We study a scenario that a hidden gauge boson constitutes the dominant
component of dark matter and decays into the standard model particles through a
gauge kinetic mixing. Interestingly, gamma rays and positrons produced from the
decay of hidden gauge boson can explain both the EGRET excess of diffuse gamma
rays and the HEAT anomaly in the positron fraction. The spectra of the gamma
rays and the positrons have distinctive features; the absence of line emission
of the gamma ray and a sharp peak in the positron fraction. Such features may
be observed by the GLAST and PAMELA satellites.Comment: 16 pages, 4 figures, adding PAMELA data, the version accepted by PL