We study the method for generating the initial data of black hole systems in Gauss-Bonnet gravity. The initial data are assumed to be momentarily static and conformally flat. Although the equation for the conformal factor is highly nonlinear, it is successfully solved by numerical relaxation for one-black-hole and two-black-hole systems. The common apparent horizon is studied in the two-black-hole initial data, and the result suggests that the Penrose inequalities are satisfied in this system. This is the first step for simulating black hole collisions in higher-curvature theories.

In this article we study the mechanical stability of spherically symmetric thin shells with charge, in Einstein-Maxwell and Einstein-Born-Infeld theories. We analyze linearized perturbations preserving the symmetry, for shells around vacuum and shells surrounding noncharged black holes.

We report a search for new gravitational physics phenomena based on Riemann-Cartan theory of general relativity including spacetime torsion. Starting from the parametrized torsion framework of Mao, Tegmark, Guth, and Cabi, we analyze the motion of test bodies in the presence of torsion, and, in particular, we compute the corrections to the perihelion advance and to the orbital geodetic precession of a satellite. We consider the motion of a test body in a spherically symmetric field, and the motion of a satellite in the gravitational field of the Sun and the Earth. We describe the torsion field by means of three parameters, and we make use of the autoparallel trajectories, which in general differ from geodesics when torsion is present. We derive the specific approximate expression of the corresponding system of ordinary differential equations, which are then solved with methods of celestial mechanics. We calculate the secular variations of the longitudes of the node and of the pericenter of the satellite. The computed secular variations show how the corrections to the perihelion advance and to the orbital de Sitter effect depend on the torsion parameters. All computations are performed under the assumptions of weak field and slow motion. To test our predictions, we use the measurements of the Moon’s geodetic precession from lunar laser ranging data, and the measurements of Mercury’s perihelion advance from planetary radar ranging data. These measurements are then used to constrain suitable linear combinations of the torsion parameters.

We develop a velocity-dependent one-scale model describing $p$-brane dynamics in flat homogeneous and isotropic backgrounds in a unified framework. We find the corresponding scaling laws in frictionless and friction-dominated regimes considering both expanding and collapsing phases.

We discuss the dynamics of the Universe within the framework of the massive graviton cold dark matter scenario (MGCDM) in which gravitons are geometrically treated as massive particles. In this modified gravity theory, the main effect of the gravitons is to alter the density evolution of the cold dark matter component in such a way that the Universe evolves to an accelerating expanding regime, as presently observed. Tight constraints on the main cosmological parameters of the MGCDM model are derived by performing a joint likelihood analysis involving the recent supernovae type Ia data, the cosmic microwave background shift parameter, and the baryonic acoustic oscillations as traced by the Sloan Digital Sky Survey red luminous galaxies. The linear evolution of small density fluctuations is also analyzed in detail. It is found that the growth factor of the MGCDM model is slightly different ($\sim 1–4\%$) from the one provided by the conventional flat $\Lambda \mathrm{CDM}$ cosmology. The growth rate of clustering predicted by MGCDM and $\Lambda \mathrm{CDM}$ models are confronted to the observations and the corresponding best fit values of the growth index ($\gamma$) are also determined. By using the expectations of realistic future x-ray and Sunyaev-Zeldovich cluster surveys we derive the dark matter halo mass function and the corresponding redshift distribution of cluster-size halos for the MGCDM model. Finally, we also show that the Hubble flow differences between the MGCDM and the $\Lambda \mathrm{CDM}$ models provide a halo redshift distribution departing significantly from the those predicted by other dark energy models. These results suggest that the MGCDM model can observationally be distinguished from $\Lambda \mathrm{CDM}$ and also from a large number of dark energy models recently proposed in the literature.

To date, 14 high-redshift ($z>1.0$) galaxy clusters with mass measurements have been observed, spectroscopically confirmed, and are reported in the literature. These objects should be exceedingly rare in the standard $\Lambda$ cold dark matter ($\Lambda \mathrm{CDM}$) model. We conservatively approximate the selection functions of these clusters’ parent surveys and quantify the tension between the abundances of massive clusters as predicted by the standard $\Lambda \mathrm{CDM}$ model and the observed ones. We alleviate the tension, considering non-Gaussian primordial perturbations of the local type, characterized by the parameter $f_{\mathrm{NL}}$, and derive constraints on $f_{\mathrm{NL}}$ arising from the mere existence of these clusters. At the $95\%$ confidence level, $f_{\mathrm{NL}}>467$, with cosmological parameters fixed to their most likely WMAP5 values, or $f_{\mathrm{NL}}\gtrsim 123$ (at $95\%$ confidence) if we marginalize over prior WMAP5 parameters. In combination with $f_{\mathrm{NL}}$ constraints from cosmic microwave background and halo bias, this determination implies a scale dependence of $f_{\mathrm{NL}}$ at $\simeq 3\sigma$. Given the assumptions made in the analysis, we expect any future improvements to the modeling of the non-Gaussian mass function, survey volumes, or selection functions to increase the significance of $f_{\mathrm{NL}}>0$ found here. In order to reconcile these massive, high-$z$ clusters with $f_{\mathrm{NL}}=0$, their masses would need to be systematically lowered by $1.5\sigma$, or the ${\sigma }_8$ parameter should be $\sim 3\sigma$ higher than cosmic microwave background (and large-scale structure) constraints. The existence of these objects is a puzzle: it either represents a challenge to the $\Lambda \mathrm{CDM}$ paradigm or it is an indication that the mass estimates of clusters are dramatically more uncertain than we think.

We confirm that in order to account for the recent D0 result of large like-sign dimuon charge asymmetry, a considerable large new physics effect in ${\Gamma }_{12}^s$ is required in addition to a large $CP$ violating phase in $B_s-{\overline{B}}_s$ mixing. In the Randall-Sundrum model of warped geometry, where the fermion fields reside in the bulk, new sources of flavor and $CP$ violation are obtained. We analyze the like-sign dimuon asymmetry in this class of model as an example of the desired new physics. We show that the wrong-charge asymmetry, $a_{sl}^s$, which is related to the dimuon asymmetry, is significantly altered compared to the standard model value. However, experimental limits from $\Delta M_s$, $\Delta {\Gamma }_s$ as well as $K$ mixing and electroweak corrections constrain it to be greater than a $\sigma$ away from its experimental average value. This model cannot fully account for the D0 anomaly due to its inability to generate a sufficient new contribution to the width difference ${\Gamma }_{12}^s$, even though the model can generate large contribution to the mass difference $M_{12}^s$.

Recently the radiative $B$ decay to the strange axial-vector mesons, $B\to K_1(1270)\gamma$, has been observed with a rather large branching ratio. This process is particularly interesting as the subsequent $K_1$ decay into its three-body final state allows us to determine the polarization of the photon, which is mostly left- (right-)handed for $\overline{B}(B)$ in the SM while various new physics models predict additional right- (left-)handed components. A new method is proposed to determine the polarization, exploiting the full Dalitz plot distribution, which seems to reduce significantly the statistical errors. This polarization measurement requires, however, detailed knowledge of the $K_1\to K\pi \pi$ strong interaction decays, namely, the various partial wave amplitudes into the several possible quasi-two-body channels, as well as their relative phases. The pattern of partial waves is especially complex for the $K_1(1270)$. We attempt to obtain the information through the combination of an experimental input and a theoretical one, provided by the ${}^{3}P_0$ quark-pair-creation model.

We determine the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon using the framework of Dyson-Schwinger and Bethe-Salpeter equations of QCD. Our result for the pseudoscalar $({\pi }^0,\eta ,{\eta }^{\prime })$ meson-exchange diagram is commensurate with previous calculations. In our calculation of the quark-loop contribution we improve upon previous approaches by explicitly implementing constraints due to gauge invariance. The impact of transverse contributions, presumably dominated by vector-meson poles, are only estimated at this stage. As a consequence, our value $a_{\mu }^{\mathrm{LBL};\mathrm{quarkloop}}=(136\pm 59)\times {10}^{-11}$ is significantly larger. Taken at face value, this then leads to a revised estimate of the total $a_{\mu }=116591891.0(105.0)\times {10}^{-11}$.

The ${\Lambda }_c(2940{)}^{+}$ baryon with quantum numbers $J^P={\frac{1}{2}}^{+}$ is considered as a hadronic molecule composed of a nucleon and $D^{*}$ meson. We give predictions for the width of the strong three-body decay processes ${\Lambda }_c(2940{)}^{+}\to {\Lambda }_c(2286{)}^{+}{\pi }^{+}{\pi }^{-}$ and ${\Lambda }_c(2286{)}^{+}{\pi }^0{\pi }^0$ in this interpretation. Upcoming experimental facilities like a Super $B$ factory at KEK or LHCb might be able to provide data on these decay modes.

The search for new interactions of neutrinos beyond those of the standard model may help to elucidate the mechanism responsible for neutrino masses. Here, we combine existing accelerator neutrino data with restrictions coming from a recent atmospheric neutrino data analysis in order to lift parameter degeneracies and improve limits on new interactions of muon neutrinos with quarks. In particular, we reconsider the results of the E-815 experiment at Fermilab (NuTeV) in view of a new evaluation of its systematic uncertainties. We find that, although constraints for muon neutrinos are better than those applicable to tau or electron neutrinos, they lie at the $\mathrm{\text{few}}\times {10}^{-2}$ level, not as strong as previously believed. We briefly discuss prospects for further improvement.

The measurement of forward-backward asymmetry in the top and antitop quark ($t\overline{t}$) production has been recently reconfirmed by the CDF Collaboration and shows a more than $3\sigma$ deviation from the standard model prediction in the large $t\overline{t}$ invariant mass region. Models with new $W^{\prime }$ or $Z^{\prime }$ bosons have been invoked to explain this deviation. In the context of these models we perform a ${\chi }^2$ analysis with all the available experimental numbers in different $\Delta Y$ and $M_{t\overline{t}}$ bins. We show that for the $Z^{\prime }$ model the region of parameter space which explains the Tevatron asymmetry can be probed in the same sign top production channel by Tevatron itself. Moreover, we consider a recently proposed observable, the one-sided forward-backward asymmetry ($A_{\mathrm{OFB}}$) at the LHC and conclude that both the $W^{\prime }$ and $Z^{\prime }$ models can lead to sizable $A_{\mathrm{OFB}}$ even at the LHC running at a center of mass energy of 7 TeV for the model parameters consistent with the Tevatron measurements.

The cosmological consequences of Horava’s gravity are reviewed in the frameworks of the PAMELA experiment (which has reported an excess of positron events that likely can be ascribed to weakly interacting massive particles dark matter) and of big bang nucleosynthesis. Constraints on parameters characterizing Horawa’s cosmology are derived.

We study the spectrum of off-diagonal fluctuations between displaced fuzzy spheres in the Berenstein-Maldacena-Nastase plane wave matrix model. The displacement is along the plane of the fuzzy spheres. We find that when two fuzzy spheres intersect at angles, classical tachyons develop and that the spectrum of these modes can be computed analytically. These tachyons can be related to the familiar Nielsen-Olesen instabilities in Yang-Mills theory on a constant magnetic background. Many features of the problem become more apparent when we compare with maximally supersymmetric Yang-Mills theory on a sphere, of which this system is a truncation. We also set up a simple oscillatory trajectory on the displacement between the fuzzy spheres and study the dynamics of the modes as they become tachyonic for part of the oscillations. We speculate on their role regarding the possible thermalization of the system.

A fully geometrical treatment of general relativistic magnetohydrodynamics is developed under the hypotheses of perfect conductivity, stationarity, and axisymmetry. The spacetime is not assumed to be circular, which allows for greater generality than the Kerr-type spacetimes usually considered in general relativistic magnetohydrodynamics. Expressing the electromagnetic field tensor solely in terms of three scalar fields related to the spacetime symmetries, we generalize previously obtained results in various directions. In particular, we present the first relativistic version of the Soloviev transfield equation, subcases of which lead to fully covariant versions of the Grad-Shafranov equation and of the Stokes equation in the hydrodynamical limit. We have also derived, as another subcase of the relativistic Soloviev equation, the equation governing magnetohydrodynamical equilibria with purely toroidal magnetic fields in stationary and axisymmetric spacetimes.

We consider the measure problem in standard slow-roll inflationary models from the perspective of loop quantum cosmology (LQC). Following recent results by Ashtekar and Sloan, we study the probability of having enough $e$-foldings and focus on its dependence on the quantum gravity scale, including the transition of the theory to the limit where general relativity (GR) is recovered. Contrary to the standard expectation, the probability of having enough inflation, that is close to 1 in LQC, grows and tends to 1 as one approaches the GR limit. We study the origin of the tension between these results with those by Gibbons and Turok, and offer an explanation that brings these apparent contradictory results into a coherent picture. As we show, the conflicting results stem from different choices of initial conditions for the computation of probability. The singularity-free scenario of loop quantum cosmology offers a natural choice of initial conditions, and suggests that enough inflation is generic.

Some interesting gravitational properties of the Bergshoeff-Hohm-Townsend model (massive 3D gravity), such as the presence of a short-range gravitational force in the nonrelativistic limit and the existence of an impact-parameter-dependent gravitational deflection angle, are studied. Interestingly enough, these phenomena have no counterpart in the usual Einstein 3D gravity. In order to better understand the two aforementioned gravitational properties, they are also analyzed in the framework of 3D higher-derivative gravity with the Einstein-Hilbert term with the “wrong sign.”

In this paper we find different types of black holes for the Born-Infeld extended new massive gravity. Our solutions include (un)charged warped (anti-)de Sitter black holes for four and six derivative expanded action. We also look at the black holes in unexpanded Born-Infeld action. In each case we calculate the entropy, angular momentum and mass of the black holes. We also find the central charges for the conformal field theory duals.

We study the classical and quantum models of a flat Friedmann-Robertson-Walker space-time, coupled to a perfect fluid, in the context of the consensus and a gauge-fixed Lagrangian frameworks. It is shown that, either in the usual or in the gauge-fixed actions, the evolution of the Universe based on the classical cosmology represents a late time power law expansion, coming from a big-bang singularity in which the scale factor goes to zero for the standard matter, and tending towards a big-rip singularity in which the scale factor diverges for the phantom fluid. We then employ the familiar canonical quantization procedure in the given cosmological setting to find the cosmological wave functions in the corresponding minisuperspace. Using a gauge-fixed (reduced) Lagrangian, we show that it may lead to a Schrödinger equation for the quantum-mechanical description of the model under consideration, the eigenfunctions of which can be used to construct the time dependent wave function of the Universe. We use the resulting wave function in order to investigate the possibility of the avoidance of classical singularities due to quantum effects by means of the many-worlds and ontological interpretation of quantum cosmology.

We study the scale and redshift dependence of the power spectra for density perturbations and peculiar velocities, and the evolution of a coarse grained phase space density for warm dark matter (WDM) particles that decoupled during the radiation dominated stage. The WDM corrections are obtained in a perturbative expansion valid in the range of redshifts at which N-body simulations set up initial conditions, and for a wide range of scales. The redshift dependence is determined by the kurtosis ${\beta }_2$ of the distribution function at decoupling. At large redshift there is an enhancement of peculiar velocities for ${\beta }_2>1$ that contributes to free streaming and leads to further suppression of the matter power spectrum and an enhancement of the peculiar velocity autocorrelation function at scales smaller than the free streaming scale. Statistical fluctuations of peculiar velocities are also suppressed on these scales by the same effect. In the linearized approximation, the coarse grained phase space density features redshift dependent WDM corrections from gravitational perturbations determined by the power spectrum of density perturbations and ${\beta }_2$. For ${\beta }_2>25/21$ it grows logarithmically with the scale factor as a consequence of the suppression of statistical fluctuations. Two specific models for WDM are studied in detail. The WDM corrections relax the bounds on the mass of the WDM particle candidate.