Limits on direct detection of gravitational waves.

We compute energy density and strain induced by a primordial spectrum of gravitational waves on terrestrialand space-based detectors (e.g., LIGO) as constrained by the COBE detection of microwave background anisotropy. For the case where the spectrum is created during in ation, we nd new, stricter upper bounds on the induced strain, making detection unlikely. However, detectors might be useful for discovering (or ruling out) exotic, non-in ationary sources. PACS numbers 98.80.Cq, 04.30.-w, 04.80.Nn Events in the early universe may have left a primordial spectrum of gravitational waves. Detecting these elusive remnants would not only establish the existence of this as-yet-unveri ed prediction of General Relativity, but it would also provide a new critical test for all proposed scenarios of the evolution of the early universe. In particular, a basic feature of the in ationary model of the universe is the prediction of a relic spectrum of gravitational waves [1], whose detection would lend strong support to the theory. Such a detection might occur in three possible ways. Gravitational waves distort the Cosmic Microwave Background (CMB) through the Sachs-Wolfe e ect [2], thus raising the possibility that some or even most of the temperature variations observed by COBE [3] are due to gravitational waves [4]. 1 email: [email protected]