  We revisit Lorentz violation in the Type IIB string theory with D3-branes and
D7-branes. We study the relativistic particle velocities in details, and show
that there exist both subluminal and superluminal particle propagations. In
particular, the additional contributions to the particle velosity \delta
v\equiv (v-c)/c from string theory is proportional to both the particle energy
and the D3-brane number density, and is inversely proportional to the string
scale. Thus, we can realize the background dependent Lorentz violation
naturally by varying the D3-brane number density in space time. To explain the
superluminal neutrino propagations in the OPERA and MINOS experiments, the
string scale should be around 10^5 GeV. With very tiny D3-brane number density
on the interstellar scale, we can also explain the time delays for the high
energy photons compared to the low energy photons in the MAGIC, HESS, and FERMI
experiments simultaneously. Interestingly, we can automatically satisfy all the
stringent constraints from the synchrotron radiation of the Crab Nebula, the
SN1987a observations on neutrinos, and the cosmic ray experiments on charged
leptons. We also address the possible phenomenological challenges to our models
from the relevant experiments done on the Earth.
