Gravitational-Wave Background as a Probe of the Primordial Black-Hole Abundance

Abstract

The formation of a significant number of black holes (PBHs) is realized if and only if primordial density fluctuations have a large amplitude, which means that tensor perturbations generated from these scalar perturbations as a second-order effect are also large and comparable to the observational data. We show that pulsar timing data essentially rule out PBHs with 10;{2}-10;{4}M_{middle dot in circle}, which were previously considered as a candidate of intermediate-mass black holes, and that PBHs with a mass range of 10;{20} to 10;{26} g, which serves as a candidate of dark matter, may be probed by future space-based laser interferometers and atomic interferometers.

Cosmology with space-based gravitational-wave detectors: Dark energy and primordial gravitational waves

“…Then the luminosity distance and the cosmological phase correction in Eqs. (8) and (9) are written as…”

“…These GW sources enable us to probe inflation and density perturbation in the early universe [5][6][7][8][9], to measure the cosmic expansion with unprecedented precision [4,10], to investigate the population and formation history of compact binary objects [11], and to test alternative theories of gravity [12][13][14][15]. Therefore, DECIGO and BBO will open up the window of gravitational-wave cosmology.…”

DECIGO: the Japanese Space Gravitational Wave Antenna

“…As for black-hole binaries, DECIGO will observe GWs from coalescences of intermediate-mass (10 3 Msolar) black hole binaries, which could reveal the mechanism of the formation of super-massive black holes in the center of galaxies. The most exciting target of DECIGO will be the stochastic background GWs from the early universe; GWs could be radiated from density fluctuations in early universe, primordial blackholes 15) , and so on. This target cannot be observed by electro-magnetic waves directly, because of scattering in high-energy plasma in the early universe.…”

Constraints on the induced gravitational wave background from primordial black holes

“…By other words, the stochastic spectrum of second-order GWs is induced by the first-order scalar perturbations. Calculations of GW at second order and discussions on perspectives of measurements of the second-order GWs are contained in works [4][5][6][7][8][9].…”