In February 2014, different analyses have extracted from the spectrum of X-ray emissions observed by XMM-Newton, a monochromatic signal around 3.5 keV. This signal is coming from different galaxy clusters (like Perseus and Centaurus) and several scenarios of warm dark matter can justify such a line. We can cite, for example, a 3.5 keV candidate annihilating into 2 photons, or a 7 keV dark matter particle decaying into a photon and a neutrino.