String Theory seminar - Dominik Neuenfeld Seminar

Abstract: Doubly-holographic models allow for superluminal signalling in the brane perspective, which raises questions about their usefulness, e.g., in discussing the information paradox. We will argue that such causality violations are not observable at length scales for which the brane description is valid, implying that superluminal signalling is a UV effect which can be understood within the framework of effective field theory. Moreover, we explain how short-distance non-localities in Anti-de Sitter space can generally give rise to apparent causality violations. However, the causal structure in the brane description of double holography is in fact not simply determined by the induced metric on the brane. We introduce the notion of a "Unitary Domain of Dependence" (UDoD), which defines a subregion where the density matrix can be computed from an initial state using an effective local and unitary description. The UDoD can be bounded using entropic inequalities. For a certain class of examples, the UDoD is strictly contained within the classical domain of dependence, but outside the region where effective field theory is naively expected to hold.