Is the Turner Window Open? Seeking Closure with Resonant Absorption of Galactic Axions in NaI Dark Matter Detectors
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Abstract
Motivated by the DAMA/LIBRA annual modulation signal, the dark matter community has invested heavily in ultra-clean underground NaI detectors to search for light WIMPs. We point out a new target of opportunity for these detectors — axions produced by the carbon-burning stars within our galaxy. These stars synthesize large quantities of 
Na, keeping it at temperatures 
K for periods up to tens of thousands of years. Under these conditions, Na radiates 440 keV axions through repeated photo-excitation and axio-deexcitation of its first excited state. Upon reaching a NaI detector, the process is reversed: the axion is resonantly absorbed, producing a 440 keV deexcitation photon. NaI thus serves as both 
source and detector. We find that existing NaI detectors can probe axion-nucleon couplings 
—
, including QCD axions with 
eV. While there are several astrophysical constraints on axions with these couplings, our re-examination of these bounds shows that substantial gaps remain, providing strong motivation for the proposed searches.
