The light quark current mass ratios and eta - eta-prime mixing

Chiral corrections to the Weinberg quark current-mass ratios mu/md=0.55 and ms/md=20.1 are analysed in the large N limit, N being the number of colors. A consistent derivation of the η—η′ mixing excludes the possibility of a massless up quark and implies the second-order values mu/md ≃ 0.66 and ms/md ≈ 17.7