Dynamical Relaxation of the Cosmological Constant and Matter Creation in the Universe

TL;DR

This paper explores a scenario where long wavelength cosmological perturbations induce a negative contribution to the cosmological constant, leading to its dynamical relaxation, and proposes a matter creation mechanism via decay of a condensate after inflation.

Contribution

It introduces a novel relaxation mechanism for the cosmological constant driven by back-reaction effects and suggests a matter generation process without an inflaton field.

Findings

Long wavelength fluctuations induce a negative effective cosmological constant.

A condensate decay mechanism can produce matter after relaxation.

The scenario provides a unified view of inflation exit and matter creation.

Abstract

In this Letter we discuss the issues of the graceful exit from inflation and of matter creation in the context of a recent scenario \cite{RHBrev} in which the back-reaction of long wavelength cosmological perturbations induces a negative contribution to the cosmological constant and leads to a dynamical relaxation of the bare cosmological constant. The initially large cosmological constant gives rise to primordial inflation, during which cosmological perturbations are stretched beyond the Hubble radius. The cumulative effect of the long wavelength fluctuations back-reacts on the background geometry in a form which corresponds to the addition of a negative effective cosmological constant to the energy-momentum tensor. In the absence of an effective scalar field driving inflation, whose decay can reheat the Universe, the challenge is to find a mechanism which produces matter at the end of the relaxation process. In this Letter, we point out that the decay of a condensate representing the order parameter for a ``flat'' direction in the field theory moduli space can naturally provide a matter generation mechanism. The order parameter is displaced from its vacuum value by thermal or quantum fluctuations, it is frozen until the Hubble constant drops to a sufficiently low value, and then begins to oscillate about its ground state. During the period of oscillation it can decay into Standard Model particles similar to how the inflaton decays in scalar-field-driven models of inflation.