I'm trying to understand the Kosterlitz-Thouless transition in 2d systems. There is a section in Altland and Simons' Condensed Matter Field Theory that discusses the phenomenon, but I don't really understand the role of renormalization group theory in the KT transition.

I don't have a background in group theory so the equations are confusing. I would really appreciate a more qualitative description of the main points and motivations.