TILTING OF THE PRIMORDIAL POWER SPECTRUM WITH BULK VISCOSITY

Within the context of the cold dark matter model, current observations suggest that inflationary models that generate a tilted primordial power spectrum with negligible gravitational waves provide the most promising mechanism for explaining large-scale clustering. The general form of the inflationary potential which produces such a spectrum is a hyperbolic function and is interpreted physically as a bulk viscous stress contribution to the energy momentum of a perfect baryotropic fluid. This is equivalent to expanding the equation of state as a truncated Taylor series. Particle physics models that lead to such a potential are discussed.