Null orbifolds in AdS, Time Dependence and Holography

TL;DR

This paper explores null orbifolds in AdS spaces and their holographic duals, providing insights into string theory in time-dependent backgrounds through brane configurations, T-duality, and gauge theory descriptions.

Contribution

It introduces a detailed analysis of null orbifolds in AdS, their boundary singularities, and dual gauge theories, advancing understanding of holography in time-dependent settings.

Findings

Null orbifolds in AdS have singular conformal boundaries.

Dual gauge theories are described by Super Yang-Mills in null-brane backgrounds.

Proposes a non-perturbative approach to string theory in time-dependent spacetimes.

Abstract

We study M/D-branes in a null-brane background. By taking a near horizon limit, one is left with cosmological models in the corresponding Poincar\'e patches. To deal with their usual horizons, we either extend these models to global AdS or remain in the Poincar\'e patch and apply a T-duality transformation whenever the effective radius of the compact dimension associated with the null-brane probes distances smaller than the string scale. The first scenario gives rise to null orbifolds in AdS spaces, which are described in detail. Their conformal boundaries are singular. The second has a dual gauge theory description in terms of Super Yang-Mills in the null-brane background. The latter is a good candidate for a non-perturbative definition of string theory in a time-dependent background.