RG flows of integrable ?-models and the twist function

A bstract In the study of integrable non-linear ? -models which are assemblies and/or deformations principal chiral models WZW models, a rational function called twist plays central rôle. For large class such we show that they one-loop renormalizable, and renormalization group flow equations can be written directly in terms remarkably simple way. The resulting equation appears to have universal character when model is characterized by function.