Gravitational wave spectra from pole-like inflations based on generalized gravity theories

We present a general and unified formulation which can handle the classical evolution and quantum generation processes of the cosmological gravitational wave in a broad class of generalized gravity theories. Applications are demonstrated in several inflation models based on the scalar-tensor theory, the induced gravity and the low-energy effective action of string theories. The gravitational wave power spectra based on the vacuum expectation value of the quantized fluctuating metric during the pole-like inflation stages are derived in analytic forms. Assuming that the gravity theory transits to an Einstein one while the relevant scales remain in the superhorizon scale, we derive the consequent power spectra and the directional fluctuations of the relic radiation produced by the gravitational wave. The spectra seeded by the vacuum fluctuations in the pole-like inflation models based on the generalized gravity show a distinguished common feature ( spectrum) which differs from the scale-invariant one ( spectrum) generated in an exponential inflation in Einstein gravity which is supported by observations.