Braneworld models with variable tension are investigated, and the corrections on the black string horizon along the extra dimension are provided. Such corrections are encrypted in additional terms involving the covariant derivatives of the variable tension on the brane, providing profound consequences concerning the black string horizon variation along the extra dimension, near the brane. The black string horizon behavior is shown to be drastically modified by the terms corrected by the brane variable tension. In particular, a model motivated by the phenomenological interesting case regarding Eötvös branes is investigated. It forthwith provides further physical features regarding variable tension braneworld scenarios, heretofore concealed in all previous analysis in the literature. All precedent analysis considered uniquely the expansion of the metric up to the second order along the extra dimension, which is able to evince solely the brane variable tension absolute value. Notwithstanding, the expansion terms aftermath, further accomplished in this paper from the third order on, elicits the successive covariant derivatives of the brane variable tension, and their respective coupling with the extrinsic curvature, the Weyl tensor, and the Riemann and Ricci tensors, as well as the scalar curvature. Such additional terms are shown to provide sudden modifications in the black string horizon in a variable tension braneworld scenario.

Lifshitz spacetimes are possible gravitational duals to strongly coupled field theories with an anisotropic scaling symmetry. These spacetimes, however, have a null curvature singularity. We find that higher-dimensional embeddings of Lifshitz also have a similar singularity. We study the propagation of test strings in this background and find that they become infinitely excited if they propagate through the singularity. This means that the Lifshitz geometry is unstable and will receive large corrections in string theory.

We revisit the renormalization of $\Phi$-derivable approximations from a slightly different point of view than the one which is usually followed in previous works. We pay particular attention to the question of the existence of a solution to the self-consistent equation that defines the two-point function in the Cornwall-Jackiw-Tomboulis formalism and to the fact that some of the ultraviolet divergences which appear if one formally expands the solution in powers of the bare coupling do not always appear as divergences at the level of the solution itself. We discuss these issues using a particular truncation of the $\Phi$ functional, namely, the simplest truncation which brings nontrivial momentum and field dependence to the two-point function.

In second-order scalar-tensor theories we study how the Vainshtein mechanism works in a spherically symmetric background with a matter source. In the presence of the field coupling $F(\varphi )=e^{-2Q\varphi }$ with the Ricci scalar $R$ we generally derive the Vainshtein radius within which the general relativistic behavior is recovered even for the coupling $Q$ of the order of unity. Our analysis covers the models such as the extended Galileon and Brans-Dicke theories with a dilatonic field self-interaction. We show that, if these models are responsible for the cosmic acceleration today, the corrections to gravitational potentials are generally small enough to be compatible with local gravity constraints.

A superstrong magnetic field stimulates the spontaneous production of positrons by naked nuclei by diminishing the value of the critical charge $Z_{\mathrm{cr}}$. The recently discovered phenomenon of screening of the Coulomb potential by a superstrong magnetic field acts in the opposite direction and prevents the nuclei with $Z<52$ from becoming critical. For a nucleus with $Z>52$ to become critical, stronger $B$ are needed than without taking screening into account.

We propose a model of inflation in the framework of brane cosmology driven by background supergravity. Starting from bulk supergravity we construct the inflaton potential on the brane and employ it to investigate for the consequences to inflationary paradigm. To this end, we derive the expressions for the important parameters in brane inflation, which are somewhat different from their counterparts in standard cosmology, using the one-loop radiative corrected potential. We further estimate the observable parameters and find them to fit well with recent observational data by confronting with Wilkinson Microwave Anisotropy Probe 7 (WMAP) using the Code for Anisotropies in the Microwave Background (CAMB). We also analyze the typical energy scale of brane inflation with our model, which resonates well with present estimates from cosmology and the standard model of particle physics.

The long wavelength physics in a de Sitter region depends on the initial quantum state. While such long wavelength physics is under control for massive fields near the Hartle-Hawking vacuum state, such initial states make unnatural assumptions about initial data outside the region of causal contact of a local observer. We argue that a reasonable approximation to a maximum entropy state, one that makes minimal assumptions outside an observer’s horizon volume, is one where a cutoff is placed on a surface bounded by timelike geodesics, just outside the horizon. For sufficiently early times, such a cutoff induces secular logarithmic divergences with the expansion of the region. For massive fields, these effects sum to finite corrections at sufficiently late times. The difference between the cutoff correlators and Hartle-Hawking correlators provides a measure of the theoretical uncertainty due to lack of knowledge of the initial state in causally disconnected regions. These differences are negligible for primordial inflation, but can become significant during epochs with very long-lived de Sitter regions, such as we may be entering now.

It is appealing to stabilize dark matter by the same discrete non-Abelian symmetry that is used to explain the structure of quark and lepton mass matrices. However, to generate exact tribimaximal neutrino mixing at tree level, the non-Abelian flavor symmetry must necessarily be broken by vacuum expectation values of flavon scalars, rendering dark matter unstable. We study singlet, doublet, and triplet $SU(2)$ multiplets of both scalar and fermion dark matter candidates and enumerate the conditions under which no $d<6$ dark matter decay operators are generated even in the case if the flavor symmetry is broken to nothing. We show that under the assumptions that the flavor group is fully broken and that the dark matter decay operators are suppressed only by a high scale, the vacuum expectation values of flavon scalars transforming as higher multiplets (e.g., triplets) of the flavor group must be at the electroweak scale. The most economical way for that is to use standard model Higgs boson(s) as flavons. Such models can be tested by the LHC experiments. This scenario requires the existence of additional Froggatt-Nielsen scalars that generate hierarchies in Yukawa couplings. We study the conditions under which large and small flavor breaking parameters can coexist without destabilizing the dark matter.

Measurements of $b$ hadron production ratios in proton-proton collisions at a center-of-mass energy of 7 TeV with an integrated luminosity of $3{\mathrm{pb}}^{-1}$ are presented. We study the ratios of strange $B$ meson to light $B$ meson production $f_s/(f_u+f_d)$ and ${\Lambda }_b^0$ baryon to light $B$ meson production $f_{{\Lambda }_b}/(f_u+f_d)$ as a function of the charmed hadron-muon pair transverse momentum $p_{\mathrm{T}}$ and the $b$ hadron pseudorapidity $\eta$, for $p_{\mathrm{T}}$ between 0 and 14 GeV and $\eta$ between 2 and 5. We find that $f_s/(f_u+f_d)$ is consistent with being independent of $p_{\mathrm{T}}$ and $\eta$, and we determine $f_s/(f_u+f_d)=0.134\pm {0.004}_{-0.010}^{+0.011}$, where the first error is statistical and the second systematic. The corresponding ratio $f_{{\Lambda }_b}/(f_u+f_d)$ is found to be dependent upon the transverse momentum of the charmed hadron-muon pair, $f_{{\Lambda }_b}/(f_u+f_d)=(0.404\pm 0.017(\mathrm{stat})\pm 0.027(\mathrm{syst})\pm 0.105(\mathrm{Br}))\times [1-(0.031\pm 0.004(\mathrm{stat})\pm 0.003(\mathrm{syst}))\times p_{\mathrm{T}}(\mathrm{GeV})]$, where Br reflects an absolute scale uncertainty due to the poorly known branching fraction $\mathcal{B}({\Lambda }_c^{+}\to p{K}^{-}{\pi }^{+})$. We extract the ratio of strange $B$ meson to light neutral $B$ meson production $f_s/f_d$ by averaging the result reported here with two previous measurements derived from the relative abundances of ${\overline{B}}_s^0\to D_s^{+}{\pi }^{-}$ to ${\overline{B}}^0\to D^{+}{K}^{-}$ and ${\overline{B}}^0\to D^{+}{\pi }^{-}$. We obtain $f_s/f_d={0.267}_{-0.020}^{+0.021}$.

The SciBooNE and MiniBooNE collaborations report the results of a ${\nu }_{\mu }$ disappearance search in the $\Delta m^2$ region of $0.5–40{\mathrm{eV}}^2$. The neutrino rate as measured by the SciBooNE tracking detectors is used to constrain the rate at the MiniBooNE Cherenkov detector in the first joint analysis of data from both collaborations. Two separate analyses of the combined data samples set 90% confidence level (CL) limits on ${\nu }_{\mu }$ disappearance in the $0.5–40{\mathrm{eV}}^2$ $\Delta m^2$ region, with an improvement over previous experimental constraints between 10 and $30{\mathrm{eV}}^2$.

We consider field-theoretic models, one consisting purely of scalars, the other also involving fermions, that couple to a set of constant background coupling coefficients transforming as a symmetric observer Lorentz two-tensor. We show that the exact propagators can be cast in the form of a Källén-Lehmann representation. We work out the resulting form of the Feynman propagators and the equal-time field commutators, and derive sum rules for the spectral density functions.

Supernova explosions provide the most sensitive probes of neutrino propagation, such as the possibility that neutrino velocities might be affected by the foamy structure of space-time thought to be generated by quantum-gravitational effects. Recent two-dimensional simulations of the neutrino emissions from core-collapse supernovae suggest that they might exhibit variations in time on the scale of a few milliseconds. We analyze simulations of such neutrino emissions using a wavelet technique, and consider the limits that might be set on a linear or quadratic violation of Lorentz invariance in the group velocities of neutrinos of different energies, $v/c=[1\pm (E/M_{\nu \mathrm{LV}1})]$ or $[1\pm (E/M_{\nu \mathrm{LV}2}{)}^2]$, if variations on such short time scales were to be observed, where the mass scales $M_{\nu \mathrm{LVi}}$ might appear in models of quantum gravity. We find prospective sensitivities to $M_{\nu \mathrm{LV}1}\sim 2\times {10}^{13}\mathrm{GeV}$ and $M_{\nu \mathrm{LV}2}\sim {10}^6\mathrm{GeV}$ at the 95% confidence level, up to 2 orders of magnitude beyond estimates made using previous one-dimensional simulations of core-collapse supernovae. We also analyze the prospective sensitivities to scenarios in which the propagation times of neutrinos of fixed energies are subject to stochastic fluctuations.

Hill’s equations, which first arose in the study of the Earth-Moon-Sun system, admit the two-parameter centrally extended Newton-Hooke symmetry without rotations. This symmetry allows us to extend Kohn’s theorem about the center-of-mass decomposition. Particular light is shed on the problem using Duval’s “Bargmann” framework. The separation of the center-of-mass motion into that of a guiding center and relative motion is derived by a generalized chiral decomposition.

We study the corrections to the Casimir effect in the classical geometry of two parallel metallic plates, separated by a distance $a$, due to the presence of a minimal length ($\hslash \sqrt{\beta }$) arising from quantum mechanical models based on a generalized uncertainty principle (GUP). The approach for the quantization of the electromagnetic field is based on projecting onto the maximally localized states of a few specific GUP models and was previously developed to study the Casimir-Polder effect. For each model we compute the lowest order correction in the minimal length to the Casimir energy and find that it scales with the fifth power of the distance between the plates $a^{-5}$ as opposed to the well known QED result which scales as $a^{-3}$ and, contrary to previous claims, we find that it is always attractive. The various GUP models can be in principle differentiated by the strength of the correction to the Casimir energy as every model is characterized by a specific multiplicative numerical constant.

We present a general method that can be used for geometrical and physical interpretation of an arbitrary spacetime in four or any higher number of dimensions. It is based on the systematic analysis of relative motion of free test particles. We demonstrate that the local effect of the gravitational field on particles, as described by the equation of geodesic deviation with respect to a natural orthonormal frame, can always be decomposed into a canonical set of transverse, longitudinal and Newton–Coulomb-type components, isotropic influence of a cosmological constant, and contributions arising from specific matter content of the Universe. In particular, exact gravitational waves in Einstein’s theory always exhibit themselves via purely transverse effects with $D(D-3)/2$ independent polarization states. To illustrate the utility of this approach, we study the family of pp-wave spacetimes in higher dimensions and discuss specific measurable effects on a detector located in four spacetime dimensions. For example, the corresponding deformations caused by generic higher-dimensional gravitational waves observed in such physical subspace need not be trace-free.

Numerical studies of gravitational collapse in isotropic coordinates have recently shown an interesting connection between the gravitational Lagrangian and black hole thermodynamics. A study of the actual spacetime was not the main focus of this work and, in particular, the rich and interesting structure of the interior has not been investigated in much detail and remains largely unknown. We elucidate its features by performing a numerical study of the spacetime in isotropic coordinates during gravitational collapse of a massless scalar field. The most salient feature to emerge is the formation of a thin shell of matter just inside the apparent horizon. The energy density and Ricci scalar peak at the shell and there is a jump discontinuity in the extrinsic curvature across the apparent horizon, the hallmark that a thin shell is present in its vicinity. At late stages of the collapse, the spacetime consists of two vacuum regions separated by the thin shell. The interior is described by an interesting collapsing isotropic universe. It tends towards a vacuum (never reaches a perfect vacuum) and there is a slight inhomogeneity in the interior that plays a crucial role in the collapse process as the areal radius tends to zero. The spacetime evolves towards a curvature (physical) singularity in the interior, both a Weyl and Ricci singularity. In the exterior, our numerical results match closely the analytical form of the Schwarzschild metric in isotropic coordinates, providing a strong test of our numerical code.

We study the possibility of reheating the universe through the evaporation of primordial black holes created at the end of inflation. This is shown to allow for the unification of inflation with dark matter or dark energy, or both, under the dynamics of a single scalar field. We determine the necessary conditions to recover the standard big bang by the time of nucleosynthesis after reheating through black holes.

Chern-Simons gravitational theories are extensions of general relativity in which the parity is violated due to the Chern-Simons term. We study linear perturbations on the static and spherically symmetric background spacetime both for nondynamical and dynamical Chern-Simons theories. We do not make an assumption that the background Chern-Simons scalar field vanishes, which has been adopted in the literature. By eliminating nondynamical variables using their constraint equations, we derive the reduced second order action from which a set of closed evolution equations containing only dynamical variables are immediately obtained and therefore the number of propagating degrees of freedom as well. It is found that ghost is present both for the nondynamical case and for the dynamical case unless the background Chern-Simons scalar field vanishes. It is also found that if the background scalar field vanishes, ghost degrees of freedom are killed and all the modes propagate at the speed of light.