Functional Renormalisation Group: A bird's-eye view

Aiman Al-Eryani 

As far as macroscopic beings like us are concerned, a microscopic view of the world is hopelessly busy. The number of degrees of freedom is of order of Avogadro's number. But as we squint our eyes, and let these details wash out little by little, the picture morphs and changes, and it becomes more appropriate (and sometimes *only* appropriate) to talk about effective constituents in a sequence - a flow - of new effective theories.

The theory of the Renormalisation Group makes this procedure precise. In this talk, I give a bird's-eye view of the physics and the mathematics, and show how these ideas are being advanced and used today; in particular, to the study of strong correlations, where separation of scales is not clear-cut and the physics at many different scales can compete.