Erratum to: Effects of electron beam velocity spread, temperature, and self-fields on dispersion relation and growth rate in a Cherenkov radiationGolshad Kheiri and Mahdi EsmaeilzadehEur. Phys. J. D, 69 2 (2015) 58DOI: https://doi.org/10.1140/epjd/e2015-60081-0