Metastable vacuum decay and $\theta$ dependence in gauge theory. Deformed QCD as a toy model

TL;DR

This paper investigates the properties of metastable vacuum states and $ heta$ dependence in a simplified, weakly coupled gauge theory called deformed QCD, providing insights into complex features of real strongly coupled QCD.

Contribution

It demonstrates how metastable states emerge and persist in deformed QCD, offering a controllable model to study phenomena relevant to real QCD and heavy ion collisions.

Findings

Metastable states appear with large lifetimes in deformed QCD.

Metastable states are essential for the consistency of the QCD vacuum picture.

Possible relevance of metastable states to $ m{CP}$ violation in heavy ion collisions.

Abstract

We study a number of different ingredients related to the $\theta$ dependence, metastable excited vacuum states and other related subjects using a simplified version of QCD, the so-called "deformed QCD". This model is a weakly coupled gauge theory, which however preserves all the relevant essential elements allowing us to study hard and nontrivial features which are known to be present in real strongly coupled QCD. Our main focus in this work is to test the ideas related to the metastable vacuum states (which are known to be present in strongly coupled QCD in large $N$ limit) in a theoretically controllable manner using the "deformed QCD" as a toy model. We explicitly show how the metastable states emerge in the system, why their life time is large, and why these metastable states must be present in the system for the self-consistency of the entire picture of the QCD vacuum. We also speculate on possible relevance of the metastable vacuum states in explanation of the violation of local $\cal{P}$ and $\cal{CP}$ symmetries in heavy ion collisions.