We obtain explicit formulas for the Neumann coefficients and associated
quantities that appear in the three-string vertex for type IIB string theory in
a plane-wave background, for any value of the mass parameter mu. The derivation
involves constructing the inverse of a certain infinite-dimensional matrix, in
terms of which the Neumann coefficients previously had been written only
implicitly. We derive asymptotic expansions for large mu and find unexpectedly
simple results, which are valid to all orders in 1/mu. Using BMN duality, these
give predictions for certain gauge theory quantities to all orders in the
modified 't Hooft coupling lambda'. A specific example is presented.Comment: 28 pages, 2 figures, v2: reference added, new comments and appendix,
typos fixed in eqs. (86) and (89