  We study some aspects of open string theories on D-branes with critical
electric fields. We show that the massless open string modes that move in the
direction of the electric field decouple. In the 1+1 dimensional case the dual
theory is U(N) SYM with electric flux, and the decoupling of massless open
strings is dual to the decoupling of the U(1) degrees of freedom. We also show
that, if the direction along the electric field is compact, then there are
finite energy winding closed string modes. They are dual to Higgs branch
excitations of the SYM theory, and their energetics works accordingly. These
properties provide new non-trivial evidence for the duality.
