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

Abstract

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 ${10}^{\ensuremath{-}2}\mathrm{eV}$ (corresponding to an effective axion-photon coupling ${g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}\ensuremath{\approx}2.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}{\mathrm{GeV}}^{\ensuremath{-}1})$ in theories with 2 extra dimensions and a fundamental quantum-gravity scale ${M}_{\mathrm{F}}$ of order 100 TeV, and up to $3.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\mathrm{eV}$ (corresponding to ${g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}\ensuremath{\approx}6.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}{\mathrm{GeV}}^{\ensuremath{-}1})$ in theories with 3 extra dimensions and ${M}_{\mathrm{F}}=1\mathrm{TeV}.$ For comparison, based on recent data obtained from lowest level underground experiments, we derive the experimental limits ${g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}\ensuremath{\lesssim}2.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}{\mathrm{GeV}}^{\ensuremath{-}1}$ and ${g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}\ensuremath{\lesssim}1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}{\mathrm{GeV}}^{\ensuremath{-}1}$ in the aforementioned theories with 2 and 3 large compact dimensions, respectively.