The workshop organizers gratefully acknowledge the funding received from the European Union's Seventh Framework Programme (FP7/PEOPLE-2011-CIG) through the Marie Curie Career Integration Grant (GALFORMBHS PCIG11-GA-2012-321608), from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 690904, and from the ILP LABEX (under reference ANR-10-LABX-63), supported by French state funds managed by the ANR within the Investissements d’Avenir programme under reference ANR-11-IDEX-0004-02 and the the European
Research Council under the European Union's Seventh Framework Programme
(FP7/2007-2013) / ERC grant agreement n.~306425 ``Challenging General
Relativity''.