  Non-vanishing U_{e3} has been theoretically related to a certain flavor
symmetry breaking in the neutrino sector. We propose a scenario to break the
mu-tau symmetry so as to accommodate the non-vanishing U_{e3}. Our scenario is
constructed in the context of a seesaw model, and the mu-tau symmetry breaking
is achieved by introducing a CP phase in the Dirac Yukawa matrix. We also show
how the deviation of theta_{23} from the maximal mixing and non-vanishing
U_{e3} depend on the CP phase. Neutrino mixings and the neutrino mass-squared
differences are discussed, and the amplitude in neutrinoless double beta decay
m_{ee} are also predicted. We found that a tiny breaking of the mu-tau symmetry
due to mass splitting between two degenerate heavy Majorana neutrinos on top of
the Dirac CP phase can lead to successful leptogenesis. We examine how
leptogenesis can be related with low energy neutrino measurement, and show that
our predictions for U_{e3} and m_{ee} can be constrained by the current
observation of baryon asymmetry.
