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On the periodicity of geodesic continued fractions

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Hohto Bekki
Wed, 2018-03-07 16:30 - 17:30
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

In this talk, we present some generalizations of Lagrange's periodicity theorem in the classical theory of continued fractions. The main idea is to use a geometric interpretation of the classical theory in terms of closed geodesics on the modular curve. As a result, for an extension F/F' of number fields with rank one relative unit group, we construct a geodesic multi-dimensional continued fraction algorithm to "expand'' a basis of F over the rationals, and prove its periodicity. Furthermore, we show that the periods describe the relative unit group. By extending the above argument adelically, we also obtain a p-adelic continued fraction algorithm and its periodicity for imaginary quadratic irrationals.

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