Cosmological gravitational wave backgrounds

An overview is presented of possible cosmologically distant sources of gravitational wave backgrounds, especially those which might produce detectable backgrounds in the LISA band between 0.1 and 100 mHz. Examples considered here include inflation-amplified vacuum fluctuations in inflaton and graviton fields, bubble collisions in first-order phase transitions, Goldstone modes of classical self-ordering scalars, and cosmic strings and other gauge defects. Characteristic scales and basic mechanisms are reviewed and spectra are estimated for each of these sources. The unique impact of a LISA detection on fundamental physics and cosmology is discussed.