A new bigravity model with exclusively positive branes

TL;DR

This paper introduces a bigravity model with two positive tension branes in AdS_5, producing a light graviton mode while satisfying energy conditions and avoiding ghosts, but faces phenomenological challenges due to a negative brane cosmological constant.

Contribution

It presents a novel bigravity setup with only positive tension branes, avoiding negative branes and ghosts, and mimics negative brane effects through warp factor bounce.

Findings

Achieves a light graviton KK mode without negative tension branes.

Satisfies weak energy condition and avoids ghost states.

Extra graviton polarization states decouple, aligning with Einstein gravity.

Abstract

We propose a new ``bigravity'' model with two positive tension AdS_4 branes in AdS_5 bulk and no negative tension branes. The bounce of the ``warp'' factor mimics the effect of a negative brane and thus gives rise to an anomalously light graviton KK mode. This configuration satisfies the weak energy condition and has no ghost state. In addition, the extra polarization states of the massive graviton practically decouple and thus it does not contradict to Einsteinian gravity. However, the model has certain phenomenological difficulties associated with the presence of a negative cosmological constant on the branes.