We explore the physics potential of a terrestrial detector for observing axionic Kaluza-Klein excitations coming from the Sun within the context 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 ${10}^{-2}\mathrm{eV}$ (corresponding to an effective axion-photon coupling $g_{a\gamma \gamma }\approx 2.0\times {10}^{-12}{\mathrm{GeV}}^{-1})$ in theories with 2 extra dimensions and a fundamental quantum-gravity scale $M_{\mathrm{F}}$ of order 100 TeV, and up to $3.0\times {10}^{-3}\mathrm{eV}$ (corresponding to $g_{a\gamma \gamma }\approx 6.0\times {10}^{-13}{\mathrm{GeV}}^{-1})$ in theories with 3 extra dimensions and $M_{\mathrm{F}}=1\mathrm{}\mathrm{TeV}.$ For comparison, based on recent data obtained from lowest level underground experiments, we derive the experimental limits $g_{a\gamma \gamma }\lesssim 2.5\times {10}^{-11}{\mathrm{GeV}}^{-1}$ and $g_{a\gamma \gamma }\lesssim 1.2\times {10}^{-11}{\mathrm{GeV}}^{-1}$ in the aforementioned theories with 2 and 3 large compact dimensions, respectively.

• Received 5 July 2000

DOI:https://doi.org/10.1103/PhysRevD.62.125011