J. A. S. Lima

Thermodynamics of decaying vacuum cosmologies.

The thermodynamic behavior of decaying vacuum cosmologies is investigated within a manifestly covariant formulation. Such a process corresponds to a continuous, irreversible energy flow from the vacuum component to the created matter constituents. It is shown that if the specific entropy per particle remains constant during the process, the equilibrium relations are preserved. In particular, if the vacuum decays into photons, the energy density {rho} and average number density of photons {ital n} scale with the temperature as {rho}{approximately}{ital T}{sup 4} and {ital n}{approximately}{ital T}{sup 3}. The temperature law is determined and a generalized Planckian-type form of the spectrum, which is preserved in the course of the evolution, is also proposed. Some consequences of these results for decaying vacuum FRW-type cosmologies as well as for models with {open_quote}{open_quote}adiabatic{close_quote}{close_quote} photon creation are discussed. {copyright} {ital 1996 The American Physical Society.}

Nonsingular FRW cosmology and nonlinear electrodynamics

The possibility to avoid the cosmic initial singularity as a consequence of nonlinear effects on the Maxwell eletromagnetic theory is discussed. For a flat FRW geometry we derive the general nonsingular solution supported by a magnetic field plus a cosmic fluid and a nonvanishing vacuum energy density. The nonsingular behavior of solutions with a time-dependent

Extended warm inflation

\Lambda(t)

Deflationary cosmology: Constraints from angular size and ages of globular clusters

-term are also examined. As a general result, it is found that the functional dependence of

Graviton production in elliptical and hyperbolic universes.

\Lambda(t)

On the thickness of a mildly relativistic collisional shock wave

can uniquely be determined only if the magnetic field remains constant. All these models are examples of bouncing universes which may exhibit an inflationary dynamics driven by the nonlinear corrections of the magnetic field.

Constraining the dark energy with galaxy cluster x-ray data

A bidimensional parameter space of unitary area is introduced to study phenomenologically the dynamic and thermodynamic behavior of inflationary models driven by a scalar field coupled to a thermal component. In this enlarged context the isentropic and warm pictures are just extreme cases of an infinite two-parametric family of possible inflationary scenarios. It is also shown that strong couplings are responsible by an alteration in the standard slow roll conditions which relax the smallness constraint on the first and the second derivatives of the potential.

Thickness of a mildly relativistic collisional shock wave

Observational constraints to a large class of decaying vacuum cosmologies are derived using the angular size data of compact radio sources and the latest age estimates of globular clusters. For this class of deflationary

On the thickness of a relativistic shock wave

\ensuremath{\Lambda}(t)