Primordial black holes and scalar-induced gravitational waves from the generalized Brans-Dicke theory
Zhu Yi
Abstract
Abstract The power spectrum of the scalar-tensor inflation with a quadratic form Ricci scalar coupling function Ω( ϕ ) = 1 - 2 ϕ / ϕ c + (1 + δ 2 )( ϕ / ϕ c ) 2 can be enhanced enough to produce primordial black holes and generate scalar-induced gravitational waves. The masses of primordial black holes and the frequencies of scalar-induced gravitational waves are controlled by the parameter ϕ c , and their amplitudes are determined by the parameter δ . Primordial black holes with stellar masses, planetary masses, and masses around 10 -12 M ⊙ are produced and their abundances are obtained from the peak theory. The frequencies of the corresponding scalar-induced gravitational waves are around 10 -9 Hz, 10 -6 Hz, and 10 -3 Hz, respectively. The primordial black holes with masses around 10 -12 M ⊙ can account for almost all of the dark matter, and the scalar-induced gravitational waves with frequencies around 10 -9 Hz can explain the NANOGrav 12.5 yrs signal.