4.5 Finding Fixed Points » Quiz Solution
What's the renormalization group flow for the Ising model in our coarse-grained approximation?
A. a 1-dimensional model space flows to a single point
B. a 1-dimensional model space flows to one of two distinct points
C. a 1-dimensional model space flows to one of three distinct points
D. none of the above
Answer: (C). When beta is below a critical value, repeated renormalizations drive you to zero -- a decoupled state. When it's above a critical value, beta gets extremely large. When it's precisely at the critical value, it stays fixed at a finite (non-zero) value.