4 research outputs found
Evolution of the Scale Factor with a Variable Cosmological Term
Evolution of the scale factor a(t) in Friedmann models (those with zero
pressure and a constant cosmological term Lambda) is well understood, and
elegantly summarized in the review of Felten and Isaacman [Rev. Mod. Phys. 58,
689 (1986)]. Developments in particle physics and inflationary theory, however,
increasingly indicate that Lambda ought to be treated as a dynamical quantity.
We revisit the evolution of the scale factor with a variable Lambda-term, and
also generalize the treatment to include nonzero pressure. New solutions are
obtained and evaluated using a variety of observational criteria. Existing
arguments for the inevitability of a big bang (ie., an initial state with a=0)
are substantially weakened, and can be evaded in some cases with Lambda_0 (the
present value of Lambda) well below current experimental limits.Comment: 29 pages, 12 figures (not included), LaTeX, uses Phys Rev D style
files (revtex.cls, revtex.sty, aps.sty, aps10.sty, prabib.sty). To appear in
Phys Rev
Cosmological models with dynamical lambda in scalar-tensor theories
In the context of a family os scalar-tensor theories with a dynamical
, that is a binomial on the scalar field, the cosmological equations
are considered. A general barotropic state equation , for a
perfect fluid is used for the matter content of the Universe. Some Friedmann-
Robertson-Walker exact solutions are found, they have scale factor wich shows
exponential or power law dependence on time. For some models the singularity
can be avoided. Cosmological parameters as , ,
and are obtained and compared with observational data.Comment: 20 pages, Latex file, a sign in Eq. (2.17) was corrected, reference
[37] was correcte