Title: Testing α-attractor inflation on all scales

Abstract: Hybrid cosmological α-attractors can lead to enhanced scalar fluctuations on small scales, with testable phenomenology including primordial black hole (PBH) production and large second-order gravitational waves (GW). In this presentation, I will show the results we obtained in our detailed analysis of these models, focusing on a reduced parameter space featuring the two potential parameters that roughly determine the position of the peak in the scalar power spectrum, Pζ , and its amplitude.

In particular, we constrain the parameter space by comparing the large-scale predictions for Pζ with current CMB anisotropies measurements and upper limits on μ-distortions, while taking into account uncertainties due to the reheating phase. We then move to smaller scales, where we find that non-Gaussianity at peak scales is of the local type and has amplitude fNL ∼ O(0.1), ensuring that non-linear effects are subdominant. By computing the abundance of Primordial Black Holes (PBHs), we further constrain the parameter space, by excluding models which over-produce them. We find that a subset of viable models can lead to significant production of PBHs, and a fraction of these is within reach for LISA, having a signal-to-noise ratio larger than that of astrophysical foregrounds.

Our results show that hybrid α-attractors have a rich phenomenology, especially at interferometer scales, while still complying with large-scale observations. Our first-of-its-kind study establishes a paradigm for constraining inflationary models by systematically combining tests at different scales, and exploiting the synergy between cosmological observations and theoretical consistency requirements.