Cosmological particle production, causal thermodynamics, and inflationary expansion

Combining the equivalence between cosmological particle creation and an effective viscous fluid pressure with the fact that the latter represents a dynamical degree of freedom within the second-order Israel-Stewart theory for imperfect fluids, we reconsider the possibility of accelerated expansion in fluid cosmology. We find an inherent self-limitation for the magnitude of an effective bulk pressure which is due to adiabatic (isentropic) particle production. For a production rate which depends quadratically on the Hubble rate we confirm the existence of solutions which describe a smooth transition from inflationary to noninflationary behavior and discuss their interpretation within the model of a decaying vacuum energy density. An alternative formulation of the effective imperfect fluid dynamics in terms of a minimally coupled scalar field is given. The corresponding potential is discussed and an entropy equivalent for the scalar field is found.Comment: 16 pages, revtex file, submitted to Phys. Rev.

Renormalization, the trace anomaly and spacetime anisotropy

The authors investigate some aspects of the dependence of the trace anomaly on the regularization method used in the case of a scalar field with conformal coupling to gravity in a Bianchi I type universe. In the isotropic case, one of the regularization procedures one may use, the so-called 'minimal regularization', gives no trace anomaly. In the anisotropic case, however, the same procedure is no longer sufficient to remove all divergences; one must perform a further regularization, which in effect makes the whole procedure equivalent to covariant regularization; this necessarily gives a trace anomaly, which does not vanish when one takes its isotropic limit. One may thus consider that the choice of regularization procedure even in the isotropic case is forced by the more general situation, and the corresponding anomaly as a remnant of the renormalized stress-energy tensor in the anisotropic case.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Inflationary Cosmology and Thermodynamics

SCOPUS: ar.jinfo:eu-repo/semantics/publishe