  The Schwinger representation gives a systematic procedure for recasting large
N field theory amplitudes as integrals over closed string moduli space. This
procedure has recently been applied to a class of free field four point
functions by Aharony, Komargodski and Razamat, to study the leading terms in
the putative worldsheet OPE. Here we observe that the dictionary between
Schwinger parameters and the cross ratio of the four punctured sphere actually
yields an explicit expression for the full worldsheet four point correlator in
many such cases. This expression has a suggestive form and obeys various
properties, such as crossing symmetry and mutual locality, expected of a
correlator in a two dimensional CFT. Therefore one may take this to be a
candidate four point function in a worldsheet description of closed strings on
highly curved AdS_5 \times S^5. The general framework, that we develop for
computing the relevant Strebel differentials, also admits a systematic
perturbation expansion which would be useful for studying more general four
point correlators.
