VISCOSITY EFFECTS IN (1-DIMENSIONAL COSMOLOGIES(1))

We investigate the behaviour of the solutions to the gravitational (1 + 1)-dimensional equations with a viscous fluid source in the case of a Robertson-Walker metric. In our model the bulk viscosity coefficient is related to the energy density as xi = alpha rho(m) and we also tak e into account the effects of a nonlinear viscosity beta. We find exac t solutions of the field equations for several physically interesting cases which include Friedmann cosmologies and the time reversal of Mur phy's class of cosmological solutions. We find that the global effect of bulk viscosity is to decrease the expansion rate while the nonlinea r viscosity does not qualitatively-change the models. On the other han d, the bulk viscosity is able to remove the initial singularities whic h are present in the corresponding viscosity free models as in the fou r-dimensional case.