  When matter fields are included in chiral perturbation theory, the
nonvanishing mass in the chiral limit introduces a new energy scale so that the
loop diagrams including such matter field propagators spoil the usual power
counting. However, the power counting breaking terms can be absorbed into
counterterms in the chiral Lagrangian. In this paper, we systematically derive
these terms to leading one-loop order (next-to-next-to leading order in the
chiral expansion) at once by calculating the generating functional using the
path integral. They are then absorbed by counterterms in the next-to-leading
order Lagrangian. The method can be extended to calculating power counting
breaking terms for other matter fields.
