We present formulas for the chiral extrapolation of spin-dependent and spin-independent moments of quark distributions of octet baryons, including loop corrections and counterterms, to leading nonanalytic order. This analysis allows for isospin breaking, and may be used for the chiral extrapolation of both ($2+1$)- and ($1+1+1$)-flavor lattice QCD results. An example of such an application is given, with the extrapolation formulas applied, using the finite-range regularization scheme, to recent ($2+1$)-flavor QCDSF/UKQCD Collaboration lattice results for the first spin-independent and first two spin-dependent Mellin moments.

The decays $B_c^{+}\to J/\psi D_s^{+}$ and $B_c^{+}\to J/\psi D_s^{*+}$ are observed for the first time using a dataset, corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$, collected by the LHCb experiment in proton-proton collisions at center-of-mass energies of $\sqrt{s}=7$ and 8 TeV. The statistical significance for both signals is in excess of 9 standard deviations. The following ratios of branching fractions are measured to be $\frac{\mathcal{B}(B_c^{+}\to J/\psi D_s^{+})}{\mathcal{B}(B_c^{+}\to J/\psi {\pi }^{+})}=2.90\pm 0.57\pm 0.24$, $\frac{\mathcal{B}(B_c^{+}\to J/\psi D_s^{*+})}{\mathcal{B}(B_c^{+}\to J/\psi D_s^{+})}=2.37\pm 0.56\pm 0.10$, where the first uncertainties are statistical and the second systematic. The mass of the $B_c^{+}$ meson is measured to be $m_{B_c^{+}}=6276.28\pm 1.44(\mathrm{stat})\pm 0.36(\mathrm{syst})\mathrm{MeV}/c^2$, using the $B_c^{+}\to J/\psi D_s^{+}$ decay mode.

In this paper, we show how classical statistical field theory techniques can be used to efficiently perform the numerical evaluation of the nonperturbative Schwinger mechanism of particle production by quantum tunneling. In some approximation, we also consider the backreaction of the produced particles on the external field, as well as the self-interactions of the produced particles.

Cosmology and short-baseline (SBL) neutrino oscillation data both hint at the existence of light sterile neutrinos with masses in the 1 eV range. Here we perform a detailed analysis of the sterile neutrino scenario using both cosmological and SBL data. We have additionally considered the possibility that the extra neutrino degrees of freedom are not fully thermalized in the early universe. Even when analyzing only cosmological data we find a preference for the existence of massive sterile neutrinos in both ($3+1$) and ($3+2$) scenarios, and with the inclusion of SBL data the evidence is formally at the $3.3\sigma$ level in the case of a ($3+1$) model. Interestingly, cosmological and SBL data both point to the same mass scale of approximately 1 eV. In the ($3+1$) framework $\mathrm{WMAP}9+\mathrm{SPT}$ provide a value of the sterile mass eigenstate $m_4=(1.72\pm 0.65)\mathrm{eV}$; this result is strengthened by adding the prior from SBL posterior to $m_4=(1.27\pm 0.12)\mathrm{eV}$ [$m_4=(1.23\pm 0.13)\mathrm{eV}$ when data from the Sloan Digital Sky Survey is also considered in the cosmological analysis]. In the ($3+2$) scheme, two additional, nonfully thermalized neutrinos are compatible with the whole set of cosmological and SBL data, leading to mass values of $m_4=(0.95\pm 0.30)\mathrm{eV}$ and $m_5=(1.59\pm 0.49)\mathrm{eV}$. The inclusion of Planck data does not change our considerations about the mass scale; concerning the extra neutrino degrees of freedom, by invoking a partial thermalization the $3+1$ model is still consistent with the latest data.

Quantum field theory in curved spacetime may be defined either through a manifestly unitary canonical approach or via the manifestly covariant path integral formalism. For gauge theories, these two approaches have produced conflicting results, leading to the question of whether the canonical approach is covariant, and whether the path integral approach is unitary. We show the unitarity of the covariant U(1) Maxwell theory, defined via the Wick rotation of a Euclidean path integral. We begin by gauge-fixing the path integral, taking care with zero modes, large gauge transformations, and nontrivial bundles. We find an extra geometric factor in the partition function that has been overlooked in previous work, coming from the zero mode of the gauge symmetry, which affects the entropy and stress-energy tensor. With this extra factor, the covariant calculation agrees with the canonical result for ultrastatic manifolds, and in $D=2$. Finally, we argue that if there exists a unitary (but not necessarily covariant) canonical formulation, then the covariant formulation must also be unitary, even if the two approaches disagree.

The influence of the finiteness of the proton radius and mass on the energies of a hydrogen atom and hydrogenlike ions in a superstrong magnetic field is studied. The finiteness of the nucleus size pushes the ground energy level up leading to a nontrivial dependence of the value of the critical nucleus charge on the external magnetic field.

Recently, constraints on bosonic asymmetric dark matter have been imposed based on the existence of old neutron stars, excluding dark matter masses in the range from $\sim 2\mathrm{keV}$ up to several GeV. The constraints are based on the star destruction scenario where the dark matter particles captured by the star collapse, forming a black hole that eventually consumes the host star. In addition, there were claims in the literature that similar constraints can be obtained for dark matter masses heavier than a few TeV. Here we argue that it is not possible to extend to these constraints. We show that in the case of heavy dark matter, instead of forming a single large black hole that consumes the star, the collapsing dark matter particles form a series of small black holes that evaporate quickly without leading to the destruction of the star. Thus, no constraints arise for bosonic asymmetric dark matter particles with masses of a few TeV or higher.

We investigate cosmological behavior in the quasidilaton nonlinear massive gravity. We perform a detailed dynamical analysis and examine the stable late-time solutions relevant to late-time cosmic acceleration. We demonstrate that a dark-energy-dominated, cosmological-constant-like solution is a late attractor of the dynamics. We also analyze the evolution of the universe at intermediate times, showing that the observed epoch sequence can be easily obtained in the model under consideration. Furthermore, we study the nonsingular bounce and the cosmological turnaround which can be realized for a region of the parameter space. Last but not least, we use observational data from type Ia supernovae, baryon acoustic oscillations and the cosmic microwave background in order to constrain the parameters of the theory.

The 21 cm signatures induced by moving cosmic string loops are investigated. Moving cosmic string loops seed filamentary nonlinear objects. We analytically evaluate the differential 21 cm brightness temperature from these objects. We show that the brightness temperature reaches 200 mK for a loop whose tension is about the current upper limit, $G\mu \sim {10}^{-7}$. We also calculate the angular power spectrum, assuming scaling in loop distribution. We find that the angular power spectrum for $G\mu >{10}^{-8}$ at $z=30$ or $G\mu >{10}^{-10}$ at $z=20$ can dominate the spectrum of the primordial density fluctuations. Finally we show that a future SKA-like observation has the potential to detect the power spectrum due to loops with $G\mu ={10}^{-8}$ at $z=20$.

We consider regions of the parameter space of the minimal supersymmetric standard model with bino-like neutralino dark matter in which a large fraction of the total dark matter annihilation cross section in the present era arises from annihilation to final states with monoenergetic photons. The region of interest is characterized by light sleptons and heavy squarks. We find that it is possible for the branching fraction to final states with monoenergetic photons to be comparable to that for continuum photons, but in those cases the total cross section will be so small that it is unlikely to be observable. For models where dark matter annihilation may be observable in the present era, the branching fraction to final states with monoenergetic photons is $\mathcal{O}(1\%–10\%)$.

A differentially rotating hypermassive neutron star (HMNS) is a metastable object which can be formed in the merger of neutron-star binaries. The eventual collapse of the HMNS into a black hole is a key element in generating the physical conditions expected to accompany the launch of a short gamma-ray burst. We investigate the influence of magnetic fields on HMNSs by performing three-dimensional simulations in general-relativistic magnetohydrodynamics. In particular, we provide direct evidence for the occurrence of the magnetorotational instability (MRI) in HMNS interiors. For the first time in simulations of these systems, rapidly-growing and spatially-periodic structures are observed to form with features like those of the channel flows produced by the MRI in other systems. Moreover, the growth time and wavelength of the fastest-growing mode are extracted and compared successfully with analytical predictions. The MRI emerges as an important mechanism to amplify magnetic fields over the lifetime of the HMNS, whose collapse to a black hole is accelerated. The evidence provided here that the MRI can actually develop in HMNSs could have a profound impact on the outcome of the merger of neutron-star binaries and on its connection to short gamma-ray bursts.

We study the implications at the LHC for the minimal (least) version of the supersymmetric standard model. In this model, supersymmetry is broken by gravity and extra gauge interaction effects, providing a spectrum similar in several aspects to that in natural supersymmetric scenarios. Having the first two generations of sparticles partially decoupled means that any significant signal can only involve gauginos and the third family of sfermions. In practice, the signals are dominated by gluino production with subsequent decays into the stop sector. As we show, for gluino masses below 2300 GeV, a discovery at the LHC is possible at $\sqrt{s}=14\mathrm{TeV}$, but will require large integrated luminosities.

We examine the axial U(1) symmetry near and above the finite-temperature phase transition in two-flavor QCD using lattice QCD simulations. Although the axial U(1) symmetry is always violated by quantization, i.e., the chiral anomaly, the correlation functions may manifest effective restoration of the symmetry in the high-temperature phase. We explicitly study this possibility by calculating the meson correlators as well as the Dirac operator spectral density near the critical point. Our numerical simulations are performed on a ${16}^3\times 8$ lattice with two flavors of dynamical quarks represented by the overlap fermion formalism. Chiral symmetry and its violation due to the axial anomaly is manifestly realized with this formulation, which is a prerequisite for the study of the effective restoration of the axial U(1) symmetry. In order to avoid discontinuity in the gauge configuration space, which occurs for the exactly chiral lattice fermions, the simulation is confined in a fixed topological sector. It induces a finite-volume effect, which is well described by a formula based on the Fourier transform from the $\theta$ vacua. We confirm this formula at finite temperature by calculating the topological susceptibility in the quenched theory. Our two-flavor simulations show degeneracy of the meson correlators and a gap in the Dirac operator spectral density, which implies that the axial U(1) symmetry is effectively restored in the chirally symmetric phase.

The predictions from a nonextensive self-consistent theory recently proposed are investigated. Transverse momentum ($p_T$) distribution for several hadrons obtained in $p+p$ collisions are analyzed to verify if there is evidence for a limiting effective temperature and a limiting entropic index. In addition, the hadron-mass spectrum proposed in that theory is confronted with available data. It turns out that all $p_T$ distributions and the mass spectrum obtained in the theory are in good agreement with experiment with constant effective temperature and constant entropic index. The results confirm that the nonextensive statistics plays an important role in the description of the termodynamics of hadronic systems, and also that the self-consistent principle holds for energies as high as those achieved in the LHC. A discussion on the best $p_T$-distribution formula for fitting experimental data is presented.

Double parton correlations, having effects on the double parton scattering processes occurring in high-energy hadron-hadron collisions, for example at the LHC, are studied in the valence quark region by means of constituent quark models. In this framework, two particle correlations are present without any additional prescription, at variance with what happens, for example, in independent particle models, such as the MIT bag model in its simplest version. From the present analysis, conclusions similar to the ones obtained recently in a modified version of the bag model can be drawn: correlations in the longitudinal momenta of the active quarks are found to be sizable, while those in transverse momentum are much smaller. However, the framework used allows us to understand clearly the dynamical origin of the correlations. In particular, it is shown that the small size of the correlations in transverse momentum is a model-dependent result, which would not occur if models with sizable quark orbital angular momentum were used to describe the proton. Our analysis permits us, therefore, to clarify the dynamical origin of the double parton correlations and to establish which, among the features of the results, are model independent. The possibility of testing the studied effects experimentally is discussed.

We study an approximate version of the Schwinger-Dyson equation that controls the nonperturbative behavior of the ghost-gluon vertex in the Landau gauge. In particular, we focus on the form factor that enters in the dynamical equation for the ghost dressing function, in the same gauge, and derive its integral equation, in the “one-loop dressed” approximation. We consider two special kinematic configurations, which simplify the momentum dependence of the unknown quantity; in particular, we study the soft gluon case and the well-known Taylor limit. When coupled with the Schwinger-Dyson equation of the ghost dressing function, the contribution of this form factor provides considerable support to the relevant integral kernel. As a consequence, the solution of this coupled system of integral equations furnishes a ghost dressing function that reproduces the standard lattice results rather accurately, without the need to artificially increase the value of the gauge coupling.

The experimental data on the yield of muon-induced neutrons for liquid scintillator, iron, and lead accumulated during 60 years of muon interaction underground study have been analyzed. A universal formula connecting the yield with muon energy loss in the matter and neutron production in hadronic and electromagnetic showers is presented.

We report a search for the rare decays $B\to h^{(*)}\nu \overline{\nu }$, where $h^{(*)}$ stands for $K^{+}$, $K_S^0$, $K^{*+}$, $K^{*0}$, ${\pi }^{+}$, ${\pi }^0$, ${\rho }^{+}$, ${\rho }^0$ and $\varphi$. The results are obtained from a $711{\mathrm{fb}}^{-1}$ data sample that contains $772\times {10}^{6}B\overline{B}$ pairs collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB $e^{+}{e}^{-}$ collider. We search for signal candidates by fully reconstructing a hadronic decay of the accompanying $B$ meson and requiring a single $h^{(*)}$ meson left on the signal side. No significant signal is observed and we set upper limits on the branching fractions at 90% confidence level. The measurements of $B^{+}\to K^{*+}\nu \overline{\nu }$, $B^{+}\to {\pi }^{+}\nu \overline{\nu }$, $B^0\to {\pi }^0\nu \overline{\nu }$ and $B^0\to {\rho }^0\nu \overline{\nu }$ provide the world’s currently most restrictive limits.

The renormalization-group procedure for effective particles is applied to the model quantum theory of free fermions to which one adds an interaction in the form of a mass-mixing term. If one used a standard approach based on the instant form of dynamics, the theory would suffer from a generic vacuum problem caused by a divergent production of virtual quanta out of a bare vacuum and it would require an adjustment of its degrees of freedom to the added interaction term before quantization, considered a means of avoiding the quantum vacuum problem. In the effective particle approach, the quantum vacuum problem is dealt with instead by using the front form of dynamics, where the pair production is excluded by momentum conservation. The corresponding Hamiltonian includes mass parameters through constraint equations while the required quantum field operators are constructed independently of all mass parameters, including the parameters that appear in the added mass-mixing interaction term. Then the masses and states of physical fermions emerge at an end of the nonperturbative calculation that is carried out entirely in one and the same interacting quantum theory with a trivial vacuum and no quantization adjustment. An a priori infinite set of renormalization-group equations for all momentum modes of fermion fields is reduced to just one equation for a two-by-two mass squared matrix, thanks to seven kinematical symmetries of the front form (the instant form has only six). For strong mass-mixing interactions, the fermion-model solutions qualitatively differ from the analogous, earlier found boson-model solutions by the absence of tachyons.