  Compactifying the A_1 version of (2,0) theory on a circle gives rise to
five-dimensional, maximally supersymmetric Yang-Mills theory. In the Coulomb
branch, where the SU(2) gauge group is spontaneously broken to a U(1) subgroup,
the degrees of freedom are constituted by one massless and two massive vector
multiplets. Because of the relation to the six-dimensional (2,0) theory, we are
then interested in scattering processes where both the in-state and the
out-state consist of one massless and one massive particle. We show that the
corresponding part of the S matrix is determined by the symmetries of the
theory up to a single unknown function, which depends on the energy and mass of
the incoming particles, together with the scattering angle. Performing a
straight forward scattering calculation by means of Feynman diagrams, this
function is determined to leading order in a low-energy approximation. The
result is strikingly simple, and it coincides exactly with the corresponding
function in the (2,0) theory.
