  A simple ansatz is suggested for the structure of threshold resummation of
the momentum space physical evolution kernels (`physical anomalous dimensions')
at all orders in (1-x), taking as examples Deep Inelastic Scattering (F_2(x,
Q^2) and F_L(x, Q^2)) and the Drell-Yan process. Each term in the expansion is
associated to a distinct renormalization group and scheme invariant
perturbative object (`physical Sudakov anomalous dimension') depending on a
single momentum scale variable. Both logarithmically enhanced terms and
constant terms are captured by the ansatz at any order in the expansion. The
ansatz is motivated by a large--beta_0 dispersive calculation. A dispersive
representation at finite beta_0 of the physical Sudakov anomalous dimensions is
also obtained, associated to a set of `Sudakov effective charges' which
encapsulate the non-Abelian nature of the interaction. It is found that the
dispersive representation requires a non-trivial, and process-dependent, choice
of variables in the (x,Q^2) plane. Some interesting properties of the physical
Sudakov anomalous dimensions are pointed out. The ensuing 1/N expansion in
moment space is straightforwardly derived from the momentum space expansion.
