Axions, strong and weak CP, and KNP inflation

TL;DR

This paper reviews the theoretical development of axions, their role in solving the strong CP problem, weak CP violation, and their connection to Kim-Nilles-Peloso inflation, emphasizing the importance of discrete gauge symmetries and string theory considerations.

Contribution

It provides a comprehensive overview of axion physics, CP violation, and inflation models, highlighting the role of discrete gauge symmetries and string compactification in protecting global symmetries from gravity effects.

Findings

String compactification preserves global symmetries from gravity.

Axions are central to solving the strong CP problem and inflation.

Discrete gauge symmetries underpin the theoretical consistency of these models.

Abstract

I review the ideas leading to the QCD axion and also comment on the Jarlskog determinant describing the observed weak CP violation, and the axion-related Kim-Nilles-Peloso inflation. All of these use pseudoscalars, and the underlying principle is the discrete gauge symmetry either in the bottom-up or top-down approaches. Here, the effects of gravity are required to be unimportant in the low energy effective theory. String compactification is safe from the gravity spoil of global symmetries and some examples from string compactification are commented.