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We show that the present dark matter abundance can be accounted for by anoscillating scalar field that acquires both mass and a non-zero expectationvalue from interactions with the Higgs field. The dark matter scalar field canbe sufficiently heavy during inflation, due to a non-minimal coupling togravity, so as to avoid the generation of large isocurvature modes in the CMBanisotropies spectrum. The field begins oscillating after reheating, behavingas radiation until the electroweak phase transition and afterwards asnon-relativistic matter. The scalar field becomes unstable, althoughsufficiently long-lived to account for dark matter, due to mass mixing with theHiggs boson, decaying mainly into photon pairs for masses below the MeV scale.In particular, for a mass of $\sim 7$ keV, which is effectively the only freeparameter, the model predicts a dark matter lifetime compatible with the recentgalactic and extragalactic observations of a 3.5 keV X-ray line.

Scalar field dark matter with spontaneous symmetry breaking and the $3.5$ keV line