Chiral Perturbation Theory with tensor sources

Understand

We construct the most general chirally-invariant Lagrangian for mesons in the presence of external sources coupled to the tensor current \bar{\psi}\sigma_{\mu\nu}\psi.

• In order to have only even terms in the chiral expansion, we consider the new source of O(p^2).
• With this choice, we build the even-parity effective Lagrangian up to the p^6-order (NLO).
• While there are only 4 new terms at the p^4-order, at p^6-order we find 78 terms for n_f=2 and 113 terms for n_f=3.