If the Universe is flat, as predicted by inflationary cosmology, then the vast majority of the cosmic energy density is non-baryonic. One possibility is that a substantial fraction of this missing, non-baryonic energy consists of quintessence, a time-dependent and spatially inhomogeneous component whose equation-of-state differs from that of baryons, neutrinos, dark matter, or radiation or cosmological constant. An example is a scalar field evolving in a potential, but our treatment is more general. Including this component as a replacement of the cosmological constant alters cosmic evolution in a way that fits current observations well. Unlike the cosmological constant, it evolves dynamically and develops fluctuations, leaving a distinctive imprint on the microwave background anisotropy and mass power spectrum. This work describes the effects of quintessence on the Cosmic Microwave Background Radiation (CMBR) anisotropy. It shows that the evolution of fluctuations in this component, and the resulting CMB anisotropy, is independent of the initial conditions on the fluctuations. The microwave background anisotropy power spectrum in models which include quintessence is numerically computed and analytically explained, and the imprints left by quintessence are categorized by epoch and physical effect. There exists a fundamental degeneracy which will prevent near-future CMBR satellite experiments from discriminating between quintessence and alternative candidates for the missing energy by themselves. However, combining these measurements with those from high redshift supernovas will enable us to set loose constraints on the relevant parameters. If quintessence is discovered, there may be fundamental implications for the cosmological constant problem, and there will be a lot of interesting low energy particle physics to explore.
- Pub Date:
- August 2002
- Physics: Astronomy and Astrophysics, Physics: Elementary Particles and High Energy