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arXiv · 1804.07109

Explicit calculation of the mod 4 Galois representation associated with the Fermat quartic

Yasuhiro Ishitsuka·Tetsushi Ito·Tatsuya Ohshita
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Abstract

We use explicit methods to study the 4-torsion points on the Jacobian variety of the Fermat quartic. With the aid of computer algebra systems, we explicitly give a basis of the group of 4-torsion points. We calculate the Galois action, and show that the image of the mod 4 Galois representation is isomorphic to the dihedral group of order 8. As applications, we calculate the Mordell-Weil group of the Jacobian variety of the Fermat quartic over each subfield of the 8-th cyclotomic field. We determine all of the points on the Fermat quartic defined over quadratic extensions of the 8-th cyclotomic field. Thus we complete Faddeev's work in 1960.

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Yasuhiro Ishitsuka, Tetsushi Ito, Tatsuya Ohshita. 2018-04-19. Explicit calculation of the mod 4 Galois representation associated with the Fermat quartic. https://arxiv.org/abs/1804.07109

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