where V is a scalar operator in the CFT of scaling dimension Δ Δ V ≤ ≤ d . At large distances, such theories are strongly coupled. It is convenient to study such RG flows on the cylinder R × × S d − − 1 , taking the sphere to have radius R and endowing the full space with coordinates ( t , n ) . The reason is that the unperturbed (g =0) theory admits a simple description owing to radial quantization. Schematically, states | i ⟩ ⟩ on the cylinder are in one-to-one correspondence with local operators O i inserted at the origin of flat space: