1-dimensional formal groups and variants of the logarithm

-
Sanath Devalapurkar, IAS
Fine Hall 110

There are many interesting "q-deformations" of classical constructions/facts, like the q-binomial theorem, q-derivatives, etc., where setting q = 1 produces the known objects. In this talk, I'll describe how to deform even further: namely, I'll describe how every 1-dimensional formal group produces a deformation of the derivative and of the integers. This recovers ordinary calculus (and the usual integers) for the additive formal group, and recovers q-deformed calculus (and the q-integers (q^n - 1)/(q - 1)) for the multiplicative formal group. I'll explain how to use this to deform the logarithm, and in particular describe an interesting generalization of the identity Σ (y*log(x))^n/n! = Σ [y choose n] (x-1)^n. Time permitting, I will explain how I came about this story via homotopy theory and its relationship to prismatic cohomology.