Insights on Entanglement Entropy in $1+1$ Dimensional Causal Sets

TL;DR

This paper investigates entanglement entropy in 1+1D causal sets, revealing that truncated contributions behave as fluctuations and encode causal set-specific features, extending results to Rényi and massive cases.

Contribution

It provides new insights into truncated contributions, extends entanglement entropy analysis to Rényi and massive theories, and discusses broader implications for causal set quantum field theory.

Findings

Truncated contributions behave as fluctuations.

Evidence that contributions encode causal set-specific features.

Extended analysis to Rényi and massive entanglement entropy.

Abstract

Entanglement entropy in causal sets offers a fundamentally covariant characterisation of quantum field degrees of freedom. A known result in this context is that the degrees of freedom consist of a number of contributions that have continuum-like analogues, in addition to a number of contributions that do not. The latter exhibit features below the discreteness scale and are excluded from the entanglement entropy using a "truncation scheme". This truncation is necessary to recover the standard spatial area law of entanglement entropy. In this paper we build on previous work on the entanglement entropy of a massless scalar field on a causal set approximated by a 1+1D causal diamond in Minkowski spacetime. We present new insights into the truncated contributions, including evidence that they behave as fluctuations and encode features specific to a particular causal set sprinkling. We extend previous results in the massless theory to include R\'enyi entropies and include new results for the massive theory. We also discuss the implications of our work for the treatment of entanglement entropy in causal sets in more general settings.