A Breathing Mode for Warped Compactifications

TL;DR

The paper shows that in warped compactifications the warped volume modulus and the dilaton are not independent: warp-induced diffeomorphism breaking and Einstein constraint equations force them to combine into a single gauge-invariant degree of freedom, the warped breathing mode, valid for all warp strengths. By developing warped perturbation theory and a specific ansatz, the authors derive the breathing mode's kinetic term from dimensional reduction, demonstrating how gravity and dilaton contributions mix. They confirm the breathing mode as a natural zero mode in p-brane backgrounds and discuss broader implications for flux compactifications, moduli stabilization, and no-go theorems that rely on unwarped degrees of freedom. Altogether, this work reframes how low-energy effective theories from flux backgrounds should identify physical DOFs, highlighting the inseparability of volume and dilaton fluctuations in warped settings.

Abstract

In general warped compactifications, non-trivial backgrounds for the warp factor and the dilaton break $D$-dimensional diffeomorphism invariance, so that dilaton fluctuations can be gauged away completely and eaten by the metric. More specifically, the warped volume modulus and the dilaton are not independent, but combine into a single gauge-invariant degree of freedom in the lower dimensional effective theory, the warped breathing mode. This occurs for all strengths of the warping, even the weakly warped limit. This warped breathing mode appears as a natural zero mode deformation of backgrounds sourced by p-branes, and affects the identification of the independent degrees of freedom of flux compactifications.