  Recently the Milagro experiment observed diffuse multi-TeV gamma-ray emission
in the Cygnus region, which is significantly stronger than what predicted by
the Galactic cosmic ray model. However, the sub-GeV observation by EGRET shows
no excess to the prediction based on the same model. This TeV excess implies
possible high energy cosmic rays populated in the region with harder spectrum
than that observed on the Earth. In the work we studied this theoretical
speculation in detail. We find that, a diffuse proton source with power index
$\alpha_p\lesssim 2.3$, or a diffuse electron source with power index
$\alpha_e\lesssim2.6$ can reproduce the Milagro's observation without
conflicting with the EGRET data. Further detections on neutrinos, a diagnostic
of the hadronic model, and hard X-ray synchrontron radiation, a diagnostic of
the lepton model, help to break this degeneracy. In combination with the gamma
ray observations to several hundred GeV by Fermi, we will be able to understand
the diffuse emission mechanisms in the Cygnus region better.
