  It has recently been observed that IIB string theory in the pp-wave
background can be used to calculate certain quantities, such as the dimensions
of BMN operators, as exact functions of the effective coupling lambda' =
lambda/J^2. These functions interpolate smoothly between the weak and strong
effective coupling regimes of N=4 SYM theory at large R charge J. In this paper
we use the pp-wave superstring field theory of hep-th/0204146 to study more
complicated observables. The expansion of the three-string interaction vertex
suggests more complicated interpolating functions which in general give rise to
fractional powers of lambda' in physical observables at weak effective
coupling.
