Stable Inflationary Dissipative Cosmologies

Inflationary cosmic expansions driven by a dissipative fluid has attracted some attention in the past as a mechanism able to solve the problems usually attached to the standard hot big-bang scenario (i.e. flatness, horizons, and monopoles abundance) different from those based on one (or more) scalar fields. The main dynamic effect of either the scalar field(s) or the dissipative fluid is to produce a state of cosmic accelerated expansion through the violation of the strong energy condition. If this accelerated state is sufficiently long, and if the Universe is able to exit it, the mentioned problems may find a satisfactory solution. Very often this analysis has been restricted to spatially-flat Friedmann-Lemâıtre-Robertson-Walker (FLRW for short) space-times, if only because the dependence of the scale factor on the spatial curvature k becomes negligible shortly after inflation has set in. However, one should be mindful that this curvature may have some impact on the stability of the inflationary solutions. Given the potential importance of such a scenario, it is advisable to stablish its generality with respect to the effect of spatial curvature. In 1 we studied the stability of inflationary expansions caused by a dissipative fluid governed by a causal transport equation (i.e. one that respects both relativistic causality and hydrodynamic stability of the fluid , ), assuming k = 0. Before going any further, a word of caution seems in order. The stability of the dissipative fluid, in the sense this expression is used here, depends on the physical properties of the fluid under consideration, i.e. on its state and transport equations , . Accordingly it should not be confused with the stability of the cosmic expansion -either inflationary or not. The stability of inflationary expansions driven by dissipative fluids in curved FLRW space-times was briefly discussed by Barrow , . However, his study was confined to fluids governed by transport equations of Eckart’s type 8 which, as is well-known, entails the aforesaid problems of acausality and instability.