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We present results of a search for unidentified line emission and absorptionsignals in the 2-12keV energy band of spectra extracted from Perseus Clustercore region observations obtained with the 5eV energy resolution Hitomi SoftX-ray Spectrometer. No significant unidentified line emission or absorption isfound. Line flux upper limits (1 sigma per resolution element) vary with photonenergy and assumed intrinsic width, decreasing from 100 photons cm$^{-2}$s$^{-1}$ sr $^{-1}$ at 2keV to $<10$ cm$^{-2}$ s$^{-1}$ sr $^{-1}$ over most ofthe 5-10 keV energy range for a Gaussian line with Doppler broadening of 640km/s. Limits for narrower and broader lines have a similar energy dependenceand are systematically smaller and larger, respectively. These line flux limitsare used to constrain the decay rate of hypothetical dark matter candidates.For the sterile neutrino decay rate, new constraints over the the mass range of4-24 keV with mass resolution better than any previous X-ray analysis areobtained. Additionally, the accuracy of relevant thermal spectral models andatomic data are evaluated. The Perseus cluster spectra may be described by acomposite of multi-temperature thermal and AGN power-law continua. Superposedon these, a few line emission signals possibly originating from unmodeledatomic processes (including Si XIV and Fe XXV) are marginally detected andtabulated. Comparisons with previous X-ray upper limits and future prospectsfor dark matter searches using high-energy resolution spectroscopy arediscussed.

An X-ray spectroscopic search for dark matter and unidentified line signatures in the Perseus cluster with Hitomi