  We consider the dimensional reduction of a CFT, breaking multiplets of the
d-dimensional conformal group SO(d+1,1) up into multiplets of SO(d,1). This
leads to an expansion of d-dimensional conformal blocks in terms of blocks in
d-1 dimensions. In particular, we obtain a formula for 3d conformal blocks as
an infinite sum over 2F1 hypergeometric functions with closed-form
coefficients.
