  Within the context of the cold dark matter model, current observations
suggest that inflationary models which 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
which lead to such a potential are discussed.
