Cosmological Coincidence without Fine Tuning

TL;DR

This paper proposes a cosmological model where a single scalar field drives both early universe inflation and late-time acceleration, naturally explaining the dark energy density without fine tuning.

Contribution

It introduces a non-minimally coupled scalar field with a quartic potential that accounts for both inflation and dark energy, reducing the need for fine tuning.

Findings

Scalar field explains dark energy density naturally.

Model unifies early and late universe acceleration.

Matches observed dark energy scale without fine tuning.

Abstract

We present a simple cosmological model in which a single, non-minimally coupled scalar field with a quartic potential is responsible for both inflation at early times and acceleration at late times. Little or no fine tuning is needed to explain why the present density of dark energy is comparable to that of pressureless matter. Dark energy is identified with the potential of the scalar field, which is sourced by the trace of the energy-momentum tensor. This becomes significant when matter has decoupled from radiation and become fully non-relativistic, so that $\phi\propto\rho_m^{1/3}\propto\rho_{m,0}^{1/3}(a_0/a)\sim(10^{-120})^{1/3}(10^{10})\sim10^{-30}$ and $V\sim\phi^4\sim10^{-120}$ in Planck units, as observed.