A beginner's guide to functional methods in particle physics

Abstract

Functional methods like Dyson-Schwinger equations, the $n$PI effective action formalism, bound state equations and the functional renormalization group are versatile tools to study quantum field theories. They are exact, nonperturbative equations but have to be truncated for practical calculations. After a general introduction, I focus on their use in particle physics and discuss common truncations and solution techniques. The complete process from choosing a truncation to calculating observable quantities is exemplified by means of the glueball spectrum.

Comments: 27 pages, 16 figures, commissioned article for the Encyclopedia of Particle Physics; v2: typos corrected and references added, as published in Encyclopedia of Particle Physics