Relativistic wave-breaking limit of electrostatic waves in cold electron-positron-ion plasmas Mithun Karmakar, Chandan Maity, Nikhil Chakrabarti and Sudip Sengupta Eur. Phys. J. D, 70 6 (2016) 144 Published online: 28 June 2016 DOI: 10.1140/epjd/e2016-70094-8