RG calculations for some lattice models

Lattice models were originally introduced as a discrete approximation to physical theories, mostly as a computational device rather than a theoretical understanding, though mathematically they have gained deep interest. A classical example is the Ising model for ferromagnets, e.g. the things sticking to our refrigerators. We’ll discuss some physical phenomena behind this model, like phase transition and criticality, and some unfortunate history. We’ll also introduce the corresponding renormalization group (RG) to provide an explanation of these phenomena, some of which is rigorous and some of which is not. Hopefully, at least one of the audience members feels inclined to try out their own RG calculations and/or simulations, as well.