuations, which are stretched outside the Hubble patch during inflation. However, the cyclic-inflation scenario, in which the Universe undergoes many asymmetric cycles leading to an overall exponential growth, operates in the presence of thermal matter. Thus, while some of the nice properties of cold inflation are preserved, in cyclic inflationary models, thermal excitations are continually produced, and there exists a unique opportunity of imprinting interesting thermal history in cosmic microwave background radiation. In particular, we will see that a phase transition can lead to observably large higher-order non-Gaussianities as the critical temperature is approached and that these are increasingly divergent with the order of the correlations.

The spectrum and event rate of supernova relic neutrinos are calculated, taking into account the dependence on the time it takes for the shock wave in supernova cores to revive. The shock revival time should depend on the still unknown explosion mechanism of collapse-driven supernovae. The contribution of black-hole-forming failed supernovae is also considered. The total event rate is higher for models with a longer shock revival time and/or a failed-supernova contribution. The hardness of the spectrum does not strongly depend on the shock revival time, but the spectrum becomes hard owing to the failed supernovae. Therefore, the shock-revival-time dependence of supernova relic neutrinos has different systematics from the fractions of failed supernovae.

We use an exact general relativistic model structure within a Friedmann-Robertson-Walker cosmological background based on a Lemaître, Tolman, and Bondi metric to study the gravitational lensing by a cosmological and dynamical structure. Using different density profiles for the model structure, the deviation angle and the time delay through the gravitational lensing has been studied by solving the geodesic equations. The results of these exact calculations have been compared to the thin lens approximation. We have shown that the result for the thin lens approximation based on a modified Navarro-Frenk-White density profile with a void before going over to the Friedmann-Robertson-Walker background matches very well with the exact general relativistic calculations. However, the thin lens approximation based on a normal Navarro-Frenk-White profile does differ from the exact relativistic calculation. The difference is more the less compact the structure is. We have also looked at the impact of our calculation on the observational interpretation of arcs in the case of strong lensing and also the reduced shear in the case of weak lensing. No significant difference has been seen in the data available.

We use recently released data on the positron-to-electron ratio in cosmic rays from the AMS-02 experiment to constrain dark matter annihilation in the Milky Way. Due to the yet unexplained positron excess, limits are generally weaker than those obtained using other probes, especially gamma rays. This also means that explaining the positron excess in terms of dark matter annihilation is difficult. Only if very conservative assumptions on the dark matter distribution in the Galactic center region are adopted, it may be possible to accommodate dark matter annihilating to leptons with a cross section above ${10}^{-24}{\mathrm{cm}}^3/\sec $. We comment on several theoretical mechanisms to explain such large annihilation cross sections.

A singlet fermion which interacts only with a new singlet scalar provides a viable and minimal scenario that can explain the dark matter. The singlet fermion is the dark matter particle whereas the new scalar mixes with the Higgs boson providing a link between the dark matter sector and the standard model. In this paper, we present an updated analysis of this model focused on its detection prospects. Both the parity-conserving case and the most general case are considered. First, the full parameter space of the model is analyzed, and the regions compatible with the dark matter constraint are obtained and characterized. Then, the implications of current and future direct detection experiments are taken into account. Specifically, we determine the regions of the multidimensional parameter space that are currently excluded and those that are going to be probed by next generation experiments. Finally, indirect detection prospects are discussed and the expected signal at neutrino telescopes is calculated.

In most (weakly interacting) extensions of the Standard Model the relation mapping the parameter values onto experimentally measurable quantities can be computed (with some uncertainties), but the inverse relation is usually not known. In this paper we demonstrate the ability of artificial neural networks to find this unknown relation, by determining the unknown parameters of the constrained minimal supersymmetric extension of the Standard Model from quantities that can be measured at the LHC. We expect that the method works also for many other new physics models. We compare its performance with the results of a straightforward ${\chi }^2$ minimization. We simulate LHC signals at a center of mass energy of 14 TeV at the hadron level. In this proof-of-concept study we do not explicitly simulate Standard Model backgrounds, but apply cuts that have been shown to enhance the signal-to-background ratio. We analyze four different benchmark points that lie just beyond current lower limits on superparticle masses, each of which leads to around 1000 events after cuts for an integrated luminosity of $10{\mathrm{fb}}^{-1}$. We use up to 84 observables, most of which are counting observables; we do not attempt to directly reconstruct (differences of) masses from kinematic edges or kinks of distributions. We nevertheless find that $m_0$ and $m_{1/2}$ can be determined reliably, with errors as small as 1% in some cases. With $500{\mathrm{fb}}^{-1}$ of data $\tan \beta$ as well as $A_0$ can also be determined quite accurately. For comparable computational effort the ${\chi }^2$ minimization yielded much worse results.