Detection strategies for scalar gravitational waves with interferometers and resonant spheres

We compute the response and the angular pattern function of an interferometer for a scalar component of gravitational radiation in Brans-Dicke theory. We examine the problem of detecting a stochastic background of scalar GWs and compute the scalar overlap reduction function in the correlation between an interferometer and the monopole mode of a resonant sphere. While the correlation between two interferometers is maximized taking them as close as possible, the interferometer-sphere correlation is maximized at a finite value of f×d, where f is the resonance frequency of the sphere and d the distance between the detectors. This defines an optimal resonance frequency of the sphere as a function of the distance. For the correlation between the VIRGO interferometer located near Pisa and a sphere located in Frascati, near Rome, we find an optimal resonance frequency f590Hz. We also briefly discuss the difficulties in applying this analysis to the dilaton and moduli fields predicted by string theory.