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

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

ajA:M‾g,n→Picg,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(D∣C)\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))∈CHg−ρ(M‾g,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∗(M‾g,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.

References

Primary source

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

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