We consider an anisotropic braneworld model with Bianchi type I and V geometry, without mirror symmetry or any form of junction conditions. The generalized Chaplygin gas, which interpolates between a high density relativistic era and a nonrelativistic matter phase, is a popular candidate for the present accelerated expansion of the Universe. Considering the generalized Chaplygin gas as a geometrical dark energy, we obtain the general solutions in an exact parametric form for both Bianchi type I and V space-times. Finally, we study the behavior of the observationally important parameters such as the shear, anisotropic, and deceleration parameters in this model.

We investigate conformal scalar, electromagnetic, and massless Dirac quasinormal modes of a brane-localized black hole. The background solution is the four-dimensional black hole on a 2-brane that has been constructed by Emparan, Horowitz, and Myers in the context of a lower-dimensional version of the Randall-Sundrum model. The conformally transformed metric admits a Killing tensor, allowing us to obtain separable field equations. We find that the radial equations take the same form as in the four-dimensional braneless Schwarzschild black hole. The angular equations are, however, different from the standard ones, leading to a different prediction for quasinormal frequencies.

Massive black hole binaries are key targets for the space based gravitational wave Laser Interferometer Space Antenna (LISA). Several studies have investigated how LISA observations could be used to constrain the parameters of these systems. Until recently, most of these studies have ignored the higher harmonic corrections to the waveforms. Here we analyze the effects of the higher harmonics in more detail by performing extensive Monte Carlo simulations. We pay particular attention to how the higher harmonics impact parameter correlations, and show that the additional harmonics help mitigate the impact of having two laser links fail, by allowing for an instantaneous measurement of the gravitational wave polarization with a single interferometer channel. By looking at parameter correlations we are able to explain why certain mass ratios provide dramatic improvements in certain parameter estimations, and illustrate how the improved polarization measurement improves the prospects for single interferometer operation.

Based on the stochastic gravity, we study the loop corrections to the scalar and tensor perturbations during inflation. Since the loop corrections to scalar perturbations suffer infrared divergence, we consider the IR regularization to obtain the finite value. We find that the loop corrections to the scalar perturbations are amplified by the e-folding; in other words there appears the logarithmic correction, just as discussed by M. Sloth et al. On the other hand, we find that the tensor perturbations do not suffer from infrared divergence.

The structure of the effective potential $V$ describing causal geodesics near the throat of an arbitrary spherical wormhole is analyzed. Einstein’s equations relative to a set of regular coordinates covering a vicinity of the throat imply that any spherical wormhole can be constructed from solutions of an effective initial value problem with the throat serving as an initial value surface. The initial data involve matter variables, the area $A(0)$ of the throat, and the gradient $\Lambda (0)$ of the redshift factor on the throat. Whenever $\Lambda (0)=0$, the effective potential $V$ has a critical point on the throat. Conditions upon the data are derived ensuring that the critical point is a local minimum (respectively maximum). For particular families of quasi-Schwarzschild wormholes, $V$ exhibits a local minimum on the throat independently upon the energy $E$ and angular momentum $L^2$ of the test particles and thus such wormholes admit stable circular timelike and null geodesics on the throat. For families of Chaplygin wormholes, we show that such geodesics are unstable. Based on a suitable power series representation of the metric, properties of $V$ away from the throat are obtained that are useful for the analysis of accretion disks and radiation processes near the throat of any spherical wormhole.

We consider the scattering of a photon by a weak gravitational field, treated as an external field, up to second order of the perturbation expansion. The resulting cross section is energy dependent which indicates a violation of Galileo’s equivalence principle (universality of free fall) and, consequently, of the classical equivalence principle. The deflection angle $\theta$ for a photon passing by the sun is evaluated afterward and the likelihood of detecting $\frac{\Delta \theta }{{\theta }_E}\equiv \frac{\theta -{\theta }_E}{{\theta }_E}$ (where ${\theta }_E$ is the value predicted by Einstein’s geometrical theory for the light bending) in the foreseeable future, is discussed.

We study the dynamical stability of the Banados-Teitelboim-Zanelli (BTZ) black string against fermionic and gravitational perturbations. The BTZ black string is not always stable against these perturbations. There exist threshold values for $m^2$ related to the compactification of the extra dimension for fermionic perturbation, the scalar part of the gravitational perturbation, and the tensor perturbation, respectively. Above the threshold values, perturbations are stable; while below these thresholds, perturbations can be unstable. We find that this nontrivial stability behavior qualitatively agrees with that predicted by a thermodynamical argument, showing that the BTZ black string phase is not the privileged stable phase.

We propose a new cosmological paradigm in which our observed expanding phase is originated from an initially large contracting Universe that subsequently experienced a bounce. This category of models, being geodesically complete, is nonsingular and horizon-free and can be made to prevent any relevant scale to ever have been smaller than the Planck length. In this scenario, one can find new ways to solve the standard cosmological puzzles. One can also obtain scale invariant spectra for both scalar and tensor perturbations: this will be the case, for instance, if the contracting Universe is dust-dominated at the time at which large wavelength perturbations get larger than the curvature scale. We present a particular example based on a dust fluid classically contracting model, where a bounce occurs due to quantum effects, in which these features are explicit.

We study high energy cosmic rays from the decay of the gravitino dark matter in the framework of supersymmetric model with $R$-parity violation. Even though $R$ parity is violated, the lifetime of the gravitino, which is assumed to be the lightest superparticle, can be longer than the present age of the Universe if $R$-parity violating interactions are weak enough. We have performed a detailed calculation of the fluxes of gamma ray and positron from the decay of the gravitino dark matter. We also discuss the implication of such a scenario to present and future observations of high energy cosmic rays. In particular, we show that the excess of the gamma-ray flux observed by Energetic Gamma Ray Experiment Telescope and the large positron fraction observed by High Energy Antimatter Telescope can be simultaneously explained by the cosmic rays from the decay of the gravitino dark matter.

It is nowadays accepted that the universe is undergoing a phase of accelerated expansion as tested by the Hubble diagram of type Ia supernovae (SNeIa) and several large scale structure observations. Future SNeIa surveys and other probes will make it possible to better characterize the dynamical state of the universe, renewing the interest in cosmography which allows a model independent analysis of the distance-redshift relation. On the other hand, fourth order theories of gravity, also referred to as $f(R)$ gravity, have attracted a lot of interest since they could be able to explain the accelerated expansion without any dark energy. We show here how it is possible to relate the cosmographic parameters (namely, the deceleration $q_0$, the jerk $j_0$, the snap $s_0$, and the lerk $l_0$ parameters) to the present-day values of $f(R)$ and its derivatives $f^{(n)}(R)=d^{n}f/d{R}^n$ (with $n=1$, 2, 3), thus offering a new tool to constrain such higher order models. Our analysis thus offers the possibility to relate the model independent results coming from cosmography to the theoretically motivated assumptions of $f(R)$ cosmology.

Modifications of general relativity provide an alternative explanation to dark energy for the observed acceleration of the Universe. Modified gravity theories have richer observational consequences for large-scale structures than conventional dark energy models, in that different observables are not described by a single growth factor even in the linear regime. We examine the relationships between perturbations in the metric potentials, density and velocity fields, and discuss strategies for measuring them using gravitational lensing, galaxy cluster abundances, galaxy clustering/dynamics, and the integrated Sachs-Wolfe effect. We show how a broad class of gravity theories can be tested by combining these probes. A robust way to interpret observations is by constraining two key functions: the ratio of the two metric potentials, and the ratio of the gravitational “constant” in the Poisson equation to Newton’s constant. We also discuss quasilinear effects that carry signatures of gravity, such as through induced three-point correlations. Clustering of dark energy can mimic features of modified gravity theories and thus confuse the search for distinct signatures of such theories. It can produce pressure perturbations and anisotropic stresses, which break the equality between the two metric potentials even in general relativity. With these two extra degrees of freedom, can a clustered dark energy model mimic modified gravity models in all observational tests? We show with specific examples that observational constraints on both the metric potentials and density perturbations can in principle distinguish modifications of gravity from dark energy models. We compare our result with other recent studies that have slightly different assumptions (and apparently contradictory conclusions).

We study the effect of thermal corrections on the evolution of moduli in effective supergravity models. This is motivated by previous results in the literature suggesting that these corrections could alter and even erase the presence of a minimum in the zero temperature potential, something that would have disastrous consequences in these particular models. We show that, in a representative sample of flux compactification constructions, this need not be the case, although we find that the inclusion of thermal corrections can dramatically decrease the region of initial conditions for which the moduli are stabilized. Moreover, the bounds on the reheating temperature coming from demanding that the full, finite temperature potential, has a minimum can be considerably relaxed given the slow pace at which the evolution proceeds.

The Hubble relation between distance and redshift is a purely cosmographic relation that depends only on the symmetries of a Friedmann-Lemaitre-Robertson-Walker spacetime, but does not intrinsically make any dynamical assumptions. This suggests that it should be possible to estimate the parameters defining the Hubble relation without making any dynamical assumptions. To test this idea, we perform a number of interrelated cosmographic fits to the $\mathtt{l}\mathtt{e}\mathtt{g}\mathtt{a}\mathtt{c}\mathtt{y}\mathtt{05}$ and $\mathtt{g}\mathtt{o}\mathtt{l}\mathtt{d}\mathtt{06}$ supernova data sets. Based on this supernova data, the “preponderance of evidence” certainly suggests an accelerating universe. However, we would argue that (unless one uses additional dynamical and observational information) this conclusion is not currently supported “beyond reasonable doubt.” As part of the analysis we develop two particularly transparent graphical representations of the redshift-distance relation—representations in which acceleration versus deceleration reduces to the question of whether the relevant graph slopes up or down. Turning to the details of the cosmographic fits, three issues in particular concern us: First, the fitted value for the deceleration parameter changes significantly depending on whether one performs a ${\chi }^2$ fit to the luminosity distance, proper motion distance, angular diameter distance, or other suitable distance surrogate. Second, the fitted value for the deceleration parameter changes significantly depending on whether one uses the traditional redshift variable $z$ or what we shall argue is, on theoretical grounds, an improved parametrization $y=z/(1+z)$. Third, the published estimates for systematic uncertainties are sufficiently large that they certainly impact on, and to a large extent undermine, the usual purely statistical tests of significance. We conclude that the supernova data should be treated with some caution.

The propagation of photons, electrons and positrons at ultrahigh energies above $\sim {10}^{19}\mathrm{eV}$ can be changed considerably if the dispersion relations of these particles are modified by terms suppressed by powers of the Planck scale. We recently pointed out that the current nonobservation of photons in the ultrahigh-energy cosmic ray flux at such energies can put strong constraints on such modified dispersion relations. In the present work we generalize these constraints to all three Lorentz invariance-breaking parameters that can occur in the dispersion relations for photons, electrons and positrons at first- and second-order suppression with the Planck scale. We also show how the excluded regions in these three-dimensional parameter ranges would be extended if ultrahigh-energy photons were detected in the future.

The detection of Earth-skimming tau neutrinos has turned into a very promising strategy for the observation of ultra-high-energy cosmic neutrinos. The sensitivity of this channel crucially depends on the parameters of the propagation of the tau neutrinos through the terrestrial crust, which governs the flux of emerging tau leptons that can be detected. One of the characteristics of this propagation is the possibility of regeneration through multiple ${\nu }_{\tau }\leftrightarrow \tau$ conversions, which are often neglected in the standard picture. In this paper, we solve the transport equations governing the ${\nu }_{\tau }$ propagation and compare the flux of emerging tau leptons obtained allowing regeneration or not. We discuss the validity of the approximation of neglecting the ${\nu }_{\tau }$ regeneration using different scenarios for the neutrino-nucleon cross sections and the tau energy losses.

We study the dynamics of a phantom scalar field dark energy interacting with dark matter in loop quantum cosmology. Two kinds of coupling of the form $\alpha {\rho }_m\dot{\varphi }$ (case I) and $3\beta H({\rho }_{\varphi }+{\rho }_m)$ (case II) between the phantom energy and dark matter are examined with the potential for the phantom field taken to be exponential. For both kinds of interactions, we find that the future singularity appearing in the standard Friedmann-Robertson-Walker cosmology can be avoided by loop quantum gravity effects. In case II, if the phantom field is initially rolling down the potential, the loop quantum effect has no influence on the cosmic late time evolution and the universe will accelerate forever with a constant energy ratio between the dark energy and dark matter.

In the framework of general relativity we develop a method for the analysis of the operation of the optical position meters in their photodetectors proper reference frames. These frames are noninertial in general due to the action of external fluctuative forces on meters test masses, including detectors. For comparison we also perform the calculations in the laboratory (globally inertial) reference frame and demonstrate that for certain optical schemes laboratory-based analysis results in unmeasurable quantities, in contrast to the detector-based analysis. We also calculate the response of the simplest optical meters to weak plane gravitational waves and fluctuative motions of their test masses. It is demonstrated that for the round-trip meter analysis in both the transverse-traceless (TT) and local Lorentz (LL) gauges produces equal results, while for the forward-trip meter corresponding results differ in accordance with different physical assumptions (e.g. procedure of clocks synchronization) implicitly underlying the construction of the TT and LL gauges.

We consider a generic Abelian hidden sector that couples to the standard model only through gauge-invariant renormalizable operators. This allows the exotic Higgs boson to mix with the standard model Higgs boson, and the exotic Abelian gauge boson to mix with the standard model hypercharge gauge boson. One immediate consequence of spontaneous breaking of the hidden sector gauge group is the possible decay of the lightest Higgs boson into four fermions through intermediate exotic gauge bosons. We study the implications of this decay for Higgs boson phenomenology at the Fermilab Tevatron Collider and the CERN Large Hadron Collider. Our emphasis is on the four-lepton final state.

Applying a likelihood analysis to the next-to-minimal supergravity-motivated model, we identify parameter space regions preferred by present experimental limits from collider, astrophysical, and low energy measurements. We then show that favored regions are amenable to detection by a combination of the CERN Large Hadron Collider and an upgraded cryogenic dark matter search, provided that the more than three sigma discrepancy in the difference of the experimental and the standard theoretical values of the anomalous magnetic moment of the muon prevails in the future.

In this work we perform the parameter tuning of three flavors of dynamical clover quarks on anisotropic lattices. The fermion action uses three-dimensional spatial stout-link smearing. The gauge anisotropy is determined in a small box with Schrödinger background using Wilson-loop ratios. The fermion anisotropy is obtained from studying the meson dispersion relation with antiperiodic boundary conditions in the time direction. The spatial and temporal clover coefficients are fixed to the tree-level tadpole-improved values, and we demonstrate that they satisfy the nonperturbative conditions as determined by the Schrödinger-functional method. For the desired lattice spacing $a_s\approx 0.12\mathrm{fm}$ and renormalized anisotropy $\xi =3.5$, we find the gauge and fermionic anisotropies can be fixed to quark mass independent values up through the strange quark mass. This work lays the foundation needed for further studies of the excited-state hadron spectrum.