Quantum Corrections to the Cosmological Evolution of Conformally Coupled
  Fields
  Because the source term for the equations of motion of a conformally coupled
scalar field, such as the dilaton, is given by the trace of the matter energy
momentum tensor, it is commonly assumed to vanish during the radiation
dominated epoch in the early universe. As a consequence, such fields are
generally frozen in the early universe. Here we compute the finite temperature
radiative correction to the source term and discuss its consequences on the
evolution of such fields in the early universe. We discuss in particular, the
case of scalar tensor theories of gravity which have general relativity as an
attractor solution. We show that, in some cases, the universe can experience an
early phase of contraction, followed by a non-singular bounce, and standard
expansion. This can have interesting consequences for the abundance of thermal
relics; for instance, it can provide a solution to the gravitino problem. We
conclude by discussing the possible consequences of the quantum corrections to
the evolution of the dilaton.
