-Online participants: our Jitsi meeting room is https://meet.jit.si/WorkingWithWallcrossing and the password is the Euler Characteristic of the complex projective line spelled backwards.

-Utrecht participants: we will stream the session from the seminar room on the 7th floor HFG 7.07

-SIMIS (Shanghai) partipants: please reach out to Arkadij for details.

We meet on Thursdays from 1pm to 2:30pm Utrecht time (for participants in Shanghai: note the time change on March 29th)

Schedule description and references (old schedule, find the correct updated schedule below)

-----------------------------------------------------

Titles and speakers:

• Thursday March 19, 1pm - 2:30pm, Wallcrossing for moduli of sheaves on surfaces, Tomás
• Thursday March 26, 1pm - 2:30pm, Theta Functions, Tomás
• Thursday April 2, 1pm - 2:30pm, Talk Cancelled

• Thursday April 9, 11am - 12:30pm, Examples Session, Tomás

  ^different time due to Log Geometry Day

• Thursday April 23, 1pm - 2:30pm, Gross’ Vertex Algebra Construction and Lattice Vertex Algebras, Tomás
• Thursday May 7, 1pm - 2:30pm, Boijko's construction, Pim
• Monday May 11th (online), 1pm - 2:30pm, Joyce's Wallcrossing Result, Yun
• Thursday May 14, 1pm - 2:30pm Virtual Classes of Hilbert Schemes of Points, Tomás
• No talk on Thursday May 21 due to Ieke Moerdijk Simposium
• Monday May 25th (online), 1pm - 2:30pm (online), Examples Session, Yun
• Thursday May 28, 1pm - 2:30pm Examples Session, Pim & Tomás
• No talk on Thursday June 4 due to Marseille Conference
• Thursday June 11, 1pm - 2:30pm The Vertex Algebra in equivariant geometry, Arkadij
• Thursday June 18, 1pm - 2:30pm Examples Session, Arkadij

----------------------------------------------------------------------

Arkadij's talk before March:

26/2 - Arkadij Bojko, Equivariant homology theories, T-deformed vertex algebras, and equivariant wall-crossing (abstract below)

Abstracts:

Equivariant homology theories, T-deformed vertex algebras, and equivariant wall-crossing.

Over the last few sessions, we have explored Joyce’s wall-crossing framework and his construction of vertex algebras from multiple different perspectives. However, we have not yet discussed how it can be applied to study equivariant enumerative invariants. To do this, we first need to understand a prototypical, simple example. Building upon it, I will isolate the appropriate definition of equivariant generalized homology theories for stacks. This construction produces adic-complete modules. In homology, this provides precisely the framework for T-deformed vertex algebras, which I previously termed additive deformations. These refine Haisheng Li's axioms by controlling the poles and can often be computed explicitly. Using the whole package, we finish by studying Hilbert schemes of points on affine spaces.