Sub-GeV galactic cosmic-ray antiprotons from primordial black holes in the Randall-Sundrum braneworld

We investigate cosmic-ray antiprotons emitted from the galactic primordial black holes (PBHs) in the Randall-Sundrum type-2 braneworld. The recent results of the Balloon-borne Experiment with a Superconducting Spectrometer (BESS) antiproton observation imply the existence of exotic primary sub-GeV antiprotons, one of whose most probable origin is PBHs in our Galaxy. We show that the magnitude of antiproton flux from PBHs in the Randall-Sundrum braneworld is proportional to negative power of the anti-de Sitter radius and immediately find that a large extra dimension can relax upper limits on the abundance of the galactic PBHs. If actually there are more PBHs than the known upper limit obtained in the pure 4D case, they set a lower bound on the size of the extra dimension above at least 1020 times 4D Planck length to avoid inconsistency. On completion of the numerical studies, we show that these constraints on the AdS radius are comparable to those obtained from the diffuse photon background by some of the authors in the previous paper. Moreover, in the low accretion rate case, only antiprotons can constrain the braneworld. We show that we will detect signatures of the braneworld as a difference between the flux of the antiprotons predicted in 4D and 5D by future observations in sub-GeV region with a few percent precision.