Cosmological Imprint of an Energy Component with General Equation of State

Abstract

We examine the possibility that a significant component of the energy density of the universe has an equation-of-state different from that of matter, radiation or cosmological constant ($\Lambda$). An example is a cosmic scalar field evolving in a potential, but our treatment is more general. Including this component alters cosmic evolution in a way that fits current observations well. Unlike $\Lambda$, it evolves dynamically and develops fluctuations, leaving a distinctive imprint on the microwave background anisotropy and mass power spectrum.

Comments: revised version, with added references, to appear in Phys. Rev. Lett. (4 pages Latex, 2 postscript figures)