What is needed of a scalar field if it is to unify inflation and late time acceleration ?

TL;DR

This review discusses the conditions and mechanisms by which a single scalar field can unify early universe inflation and late-time cosmic acceleration, emphasizing potential shapes, scaling solutions, and neutrino coupling effects.

Contribution

It provides a comprehensive analysis of the formalism, scaling solutions, and exit mechanisms, including the role of neutrino coupling, for quintessential inflation models.

Findings

Scaling solutions are central to unification of inflation and late acceleration.

Neutrino coupling can trigger late-time acceleration.

Potential shape requirements include initial shallow, steep, then shallow again.

Abstract

Quintessential inflation refers to scenarios in which a single scalar field is used to describe inflation and late-time acceleration. This review is dedicated to the framework of quintessential inflation, with a focus on the building blocks of formalism. Consistent unification of inflation and late time acceleration using a single scalar field asks for a shallow field potential initially followed by steep behaviour thereafter and shallow again around the present epoch. The requirement of non-interference of scalar field with thermal history dictates steep nature of potential in the post-inflationary era, with a further restriction that late time physics be independent of initial conditions. We describe, in detail the scaling and asymptotic scaling solutions and the mechanism of exit from the scaling regime to late time acceleration. Review includes a fresh look at scaling solutions which are central to the theme of unification of inflation and late time acceleration. As for the exit mechanism, special attention is paid to the coupling of massive neutrino matter to the scalar field, which builds up dynamically and can give rise to late time acceleration. We present a detailed analytical treatment of scalar field dynamics in the presence of coupling. We briefly discuss the distinguished feature of quintessential inflation, namely, the blue spectrum of gravity waves produced during the transition from inflation to the kinetic regime.