Indirect Detection of eV Dark Matter via Infrared Spectroscopy

Infrared spectroscopy has been developed significantly. In particular, infrared photons can be measured with high spectral and angular resolution in state-of-art spectrographs. They are sensitive to monochromatic photons due to the decay and annihilation of particles beyond the Standard Model, such as dark matter (DM), while insensitive to background photons that form a continuous spectrum. In this paper, we study the indirect detection of the DM decaying into infrared light using infrared spectrographs. In particular, we show that serious thermal and astrophysical noises can be overcome. As concrete examples, the Warm INfrared Echelle spectrograph to Realize Extreme Dispersion and sensitivity (WINERED) installed at the Magellan Clay 6.5m telescope and Near-Infrared Spectrograph (NIRSpec) at the James Webb Space Telescope (JWST) are discussed. We show that a few hours of measurements of a faint dwarf spheroidal galaxy with WINERED (NIRSpec-like spectrograph) in the Magellan telescope (JWST) can probe an axion-like particle DM in the mass range $m_\phi=1.8 - 2.7\,$eV ($0.5-4\,$eV) with a photon coupling $g_{\phi\gamma\gamma}\gtrsim 10^{-11}{\rm GeV}^{-1}$. Complemental approaches, taking advantage of the high resolutions, such as the measurement of the Doppler shift of the signal photon lines and the possible search of the DM decay around the Milky Way galaxy center with Infrared Camera and Spectrograph (IRCS) at 8.2m Subaru telescope, are also presented.