Revisiting pre-inflationary universe of family of $\alpha-$attractor in loop quantum cosmology

TL;DR

This paper explores the pre-inflationary universe in loop quantum cosmology with $ ext{alpha}$-attractor potentials, demonstrating that quantum effects resolve the big bang singularity into a bounce and lead to viable slow-roll inflation consistent with observations.

Contribution

It provides a detailed numerical and analytical study of initial conditions, phase space trajectories, and the dynamics of the bounce in $ ext{alpha}$-attractor models within loop quantum cosmology, highlighting the universality of the bouncing phase.

Findings

Quantum bounce replaces big bang singularity.

Viable initial conditions lead to sufficient inflation.

Bouncing phase is independent of initial data and potential in kinetic energy dominance.

Abstract

In this work, we revisit the dynamics of pre-inflationary universe with a family of $\alpha-$attractor potentials, in the framework of loop quantum cosmology, in which the big bang singularity is generically resolved purely with quantum geometric effects, and replaced by a quantum bounce. At the bounce, the background evolution is divided into two distinct classes, the first is dominated by the kinetic energy of the inflaton field and the second by the potential energy. In both classes, we find the physically viable initial conditions numerically that provide not only the slow-roll inflation, but also sufficient e-folds to be compatible with observations. In the entire range of kinetic energy dominated initial conditions (except some subsets of Models 2 and 4), the background evolution prior to reheating is always split into three different phases: bouncing, transition and slow-roll inflation. In the bouncing phase, the numerical evolution of the scale factor is independent not only of the initial data, but also the inflationary potentials, as long as it is dominated by the kinetic energy, and can be well approximated by an analytical solution, whereas in the potential energy dominated case, such approximated results do not exist. Moreover, we study the phase space analysis for a class of $\alpha-$attractor potentials, and discuss the phase space trajectories for physically viable initial conditions of the inflaton field.