  Recent cosmic-ray measurements have found an anomaly in the cosmic-ray energy
spectrum at GeV-TeV energies. Although the origin of the anomaly is not clearly
understood, suggested explanations include effect of cosmic-ray source
spectrum, propagation effects, and the effect of nearby sources. In this paper,
we propose that the spectral anomaly might be an effect of re-acceleration of
cosmic rays by weak shocks in the Galaxy. After acceleration by strong
supernova remnant shock waves, cosmic rays undergo diffusive propagation
through the Galaxy. During the propagation, cosmic rays may again encounter
expanding supernova remnant shock waves, and get re-accelerated. As the
probability of encountering old supernova remnants is expected to be larger
than the younger ones due to their bigger sizes, re-acceleration is expected to
be mainly due to weaker shocks. Since weaker shocks generate a softer particle
spectrum, the resulting re-accelerated component will have a spectrum steeper
than the initial cosmic-ray source spectrum produced by strong shocks. For a
reasonable set of model parameters, it is shown that such re-accelerated
component can dominate the GeV energy region while the non-reaccelerated
component dominates at higher energies, explaining the observed GeV-TeV
spectral anomaly.
