# Square root Euler classes and counting sheaves on Calabi-Yau 4-folds

### Richard Thomas (Imperial College London)

 Fri Sep 25, 19:00-20:00 (3 days from now) Login required for livestream access

Abstract: I will explain a nice characteristic class of $SO(2n,\mathbf{C})$ bundles in both Chow cohomology and K-theory, and how to localise it to the zeros of an isotropic section. This builds on work of Edidin-Graham, Polishchuk-Vaintrob, Anderson and many others.

This can be used to construct an algebraic virtual cycle (and virtual structure sheaf) on moduli spaces of stable sheaves on Calabi-Yau 4-folds. It recovers the real derived differential geometry virtual cycle of Borisov-Joyce but has nicer properties, like a torus localisation formula. Joint work with Jeongseok Oh (KIAS).

algebraic geometry

Audience: researchers in the topic

Comments: The discussion for Richard Thomas’s talk is taking place not in zoom-chat, but at tinyurl.com/2020-09-25-rt (and will be deleted after 3-7 days).

Series comments: This seminar requires both advance registration, and a password. If you have registered once, you are always registered. Register at stanford.zoom.us/meeting/register/tJEvcOuprz8vHtbL2_TTgZzr-_UhGvnr1EGv Password: 362880

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

 Organizer: Ravi Vakil* *contact for this listing

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