The Large-charge Expansion in QFT

These are the recordings of a course on the large charge expansion held in Kyoto in December 2023 for the 18th Kavli Asian Winter School.

We discuss the general construction of the large charge using the examples of the O(2) and O(2N) model and we reproduce the results from the EFT using as microscopic model the vector model at large N. In this case we can also use resurgence to compute non-perturbative exponentially-suppressed terms.

Lecture 1: the O(2) model

Lecture 2: the non-linear sigma model

Lecture 3: the O(N) model at large N

Lecture 4: resurgence