Astrophysical detection of heavy-particle-induced spectral shifts in muonic iron

By significantly increasing the nuclear mass, a strongly interacting massive particle (SIMP) bound to an iron nucleus would cause a characteristic change in the spectrum of muonic iron. At temperatures high enough that such atoms are completely stripped of electrons, the effect is directly observable as a $0.2\%$ shift in the energies of high angular momentum states. This phenomenon provides a new test for the existence of SIMPs, which have been proposed as dark matter candidates, and as candidates for the lightest supersymmetric particle.