Relic Gravitational Waves and Cosmology

Abstract

This is an expanded version of my talk given at the international conference "Zeldovich-90". I start with a brief recollection of interactions with Zeldovich in the context of the study of relic gravitational waves. I then summarise the principles and early results on the quantum-mechanical generation of cosmological perturbations. The expected amplitudes of relic gravitational waves are different in different frequency windows, and therefore the techniques and prospects of their detection are different. One section of the paper describes the present state of efforts in direct detection of relic gravitational waves. Another section is devoted to indirect detection via the anisotropy and polarisation measurements of the cosmic microwave background radiation (CMB). It is emphasized throughout the paper that the conclusions on the existence and expected amount of relic gravitational waves are based on a solid theoretical foundation and the best available cosmological observations. I also explain in great detail what went wrong with the so-called `inflationary gravitational waves', whose amount is predicted by inflationary theorists to be negligibly small, thus depriving them of any observational significance.Comment: 36 pages including 8 figures; expanded version of a talk at the international conference `Zeldovich-90', Moscow, December 2004; http://hea.iki.rssi.ru/Z-90; v.2: additional formulas and explanations in response to remarks of anonymous referee; v.3: extra details about 'scalar' perturbations and T/S ratio, scheduled to appear in Uspekhi Fiz. Nauk v.176 (2006); v.4: matches published paper: Physics-Uspekhi, 48(12) 1235-1247 (2005) [Russian version: Uspekhi Fiz. Nauk, 175(12) 1289-1303 (2005)