The Running of the Cosmological and the Newton Constant controlled by the Cosmological Event Horizon

We study the renormalisation group running of the cosmological and the Newton constant, where the renormalisation scale is given by the inverse of the radius of the cosmological event horizon. In this framework, we discuss the future evolution of the universe, where we find stable de Sitter solutions, but also "big crunch"-like and "big rip"-like events, depending on the choice of the parameters in the model.Comment: 14 pages, 7 figures, minor improvements, references adde

Transition from Poisson to gaussian unitary statistics: The two-point correlation function

We consider the Rosenzweig-Porter model of random matrix which interpolates between Poisson and gaussian unitary statistics and compute exactly the two-point correlation function. Asymptotic formulas for this function are given near the Poisson and gaussian limit.Comment: 19 pages, no figure

A Four-Dimensional Theory for Quantum Gravity with Conformal and Nonconformal Explicit Solutions

The most general version of a renormalizable $d=4$ theory corresponding to a dimensionless higher-derivative scalar field model in curved spacetime is explored. The classical action of the theory contains $12$ independent functions, which are the generalized coupling constants of the theory. We calculate the one-loop beta functions and then consider the conditions for finiteness. The set of exact solutions of power type is proven to consist of precisely three conformal and three nonconformal solutions, given by remarkably simple (albeit nontrivial) functions that we obtain explicitly. The finiteness of the conformal theory indicates the absence of a conformal anomaly in the finite sector. The stability of the finite solutions is investigated and the possibility of renormalization group flows is discussed as well as several physical applications.Comment: LaTeX, 18 pages, no figure

Effective growth of matter density fluctuations in the running LCDM and LXCDM models

We investigate the matter density fluctuations \delta\rho/\rho for two dark energy (DE) models in the literature in which the cosmological term \Lambda is a running parameter. In the first model, the running LCDM model, matter and DE exchange energy, whereas in the second model, the LXCDM model, the total DE and matter components are conserved separately. The LXCDM model was proposed as an interesting solution to the cosmic coincidence problem. It includes an extra dynamical component, the "cosmon" X, which interacts with the running \Lambda, but not with matter. In our analysis we make use of the current value of the linear bias parameter, b^2(0)= P_{GG}/P_{MM}, where P_{MM} ~ (\delta\rho/\rho)^2 is the present matter power spectrum and P_{GG} is the galaxy fluctuation power spectrum. The former can be computed within a given model, and the latter is found from the observed LSS data (at small z) obtained by the 2dF galaxy redshift survey. It is found that b^2(0)=1 within a 10% accuracy for the standard LCDM model. Adopting this limit for any DE model and using a method based on the effective equation of state for the DE, we can set a limit on the growth of matter density perturbations for the running LCDM model, the solution of which is known. This provides a good test of the procedure, which we then apply to the LXCDM model in order to determine the physical region of parameter space, compatible with the LSS data. In this region, the LXCDM model is consistent with known observations and provides at the same time a viable solution to the cosmic coincidence problem.Comment: LaTeX, 38 pages, 8 figures. Version accepted in JCA

Neutron star, β\beta-stable ring-diagram equation of state and Brown-Rho scaling

Neutron star properties, such as its mass, radius, and moment of inertia, are calculated by solving the Tolman-Oppenheimer-Volkov (TOV) equations using the ring-diagram equation of state (EOS) obtained from realistic low-momentum NN interactions $V_{low-k}$. Several NN potentials (CDBonn, Nijmegen, Argonne V18 and BonnA) have been employed to calculate the ring-diagram EOS where the particle-particle hole-hole ring diagrams are summed to all orders. The proton fractions for different radial regions of a $\beta$-stable neutron star are determined from the chemical potential conditions $\mu_n-\mu_p = \mu_e = \mu_\mu$. The neutron star masses, radii and moments of inertia given by the above potentials all tend to be too small compared with the accepted values. Our results are largely improved with the inclusion of medium corrections based on Brown-Rho scaling where the in-medium meson masses, particularly those of $\omega$, $\rho$ and $\sigma$, are slightly decreased compared with their in-vacuum values. Representative results using such medium corrected interactions are neutron star mass $M\sim 1.8 M_{\odot}$, radius $R\sim 9$ km and moment of inertia $\sim 60 M_{\odot}km^2$. The mass-radius trajectories given by the above four realistic NN potentials are by and large overlapping.Comment: 12.7 pages, 13 figures, 3 table

Collapse to Black Holes in Brans-Dicke Theory: I. Horizon Boundary Conditions for Dynamical Spacetimes

We present a new numerical code that evolves a spherically symmetric configuration of collisionless matter in the Brans-Dicke theory of gravitation. In this theory the spacetime is dynamical even in spherical symmetry, where it can contain gravitational radiation. Our code is capable of accurately tracking collapse to a black hole in a dynamical spacetime arbitrarily far into the future, without encountering either coordinate pathologies or spacetime singularities. This is accomplished by truncating the spacetime at a spherical surface inside the apparent horizon, and subsequently solving the evolution and constraint equations only in the exterior region. We use our code to address a number of long-standing theoretical questions about collapse to black holes in Brans-Dicke theory.Comment: 46 pages including figures, uuencoded gz-compressed postscript, Submitted to Phys Rev

Field cooling memory effect in Bi2212 and Bi2223 single crystals

A memory effect in the Josephson vortex system created by magnetic field in the highly anisotropic superconductors Bi2212 and Bi2223 is demonstrated using microwave power absorption. This surprising effect appears despite a very low viscosity of Josephson vortices compared to Abrikosov vortices. The superconductor is field cooled in DC magnetic field H_{m} oriented parallel to the CuO planes through the critical temperature T_{c} down to 4K, with subsequent reduction of the field to zero and again above H_{m}. Large microwave power absorption signal is observed at a magnetic field just above the cooling field clearly indicating a memory effect. The dependence of the signal on deviation of magnetic field from H_{m} is the same for a wide range of H_{m} from 0.15T to 1.7T

Generating Entangled Two-Photon States with Coincident Frequencies

It is shown that parametric downconversion, with a short-duration pump pulse and a long nonlinear crystal that is appropriately phase matched, can produce a frequency-entangled biphoton state whose individual photons are coincident in frequency. Quantum interference experiments which distinguish this state from the familiar time-coincident biphoton state are described.Comment: Revised version (a typo was corrected) as published on PR

On different actions for the vacuum of bosonic string field theory

We study a family of kinetic operators in string field theory describing the theory around the closed string vacuum. Those operators are based on the analytical classical solutions of Takahashi and Tanimoto and are analogous to the pure ghost action usually referred to as "vacuum string field theory," but are much more general, and less singular than the pure ghost operator. The closed string vacuum is related to the D-brane vacuum by large, singular, gauge transformations or field redefinition, and all those different representations are related to each other by small gauge transformations. We try to clarify the nature of this singular gauge transformation. We also show that by choosing the Siegel gauge one recovers the propagator proposed in hep-th/0207266 that generates closed string surfaces.Comment: 15 page