Warm inflationary universe models in a tachyon field theory are studied. General conditions required for these models to be realizable are derived and discussed. We describe scalar perturbations (in the longitudinal gauge) and tensor perturbations for these scenarios. We develop our models for a constant dissipation parameter Γ in one case and one dependent on φ in the other case. We have been successful in describing such of inflationary universe models. We use recent astronomical observations for constraining the parameters appearing in our model. Also, our results are compared with their analogous found in the cool inflationary case.
Via a straightforward integration of the Einstein equations with cosmological constant, all static circularly symmetric perfect fluid 2+1 solutions are derived. The structural functions of the metric depend on the energy density, which remains in general arbitrary. Spacetimes for fluids fulfilling linear and polytropic state equations are explicitly derived; they describe, among others, stiff matter, monatomic and diatomic ideal gases, nonrelativistic degenerate fermions, incoherent and pure radiation. As a by-product, we demonstrate the uniqueness of the constant energy density perfect fluid within the studied class of metrics. A full similarity of the perfect fluid solutions with constant energy density of the 2+1 and 3+1 gravities is established.
It is shown that within conformally flat stationary axisymmetric spacetimes, besides of the static family, there exists a new class of metrics, which is always stationary and axisymmetric. All these spacetimes, the static and the stationary ones, are endowed with an arbitrary function depending on the two non-Killingian coordinates. The explicit form of this function can be determined once the coupled matter, i.e., the energy-momentum tensor is given. One might hope possible extensions of this result to black holes on two-branes in four dimensions.
The curvaton reheating in a tachyonic inflationary universe model with an
exponential potential is studied. We have found that the energy density in the
kinetic epoch, has a complicated dependencies of the scale factor. For
different scenarios, the temperature of reheating is computed. These
temperature result to be analogous to those obtained in the standard case of
the curvaton scenario.Comment: 9 pages, Accepted for publication in Phys. Letter
We develop a covariant scheme to describe the dynamics of small perturbations on Lovelock type extended objects propagating in a flat Minkowski spacetime. The higher-dimensional analogue of the Jacobi equation in this theory becomes a wave type equation for a scalar field Φ. Whithin this framework, we analyse the stability of membranes with a de Sitter geometry where we find that the Jacobi equation specializes to a Klein-Gordon (KG) equation for Φ possessing a tachyonic mass. This shows that, to some extent, these types of extended objects share the symmetries of the Dirac-Nambu-Goto (DNG) action which is by no means coincidental because the DNG model is the simplest included in this type of gravity.
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