Constraining DM properties with SPI

We search for a spectral line produced by a dark matter (DM) particle with the mass in the range 40 keV < M_DM < 14 MeV, decaying in the DM halo of the Milky Way, using a high-resolution spectrometer SPI on board of INTEGRAL satellite. To distinguish the DM decay line from numerous instrumental lines, found in the SPI background spectrum, we study the dependence of the intensity of the line signal on the offset of the SPI pointing from the direction toward the Galactic Center (GC). After a critical analysis of the uncertainties of the DM density profile in the inner Galaxy we find that the intensity of the DM decay line should decrease by at least a factor of 3 when the offset from GC increases from 0 to 180 degrees. We find that such a pronounced variation of the line flux across the sky is not observed for any line, detected with the significance higher than 3 sigma in the SPI background spectrum. Possible DM decay origin is not ruled out only for the unidentified spectral lines, having low (~ 3 sigma) significance or coinciding in position with the instrumental ones. In the energy interval 20 keV -- 7 MeV we derive restrictions on the DM decay line flux, implied by the (non)detection of the DM decay line. For a particular DM candidate, the sterile neutrino of mass M_DM, we derive a bound on the mixing angle.