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 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 22 eV ~corresponding to an effective axion-photon coupling gagg’2.0310 212 GeV 21 ) in theories with 2 extra dimensions and a fundamental quantum-gravity scale MF of order 100 TeV, and up to 3.0310 23 eV ~corresponding to gagg’6.0310 213 GeV 21 ) in theories with 3 extra dimensions and M F51 TeV. For comparison, based on recent data obtained from lowest level underground experiments, we derive the experimental limits gagg &2.5310 211 GeV 21 and gagg&1.2310 211 GeV 21 in the aforementioned theories with 2 and 3 large compact dimensions, respectively. PACS number~s!: 14.80.Mz