BK in the chiral limit within the 1/ Nc expansion

Abstract

I report on a recent calculation done in collaboration with E. de Rafael [7] of the invariant B̂ K factor of K 0-K̄ 0 mixing in the chiral limit and to next-to- leading order in the 1/ N c expansion. This calculation is, to the best of our knowledge, the first example of a calculation of B̂ K in which there is an explicit analytic cancellation of the μ renormalization scale and the scheme dependence between the Wilson coefficient and the corresponding kaon matrix element. I try to emphasize the ideas involved in the approach and how the method could be applied to other physical situations, rather than the details of the numerical analysis for which I refer the reader to ref. [7].