Sub-Riemannian geodesics on the Heisenberg 3D nil-manifold

We study the projection of the left-invariant sub-Riemannian structure on the 3D Heisenberg group G to the Heisenberg 3D nil-manifold~M -- the compact homogeneous space of G by the discrete Heisenberg group. First we describe dynamical properties of the geodesic flow for M: periodic and dense orbits, and a dynamical characterization of the normal Hamiltonian flow of Pontryagin maximum principle. Then we obtain sharp twoside bounds of sub-Riemannian balls and distance in~G, and on this basis we estimate the cut time for sub-Riemannian geodesics in M.