  In this note, we first explain the equivalence between the interaction
Hamiltonian of Green-Schwarz light-cone gauge superstring field theory and the
twist field formalism known from matrix string theory. We analyze the role of
the large N limit in matrix string theory, in particular in relation with
conformal perturbation theory around the orbifold SCFT that reproduces
light-cone string perturbation theory. We show how the scaling with N is
directly related to measures on the moduli space of Riemann surfaces. The
scaling dimension 3 of the Mandelstam vertex as reproduced by the twist field
interaction is in this way related to the dimension 3(h-1) of the moduli space.
We analyze the structure and scaling of the higher order twist fields that
represent the contact terms. We find one relevant twist field at each order.
More generally, the structure of string field theory seems more transparent in
the twist field formalism. Finally we also investigate the modifications
necessary to describe the pp-wave backgrounds in the light-cone gauge and we
interpret a diagram from the BMN limit as a stringy diagram involving the
contact term.
