# Constraining higher order gravities with subregion duality

## TL;DR

This paper explores how higher derivative gravity theories affect the construction of causal and entanglement wedges in holography, showing that using the fastest mode imposes stronger constraints on couplings than traditional causality conditions.

## Contribution

It demonstrates that the causal wedge inclusion condition constrains higher derivative couplings more stringently than hyperbolicity and boundary causality, using subregion duality.

## Key findings

- Causal wedge must be constructed using the fastest mode in higher derivative theories.
- Stronger constraints on couplings from causal wedge inclusion than from hyperbolicity.
- Analysis in Gauss-Bonnet gravity supports the proposed constraints.

## Abstract

In higher derivative theories, gravity can travel slower or faster than light. With this feature in mind, we revisit the construction of the causal and entanglement wedges in this type of theories, and argue that they must be constructed using the fastest mode instead of null rays. We show that the property of causal wedge inclusion, i.e., the fact that the causal wedge must be contained in the entanglement wedge, leads to more stringent constraints on the couplings than those imposed by hyperbolicity and boundary causality. Our results imply that the full power of subregion-subregion duality could lead to the same conclusions previously obtained based on high energy graviton scattering. We illustrate our findings with a systematic analysis in Gauss-Bonnet gravity.