Brane Worlds in 5D and Warped Compactifications in IIB

TL;DR

The paper questions the validity of the common factorized metric ansatz used to derive 4D moduli potentials in warped compactifications by analyzing a brane-world in five dimensions (RS1). By explicitly projecting the 5D cosmological equations onto the brane and comparing with the 4D effective action obtained from the factorized ansatz, the author shows the two are inconsistent in dynamical settings, requiring time dependence of the radion/volume modulus not captured by simple factorization, except in static cases. The work then translates these insights to the IIB context, arguing that the usual static ansatz used to derive moduli potentials can yield incorrect results away from the minimum due to neglected x-dependence of warp factors and flux backreaction. Overall, the paper cautions that accurate 4D physics in warped compactifications demands retaining full higher-dimensional dynamics (5D or 10D) and possibly KK modes, impacting moduli stabilization analyses and associated phenomenology.

Abstract

In computing potentials for moduli in for instance type IIB string theory in the presence of fluxes and branes a factorisable ansatz for the ten dimensional metric is usually made. We investigate the validity of this ansatz by examining the cosmology of a brane world in a five dimensional bulk and find that it contradicts the results obtained by using a factorizable ansatz. We explicitly identify the problem with the latter in the IIB case. These arguments support our previous work on this question.