We have performed a detailed analysis of orbital motion in the vicinity of a nearly extremal Kerr black hole. For very rapidly rotating black holes—spin parameter $a\equiv J/M>0.9524M$—we have found a class of very strong-field eccentric orbits whose orbital angular momentum $L_z$ increases with the orbit’s inclination with respect to the equatorial plane, while keeping latus rectum and eccentricity fixed. This behavior is in contrast with Newtonian intuition, and is in fact opposite to the normal behavior of black hole orbits. Such behavior was noted previously for circular orbits; since it only applies to orbits very close to the black hole, they were named “nearly horizon-skimming orbits.” Our current analysis generalizes this result, mapping out the full generic (inclined and eccentric) family of nearly horizon-skimming orbits. The earlier work on circular orbits reported that, under gravitational radiation emission, nearly horizon-skimming orbits exhibit unusual inspiral, tending to evolve to smaller orbit inclination, toward prograde equatorial configuration. Normal orbits, by contrast, always demonstrate slowly growing orbit inclination—orbits evolve toward the retrograde equatorial configuration. Using up-to-date Teukolsky-based fluxes, we have concluded that the earlier result was incorrect—all circular orbits, including nearly horizon-skimming ones, exhibit growing orbit inclination under radiative backreaction. Using kludge fluxes based on a Post-Newtonian expansion corrected with fits to circular and to equatorial Teukolsky-based fluxes, we argue that the inclination grows also for eccentric nearly horizon-skimming orbits. We also find that the inclination change is, in any case, very small. As such, we conclude that these orbits are not likely to have a clear and peculiar imprint on the gravitational waveforms expected to be measured by the space-based detector LISA.

It is known that any explicit averaging scheme of the type essential for describing the large scale behavior of the Universe must necessarily yield corrections to the Einstein equations applied in the cosmological setting. The question of whether or not the resulting corrections to the Einstein equations are significant is still a subject of debate, partly due to possible ambiguities in the averaging schemes available. In particular, it has been argued in the literature that the effects of averaging could be gauge artifacts. We apply the formalism of Zalaletdinov’s macroscopic gravity (MG), which is a fully covariant and nonperturbative averaging scheme, in an attempt to construct gauge independent corrections to the standard Friedmann-Lemaître-Robertson-Walker (FLRW) equations. We find that whereas one cannot escape the problem of dependence on one gauge choice—which is inherent in the assumption of large scale homogeneity and isotropy—it is however possible to construct space-time scalar corrections to the standard FLRW equations. This partially removes the criticism concerning the corrections being gauge artifacts. For a particular initial choice of gauge which simplifies the formalism, we explicitly construct these scalars in terms of the underlying inhomogeneous geometry, and incidentally demonstrate that the formal structure of the corrections with this gauge choice is identical to that of analogous corrections derived by Buchert in the context of spatial averaging of scalars.

In models with large extra dimensions, black holes may be produced in high-energy particle collisions. We revisit the physics of black hole formation in extensive air showers from ultrahigh-energy cosmic rays, focusing on collisional QCD and black hole emissivity effects. New results for rotating black holes are presented. Monte Carlo simulations show that QCD effects and black hole spin produce no observable signatures in air showers. These results further confirm that the main characteristics of black hole-induced air showers do not depend on the fine details of micro-black-hole models.

It has been known that the Bekenstein-Hawking entropy of the black hole in ${\mathrm{AdS}}_5\times S^5$ agrees with the free $\mathcal{N}=4$ super Yang-Mills entropy up to the famous factor $\frac{4}{3}$. This factor can be interpreted as the ratio of the entropy of the free Yang-Mills theory to the entropy of the strongly coupled Yang-Mills theory. In this paper we compute an analogous factor for infinitely many $\mathcal{N}=1$ superconformal field theories (SCFTs) which are dual to toric Sasaki-Einstein manifolds. We observed that this ratio always takes values within a narrow range around $\frac{4}{3}$. We also present explicit values of volumes and central charges for new classes of toric Sasaki-Einstein manifolds.

Gravitational lensing of the cosmic microwave background (CMB), a long-standing prediction of the standard cosmological model, is ultimately expected to be an important source of cosmological information, but first detection has not been achieved to date. We report a $3.4\sigma$ detection, by applying quadratic estimator techniques to all sky maps from the Wilkinson microwave anisotropy probe (WMAP) satellite, and correlating the result with radio galaxy counts from the NRAO VLA sky survey (NVSS). We present our methodology including a detailed discussion of potential contaminants. Our error estimates include systematic uncertainties from density gradients in NVSS, beam effects in WMAP, galactic microwave foregrounds, resolved and unresolved CMB point sources, and the thermal Sunyaev-Zel’dovich effect.

In this paper, I suppose that the Universe begins in a holographic thermal equilibrium phase with the diverged correlation length, and the phase transition to the radiation phase of standard cosmology goes with the abrupt reduction of correlation length. In this case, the primordial perturbations may be induced by thermal fluctuations in this holographic phase. I calculate the spectra of these holographic primordial perturbations and find that the scalar spectrum has a slightly red tilt and the tensor perturbation amplitude has a moderate ratio, which may be tested in coming observations. The results plotted in the $r-n_s$ plane are similar to that of large field inflation models. However, for fixed efolding number, they are generally in different positions.

Many ambitious experiments have been proposed to constrain dark energy and detect its evolution. At the present, observational constraints are consistent with a cosmological constant and there is no firm evidence for any evolution in the dark energy equation of state $w$. In this paper, we pose the following question: suppose that future dark energy surveys constrain $w$ at low redshift to be consistent with $-1$ to a percent level accuracy, what are the implications for models of dynamical dark energy? We investigate this problem in a model-independent way by following quintessence field trajectories in “energy” phase-space. Attractor dynamics in this phase-space leads to two classes of acceptable models: (1) models with flat potentials, i.e. an effective cosmological constant, and (2) models with potentials that suddenly flatten with a characteristic kink. The prospect of further constraining the second class of models from distance measurements and fluctuation growth rates at low redshift ($z\lesssim 3$) seems poor. However, in some models of this second class, the dark energy makes a significant contribution to the total energy density at high redshift. Such models can be further constrained from observation of the cosmic microwave background anisotropies and from primordial nucleosynthesis. It is possible, therefore, to construct models in which the dark energy at high redshift causes observable effects, even if future dark energy surveys constrain $w$ at low redshift to be consistent with $-1$ to high precision.

The excitation of quadrupolar quasinormal modes in a neutron star leads to the emission of a short, distinctive, burst of gravitational radiation in the form of a decaying sinusoid or “ring-down.” We present a Bayesian analysis method which incorporates relevant prior information about the source and known instrumental artifacts to conduct a robust search for the gravitational wave emission associated with pulsar glitches and soft $\gamma$-ray repeater flares. Instrumental transients are modeled as sine-Gaussian and their evidence, or marginal likelihood, is compared with that of Gaussian white noise and ring-downs via the “odds-ratio.” Tests using simulated data with a noise spectral density similar to the LIGO interferometer around 1 kHz yield 50% detection efficiency and 1% false alarm probability for ring-down signals with signal-to-noise ratio $\rho =5.2$. For a source at 15 kpc this requires an energy of $1.3\times {10}^{-5}{M}_{\odot }{c}^2$ to be emitted as gravitational waves.

A precise determination, and comparison, of the epoch of the onset of cosmic acceleration, at redshift $z_{\mathrm{acc}}$, and of dark energy domination, at $z_{\mathrm{eq}}$, provides an interesting measure with which to parametrize dark energy models. By combining several cosmological data sets, we place constraints on the redshift and age of cosmological acceleration. For a $\Lambda \mathrm{CDM}$ model, we find the constraint $z_{\mathrm{acc}}=0.76\pm 0.10$ at 95% C.L., occurring $6.7\pm 0.4\mathrm{Gyr}$ ago. Allowing a constant equation of state but different from $-1$ changes the constraint to $z_{\mathrm{acc}}=0.81\pm 0.12$ ($6.9\pm 0.5\mathrm{Gyr}$ ago), while dynamical models markedly increase the error on the constraint $z_{\mathrm{acc}}=0.81\pm 0.30$ ($6.8\pm 1.4\mathrm{Gyr}$ ago). Unified dark energy models such as silent quartessence yield $z_{\mathrm{acc}}=0.8\pm 0.16$ ($6.8\pm 0.6\mathrm{Gyr}$ ago). Interestingly, we find that the best fit $z_{\mathrm{acc}}$ and $z_{\mathrm{eq}}$ are remarkably insensitive to both the cosmological data sets and theoretical dark energy models considered.

We present pseudorapidity and transverse-momentum distributions for the cross section for the production of the lightest neutral Higgs boson in association with a high-$p_T$ hadronic jet, calculated in the framework of the minimal supersymmetric standard model. We discuss the theoretical predictions for the differential cross sections at the CERN Large Hadron Collider and the Fermilab Tevatron for the most common benchmark scenarios.

Scattering observables can be computed in lattice field theory by measuring the volume dependence of energy levels of two-particle states. The dominant volume dependence, proportional to inverse powers of the volume, is determined by the phase shifts. This universal relation (Lüscher’s formula) between energy levels and phase shifts is distorted by corrections which, in the large volume limit, are exponentially suppressed. They may be sizable, however, for the volumes used in practice, and they set a limit on how small the lattice can be in these studies. We estimate these corrections, mostly in the case of two nucleons. Qualitatively, we find that the exponentially suppressed corrections are proportional to the square of the potential (or to terms suppressed in the chiral expansion) and the effect due to pions going “around the world” vanishes. Quantitatively, the size of the lattice should be greater than $\approx (5\mathrm{fm}{)}^3$ in order to keep finite volume corrections to the phase less than 1° for realistic pion mass.

We investigate the dissipative real-time evolution of the order parameter for the deconfining transition in the pure $SU(2)$ gauge theory. The approach to equilibrium after a quench to temperatures well above the critical one is described by a Langevin equation. To fix completely the Markovian Langevin dynamics we choose the dissipation coefficient, that is a function of the temperature, guided by preliminary Monte Carlo simulations for various temperatures. Assuming a relationship between Monte Carlo time and real time, we estimate the delay in thermalization brought about by dissipation and noise.

We update the analytical estimate of the final spin of a coalescing black-hole binary derived within the effective-one-body (EOB) approach. We consider unequal-mass nonspinning black-hole binaries. It is found that a more complete account of relevant physical effects (higher post-Newtonian accuracy, ringdown losses) allows the analytical EOB estimate to “converge towards” the recently obtained numerical results within 2%. This agreement illustrates the ability of the EOB approach to capture the essential physics of coalescing black-hole binaries. Our analytical approach allows one to estimate the final spin of the black hole formed by coalescing binaries in a mass range [$\nu =m_1{m}_2/(m_1+m_2{)}^2<0.16$] which is not presently covered by numerical simulations.

We study the consequences of the gravitino decay into dark matter. We suppose that the lightest neutralino is the main component of dark matter. In our framework the gravitino is heavy enough to decay before big bang nucleosynthesis starts. We consider a model coming from a five dimensional supergravity compactified on $S^1/Z_2$ with gravity in the bulk and matter localized on tensionless branes at the orbifold fixed points. We require that the dark matter, which is produced thermally and in the decay of Kaluza-Klein modes of the gravitino, has an abundance compatible with observation. We deduce from our model that there are curves of constraints between the size of the extra dimension and the reheating temperature of the Universe after inflation.

We study the uncertainties of the determination of the ground-state parameters from Shifman-Vainshtein-Zakharov (SVZ) sum rules, making use of the harmonic-oscillator potential model as an example. In this case, one knows the exact solution for the polarization operator $\Pi (\mu )$, which allows one to obtain both the operator product expansion (OPE) to any order and the spectrum of states. We start with the OPE for $\Pi (\mu )$ and analyze the extraction of the square of the ground-state wave function, $R\propto |{\Psi }_0(\overrightarrow{r}=0){|}^2$, from an SVZ sum rule, setting the mass of the ground state $E_0$ equal to its known value and treating the effective continuum threshold as a fit parameter. We show that in a limited fiducial range of the Borel parameter there exists a solution for the effective threshold which precisely reproduces the exact $\Pi (\mu )$ for any value of $R$ within the range $0.7\le R/R_0\le 1.15$ ($R_0$ is the known exact value). Thus, the value of $R$ extracted from the sum rule is determined to a great extent by the contribution of the hadron continuum. Our main finding is that in the cases where the hadron continuum is not known and is modeled by an effective continuum threshold, the systematic uncertainties of the sum-rule procedure cannot be controlled.

Recent observations of the $J/\psi$ spectrum produced in $e^{+}{e}^{-}$ collisions at the ${\rm Y}(4S)$ resonance are in conflict with fixed-order calculations using the nonrelativsitic QCD effective theory (NRQCD). One problem is an enhancement in the cross section when the $J/\psi$ has maximal energy, due to large perturbative corrections (Sudakov logarithms). In a recent paper, the Sudakov logarithms in the color-octet contribution were summed by combining NRQCD with the soft-collinear effective theory. However, to be consistent, the color-singlet contributions must also be summed in the endpoint region which was not done in that paper. In this paper, we sum the leading logarithms in the color-singlet contribution to the $J/\psi$ production cross section. We find that the color-singlet cross section is suppressed near the endpoint compared to the fixed-order NRQCD prediction.

In this paper, we will consider the chiral symmetry breaking in the holographic model constructed from the intersecting brane configuration, and investigate the Nambu-Goldstone bosons associated with this symmetry breaking.

It is shown that, in a model in which up-type and down-type fermions acquire mass from different Higgs doublets, the anthropic tuning of the Higgs mass parameters can explain the fact that the observed masses of the $d$ and $u$ quarks are nearly the same with $d$ slightly heavier. If Yukawa couplings are assumed not to scan (vary among domains), this would also help explain why $t$ is much heavier than $b$. It is also pointed out that the existence of dark matter invalidates some earlier anthropic arguments against the viability of domains where the standard model Higgs has positive ${\mu }^2$, but makes other even stronger arguments possible.

It is possible that the scale of gravity, parametrized by the apparent Planck mass, may obtain different values within different universes in an encompassing multiverse. We investigate the range over which the Planck mass may scan while still satisfying anthropic constraints. The window for anthropically allowed values of the Planck mass may have important consequences for landscape predictions. For example, if the likelihood to observe some value of the Planck mass is weighted by the inflationary expansion factors of the universes that contain that value, then it appears extremely unlikely to observe the value of the Planck mass that is measured within our universe. This is another example of the runaway inflation problem discussed in recent literature. We also show that the window for the Planck mass significantly weakens the anthropic constraint on the cosmological constant when both are allowed to vary over a landscape.

We reconstruct from the Wilkinson microwave anisotropy probe three-year data the slow-roll parameters in the standard slow-roll inflation model and the noncommutative inflation model. We also investigate the evolution of these slow-roll parameters. Requiring that slow-roll inflation lasts more than 20 e-folds after cosmic microwave background scales leave the horizon, we find that the potential at the last stage of inflation takes the form $V(\varphi )=V_0(1+\frac{{\eta }_c}{2}\frac{(\varphi -{\varphi }_c{)}^2}{M_p^2})$, where ${\eta }_c$ is a constant. A natural mechanism to end inflation at $\varphi ={\varphi }_c$ is the hybrid-type inflation.