Rigidity Of Square-Tiled Interval Exchange Transformations

We look at interval exchange transformations defined as first return maps on the set of diagonals of a flow of direction theta on a square-tiled surface: using a combinatorial approach, we show that, when the surface has at least one true singularity both the flow and the interval exchange are rigid if and only if tan theta has bounded partial quotients. Moreover, if all vertices of the squares are singularities of the flat metric, and tan theta has bounded partial quotients, the square-tiled interval exchange transformation T is not of rank one. Finally, for another class of surfaces, those defined by the unfolding of billiards in Veech triangles, we build an uncountable set of rigid directional flows and an uncountable set of rigid interval exchange transformations.