BOSE-CONDENSATION AND THE STATIC PAIR CORRELATION-FUNCTION IN HE-4

An investigation is made of the implications that the presence of a Bo se condensate (BC) has for static pair correlation function, g((r) ove r right arrow). The scattering of incident radiation from many particl e states which contribute to the BC, is compared with that from states which do not. It is shown that in the former, the scattering density of each atom is delocalised in position space, whereas in the latter i t is localised, i.e. quite different physical scattering processes occ ur fr om the two types of state, A simple model of a dilute gas, based on variational wavefunctions of the ground state, predicts that g((r) over right arrow) in the ground state depends directly on the condens ate function f. The paper provides support for the intuitive idea that localisation of atoms in momentum space is directly associated with a delocalisation in position space and consequent loss of spatial corre lations.