DESI and Gravitational Wave Constraints Challenge Quintessential {\alpha}-Attractor Inflation

TL;DR

This study investigates alpha-attractor quintessential inflation models, constraining them with DESI and other data, revealing tensions with gravitational wave bounds and highlighting detection prospects for future experiments.

Contribution

The paper provides a fully numerical analysis of alpha-attractor quintessential inflation, incorporating latest observational constraints and gravitational wave effects, to assess model viability.

Findings

Model predictions are disfavored when including ff constraints.

Scalar spectral index becomes too small under gravitational wave bounds.

Primordial gravitational wave spectrum shows potential detectability in future experiments.

Abstract

Quintessential inflation models provide a framework that simultaneously describes inflation and dynamical dark energy, the latter of which has recently received growing support from DESI observations. A distinctive feature of these models is the kination phase after inflation, which enhances primordial gravitational waves at high frequencies. In this work, we study a class of alpha-attractor quintessential inflation models using a fully numerical approach that follows the scalar-field evolution from inflation to the dark-energy-dominated era, allowing us to compute with high precision both the dynamics of dark energy and the primordial gravitational wave spectrum. Using the latest observational data, including DESI and ACT, we constrain the model parameters and show that the model becomes disfavored once constraints from the gravitational-wave contribution to the effective number of relativistic degrees of freedom, {\Delta} Neff, are included. This is because the model predicts a scalar spectral index ns that becomes too small to remain consistent with observations when the gravitational-wave abundance is constrained to stay below the {\Delta} Neff bound. Finally, we present the resulting primordial gravitational wave power spectrum computed using our constrained parameter values, which highlights prospects for detection by future CMB B-mode experiments at low frequencies and by gravitational-wave interferometer experiments at high frequencies.