Chiral perturbation theory, large-Nc and the η′ mass

Using chiral perturbation theory and the large-Nc expansion, we obtain expressions for the η′ mass and η - η′ mixing in terms of low-energy chiral Lagrangian parameters. This is accomplished through an intermediate step of “matching” the topological susceptibility in the large-Nc and chiral Lagrangian descriptions. By inserting the values of well-measured parameters we obtain predictions involving the the second order parameters L6, L7 and L8. The prediction for L6 is quite restrictive even after allowing for 1Nc corrections.