Bianchi type I cosmologies in arbitrary dimensional dilaton gravities - art. no. 124016

We study the low energy string effective action with an exponential type di laton potential and vanishing torsion in a Bianchi type I space-time geomet ry. In the Einstein and string frames the general solution of the gravitati onal field equations can be expressed in an exact parametric form. Dependin g on the values of the dilaton coupling constant and of the coefficient in the exponential, the obtained cosmological models can be generically divide d into three classes, leading to both singular and non-singular behaviors. The effect of the potential on the time evolution of the mean anisotropy pa rameter is also considered in detail, and it is shown that a Bianchi type I universe isotropizes only in the presence of a dilaton held potential or a central deficit charge.