Beauville–Debarre infinitesimal Schottky conjecture for Prym and Jacobian theta divisors

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Let (P,Ξ)(P,\Xi) be a principally polarized abelian variety of dimension p≥4p\geq 4, and let Vinf⁡,00V_{\inf,00} be the base locus of the linear system of quartic tangent cones at the origin arising from sections of Γ00⊂H0(P,2Ξ)\Gamma_{00}\subset H^0(P,2\Xi), where sections vanish to order at least 44 at the origin. For a smooth curve CC of genus gg, let (JC,Θ)(JC,\Theta) be its Jacobian, let κC\kappa C be the canonical image of CC in ∣ωC∣∗=PT0JC|\omega_C|^*=\mathbb P T_0JC, and let Jg{\cal J}_g be the Jacobian locus in the moduli space of principally polarized abelian varieties of dimension gg. Beauville–Debarre conjecture.

  1. If (P,Ξ)=(JC,Θ)(P,\Xi)=(JC,\Theta), then Vinf⁡,00V_{\inf,00} is, set-theoretically, the canonical image κC\kappa C of CC in ∣ωC∣∗=PT0JC|\omega_C|^*=\mathbb P T_0JC.
  2. If (P,Ξ)(P,\Xi) is not in Jg{\cal J}_g, then Vinf⁡,00V_{\inf,00} is empty.

The conjecture is the infinitesimal version of the preceding proposed Schottky characterization: the base locus of quartic tangent cones should recover the canonical curve for Jacobians and disappear away from the Jacobian locus. Its resolution is not specified in the source.

References

Primary source

E. Izadi, “Second order theta divisors on Pryms”, arXiv:alg-geom/9704020 (1997).

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