Entropic force of polymers on a cone tip

We consider polymers attached to the tip of a cone, and the resulting force
due to entropy loss on approaching a plate (or another cone). At separations
shorter than the polymer radius of gyration R_g, the only relevant length scale
is the tip-plate (or tip-tip) separation h, and the entropic force is given by
F=A kT/h. The universal amplitude A can be related to (geometry dependent)
correlation exponents of long polymers. We compute A for phantom polymers, and
for self-avoiding (including star) polymers by epsilon-expansion, as well as by
numerical simulations in 3 dimensions.