Dark Matter Axions Modulate Dark State Scintillation

The decay rate of the thallium-iodine dark state in the popular alkali-halide scintillator NaI(Tl) modulates in phase with the dipole anisotropy of the cosmic microwave background (CMB), it is argued. Axion dark matter particles --- at rest in the local CMB rest-frame --- couple to the static magnetic field created in their rest-frame by the static electric quadrupole field within the tetragonally-distorted thallium-iodine octahedron surrounding each dark state. For axions with rest-mass energy near the roughly 0.5 eV dark state activation energy in NaI(Tl), the resulting near-infrared electric field created by this axion electrodynamic interaction modulates the dark state scintillation lifetime by bringing home the excited hole --- from the four in-plane iodine 5p orbitals that share it --- to the Tl 6s shell where it can recombine with the excited Tl 6p electron to produce the scintillation light.