# Holographic heat engines: general considerations and rotating black holes

## TL;DR

This paper investigates the efficiency of holographic heat engines using rotating black holes, deriving exact results for rectangular cycles and establishing bounds applicable across different black hole types and spacetime dimensions.

## Contribution

It provides the first exact efficiency calculations for rotating black hole heat engines and introduces a universal efficiency bound for certain black holes.

## Key findings

- Exact efficiency for rectangular cycles with rotating black holes
- Derived an upper efficiency bound below Carnot limit
- Analyzed effects of rotation, dimension, and curvature corrections

## Abstract

We perform the first study of holographic heat engines where the working material is a rotating black hole, obtaining exact results for the efficiency of a rectangular engine cycle. We also make general considerations in the context of benchmarking these engines on circular cycles. We find an exact expression that is valid for black holes with vanishing specific heat at constant volume and derive an upper bound, below the Carnot efficiency and independent of spacetime dimension, which holds for any black hole of this kind. We illustrate our results with applications to a variety of black holes, noting the effects of spacetime dimension, rotation, and higher curvature corrections on the efficiency of the cycle.