- 9.2: Real Space Renormalization
- There are two different classes of renormalization. One class, called real space renormalization group (RSRG), eliminates local lattice-based degrees of freedom at each step in the RG process. The second class, called momentum space renormalization group (MSRG), is implemented by systematically lowering the cutoff Λ in the wavevector integrals. It turns out that the RSRG process, for reasons we shall see, is uncontrolled, and for ‘professional’ results one resorts to MSRG.
- 9.3: Block Spin Transformation
- Spin blocking refers to a process in which we replace a group of spins by a single spin whose direction is determined by ‘majority rule’. That is, if most of the spins in the group are up, then the block spin is said to be up; if most spins are down, then the block spin is down.
Thumbnail: RG flow for the Ising model with nearest and nearest neighbor interactions.