Diffuse Galactic Gamma Rays from Shock-Accelerated Cosmic Rays
  A shock-accelerated particle flux \propto p^-s, where p is the particle
momentum, follows from simple theoretical considerations of cosmic-ray
acceleration at nonrelativistic shocks followed by rigidity-dependent escape
into the Galactic halo. A flux of shock-accelerated cosmic-ray protons with s ~
2.8 provides an adequate fit to the Fermi-LAT gamma-ray emission spectra of
high-latitude and molecular cloud gas when uncertainties in nuclear production
models are considered. A break in the spectrum of cosmic-ray protons claimed by
Neronov, Semikoz, & Taylor (PRL, 108, 051105, 2012) when fitting the gamma-ray
spectra of high-latitude molecular clouds is a consequence of using a
cosmic-ray proton flux described by a power law in kinetic energy.
