We determine all modular curves X(N) (with N ≥ 7) that are hyperelliptic or bielliptic. We also give a proof that the automorphism group of X(N) is PSL₂(ℤ/Nℤ), whence it coincides with the normalizer of Γ(N) in PSL₂(ℝ) modulo ±Γ(N).
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-aa161-3-6,
author = {Francesc Bars and Aristides Kontogeorgis and Xavier Xarles},
title = {Bielliptic and hyperelliptic modular curves X(N) and the group Aut(X(N))},
journal = {Acta Arithmetica},
volume = {161},
year = {2013},
pages = {283-299},
zbl = {1304.11052},
language = {en},
url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-aa161-3-6}
}
Francesc Bars; Aristides Kontogeorgis; Xavier Xarles. Bielliptic and hyperelliptic modular curves X(N) and the group Aut(X(N)). Acta Arithmetica, Tome 161 (2013) pp. 283-299. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-aa161-3-6/