  In the recent articles \cite{PSU1,PSU3}, a number of tensor tomography
results were proved on two-dimensional manifolds. The purpose of this paper is
to extend some of these methods to manifolds of any dimension. A central
concept is the surjectivity of the adjoint of the geodesic ray transform, or
equivalently the existence of certain distributions that are invariant under
geodesic flow. We prove that on any Anosov manifold, one can find invariant
distributions with controlled first Fourier coefficients. The proof is based on
subelliptic type estimates and a Pestov identity. We present an alternative
construction valid on manifolds with nonpositive curvature, based on the fact
that a natural Beurling transform on such manifolds turns out to be essentially
a contraction. Finally, we obtain uniqueness results in tensor tomography both
on simple and Anosov manifolds that improve earlier results by assuming a
condition on the terminator value for a modified Jacobi equation.
