Sensitivity of JWST to eV-Scale Decaying Axion Dark Matter

The recently-launched James Webb Space Telescope (JWST) can resolve eV-scale emission lines arising from dark matter (DM) decay. We forecast the end-of-mission sensitivity to the decay of axions, a leading DM candidate, in the Milky Way using the blank-sky observations expected during standard operations. Searching for unassociated emission lines will constrain axions in the mass range $0.18$ eV to $2.6$ eV with axion-photon couplings $g_{a\gamma \gamma }\gtrsim 5.5\times {10}^{-12}$ GeV${}^{-1}$. In particular, these results will constrain astrophobic QCD axions to masses $\lesssim$ 0.2 eV.