We investigate some power-law solutions in inflationary cosmology, both by analytic and numerical means, considering first a simple model of a scalar field with an exponential field coupled to gravity. As has been pointed out recently by Yokoyama and Maeda, in power-law inflation viscous forces caused by couplings of the inflation to other particles can be important. We use numerical simulation to examine the effects of this viscosity on the inflation, for both a simple exponential potential and a more realistic potential motivated by particle physics. In general, the viscosity enhances the exponent of the power-law inflation, increasing the efficiency of inflation in power-law models, and we outline a specific inflationary model featuring viscosity. © 1989.
Liddle, A. R. (1989). Power-law inflation with exponential potentials. Physics Letters B, 220(4), 502–508. https://doi.org/10.1016/0370-2693(89)90776-4