Metastable Gravitons and Infinite Volume Extra Dimensions

TL;DR

This paper explores models with infinite-volume extra dimensions where gravity is mediated by metastable gravitons, revealing both promising phenomenological features and significant challenges due to massive graviton effects.

Contribution

It introduces the concept of metastable 4D gravitons in infinite-volume extra dimensions and discusses their implications for gravity and cosmology.

Findings

Correct Newtonian gravity can be obtained without a normalizable zero-mode graviton.

Theories exhibit high-dimensional behavior at large scales, affecting universe evolution.

Phenomenological issues arise from the van Dam-Veltman-Zakharov discontinuity.

Abstract

We address the issue of whether extra dimensions could have an infinite volume and yet reproduce the effects of observable four-dimensional gravity on a brane. There is no normalizable zero-mode graviton in this case, nevertheless correct Newton's law can be obtained by exchanging bulk gravitons. This can be interpreted as an exchange of a single {\it metastable} 4D graviton. Such theories have remarkable phenomenological signatures since the evolution of the Universe becomes high-dimensional at very large scales. Furthermore, the bulk supersymmetry in the infinite volume limit might be preserved while being completely broken on a brane. This gives rise to a possibility of controlling the value of the bulk cosmological constant. Unfortunately, these theories have difficulties in reproducing certain predictions of Einstein's theory related to relativistic sources. This is due to the van Dam-Veltman-Zakharov discontinuity in the propagator of a massive graviton. This suggests that all theories in which contributions to effective 4D gravity come predominantly from the bulk graviton exchange should encounter serious phenomenological difficulties.