Search for solar Kaluza-Klein axions in theories of low-scale quantum gravity

We explore the physics potential of a terrestrial detector for observing axionic Kaluza-Klein excitations coming from the Sun within the concert of higher-dimensional theories of low-scale quantum gravity. In these theories, the heavier Kaluza-Klein axions are relatively short-lived and may be detected by a coincidental triggering of their two-photon decay mode. Because of the expected high multiplicity of the solar axionic excitations, we find experimental sensitivity to a fundamental Peccei-Quinn axion mass up to 10(-2) eV (corresponding to an effective axion-photon coupling g(a gamma gamma)approximate to2.0 x 10(-1)2 GeV-1) in theories with 2 extra dimensions and a fundamental quantum-gravity scale M-F of order 100 TeV, and up to 3.0 x 10(-3) eV (corresponding to g(a gamma gamma)approximate to 6.0 x 10(-13) GeV-1) in theories with 3 extra dimensions and M-F = 1 TeV. For comparison, based on recent data obtained from lowest level underground experiments, we derive the experimental limits g(a gamma gamma) less than or similar to2.5 x 10(-11) GeV-1 and g(a gamma gamma)less than or similar to1.2 x 10(-11) GeV-1 in the aforementioned theories with 2 and 3 large compact dimensions, respectively.