Vacuum fluctuations in an ancestor vacuum: A possible dark energy candidate

TL;DR

This paper investigates how vacuum fluctuations from an ancestor de Sitter vacuum could contribute to dark energy in an open universe created by bubble nucleation, analyzing scalar field vacuum expectation values and their evolution.

Contribution

It introduces a method to compute vacuum energy effects from an ancestor vacuum on the present universe, highlighting the role of supercurvature modes and their potential as dark energy.

Findings

Vacuum energy can act as dark energy if the scalar field mass is comparable to the current Hubble parameter.

Preliminary results suggest a specific behavior of the dark energy equation of state w(z).

Supercurvature modes decay slowly and influence the vacuum energy in the open universe.

Abstract

We consider an open universe created by bubble nucleation, and study possible effects of an "ancestor vacuum" (de Sitter space in which bubble nucleation occurred) on the present universe. We compute vacuum expectation values of energy-momentum tensor for a minimally coupled scalar field, carefully taking into account the effect of the ancestor vacuum by the Euclidean prescription. In the study of the time evolution, an important role is played by the so-called supercurvature mode, which is non-normalizable on a spatial slice of open universe and decays in time most slowly. We point out that vacuum energy of a quantum field can be regarded as dark energy if mass of the field is of order the present Hubble parameter or smaller. We obtain preliminary results for the dark energy equation of state w(z) as a function of the redshift.