Brief history of the pion-nucleon sigma term

TL;DR

This paper reviews the history, significance, and methods of determining the pion-nucleon sigma term, highlighting its evolving estimated value and its importance in understanding mass origin, dark matter, and nucleosynthesis.

Contribution

It provides a comprehensive overview of the sigma term's origin, its connection to fundamental physics questions, and discusses the ongoing controversy over its precise value.

Findings

The sigma term's estimated value has increased from ~40 MeV to ~60 MeV.

Multiple methods are used to extract the sigma term, with varying results.

The controversy over its exact value persists today.

Abstract

The pion-nucleon sigma term is a quantity involved in many important aspects of particle and nuclear physics. In this review I show its origin and how it is connected to important questions as the origin of mass of the ordinary matter, studies of dark matter detection and nucleosynthesis. I mention the most common methods used to obtain the sigma term, and comment on the extracted values. As it is shown, the accepted value of the sigma term has been moving from relatively low ($\sim 40$ MeV) to larger ones ($\sim 60$ MeV) until today, where this controversy still persist.