Singular Potentials and Limit Cycles
  We show that a central $1/r^n$ singular potential (with $n\geq 2$) is renormalized by a one-parameter square-well counterterm; low-energy observables are made independent of the square-well width by adjusting the square-well strength. We find a closed form expression for the renormalization-group evolution of the square-well counterterm. 
S.R. Beane, P.F. Bedaque, L. Childress, A. Kryjevski, J. McGuire, and   U. van Kolck