We consider the limit N→+∞ of N-body type problems with weak
interaction, equal masses and −σ-homogeneous potential, 0<σ<1. We
obtain the integro-differential equation that the motions must satisfy, with
limit choreographic solutions corresponding to travelling waves of this
equation. Such equation is the Euler-Lagrange equation of a corresponding
limiting action functional. Our main result is that the circle is the absolute
minimizer of the action functional among zero mean (travelling wave) loops of
class H1