Deformations of minimal surfaces lying in constant-time slices in static space-times are studied. An exact and universal formula for a change of the area of a minimal surface under shifts of nearby pointlike particles is found. It allows one to introduce a local temperature on the surface and represent variations of its area in a thermodynamical form by assuming that the entropy in the Planck units equals the quarter of the area. These results provide a strong support to a recent hypothesis that gravity has an entropic origin, the minimal surfaces being a sort of holographic screens. The gravitational entropy also acquires a definite physical meaning related to quantum entanglement of fundamental degrees of freedom across the screen.

If the cosmological QCD phase transition is strongly first order and lasts sufficiently long, it generates a background of gravitational waves which may be detected via pulsar timing experiments. We estimate the amplitude and the spectral shape of such a background and we discuss its detectability prospects.

The no-boundary wave function (NBWF) specifies a measure for prediction in cosmology that selects inflationary histories and remains well behaved for spatially large or infinite universes. This paper explores the predictions of the NBWF for linear scalar fluctuations about homogeneous and isotropic backgrounds in models with a single scalar field moving in a quadratic potential. We treat both the spacetime geometry of the universe and the observers inhabiting it quantum mechanically. We evaluate top-down probabilities for local observations that are conditioned on the NBWF and on part of our data as observers of the universe. For models where the most probable histories do not have a regime of eternal inflation, the NBWF predicts homogeneity on large scales, a spectrum of observable fluctuations with a small non-Gaussian component, and a small amount of inflation in our past. By contrast, for models where the dominant histories have a regime of eternal inflation, the NBWF predicts significant inhomogeneity on scales much larger than the present horizon, a Gaussian spectrum of observable fluctuations, and a long period of inflation in our past. The absence or presence of non-Gaussianity in our observable universe therefore provides information about its global structure, assuming the NBWF.

Recent studies suggest that the cosmological constant affects the gravitational bending of photons, although the orbital equation for light in Schwarzschild–de Sitter space-time is free from a cosmological constant. Here we argue that the very notion of a cosmological constant independent of the photon orbit in the Schwarzschild–de Sitter space-time is not proper. Consequently, the cosmological constant has some clear contributions to the deflection angle of light rays. We stress the importance of the study of photon trajectories from the reference objects in bending calculations, particularly for asymptotically nonflat space-time. When such an aspect is taken into consideration, the contribution of a cosmological constant to the effective bending is found to depend on the distances of the source and the reference objects.

Chiral symmetry breaking (restoration) for $SU(N)$ gauge theories is a topic of great interest and not yet fully explained. We consider the phenomenon as a collective spin effect and determine its behavior in terms of the number of flavors $N_f$.

We present an analysis of the loop-induced couplings of the Higgs boson to the massless gauge fields (gluons and photons) in the warped extra dimension models where all standard model fields propagate in the bulk. We show that in such models corrections to the $hgg$ and $h\gamma \gamma$ couplings are potentially very large. These corrections can lead to generically sizable deviations in the production and decay rates of the Higgs boson, even when the new physics states lie beyond the direct reach of the LHC.

In view of the fact that the $n=1$ Kaluza-Klein (KK) modes in a model with a universal extra dimension could mimic supersymmetry signatures at the LHC, it is necessary to look for the $n=2$ KK modes, which have no analogues in supersymmetry. We discuss the possibility of searching for heavy $n=2$ vector boson resonances—especially the $g_2$—through their decays to a highly boosted top quark-antiquark pair using recently developed top-jet tagging techniques in the hadronic channel. It is shown that $t\overline{t}$ signals from the $n=2$ gluon resonance are as efficient a discovery mode at the LHC as dilepton channels from the ${\gamma }_2$ and $Z_2$ resonances.

We find the deep inelastic scattering (DIS) structure functions at strong coupling by calculating $R$-current correlators on a finite-size shock wave using AdS/CFT correspondence. We improve on the existing results in the literature by going beyond the eikonal approximation for the two lowest orders in graviton exchanges. We argue that since the eikonal approximation at strong coupling resums integer powers of $1/x$ (with $x$ the Bjorken-$x$ variable), the noneikonal corrections bringing in positive integer powers of $x$ cannot be neglected in the small-$x$ limit, as the noneikonal order-$x$ correction to the ($n+1$)st term in the eikonal series is of the same order in $x$ as the $n$th eikonal term in that series. We demonstrate that, in qualitative agreement with the earlier DIS analysis based on calculation of the expectation value of the Wilson loop in the shock wave background using AdS/CFT, after inclusion of noneikonal corrections DIS structure functions are described by two momentum scales: $Q_1^2\sim {\Lambda }^2{A}^{1/3}/x$ and $Q_2^2\sim {\Lambda }^2{A}^{2/3}$, where $\Lambda$ is the typical transverse momentum in the shock wave and $A$ is the atomic number if the shock wave represents a nucleus. We discuss possible physical meanings of the scales $Q_1$ and $Q_2$.

We discuss the two-photon decay width of heavy hadron molecules and study the dependence on the constituent meson masses and on the binding energy. In addition finite-size effects due to the extended structure of the bound state are shown to have a strong influence on the predictions for this decay width.

We investigate the properties of heavy quarkonia at finite temperature in detail using QCD sum rules. Extending previous analyses, we take into account a temperature-dependent effective continuum threshold and derive constraints on the mass, the width, and the varying effective continuum threshold. We find that at least one of these quantities of a charmonium changes abruptly in the vicinity of the phase transition. We also calculate the ratio of the imaginary time correlator to its reconstructed one, $G/G_{\mathrm{rec}}$, by constructing a model spectral function and compare it to the corresponding lattice QCD results. We demonstrate that the almost constant unity of $G/G_{\mathrm{rec}}$ can be obtained from the destructive interplay of the changes in each part of the spectral modification which are extracted from QCD sum rules.

We study the low-momentum ghost propagator Dyson-Schwinger equation in the Landau gauge, assuming for the truncation a constant ghost-gluon vertex, as it is extensively done, and a simple model for a massive gluon propagator. Then, regular Dyson-Schwinger equation solutions (the zero-momentum ghost dressing function not diverging) appear to emerge, and we show the ghost propagator to be described by an asymptotic expression reliable up to the order $\mathcal{O}(q^2)$. That expression, depending on the gluon mass and the zero-momentum Taylor-scheme effective charge, is proven to fit pretty well some low-momentum ghost propagator data [I. L. Bogolubsky, E. M. Ilgenfritz, M. Muller-Preussker, and A. Sternbeck, Phys. Lett. B 676, 69 (2009); Proc. Sci., LAT2007 (2007) 290] from big-volume lattice simulations where the so-called “simulated annealing algorithm” is applied to fix the Landau gauge.

Assuming the lightest neutralino solely composes the cosmic dark matter, we examine the constraints of the CDMS-II and XENON100 dark matter direct searches on the parameter space of the minimal supersymmetric standard model (MSSM) Higgs sector. We find that the current CDMS-II/XENON100 limits can exclude some of the parameter space which survive the constraints from the dark matter relic density and various collider experiments. We also find that in the currently allowed parameter space, the charged Higgs boson is hardly accessible at the LHC for an integrated luminosity of $30{\mathrm{fb}}^{-1}$, while the neutral non-SM (standard model) Higgs bosons $(H,A)$ may be accessible in some allowed region characterized by a large $\mu$. The future XENON100 (6000 kg-days exposure) will significantly tighten the parameter space in case of nonobservation of dark matter.

In this paper the soft gluon radiation from the partonic interaction of the type $2\to 2+\mathrm{\text{gluon}}$ has been revisited and a correction term to the widely used Gunion-Bertsch formula is obtained.

Unimodular gravity is based on a modification of the usual Einstein-Hilbert action that allows one to recover general relativity with a dynamical cosmological constant. It also has the interesting property of providing, as the momentum conjugate to the cosmological constant, an emergent clock variable. In this paper we investigate the cosmological reduction of unimodular gravity, and its quantization within the framework of flat homogeneous and isotropic loop quantum cosmology. It is shown that the unimodular clock can be used to construct the physical state space, and that the fundamental features of the previous models featuring scalar field clocks are reproduced. In particular, the classical singularity is replaced by a quantum bounce, which takes place in the same condition as obtained previously. We also find that requirement of semiclassicality demands the expectation value of the cosmological constant to be small (in Planck units). The relation to spin foam models is also studied, and we show that the use of the unimodular time variable leads to a unique vertex expansion.

We show that Hořava’s theory of gravitation with the global Hamiltonian constraint does not reproduce general relativity in the infrared domain. There is one extra propagating degree of freedom, besides those two associated with the massless graviton, which does not decouple.

General relativity has very specific predictions for the gravitational waveforms from inspiralling compact binaries obtained using the post-Newtonian (PN) approximation. We investigate the extent to which the measurement of the PN coefficients, possible with the second generation gravitational-wave detectors such as the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and the third generation gravitational-wave detectors such as the Einstein Telescope (ET), could be used to test post-Newtonian theory and to put bounds on a subclass of parametrized-post-Einstein theories which differ from general relativity in a parametrized sense. We demonstrate this possibility by employing the best inspiralling waveform model for nonspinning compact binaries which is 3.5PN accurate in phase and 3PN in amplitude. Within the class of theories considered, Advanced LIGO can test the theory at 1.5PN and thus the leading tail term. Future observations of stellar mass black hole binaries by ET can test the consistency between the various PN coefficients in the gravitational-wave phasing over the mass range of $11–44M_{\odot }$. The choice of the lower frequency cutoff is important for testing post-Newtonian theory using the ET. The bias in the test arising from the assumption of nonspinning binaries is indicated.

We show that a possible astrophysical experiment, detection of lensed images of stars orbiting close to Sgr A*, can provide insight into the form of the metric around a black hole. We model Sgr A* as a black hole and add in a $\frac{1}{r^2}$ term to the Schwarzschild metric near the black hole. We then attempt to determine the effect of this extra term on the properties of the secondary images of the S stars in the Galactic center. When the $\frac{1}{r^2}$ term is positive, this represents a Reissner-Nordstrom metric. We show that there is little observational difference between a Schwarzschild black hole and a Reissner-Nordstrom black hole, leading to the conclusion that secondary images may not be a useful probe of electrical charge in black holes. A negative value for the $\frac{1}{r^2}$ term can enter through modified gravity scenarios. Although physically unlikely to apply in the case of a large black hole, the Randall-Sundrum II braneworld scenario admits a metric of this form, known as the tidal Reissner-Nordstrom metric. We use values of tidal charge ($Q$ in $\frac{Q}{r^2}$) ranging from $-6.4M^2$ to $1.6M^2$. A negative value of $Q$ enhances the brightness of images at all times and creates an increase in brightness of up to 0.4 magnitudes for the secondary image of the star S2 at periapse. We show that for other stars with brighter secondary images and positions more aligned with the optic axis, using the tidal Reissner-Nordstrom metric with negative $Q$ enhances the images as well. However, the effect is less pronounced. This effect is related to the increase in the size of the photon sphere in this spacetime and, therefore, should be noticeable in other metrics with a similar effect on the photon sphere. With the next generation of instruments and increased knowledge of radiation from Sgr A*, we may be able to use properties of secondary images to place constraints on the size of the $\frac{1}{r^2}$ term. This knowledge will be useful in constraining any modified gravity theory that adds a similar term into the strong field near a black hole.

A set of energy-momentum constraint-preserving boundary conditions is proposed for the first-order Z4 case. The stability of a simple numerical implementation is tested in the linear regime (robust stability test), both with the standard corner and vertex treatment and with a modified finite-differences stencil for boundary points which avoids corners and vertices even in Cartesian-like grids. Moreover, the proposed boundary conditions are tested in a strong-field scenario, the Gowdy waves metric, showing the expected rate of convergence. The accumulated amount of energy-momentum constraint violations is similar or even smaller than the one generated by either periodic or reflection conditions, which are exact in the Gowdy waves case. As a side theoretical result, a new symmetrizer is explicitly given, which extends the parametric domain of symmetric hyperbolicity for the Z4 formalism. The application of these results to first-order Baumgarte-Shapiro-Shibata-Nakamura–like formalisms is also considered.

We first construct generalized normal coordinates by using autoparallels, instead of geodesics, in an arbitrary Riemann-Cartan spacetime. With the aid of generalized normal coordinates and their associated orthonormal frames, we obtain a momentum-space representation of the Feynman propagator for scalar fields, which is a direct generalization of Bunch and Parker’s works to curved spacetime with torsion. We further derive the proper-time representation in $n$-dimensional Riemann-Cartan spacetime from the momentum-space representation. It leads us to obtain the renormalization of the one-loop effective Lagrangians of free scalar fields by using dimensional regularization. When the torsion tensor vanishes, our resulting momentum-space representation returns to the standard Riemannian results.