Electromagnetic waves in an axion-active relativistic plasma non-minimally coupled to gravity Alexander B. Balakin, Ruslan K. Muharlyamov and Alexei E. Zayats Eur. Phys. J. C, 73 12 (2013) 2647 Published online: 26 November 2013 DOI: 10.1140/epjc/s10052-013-2647-8