Partial Reduction and Cosmology at Defect Brane

TL;DR

This paper introduces a partial reduction method in AdS/BCFT with defect branes, demonstrating its application to cosmology, graviton localization, and entropy calculations, revealing new insights into holographic dualities and brane-world cosmology.

Contribution

It develops a partial reduction approach for defect branes in AdS/BCFT, showing its utility in cosmology, graviton localization, and entropy computations, extending previous holographic methods.

Findings

Equivalence between defect extremal surface and island formula for entropy.

Existence of a 4d massless graviton on AdS4 brane via partial reduction.

Proposal of a partial reduction for 4d FRW cosmology and boundary Newton constant calculation.

Abstract

Partial reduction is a Randall-Sundrum reduction for only part of the AdS region between finite tension brane and zero tension brane. This is interesting in AdS/BCFT where the AdS bulk contains a defect brane. We employ partial reduction for a AdS bulk with a brane evolving as a $2d$ Friedmann-Robertson-Walker (FRW) cosmology and demonstrate the equivalence between defect extremal surface and island formula for a large subregion fine grained entropy in boundary CFT. We then move to higher dimensions and demonstrate the existence of $4d$ massless graviton on AdS$_4$ brane in partial reduction. We also propose a partial reduction for a $4d$ FRW cosmology at defect brane and obtain the Newton constant by computing boundary entropy.