Limits on axion quark nuggets and Kaluza-Klein gravitons from diffuse background radiation*

We revisit experimental limits on dark-matter theories involving axion quark nuggets (AQNs) and Kaluza-Klein gravitons (KKGs). The latter predict sharp signals in the diffuse gamma-ray background (DGB) and are strongly constrained by data from the FermiLAT telescope. The former predict a flatter signal due to bremsstrahlung radiation that extends into the far ultraviolet (FUV) band and may be consistent with observations by the GALEX telescope that suggest an excess over that associated with known sources (primarily dust-scattered starlight).