$B_K$ and Explicit Chiral Symmetry Breaking

Abstract

The $B_K$ parameter is discussed in the general context of calculating beyond the factorization approximation for hadronic matrix elements. A variant of the $1/N_c$ method of Bardeen et al. is used. We present calculations within a low energy approach and a calculation within the Nambu--Jona-Lasinio model. Matching with the QCD behaviour and dependence on non-zero current quark masses is studied.

Comments: 15 pages, 4 postscript figures included, NORDITA-94/44 N,P. Mistake in the numerics discovered which changed some of the conclusions. One figure also changed