Bubble Universes With Different Gravitational Constants

TL;DR

This paper explores how different gravitational constants in bubble universes, modeled via Jordan-Brans-Dicke theory, influence primordial curvature perturbations, potentially creating observable features in the power spectrum.

Contribution

It introduces a model of bubble universes with varying gravitational constants and analyzes their impact on primordial perturbations using JBD theory.

Findings

Gravitational constant differences affect superhorizon curvature perturbations.

Wall dynamics can produce a bump feature in the power spectrum.

Model links bubble nucleation to observable cosmological signatures.

Abstract

We argue a scenario motivated by the context of string landscape, where our universe is produced by a new vacuum bubble embedded in an old bubble and these bubble universes have not only different cosmological constants, but also their own different gravitational constants. We study these effects on the primordial curvature perturbations. In order to construct a model of varying gravitational constants, we use the Jordan-Brans-Dicke (JBD) theory where different expectation values of scalar fields produce difference of constants. In this system, we investigate the nucleation of bubble universe and dynamics of the wall separating two spacetimes. In particular, the primordial curvature perturbation on superhorizon scales can be affected by the wall trajectory as the boundary effect. We show the effect of gravitational constant in the exterior bubble universe can provide a peak like a bump feature at a large scale in a modulation of power spectrum.