Viscosity effects in (1+1)-dimensional cosmologies

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 take into account the effects of a nonlinear viscosity beta. We find exact solutions of the field equations for several physically interesting cases which include Friedmann cosmologies and the time reversal of Murphy's class of cosmological solutions. We find that the global effect of bulk viscosity is to decrease the expansion rate while the nonlinear viscosity does not qualitatively-change the models. On the other hand, the bulk viscosity is able to remove the initial singularities which are present in the corresponding viscosity free models as in the four-dimensional case.