Full pseudoscalar mesonic chiral Lagrangian at p6 order under the unitary group

Understand

We construct the full p6 order chiral Lagrangians for the unitary group and special unitary groups, including nf-, three- and two-flavor cases, all bilinear currents (scalar, pseudoscalar, vector, axial-vector and tensor currents) and theta parameter.

• The number of independent operators are 1391, 1326 and 969 for each of the flavor unitary groups.
• From these results, we find one extra linear relation among the traditional p4 order low-energy constants under the U(3) group, and some more linear relations with tensor sources for the p6 order low-energy constants in the special unitary groups.
• We develop a scheme to obtain the relations for the dependent operators in terms of independent operators.