Unification of inflation and dark energy {\it \`a la} quintessential inflation

TL;DR

This review explores models unifying inflation and dark energy through a single scalar field, discussing their dynamics, potential types, and observational implications like gravitational waves and B-mode polarization.

Contribution

It provides a comprehensive overview of quintessential inflation models, including new classes with non-canonical kinetic terms and their compatibility with recent observations.

Findings

Models with steep-to-shallow potentials can realize inflation via brane damping.

Non-minimal coupling with neutrinos can induce late-time minima in the potential.

Presence of a kinetic phase leads to a blue spectrum of gravitational waves.

Abstract

This pedagogical review is devoted to quintessential inflation, which refers to unification of inflation and dark energy using a single scalar field. We present a brief but concise description of the concepts needed to join the two ends, which include discussion on scalar field dynamic, conformal coupling, instant preheating and relic gravitational waves. Models of quintessential inflation broadly fall into two classes, depending upon the early and late time behavior of the field potential. In the first type we include models in which the field potential is steep for most of the history of the Universe but turn shallow at late times, whereas in the second type the potential is shallow at early times followed by a steep behavior thereafter. In models of the first category inflation can be realized by invoking high-energy brane-induced damping, which is needed to facilitate slow roll along a steep potential. In models of second type one may invoke a non-minimal coupling of the scalar field with massive neutrino matter, which might induce a minimum in the potential at late times as neutrinos turn non-relativistic. In this category we review a class of models with non-canonical kinetic term in the Lagrangian, which can comply with recent B mode polarization measurements. The scenario under consideration is distinguished by the presence of a kinetic phase, which precedes the radiative regime, giving rise to blue spectrum of gravity waves generated during inflation. We highlight the generic features of quintessential inflation and also discuss on issues related to Lyth bound.