Proton Decay in Intersecting D-brane Models

We analyze proton decay via dimension six operators in certain GUT-like models derived from Type IIA orientifolds with $D6$-branes. The amplitude is parametrically enhanced by a factor of $\alpha_{GUT}^{-1/3}$ relative to the coresponding result in four-dimensional GUT's. Nonetheless, even assuming a plausible enhancement from the threshold corrections, we find little overall enhancement of the proton decay rate from dimension six operators, so that the predicted lifetime from this mechanism remains close to $10^{36}$ years.Comment: 21 pages, LaTeX; v2: references added; v3: minor clarifications, version to appear in NP