Can the apparent expansion of the universe be attributed to an increasing vacuum refractive index ?X. Sarazin, F. Couchot, A. Djannati-Ataï and M. UrbanEur. Phys. J. C, 78 6 (2018) 444DOI: https://doi.org/10.1140/epjc/s10052-018-5932-8