# Chapter 9: Critical Phenomena

Landau theory is a mean-field theory approach to phase transitions. Although the theory does not usually provide accurate values for critical exponents, it provides a useful qualitative picture of phase transitions. The renormalization group method provides not just a calculation approach for determining the critical exponents, but also a conceptual understanding of phase transitions.

We will use the renormalization group to study the simplest statistical physics model, *percolation* as well as the Ising model.

## Programs

- Program 9.1: Percolation
- Program 9.2: Percolation RG
- Program 9.3: XY Model