Inflation from Multiple Pseudo-scalar Fields: Primordial Black Hole Dark Matter and Gravitational Waves

Abstract

We study a model of inflation with multiple pseudo-scalar fields coupled to a U(1) gauge field through Chern–Simons interactions. Because of parity-violating interactions, one polarization of the gauge field is amplified, yielding to an enhanced curvature perturbation power spectrum. Inflation proceeds in multiple stages, as each pseudo-scalar field rolls toward its minimum, yielding to distinct multiple peaks in the curvature perturbation power spectra at various scales during inflation. The localized peaks in the power spectra generate primordial black holes that can furnish a large fraction of dark matter abundance. In addition, gravitational waves with nontrivial spectra are generated that are in the sensitivity ranges of various forthcoming GW observatories.

Induced gravitational waves from non-attractor inflation and NANOGrav data

“…To explain the NANOGrav data via cosmological sources, one needs to amplify the scalar perturbations during inflation [16][17][18][19][20][21][22][23][24][25]. The amplification of scalar perturbations is also a mechanism for the production of primordial black holes (PBHs), which may explain dark matter as well [26][27][28][29][30].…”

Revisiting the stochastic QCD axion window: departure from equilibrium during inflation

“…The identity of dark matter remains an open question, and a wide range of possibilities has been explored. Examples include axion-like dark matter with a mass of order 10 −21 eV, weakly interacting massive particles with weak-scale mass (∼ 10 2 GeV), and dark matter with mass beyond the Planck scale, such as primordial black holes [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. While the mass of dark matter can vary widely, light dark-matter candidates are naturally expected from the likely symmetry breakings that occur in the early Universe, such as pseudo-Nambu-Goldstone bosons originating from the spontaneous breaking of a continuous global symmetry.…”

Induced gravitational waves from ultra slow-roll inflation and pulsar timing arrays observations

“…Scalar induced gravitational waves (SIGW) from the enhanced scalar perturbations on small scale during inflation [20][21][22][23][24][25][26][27][28][29] is a mechanism which can explain the observed SG-WBs [13,14]. In this mechanism, the GWs are sourced at the second order in perturbation theory via their interaction with the scalar sector generated during inflation.…”