Renormalization Hopf algebras and combinatorial groups

TL;DR

This paper introduces the algebraic structures underlying renormalization in quantum field theory, focusing on Hopf algebras and combinatorial groups, and illustrates their application through scalar field theory examples.

Contribution

It provides a comprehensive introduction to the Connes-Kreimer Hopf algebra framework for renormalization, connecting algebraic groups with quantum field theoretical concepts.

Findings

Hopf algebra structures encode renormalization processes

The Connes-Kreimer algebra simplifies the combinatorics of Feynman diagrams

Application to scalar $$ theory demonstrates the framework's effectiveness

Abstract

These are the notes of five lectures given at the Summer School {\em Geometric and Topological Methods for Quantum Field Theory}, held in Villa de Leyva (Colombia), July 2--20, 2007. The lectures are meant for graduate or almost graduate students in physics or mathematics. They include references, many examples and some exercices. The content is the following. The first lecture is a short introduction to algebraic and proalgebraic groups, based on some examples of groups of matrices and groups of formal series, and their Hopf algebras of coordinate functions. The second lecture presents a very condensed review of classical and quantum field theory, from the Lagrangian formalism to the Euler-Lagrange equation and the Dyson-Schwinger equation for Green's functions. It poses the main problem of solving some non-linear differential equations for interacting fields. In the third lecture we explain the perturbative solution of the previous equations, expanded on Feynman graphs, in the simplest case of the scalar $\phi^3$ theory. The forth lecture introduces the problem of divergent integrals appearing in quantum field theory, the renormalization procedure for the graphs, and how the renormalization affects the Lagrangian and the Green's functions given as perturbative series. The last lecture presents the Connes-Kreimer Hopf algebra of renormalization for the scalar theory and its associated proalgebraic group of formal series.