Exact Solutions and Scalar Fields in Gravity - Instituto Avanzado de ...

THE FRW UNIVERSES WITH
BAROTROPIC FLUIDS IN JORDAN–
BRANS–DICKE THEORY
P. Chauvet–Alducin *
Departamento de Física , Universidad Autónoma Metropolitana–Iztapalapa
P. O. Box. 55–534, México D. F., C. P. 09340 México
Abstract
The description of homogeneous and isotropic models for the expansion
of the Universe represented by a perfect, barotropic, fluid pose
mathematical difficulties that have been overcome when the space is
non–flat in scalar–tensor theories only if the energy–stress tensor is vacuous
or describes stiff matter, incoherent radiation or ultrarelativistic
matter. This paper reveals the dynamics for these and the other ideal
fluid models, in non–flat spaces mainly, for the Jordan–Brans–Dicke cosmological
theory by showing that its field equations, when written in
terms of reduced variables, allow their straightforward partial integration.
Keywords: Jordan–Brans–Dicke theory, FRW universes, exact solutions.
1. INTRODUCTION
The current evolution of the Universe in terms of Friedmann–Robertson–Walker
(FRW) metrics seems to give an acceptable description of it
over large scales even if the apparent homogeneity and isotropy on those
scales still demands justification, like possibly including indispensable
initial conditions before the onset of an inflationary epoch. Nowadays,
for theoretical and also observational [1] reasons scalar–tensor theories
that can generalize in different ways Einstein’s general relativity (GR)
theory have captured new attention, and it is worthwhile to extend the
number of allowed exact cosmological solutions where to choose from to
describe its mean evolution.
*E–mail: pcha@xanum.uam.mx
Exact Solutions and Scalar Fields in Gravity: Recent Developments
Edited by Macias et al., Kluwer Academic/Plenum Publishers, New York, 2001 91