Cosmological solutions with time-delay

Abstract

We introduce a time-delay function in bulk viscosity cosmology. Even for bulk viscosity functions where closed-form solutions are known, because of the time-delay term the exact solutions are lost. Therefore in order to study the cosmological evolution of the resulting models we perform a detail analysis of the stability of the critical points, which describe de Sitter solutions, by using Lindstedt's method. We find that for the stability of the critical points it depends also on the time-delay parameter, where a critical time-delay value is found which play the role of a bifurcation point. For time-delay values near to the critical value, the cosmological evolution has a periodic evolution, this oscillating behaviour is because of the time-delay function. We find a new behaviour near the exponential expansion point, which can be seen also as an alternative way to exit the exponential inflation.