# Unitarity Entropy Bound: Solitons and Instantons

## TL;DR

This paper demonstrates that solitons and instantons saturate unitarity entropy bounds, with their entropy proportional to their area, revealing a black hole-like entropy behavior without gravity.

## Contribution

It introduces a new formulation to apply the entropy bound to instantons and explains the black hole entropy analogy in non-gravitational systems.

## Key findings

- Solitons and instantons saturate entropy bounds at unitarity.
- Instanton entropy equals its area at critical 't Hooft coupling.
- The formulation resolves apparent violations of the Bekenstein bound.

## Abstract

We show that non-perturbative entities such as solitons and instantons saturate bounds on entropy when the theory saturates unitarity. Simultaneously, the entropy becomes equal to the area of the soliton/instanton. This is strikingly similar to black hole entropy despite absence of gravity. We explain why this similarity is not an accident. We present a formulation that allows to apply the entropy bound to instantons. The new formulation also eliminates apparent violations of the Bekenstein entropy bound by some otherwise-consistent unitary systems. We observe that in QCD, an isolated instanton of fixed size and position violates the entropy bound for strong 't Hooft coupling. At critical 't Hooft coupling the instanton entropy is equal to its area.