We study the thermodynamics of the hard wall model, which consists of the introduction of an infrared cutoff in asymptotically AdS spaces. This is a toy model for confining backgrounds in the context of the gauge/gravity correspondence. We use holographic renormalization and reproduce the existence of a Hawking-Page phase transition recently discussed by Herzog. We also show that the entropy jumps from $N^0$ to $N^2$, which reinforces the interpretation of this transition as the gravity dual of confinement/deconfinement. We also show that similar results hold for the phenomenologically motivated soft wall model, underlining the potential universality of our analysis.

In this article, we clarify the link between the conformal (i.e. Weyl) correspondence from the Minkowski space to the de Sitter space and the conformal [i.e. $\mathrm{SO}(2,d)$] invariance of the conformal scalar field on both spaces. We exhibit the realization on de Sitter space of the massless scalar representation of $\mathrm{SO}(2,d)$. It is obtained from the corresponding representation in Minkowski space through an intertwining operator inherited from the Weyl relation between the two spaces. The de Sitter representation is written in a form which allows one to take the point of view of a Minkowskian observer who sees the effect of curvature through additional terms.

In a previous article we have shown that there are difficulties in obtaining the correct graviton propagator from the loop-quantum-gravity dynamics defined by the Barrett-Crane vertex amplitude. Here we show that a vertex amplitude that depends nontrivially on the intertwiners can yield the correct propagator. We give an explicit example of asymptotic behavior of a vertex amplitude that gives the correct full graviton propagator in the large distance limit.

The effects of noncommutativity and of the existence of a minimal length on the phase space of a dilatonic cosmological model are investigated. The existence of a minimum length results in the generalized uncertainty principle (GUP), which is a deformed Heisenberg algebra between the minisuperspace variables and their momenta operators. I extend these deformed commutating relations to the corresponding deformed Poisson algebra. For an exponential dilaton potential, the exact classical and quantum solutions in the commutative and noncommutative cases, and some approximate analytical solutions in the case of GUP, are presented and compared.

We study the emission of scalar fields into the bulk from a six-dimensional rotating black hole pierced by a 3-brane. We determine the angular eigenvalues in the presence of finite brane tension by using the continued fraction method. The radial equation is integrated numerically, giving the absorption probability (graybody factor) in a wider frequency range than in the preexisting literature. We then compute the power and angular momentum emission spectra for different values of the rotation parameter and brane tension, and compare their relative behavior in detail. As is expected from the earlier result for a nonrotating black hole, the finite brane tension suppresses the emission rates. As the rotation parameter increases, the power spectra are reduced at low frequencies due to the smaller Hawking temperature and are enhanced at high frequencies due to superradiance. The angular momentum spectra are enhanced over the whole frequency range as the rotation parameter increases. The spectra and the amounts of energy and angular momentum radiated away into the bulk are thus determined by the interplay of these effects.

We investigate an infinitesimally thin cylindrical shell composed of counter-rotating dust particles. This system was studied by Apostolatos and Thorne in terms of the C-energy for a bounded domain. In this paper, we reanalyze this system by evaluating the C-energy on the future null infinity. We find that some class of momentarily static and radiation-free initial data does not settle down into static equilibrium configurations, and an otherwise infinite amount of the gravitational radiation is emitted to the future null infinity. Our result implies the existence of an instability in this system. In the framework of the Newtonian gravity, a cylindrical shell composed of counter-rotating dust particles can be in a steady state with oscillation by the gravitational attraction and centrifugal repulsion, and hence a static state is not necessarily realized as a final state. By contrast, in the framework of general relativity, the steady oscillating state will be impossible since the gravitational radiation will carry the energy of the oscillation to infinity. Thus, this instability has no counterpart in the Newtonian gravity.

We study implications of the large-$N$ species solution to the hierarchy problem, proposed by G. Dvali, for reheating of the Universe after inflation. Dvali’s proposal contains additional $N\sim {10}^{32}{Z}_2$-conserved quantum fields beyond the standard model particles with mass $\sim 1\mathrm{TeV}$, which weaken gravity by a factor of $1/N$, and thus explain the hierarchy between the Plank scale and the electroweak scale. We show that, in this scenario, the decay rates of inflaton fields through gravitational decay channels are enhanced by a factor of $N$, and thus they decay into $N$ species of the quantum fields very efficiently, in the limit that quantum gravity effects are unimportant for the gravitational decay rate. In order not to violate energy conservation or over-reheat the Universe, inflaton mass, vacuum expectation value of inflaton, or nonminimal gravitational coupling should be tightly fine-tuned. Our conclusion holds even when the gravitational decay is prohibited by some symmetry of the theory; the Universe may still be over-reheated via annihilation of inflatons, if the number density of inflaton quanta is greater than the critical value.

We study cosmological perturbations in the context of an interacting dark energy model, in which the cosmological term decays linearly with the Hubble parameter, with concomitant matter production. A previous joint analysis of the redshift-distance relation for type Ia supernovas, barionic acoustic oscillations, and the position of the first peak in the anisotropy spectrum of the cosmic microwave background has led to acceptable values for the cosmological parameters. Here we present our analysis of small perturbations, under the assumption that the cosmological term, and therefore the matter production, are strictly homogeneous. Such a homogeneous production tends to dilute the matter contrast, leading to a late-time suppression in the power spectrum. Nevertheless, an excellent agreement with the observational data can be achieved by using a higher matter density as compared to the concordance value previously obtained. This may indicate that our hypothesis of homogeneous matter production must be relaxed by allowing perturbations in the interacting cosmological term.

Measured gravitational waveforms from black hole binary inspiral events directly determine absolute luminosity distances. To use these data for cosmology, it is necessary to independently obtain redshifts for the events, which may be difficult for those without electromagnetic counterparts. Here it is demonstrated that certainly in principle, and possibly in practice, clustering of galaxies allows extraction of the redshift information from a sample statistically for the purpose of estimating mean cosmological parameters, without identification of host galaxies for individual events. We extract mock galaxy samples from the 6th data release of the Sloan Digital Sky Survey resembling those that would be associated with inspiral events of stellar mass black holes falling into massive black holes at redshift $z\approx 0.1$ to 0.5. A simple statistical procedure is described to estimate a likelihood function for the Hubble constant $H_0$: each galaxy in a LISA error volume contributes linearly to the log likelihood for the source redshift, and the log likelihood for each source contributes linearly to that of $H_0$. This procedure is shown to provide an accurate and unbiased estimator of $H_0$. It is estimated that a precision better than 1% in $H_0$ may be possible if the rate of such events is sufficiently high, on the order of 20 to $z=0.5$.

The problem of the detection and mapping of a stochastic gravitational wave background (SGWB), either cosmological or astrophysical, bears a strong semblance to the analysis of the cosmic microwave background (CMB) anisotropy and polarization, which too is a stochastic field, statistically described in terms of its correlation properties. An astrophysical gravitational wave background (AGWB) will likely arise from an incoherent superposition of unmodelled and/or unresolved sources and cosmological gravitational wave backgrounds (CGWB) are also predicted in certain scenarios. The basic statistic we use is the cross correlation between the data from a pair of detectors. In order to “point” the pair of detectors at different locations one must suitably delay the signal by the amount it takes for the gravitational waves (GW) to travel to both detectors corresponding to a source direction. Then the raw (observed) sky map of the SGWB is the signal convolved with a beam response function that varies with location in the sky. We first present a thorough analytic understanding of the structure of the beam response function using an analytic approach employing the stationary phase approximation. The true sky map is obtained by numerically deconvolving the beam function in the integral (convolution) equation. We adopt the maximum likelihood framework to estimate the true sky map using the conjugate gradient method that has been successfully used in the broadly similar, well-studied CMB map-making problem. We numerically implement and demonstrate the method on signal generated by simulated (unpolarized) SGWB for the GW radiometer consisting of the LIGO pair of detectors at Hanford and Livingston. We include “realistic” additive Gaussian noise in each data stream based on the LIGO-I noise power spectral density. The extension of the method to multiple baselines and polarized GWB is outlined. In the near future the network of GW detectors, including the Advanced LIGO and Virgo detectors that will be sensitive to sources within a thousand times larger spatial volume, could provide promising data sets for GW radiometry.

Extensions of the minimal supersymmetric standard model often predict the existence of new fermions and their scalar superpartners which are vectorlike with respect to the standard model gauge group but may be chiral under additional gauge factors. In this paper we explore the production and decay of an important example, i.e., a heavy isosinglet charge $-1/3$ quark and its scalar partner, using the charge assignments of a $\mathbf{27}$-plet of $E_6$ for illustration. We emphasize that, depending on the symmetries of the low-energy theory, such exotic particles may decay by the mixing of the fermion with the $d$, $s$, or $b$ quarks; may decay by leptoquark or diquark couplings (which may nevertheless preserve a form of $R$ parity); or may be stable with respect to renormalizable couplings but decay by higher-dimension operators on cosmological times scales. We discuss the latter two possibilities in detail for various assumptions concerning the relative masses of the exotic fermions, scalars, and the lightest neutralino, and emphasize the necessity of considering the collider signatures in conjunction with the normal minimal supersymmetric standard model processes. Existing and projected constraints from colliders, indirect experiments, proton decay, and big bang nucleosynthesis are considered.

Unitarity cuts of enhanced Pomeron diagrams are analyzed in the framework of the Reggeon field theory. Assuming the validity of the Abramovskii-Gribov-Kancheli cutting rules, we derive a complete set of cut nonloop enhanced graphs and observe important cancellations between certain subclasses of the latter. We demonstrate also how the present method can be generalized to take into consideration Pomeron loop contributions.

We generalize results of lattice QCD to determine the spin-dependent symmetries and factorization properties of meson production in Okubo-Zweig-Iizuka allowed processes. This explains some conjectures previously made in the literature about axial meson decays and gives predictions for exclusive decays of vector charmonia, including ways of establishing the structure of $Y(4260)$ and $Y(4325)$ from their $S$-wave decays. Factorization gives a selection rule which forbids $e^{+}{e}^{-}\to D^{*}{D}_2$ near threshold with the tensor meson in helicity 2. The relations among amplitudes for double charmonia production $e^{+}{e}^{-}\to \psi +{\chi }_{0,1,2}$ are expected to differ from the analogous relations among light flavor production such as $e^{+}{e}^{-}\to \omega f_{0,1,2}$.

We shortly report on the two-photon decay width of the light $\sigma$-meson interpreted as a quarkonium state. Results are given in dependence on the $\sigma$-mass and the constituent mass of the light quark. The triangle quark-loop diagram, responsible for the two-photon transition, is carefully evaluated: a term in the transition amplitude, often omitted in literature, results in destructive interference with the leading term. As a result we show that the two-photon decay width of the $\sigma$ in the quarkonium picture is less than 1 keV for the physical range of parameters.

We reexamine the question of baryogenesis via leptogenesis in schemes of the seesaw mechanism with quark-lepton symmetry. Within the phenomenological approach of textures, we propose to relax this strict symmetry and propose weaker conditions, namely, models of the neutrino Dirac mass matrix $M_D$ which have the same hierarchy as the matrix elements of $M_u$. We call this guideline generalized hierarchical quark-lepton symmetry. We consider in detail particular cases in which the moduli of the matrix elements of $M_D$ are equal to those of $M_u$. We try for the heavy Majorana mass matrix diagonal and off-diagonal forms. We find that an ansatz for $M_D$ preserving the hierarchy, together with an off-diagonal model for the heavy Majorana neutrino mass, is consistent with neutrino masses, neutrino mixing, and baryogenesis via leptogenesis for an intermediate mass scale $m_R\sim {10}^{12}\mathrm{GeV}$. The preservation of the hierarchical structure could come from a possible symmetry scheme.

Using $462{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ annihilation data recorded by the Belle detector, we report the first observation of the decay $D_{s1}(2536{)}^{+}\to D^{+}{\pi }^{-}{K}^{+}$. The ratio of branching fractions $\frac{\mathcal{B}(D_{s1}(2536{)}^{+}\to D^{+}{\pi }^{-}{K}^{+})}{\mathcal{B}(D_{s1}(2536{)}^{+}\to D^{*+}{K}^0)}$ is measured to be $(3.27\pm 0.18\pm 0.37)\%$. We also study the angular distributions in the $D_{s1}(2536{)}^{+}\to D^{*+}{K}_S^0$ decay and measure the ratio of $D$- and $S$-wave amplitudes. The $S$-wave dominates, with a partial width of ${\Gamma }_S/{\Gamma }_{\mathrm{total}}=0.72\pm 0.05\pm 0.01$.

We show that the gauge hierarchy problem can be solved in the framework of scalar-tensor theories of gravity very much in the same way as it is solved in the Randall-Sundrum scenario. Our solution involves a fine-tuning of the gravitational sector which can, however, be avoided if a supergravity extension of the dilaton sector is considered. However our mechanism does not require the introduction of extra dimensions or new physics strongly coupled to the standard model in the low energy regime. We do introduce a new scalar field which is, however, coupled only gravitationally to regular matter. The physical reason for the splitting between the weak scale and the Planck scale is a violation of Einstein’s equivalence principle.

The energy-zenith angular event distribution in a neutrino telescope provides a unique tool to determine at the same time the neutrino-nucleon cross section at extreme kinematical regions, and the high-energy neutrino flux. By using a simple parametrization for fluxes and cross sections, we present a sensitivity analysis for the case of a ${\mathrm{km}}^3$ neutrino telescope. In particular, we consider the specific case of an underwater Mediterranean telescope placed at the NEMO site, although most of our results also apply to an under-ice detector such as IceCube. We determine the sensitivity to departures from standard values of the cross sections above 1 PeV which can be probed independently from an a priori knowledge of the normalization and energy dependence of the flux. We also stress that the capability to tag downgoing neutrino showers in the PeV range against the cosmic-ray induced background of penetrating muons appears to be a crucial requirement to derive meaningful constraints on the cross section.

We examine the maximum negative energy density which can be attained in various quantum states of a massless scalar field. We consider states in which either one or two modes are excited, and show that the energy density can be given in terms of a small number of parameters. We calculate these parameters for several examples of superposition states for one mode, and entangled states for two modes, and find the maximum magnitude of the negative energy density in these states. We consider several states which have been, or potentially will be, generated in quantum optics experiments.