Cycle integrals of modular functions, Markov geodesics and a conjecture of Kaneko

Abstract

In this paper we study the values of modular functions at the Markov quadratics which are defined in terms of their cycle integrals along the associated closed geodesics. These numbers are shown to satisfy two properties that were conjectured by Kaneko. More precisely we show that the values of a modular function $f$, along any branch $B$ of the Markov tree, converge to the value of $f$ at the Markov number which is the predecessor of the tip of $B$. We also prove an interlacing property for these values.