# Examples of CM curves of genus two defined over the reflex field

Florian Bouyer, Marco Streng

Research output: Contribution to journalArticle (Academic Journal)

5 Citations (Scopus)

### Abstract

In "Proving that a genus 2 curve has complex multiplication", van Wamelen lists 19 curves of genus two over $\mathbf{Q}$ with complex multiplication (CM). For each of the 19 curves, the CM-field turns out to be cyclic Galois over $\mathbf{Q}$. The generic case of non-Galois quartic CM-fields did not feature in this list, as the field of definition in that case always contains a real quadratic field, known as the real quadratic subfield of the reflex field. We extend van Wamelen's list to include curves of genus two defined over this real quadratic field. Our list therefore contains the smallest "generic" examples of CM curves of genus two. We explain our methods for obtaining this list, including a new height-reduction algorithm for arbitrary hyperelliptic curves over totally real number fields. Unlike Van Wamelen, we also give a proof of our list, which is made possible by our implementation of denominator bounds of Lauter and Viray for Igusa class polynomials.
Original language Undefined/Unknown LMS Journal of Computation and Mathematics https://doi.org/10.1112/S1461157015000121 Published - 1 Aug 2015

### Bibliographical note

31 pages; Updated some references

• math.NT
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