Deforming the D1D5 CFT away from the orbifold point

The D1D5 brane bound state is believed to have an 'orbifold point' in its moduli space which is the analogue of the free Yang Mills theory for the D3 brane bound state. The supergravity geometry generated by D1 and D5 branes is described by a different point in moduli space, and in moving towards this point we have to deform the CFT by a marginal operator: the 'twist' which links together two copies of the CFT. In this paper we find the effect of this deformation operator on the simplest physical state of the CFT-the Ramond vacuum. The twist deformation leads to a final state that is populated by pairs of excitations like those in a squeezed state. We find the coefficients characterizing the distribution of these particle pairs (for both bosons and fermions) and thus write this final state in closed form.