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 sec...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.
