On the Bielliptic and bihyperelliptic loci

Paola Frediani; Paola Porru

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arXiv · 1807.02073

On the Bielliptic and bihyperelliptic loci

Paola Frediani·Paola Porru

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Abstract

We study some particular loci inside the moduli space $\mathcal{M}_g$, namely the bielliptic locus (i.e. the locus of curves admitting a $2:1$ cover over an elliptic curve $E$) and the bihyperelliptic locus (i.e. the locus of curves admitting a $2:1$ cover over a hyperelliptic curve $C'$, $g(C') \geq 2$). We show that the bielliptic locus is not a totally geodesic subvariety of $\mathcal{A}_g$ if $g \geq 4$ (while it is for $g=3$, see [16]) and that the bihyperelliptic locus is not totally geodesic in $\mathcal{A}_g$ if $g \geq 3g'$. We also give a lower bound for the rank of the second gaussian map on the generic point of the bielliptic locus and an upper bound for this rank for every bielliptic curve.

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Paola Frediani, Paola Porru. 2018-07-05. On the Bielliptic and bihyperelliptic loci. https://arxiv.org/abs/1807.02073

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