The polynomial growth solutions to some sub-elliptic equations on the Heisenberg group

We give an explicit description of polynomial growth solutions to some sub-elliptic operators of divergence form with H-periodic coefficients on the Heisenberg group, where the periodicity has to be meant with respect to the Heisenberg geometry. We show that the polynomial growth solutions are necessarily polynomials with H-periodic coefficients. We also prove the Liouville-type theorem for the Dirichlet problem to these sub-elliptic equations on an unbounded domain on the Heisenberg group, show that any bounded solution to the Dirichlet problem must be constant.