Inflationary theory and pulsar timing investigations of primordial black holes and gravitational waves
Nicholas Orlofsky, Aaron Pierce, James D. Wells
TL;DR
The paper probes whether LIGO-detected mergers could originate from primordial black holes formed by inflationary perturbations, and whether the associated secondary gravitational waves are observable with pulsar timing arrays. It develops a framework linking the primordial curvature spectrum to PBH abundance and to a SGW background from second-order tensor modes, then compares predictions across several inflationary scenarios to current PTA data. It finds that models with broad or extended primordial spectra are largely excluded by PTAs, while highly peaked spectra—such as those arising from parametric resonance in double inflation—remain testable with continued PTA observations, whereas some postinflation scenarios like the axion-curvaton generically push SGWs to frequencies PTAs cannot probe. Overall, PTAs provide a powerful, inflation-model-sensitive probe to discriminate PBH formation mechanisms and illuminate early-universe physics, complementary to LIGO observations.
Abstract
The gravitational waves measured at LIGO are presumed here to come from merging primordial black holes. We ask how these primordial black holes could arise through inflationary models while not conflicting with current experiments. Among the approaches that work, we investigate the opportunity for corroboration through experimental probes of gravitational waves at pulsar timing arrays. We provide examples of theories that are already ruled out, theories that will soon be probed, and theories that will not be tested in the foreseeable future. The models that are most strongly constrained are those with a relatively broad primordial power spectrum.