The spectrum of electrons and positrons originating from vacuum decay occurring in the collision of two noncollinear laser pulses is obtained. It displays high energy, highly collimated particle bunches traveling in a direction separate from the laser beams. This result provides an unmistakable signature of the vacuum-decay phenomenon and could suggest a new avenue for development of high energy electron and/or positron beams.

We discover an inner structure of QED while the gauge potential is decomposed into two orthogonal components. Based on this, the Lagrangian of the electron-photon system is expanded to a new form and by the general method of field theory, the gauge invariant spin and orbital angular momentum operators of the electron and photon are naturally obtained from Noether’s theorem. Our method, which can be generalized to the non-Abelian systems to investigate the inner structure of QCD, provides a new perspective to look on the nucleon spin crisis and opens a window into a strict and systematic resolution of this long-standing problem.

We numerically compute the ringdown amplitudes following the plunge of a particle from the innermost stable circular orbit of a Schwarzschild black hole in the extreme-mass ratio limit. We show that the ringdown amplitudes computed in this way are in good agreement with a recent analytical calculation [S. Hadar and B. Kol, this issue, Phys. Rev. D 84 DM10604 (2011)].].

We investigate modifications of the Lifshitz black hole solutions due to the presence of Maxwell charge in higher dimensions for arbitrary $z$ and any topology. We find that the behavior of large black holes is insensitive to the topology of the solutions, whereas for small black holes significant differences emerge. We generalize a relation previously obtained for neutral Lifshitz black branes, and study more generally the thermodynamic relationship between energy, entropy, and chemical potential. We also consider the effect of Maxwell charge on the effective potential between objects in the dual theory.

We use the thermofield dynamics formalism to obtain the energy-momentum tensor for the Kalb-Ramond field in a topology $S^1\times S^1\times R^2$. The compactification is carried out by a generalized thermofield dynamics-Bogoliubov transformation that is used to define a renormalized energy-momentum tensor. The expressions for the Casimir energy and pressure at finite temperature are then derived. A comparative analysis with the electromagnetic case is developed, and the results may be important for applications, as in cuprate superconductivity, for instance.

We study the finite-temperature phase of a gluon ensemble in a variational approximation to QCD in the Coulomb gauge. We derive and numerically solve the underlying Dyson-Schwinger equations up to one-loop order. Assuming the subcritical solution at $T=0$, we find a sharp transition in the infrared value of the gluon energy at a critical temperature.

The spatially flat Friedmann-Robertson-Walker cosmological model with a massless scalar field in loop quantum cosmology admits a description in terms of a completely solvable model. This has been used to prove that: (i) the quantum bounce that replaces the big bang singularity is generic; (ii) there is an upper bound on the energy density for all states, and (iii) semiclassical states at late times had to be semiclassical before the bounce. Here we consider a family of exact solutions to the theory, corresponding to generalized coherent Gaussian and squeezed states. We analyze the behavior of basic physical observables and impose restrictions on the states based on physical considerations. These turn out to be enough to select, from all the generalized coherent states, those that behave semiclassical at late times. We study then the properties of such states near the bounce where the most “quantum behavior” is expected. As it turns out, the states remain sharply peaked and semiclassical at the bounce and the dynamics is very well approximated by the “effective theory” throughout the time evolution. We compare the semiclassicality properties of squeezed states to those of the Gaussian semiclassical states and conclude that the Gaussians are better behaved. In particular, the asymmetry in the relative fluctuations before and after the bounce are negligible, thus ruling out claims of so-called “cosmic forgetfulness.”

We present a comprehensive analysis of the spacetime structure and thermodynamics of ($1+1$)-dimensional black holes in a noncommutative framework. It is shown that a wider variety of solutions are possible than the commutative case considered previously in the literature. As expected, the introduction of a minimal length $\sqrt{\theta }$ cures singularity pathologies that plague the standard two-dimensional general relativistic case, where the latter solution is recovered at large length scales. Depending on the choice of input parameters (black hole mass $M$, cosmological constant $\Lambda$, etc.), black hole solutions with zero, up to six, horizons are possible. The associated thermodynamics allows for the either complete evaporation, or the production of black hole remnants.

An extreme mass ratio inspiral consists of two parts: adiabatic inspiral and plunge. The plunge trajectory from the innermost stable circular orbit is special (somewhat independent of initial conditions). We write an expression for its solution in closedform and for the emitted waveform. In particular we extract an expression for the associated black-hole ringdown amplitudes, and evaluate them numerically.

We obtain retarded Green’s functions for massless scalar fields in the background of near-extreme, near-horizon rotating charged black holes of five-dimensional minimal gauged supergravity. The radial part of the (separable) massless Klein-Gordon equation in such general black hole backgrounds is Heun’s equation, due to the singularity structure associated with the three black hole horizons. On the other hand, we find the scaling limit for the near-extreme, near-horizon background where the radial equation reduces to a hypergeometric equation whose $SL(2,\mathbf{R}{)}^2$ symmetry signifies the underlying two-dimensional conformal invariance, with the two sectors governed by the respective Frolov-Thorne temperatures.

We study how the frequencies and damping times of oscillations of a newly born, hot proto-neutron star depend on the physical quantities which characterize the star quasistationary evolution which follows the bounce. Stellar configurations are modeled using a microscopic equation of state obtained within the Brueckner-Hartree-Fock, nuclear many-body approach, extended to the finite-temperature regime. We discuss the mode frequency behavior as a function of the lepton composition, and of the entropy gradients which prevail in the interior of the star. We find that, in the very early stages, gravitational wave emission efficiently competes with neutrino processes in dissipating the star mechanical energy residual of the gravitational collapse.

Using the standard canonical formalism, the equations of mechanics and kinetics in the Friedmann-Lemaître-Robertson-Walker (FLRW) space-times in Cartesian coordinates have been obtained. The transformation law of the generalized momentum under the shift of the origin of the coordinate system has been found, and the form invariance of the Hamiltonian function relative to the shift transformation has been proved. The derived equations allow one to shift the origin of the coordinate system to the point of location of the observer. The space in the vicinity of this point can be considered as a Euclidean one which makes straightforward the interpretation of calculations. For the distribution function in the phase space, the general solution of the collisionless Boltzmann equation has been found. The results of this work can be used for treatment of evolution of the distribution function of particles arriving from the cosmologically distant objects. We discuss, in particular, two important cases of astrophysical interest: (i) the homogenous distribution particles taking into account energy losses, and (ii) the spherically symmetric case with arbitrary angular distribution. While the first problem is linked to the diffuse distributions of particles produced at cosmological epochs, the second one is relevant to the discrete astrophysical objects.

The seasonal polar caps of Mars can be used to test the equivalence principle in general relativity. The north and south caps, which are composed of carbon dioxide, wax and wane with the seasons. If the ratio of the inertial (passive) to gravitational (active) masses of the caps differs from the same ratio for the rest of Mars, then the equivalence principle fails, Newton’s third law fails, and the caps will pull Mars one way and then the other with a force aligned with the planet’s spin axis. This leads to a secular change in Mars’s along-track position in its orbit about the Sun, and to a secular change in the orbit’s semimajor axis. The caps are a poor Eötvös test of the equivalence principle, being 4 orders-of-magnitude weaker than laboratory tests and 7 orders-of-magnitude weaker than that found by lunar laser ranging; the reason is the small mass of the caps compared to Mars as a whole. The principal virtue of using Mars is that the caps contain carbon, an element not normally considered in such experiments. The Earth with its seasonal snow cover can also be used for a similar test.

The heavy fourth generation of quarks that have sufficiently small mixing with the three known standard model families form hadrons. In the present work, we calculate the masses and decay constants of mesons containing either both quarks from the fourth generation or one from the fourth family and the other from known third family standard model quarks in the framework of the QCD sum rules. In the calculations, we take into account two-gluon condensate diagrams as nonperturbative contributions. The obtained results reduce to the known masses and decay constants of the $\overline{b}b$ and $\overline{c}c$ quarkonia when the fourth family quark is replaced by the bottom or charm quark.

In this paper we investigate the various processes that can contribute to a final state consisting of a lepton, missing transverse momentum, and two jets at next-to-leading order (NLO) at the Tevatron. In particular we consider the production of $W/Z+2$ jets, diboson pairs, single top, and the $t\overline{t}$ process with both fully leptonic and semileptonic decays. We present distributions for the invariant mass of the dijet system and normalizations of the various processes, accurate to NLO.

We construct a model of decaying, TeV-scale scalar dark matter motivated by data from the PAMELA and Fermi-LAT experiments. By introducing an appropriate Abelian discrete symmetry and an intermediate scale of vectorlike states that are responsible for generating lepton Yukawa couplings, we show that Planck-suppressed corrections may lead to decaying dark matter that is leptophilic and has the desired lifetime. The dark matter candidate decays primarily to lepton/antilepton pairs, and at a subleading rate to final states with a lepton, antilepton and standard model Higgs boson. We show that the model can reproduce the observed positron flux and positron fraction while remaining consistent with the bounds on the cosmic ray antiproton flux.

We study the behavior of the AsqTad quark propagator in Landau gauge on SU(3) Yang-Mills gauge configurations under the removal of center vortices. In SU(2) gauge theory, center vortices have been observed to generate chiral symmetry breaking and support the infrared behavior of the quark propagator. In contrast, we report a weak dependence on the vortex content of the SU(3) gauge configurations, including the survival of dynamical mass generation on configurations with vanishing string tension.

In this work, the complete one-loop calculation of meson-meson scattering amplitudes within $U(3)\otimes U(3)$ chiral perturbation theory with explicit resonance states is carried out for the first time. Partial waves are unitarized from the perturbative calculation employing a nonperturbative approach based on the $N/D$ method. Once experimental data are reproduced in a satisfactory way we then study the resonance properties, such as the pole positions, corresponding residues and their $N_C$ behaviors. The resulting $N_C$ dependence is the first one in the literature that takes into account the fact that the ${\eta }_1$ becomes the ninth Goldstone boson in the chiral limit for large $N_C$. Within this scheme the vector resonances studied, $\rho (770)$, $K^{*}(892)$ and $\varphi (1020)$, follow an $N_C$ trajectory in agreement with their standard $\overline{q}q$ interpretation. The scalars $f_0(1370)$, $a_0(1450)$ and $K^{*}(1430)$ also have for large $N_C$ a $\overline{q}q$ pole position trajectory and all of them tend to a bare octet of scalar resonances around 1.4 GeV. The $f_0(980)$ tends asymptotically to the bare pole position of a singlet scalar resonance around 1 GeV. The $\sigma$, $\kappa$ and $a_0(980)$ scalar resonances have a very different $N_C$ behavior. The case of the $\sigma$ resonance is analyzed with special detail.

We calculate the neutrino mean free path with non-Fermi liquid corrections in quark matter from scattering and absorption processes for both degenerate and nondegenerate neutrinos. We show that the mean free path decreases due to the non-Fermi liquid corrections, leading to $l_{\mathrm{mean}}^{-1}\sim [\dots +\dots C_F^2{\alpha }_s^2\ln (m_D/T{)}^2]$. This reduction results in a higher rate of scattering.