Dilaton-axion inflation with PBHs and GWs

Abstract

We discuss two-stage dilaton-axion inflation models [1] and describe α-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 α-attractor context, and develop its supergravity version. The predictions of this model following from its polynomial attractor properties are: ns and r are α-independent, r depends on the mass parameter μ 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 ℛK = -2/3α. Thereforethe masses of primordial black holes (PBHs) and the frequencies of small-scale gravitational waves (GWs) in this model show significant dependence on α.