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Recent cosmic-ray measurements have found an anomaly in the cosmic-ray energyspectrum at GeV-TeV energies. Although the origin of the anomaly is not clearlyunderstood, suggested explanations include effect of cosmic-ray sourcespectrum, propagation effects, and the effect of nearby sources. In this paper,we propose that the spectral anomaly might be an effect of re-acceleration ofcosmic rays by weak shocks in the Galaxy. After acceleration by strongsupernova remnant shock waves, cosmic rays undergo diffusive propagationthrough the Galaxy. During the propagation, cosmic rays may again encounterexpanding supernova remnant shock waves, and get re-accelerated. As theprobability of encountering old supernova remnants is expected to be largerthan the younger ones due to their bigger sizes, re-acceleration is expected tobe mainly due to weaker shocks. Since weaker shocks generate a softer particlespectrum, the resulting re-accelerated component will have a spectrum steeperthan the initial cosmic-ray source spectrum produced by strong shocks. For areasonable set of model parameters, it is shown that such re-acceleratedcomponent can dominate the GeV energy region while the non-reacceleratedcomponent dominates at higher energies, explaining the observed GeV-TeVspectral anomaly.

GeV-TeV cosmic-ray spectral anomaly as due to re-acceleration by weak shocks in the Galaxy