Szemerédi's Theorem and Nilsequences

Suppose A is a subset of the natural numbers with positive density. A classical result in additive combinatorics, Szemerédi’s theorem, states that for each positive integer k, A must have an arithmetic progression of nonzero common difference of length k.In this talk, we shall discuss various quantitative refinements of this theorem and explain the various ingredients that recently led to the best quantitative bounds for this theorem. This is joint work with Ashwin Sah and Mehtaab Sawhney.