Deflation of Vacuum Energy During Inflation Due to Bulk-Brane Interaction

TL;DR

This paper explores a brane world inflation model where a bulk scalar field interacts with matter on the brane, leading to deflation of vacuum energy and modified inflation dynamics due to extra-dimensional effects.

Contribution

It introduces a non-minimally coupled bulk scalar field in brane inflation, showing how energy transfer can deflate the cosmological constant during inflation.

Findings

Energy transfer from matter to bulk scalar can occur during inflation.

Deflation of large effective cosmological term on the brane is possible.

Numerical results support the model with quadratic and exponential potentials.

Abstract

We consider a brane world inflationary model in which inflation is driven by dynamics of a self-interacting scalar field living in the five-dimensional bulk. The scalar field is non-minimally coupled to matter fields on the brane and acts as an inflaton which induces a slow-roll inflation. We show that although the Friedmann equation is modified at early times due to effects of the extra dimension, the slow-roll condition is the same as that of the four-dimensional case. Due to the non-minimal coupling of matter with the bulk scalar, there is an energy transfer between the two components. We investigate the conditions under which the direction of this energy transfer can be from matter onto the bulk scalar. There are at least two advantages in this case: 1) It establishes a mechanism by which a large effective cosmological term on the brane is deflated during the inflation period. 2) The energy flow onto the bulk inflaton gives a more strongly damped evolution of the scalar field in the slow-roll region for a given potential. We then show that our results are supported by numerical estimations with quadratic and exponential potentials.