Search

We analyze the thermodynamic behavior of the generalized scalar Yukawa model, composed of a complex scalar field interacting with scalar and vector fields. Finite-size effects on the phase structure are investigated using methods of quantum field theory on toroidal topologies. We focus on the analysis of the phase structure of this model at effective chemical equilibrium, under change of values of the relevant parameters of the model, looking especially to the influence of the spatial compactification on the phase structure.

We employ the superpotential technique for the reconstruction of cosmological models with a non-minimally coupled scalar field evolving on a spatially flat Friedmann-Robertson-Walker background. The key point in this method is that the Hubble parameter is considered as a function of the scalar field and this allows one to reconstruct the scalar field potential and determine the dynamics of the field itself, without a priori fixing the Hubble parameter as a function of time or of the scale factor. The scalar field potentials that lead to de Sitter or asymptotic de Sitter solutions, and those that reproduce the cosmological evolution given by Einstein-Hilbert action plus a barotropic perfect fluid, have been obtained., 12 pages, 2 figures, accepted for publication in PRD

We derive a condition on the Lagrangian density describing a generic, single, non-canonical scalar field, by demanding that the intrinsic, non-adiabatic pressure perturbation associated with the scalar field vanishes identically. Based on the analogy with perfect fluids, we refer to such fields as perfect scalar fields. It is common knowledge that models that depend only on the kinetic energy of the scalar field (often referred to as pure kinetic models) possess no non-adiabatic pressure perturbation. While we are able to construct models that seemingly depend on the scalar field and also do not contain any non-adiabatic pressure perturbation, we find that all such models that we construct allow a redefinition of the field under which they reduce to pure kinetic models. We show that, if a perfect scalar field drives inflation, then, in such situations, the first slow roll parameter will always be a monotonically decreasing function of time. We point out that this behavior implies that these scalar fields can not lead to features in the inflationary, scalar perturbation spectrum., Comment: v1: 11 pages; v2: 11 pages, minor changes, journal version

I consider an extended version of Bekenstein's Tensor-Vector-Scalar theory where the action of the vector field is of a general Einstein-Ether form. This work presents the cosmological equations of this theory, both at the background and perturbed level, for scalar, vector and tensor perturbation modes. By solving the background equations in the radiation era analytically, to an excellent approximation, I construct the primordial adiabatic perturbation for a general family of scalar field kinetic functions.

The localization of metric fluctuations on scalar brane configurations breaking spontaneously five-dimensional Poincar\'e invariance is discussed. Assuming that the four-dimensional Planck mass is finite and that the geometry is regular, it is demonstrated that the vector and scalar fluctuations of the metric are not localized on the brane., Comment: 8 pages in Latex style

The dynamics of the nonlinear massless scalar field described by D/sup 7/AlembertianPhi = 4lambdaPhi/sup 3/ is numerically studied in the Schwarzschild geometry. It is found that such a scalar field is entirely radiated away during the gravitational collapse of a scalar charged star. Sawyer has argued that a quantum fluctuation can give rise to a quasistatic component of the scalar field which will trap subsequent scalar radiation and grow to a singular field. A phenomenological model used to study this situation leads to no such singular growth. All results, in fact, suggest that the dynamics of weak nonlinear fields in a black-hole background is qualitatively similar to that of linear fields.

Prescriptions are introduced for the operations of vector algebra on a random lattice. Some vector identities are preserved exactly. Others receive new terms, described as evanescent because they vanish in the continuum limit.