Extended Torelli map to the Igusa blowup in genus 6, 7, and 8


Abstract in English

It was conjectured in cite{Namikawa_ExtendedTorelli} that the Torelli map $M_gto A_g$ associating to a curve its jacobian extends to a regular map from the Deligne-Mumford moduli space of stable curves $bar{M}_g$ to the (normalization of the) Igusa blowup $bar{A}_g^{rm cent}$. A counterexample in genus $g=9$ was found in cite{AlexeevBrunyate}. Here, we prove that the extended map is regular for all $gle8$, thus completely solving the problem in every genus.

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