SPECTRUM OF RELIC GRAVITATIONAL-WAVES IN STRING COSMOLOGY

We compute the spectrum of relic gravitons in a model of string cosmol ogy. In the low- and high-frequency limits we reproduce known results. The full spectrum, however, also displays a series of oscillations wh ich could give a characteristic signature at the planned LIGO-VIRGO de tectors. For special values of the parameters of the model the signal reaches its maximum already at frequencies accessible to LIGO and VIRG O and it is close to the sensitivity of first generation experiments.