OFF-DIAGONAL DENSITY PROFILES AND CONFORMAL-INVARIANCE

Off-diagonal profiles phi(od)(upsilon) of local densities (e.g. order parameter or energy density) are calculated at the bulk critical point , by conformal methods, on a strip with transverse coordinate upsilon, for different types of boundary conditions (free, fixed and mixed). S uch profiles, which are defined by the non-vanishing matrix element [0 \<(phi)over cap>(upsilon)\phi] of the appropriate operator <(phi)over cap>(upsilon) between the ground state and the corresponding lowest ex cited state of the strip Hamiltonian, enter into the expression of two -point correlation functions on a strip. They are of interest in the f inite-size scaling study of bulk and surface critical behaviour since they allow the elimination of regular contributions. The conformal pro files, which are obtained through a conformal transformation of the co rrelation functions from the half-plane to the strip, are in agreement with the results of a direct calculation, for the energy density of t he two-dimensional Ising model.