Pagani–Ricolfi–van Zelm's tautologicality conjecture for Brill–Noether pullbacks

Fix an integer kk, integers (a1,,an)(a_1,\ldots,a_n), and a boundary divisor DD of the universal curve Cg,n\overline{\mathcal{C}}_{g,n}. Let AA denote this data, and let

ajA:Mg,nPicg,nθ\mathsf{aj}_A:\overline{\mathcal{M}}_{g,n}\to\mathsf{Pic}_{g,n}^\theta

be the rational section sending (C,x1,,xn)(C,x_1,\ldots,x_n) to ωk(aixi)O(DC)\omega^k(\sum a_i x_i)\otimes\mathcal{O}(D|_C). For the Brill–Noether class wg,dr(θ)\mathsf{w}_{g,d}^r(\theta), set

wg,A,dr(θ):=ajA(wg,dr(θ))CHgρ(Mg,n).\mathsf{w}_{g,A,d}^r(\theta):=\mathsf{aj}_A^*(\mathsf{w}_{g,d}^r(\theta))\in\mathsf{CH}^{g-\rho}(\overline{\mathcal{M}}_{g,n}).

Pagani–Ricolfi–van Zelm's conjecture. The classes wg,A,dr(θ)\mathsf{w}_{g,A,d}^r(\theta) lie in the tautological ring R(Mg,n)R^*(\overline{\mathcal{M}}_{g,n}) for any choice of g,d,Ag,d,A and generic θ\theta. This predicts that these pullbacks of Brill–Noether classes are tautological on the moduli space of stable pointed curves.

Sources & referencesView supporting material

Primary source

Sam Molcho, “Pullbacks of Brill-Noether Classes Under Abel-Jacobi Sections”, arXiv:2212.14368 (2022).

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