A family of polynomials with Galois group $PSL_5(2)$ over $\mathbb{Q}(t)$
Abstract
We compute a family of coverings with four ramification points, defined over $\mathbb{Q}$, with regular Galois group $PSL_5(2)$. On the one hand, this is (to my knowledge) the first explicit polynomial with group $PSL_5(2)$ over $\mathbb{Q}(t)$. On the other hand, it also positively answers the question whether $PSL_5(2)$ is the monodromy group of a rational function over $\mathbb{Q}$. At least this does not follow from considering class triples in $PSL_5(2)$, as there are no rigid, rational genus-zero triples. Also, for 4-tuples, our family is the only one with a Hurwitz curve of genus zero (however it does not seem immediately clear without explicit computations whether this curve can be defined as a rational curve over $\mathbb{Q}$). There are also genus zero families with five branch points, and maybe their Hurwitz spaces can be shown to have rational points; however, so far I have not seen such arguments.
- Publication:
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arXiv e-prints
- Pub Date:
- August 2013
- DOI:
- 10.48550/arXiv.1308.1566
- arXiv:
- arXiv:1308.1566
- Bibcode:
- 2013arXiv1308.1566K
- Keywords:
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- Mathematics - Number Theory;
- 11
- E-Print:
- 6 pages