Periodic continued fractions in elliptic function fields

Abstract

We construct all families of quartic polynomials over Q whose square root has a periodic continued fraction expansion, and detailthose expansions. In particular we prove that, contrary to expectation, the cases of period length nine and eleven do not occur. We conclude by providing a list of examples of pseudo-elliptic integrals involving square roots of polynomials of degree four. The primary issue is of course the existence of units in elliptic function fields over Q. That, and related issues are surveyed in the paper’s introduction.