Nambu-Goldstone modes of the two-dimensional Bose-Einstein condensed magnetoexcitonsS.A. Moskalenko, M.A. Liberman, D.W. Snoke, E.V. Dumanov, S.S. Rusu and F. CerbuEur. Phys. J. B, 85 10 (2012) 359DOI: https://doi.org/10.1140/epjb/e2012-30406-6