Getting at largeθ13with almost maximalθ23from tri-bimaximal mixing

We introduce a small correction term, $\delta M_{\nu }$, in the neutrino sector and examine whether a large ${\theta }_{13}$ and an almost maximal ${\theta }_{23}$ can simultaneously be obtained starting from the tri-bimaximal neutrino mixing. It is found that one can easily gain ${\theta }_{13}\simeq 10°$, which is favored by the recent T2K experiment, by taking account of the enhancement due to the degeneracy among three neutrino masses. We also find that $(\delta M_{\nu }{)}_{22}=(\delta M_{\nu }{)}_{33}$ is a key condition for ${\theta }_{23}\simeq 45°$. DOI: http://dx.doi.org/10.1103/PhysRevD.84.037301 © 2011 American Physical Society