Antiproton Flux in Cosmic Ray Propagation Models with Anisotropic Diffusion

Recently a cosmic ray propagation model has been introduced, where anisotropic diffusion is used as a mechanism to allow for $\mathcal{O}(100)$ km/s galactic winds. This model predicts a reduced antiproton background flux, suggesting an excess is being observed. We implement this model in GALPROP v50.1 and perform a ${\chi }^2$ analysis for B/C, ${}^{10}$Be/${}^9$Be, and the recent PAMELA $\bar{p}\mathrm{/}p$ datasets. By introducing a power-index parameter $\alpha$ that dictates the dependence of the diffusion coefficient $D_{xx}$ on height $\mathrm{\mid }z\mathrm{\mid }$ away from the galactic plane, we confirm that isotropic diffusion models with $\alpha =0$ cannot accommodate high velocity convective winds suggested by ROSAT, while models with $\alpha =1$ ($D_{xx}\propto \mathrm{\mid }z\mathrm{\mid }$) can give a very good fit. A fit to B/C and ${}^{10}$Be/${}^9$Be data predicts a lower $\bar{p}\mathrm{/}p$ flux ratio than the PAMELA measurement at energies between approximately 2 GeV to 20 GeV. A combined fit including in addition the $\bar{p}\mathrm{/}p$ data is marginal, suggesting only a partial contribution to the measured antiproton flux.