Testing $α$-attractor quintessential inflation against CMB and low-redshift data

Abstract

Due to universality and attractor properties, $α$-attractor quintessential inflation establishes direct relations between inflationary observables such as the scalar tilt $n_s$ and the tensor-to-scalar ratio $r$, and late-time dark energy equation of state parameters $w_0$ and $w_a$. In this work, we examine three different physically motivated regimes, considering complete freedom in the parameter $α$, models inspired by supergravity where $α$ takes on values up to $α=7/3$, and Starobinsky inflation ($α=1$). We investigate the consistency and constraints imposed by Cosmic Microwave Background measurements from the Planck satellite, B-mode polarization data from the BICEP/Keck collaboration, and low-redshift observations. Additionally, we consider small-scale CMB measurements released by the Atacama Cosmology Telescope, which give results approaching the Harrison-Zel'dovich spectrum ($n_s \approx 1$). Here $α$-attractors lead to an improved fit over $Λ$CDM. For the large-scale CMB measurements, $α\gtrsim2$ models can provide equally good fits as $Λ$CDM.