Nonvanishing conjecture for Abel–Jacobi product-cycle defects

Let g1g\geq 1 and s0s\geq 0. Let d53cg,2sctd53c^{\mathrm{ct}}_{g,2s} be the moduli space of stable 2s2s-pointed curves of compact type, let d52d(d53cg,2sct)d52d^*(d53c^{\mathrm{ct}}_{g,2s}) be its tautological ring, and let d4aag,2sd4aa_{g,2s} denote the Gorenstein kernel of its d706gd706_g-pairing. For the Abel–Jacobi map and defect class, set d6a5g,s=aj(Δg,s)Rg1+s(Mg,2sct)d6a5_{g,s}=\operatorname{aj}^*(\Delta_{g,s})\in\mathsf{R}^{g-1+s}(\mathcal{M}^{\mathrm{ct}}_{g,2s}).

Nonvanishing conjecture for Abel–Jacobi product-cycle defects. The class d6a5g,sd6a5_{g,s} lies in the Gorenstein kernel and is nonzero for all but finitely many pairs of the form (g2,s)(g\geq 2,s).

The kernel assertion is known in the relevant constructions, while the nonvanishing assertion is open for all s0s\geq 0 and is expected to explain failures of the d706gd706_g-pairing to be perfect.

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Primary source

Samir Canning, Lycka Drakengren, Jeremy Feusi, Daniel Holmes, Aitor Iribar López, Denis Nesterov, Dragos Oprea, Rahul Pandharipande, Johannes Schmitt and Zheming Sun, “Torelli loci, product cycles, and the homomorphism conjecture for A_g”, arXiv:2601.04353 (2026).

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