# The strict transform in logarithmic geometry

*Sam Molcho (ETH)*

**Fri Apr 9, 19:00-20:00 (10 days ago)**

**Abstract: **Let $(X,D)$ be a pair of a smooth variety and a normal crossings divisor. The loci of curves that admit a map to X with prescribed tangency along D exhibit some pathological behavior: for instance, the locus of maps to a product $(X \times Y, D \times E)$ does not coincide with the intersection of the loci of maps to $(X,D)$ and $(Y,E)$. In this talk I want to explain how the root of such pathologies arises from the difference between taking the strict and total of a cycle under a very special kind of birational map, called a logarithmic modification. I will discuss how for a logarithmic modification, the strict transform of a cycle has a modular interpretation, and how its difference with the total transform can be explicitly computed, in terms of certain piecewise polynomial functions on a combinatorial shadow of the original spaces, the tropicalization. Time permitting, I will discuss some applications -- for instance, how these calculations imply that loci of curves with a map to a toric variety lie in the tautological ring.

algebraic geometry

Audience: researchers in the topic

( slides )

**Stanford algebraic geometry seminar **

**Series comments: **This seminar requires both advance registration, and a password.
Register at stanford.zoom.us/meeting/register/tJEvcOuprz8vHtbL2_TTgZzr-_UhGvnr1EGv
Password: 362880

If you have registered once, you are always registered, and can just join the talk. Link for talk once registered: in your email, or else probably: stanford.zoom.us/j/95272114542

More seminar information (including slides and videos, when available): agstanford.com

Organizer: | Ravi Vakil* |

*contact for this listing |