  We explore the Ramond sector of the deformed two-dimensional $\cal N = (4,
4)$ superconformal $(T^4)^N /S_N$ orbifold theory, describing bound states of
D1-D5 brane system in type IIB superstring. We derive the large-$N$ limit of
the four-point function of two R-charged twisted Ramond fields and two marginal
deformation operators at the free orbifold point. Specific short-distance
limits of this function provide several structure constants, the OPE fusion
rules and the conformal dimensions of a few non-BPS operators. The second order
correction (in the deformation parameter) to the two-point function of the
Ramond fields, defined as double integrals over this four-point function, turns
out to be UV-divergent, requiring an appropriate renormalization of the fields.
We calculate the corrections to the conformal dimensions of the twisted Ramond
ground states at the large-$N$ limit. The same integral yields the first-order
deviation from zero of the structure constant of the three-point function of
two Ramond fields and one deformation operator. Similar results concerning the
correction to the two-point function of bare twist operators and their
renormalization are also obtained.
