Refraction of light by light in vacuum Xavier Sarazin, François Couchot, Arache Djannati-Ataï, Olivier Guilbaud, Sophie Kazamias, Moana Pittman and Marcel Urban Eur. Phys. J. D, 70 1 (2016) 13 Published online: 19 January 2016 DOI: 10.1140/epjd/e2015-60428-5