WAVE-FRONT SPEEDS IN POWER-LAW INFLATION DRIVEN BY BULK VISCOSITY ANDMATTER CREATION

the framework of a spatially fiat FLRW model, we account for dissipati ve effects in a simple fluid, namely bulk viscosity and matter creatio n. For an isentropic evolution, we study the wavefront speeds associat ed with the characteristics of the fluid. With the assumption of a bar otropic equation of state, we investigate the consequences on these sp eeds of power-law behaviour for the scale factor. Our conclusion is th at, in contrast to the exponential inflation, the isentropic power-law inflation is compatible with causality, under conditions linking the generalized 'adiabatic' index gamma to the exponent m of the power law .