We consider the Sudakov form factor in effective theories and we show that
one can derive correctly the double logarithms of the original, high-energy,
theory. We show that in effective theories it is possible to separate
explicitely soft and hard dynamics being these two regimes related to velocity
conserving and to velocity changing operators respectively. A new effective
theory is sketched which extracts the leading collinear singularities of the
full theory amplitudes. Finally, we show how all leading logarithmic effects in
field theory can be obtained by means of simple effective theories, where they
correspond to a renormalization effect.Comment: Latex file, 20 pages, no figures, corrected some typo
