Dan Petersen: An exotic tautological relation on the moduli space of stable curves of genus two with 14 markings

Title: An exotic tautological relation on the moduli space of stable curves of genus two with 14 markings

Abstract: We construct a relation Q between tautological classes in the cohomology ring of \overline M_{2,14}. This relation has several interesting properties:
1) It is not in the span of Pixton's generalized Faber--Zagier relations.
2) It is supported on the divisor of irreducible nodal curves: it is the first example of what Pandharipande calls a "\Delta_0-ghost". In particular, it gives a genuinely new relation in genus one Gromov--Witten theory.
3) Motivic conjectures related to special values of L-functions imply that Q is nonzero in Chow.
4) It is given by a remarkably simple formula.
This is joint work with Samir Canning, Bochao Kong, Rahul Pandharipande, Aaron Pixton, and Johannes Schmitt. That such a relation should exist was first discovered by B.K. using AI.