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

Let (P,Ξ)(P,\Xi) be a principally polarized abelian variety of dimension p4p\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 Γ00H0(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.

Sources & referencesView supporting material

Primary source

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

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