Dilaton-Axion Inflation with PBHs and GWs

TL;DR

This paper explores dilaton-axion inflation models within the $ ext{α}$-attractor framework, focusing on primordial black hole and gravitational wave production, and demonstrates how model parameters influence observable predictions.

Contribution

It introduces a supergravity version of a primordial black hole production model within the $ ext{α}$-attractor inflation context, analyzing its implications for PBHs and GWs.

Findings

PBH masses and GW frequencies depend on the parameter α.

The spectral index n_s and tensor-to-scalar ratio r are α-independent.

r varies with the mass parameter μ, affecting inflation predictions.

Abstract

We discuss two-stage dilaton-axion inflation models [1] and describe $\alpha$-attractor models with either exponential or polynomial approach to the plateau. We implement one of the models of primordial black hole production proposed in [2] in the $\alpha$-attractor context, and develop its supergravity version. The predictions of this model following from its polynomial attractor properties are: $n_s$ and $r$ are $\alpha$-independent, $r$ depends on the mass parameter $\mu$ defining the approach to the plateau. The tachyonic instability at the transition point between the two stages of inflation is proportional to the negative curvature of the hyperbolic space $\mathcal{R}_K=-2/3\alpha$. Therefore the masses of primordial black holes (PBHs) and the frequencies of small-scale gravitational waves (GWs) in this model show significant dependence on $\alpha$.