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FUJITA DECOMPOSITION AND HODGE LOCI

Published online by Cambridge University Press:  12 November 2018

Paola Frediani
Affiliation:
Università di PaviaItaly (paola.frediani@unipv.it; alessandro.ghigi@unipv.it; gianpietro.pirola@unipv.it)
Alessandro Ghigi
Affiliation:
Università di PaviaItaly (paola.frediani@unipv.it; alessandro.ghigi@unipv.it; gianpietro.pirola@unipv.it)
Gian Pietro Pirola
Affiliation:
Università di PaviaItaly (paola.frediani@unipv.it; alessandro.ghigi@unipv.it; gianpietro.pirola@unipv.it)

Abstract

This paper contains two results on Hodge loci in $\mathsf{M}_{g}$. The first concerns fibrations over curves with a non-trivial flat part in the Fujita decomposition. If local Torelli theorem holds for the fibers and the fibration is non-trivial, an appropriate exterior power of the cohomology of the fiber admits a Hodge substructure. In the case of curves it follows that the moduli image of the fiber is contained in a proper Hodge locus. The second result deals with divisors in $\mathsf{M}_{g}$. It is proved that the image under the period map of a divisor in $\mathsf{M}_{g}$ is not contained in a proper totally geodesic subvariety of $\mathsf{A}_{g}$. It follows that a Hodge locus in $\mathsf{M}_{g}$ has codimension at least 2.

Type
Research Article
Copyright
© Cambridge University Press 2018

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Footnotes

The authors were partially supported by MIUR PRIN 2015 ‘Moduli spaces and Lie theory’ and by GNSAGA of INdAM. The first author was also partially supported by FIRB 2012 ‘Moduli Spaces and their Applications’.

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