Generating functional for mesonic ChPT with virtual photons in a general covariant gaugeAndria Agadjanov, Dimitri Agadjanov, Anzor Khelashvili and Akaki RusetskyEur. Phys. J. A, 49 9 (2013) 120DOI: https://doi.org/10.1140/epja/i2013-13120-x