Getting at large θ13 with almost maximal θ23 from tri-bimaximal mixing

We introduce a small correction term, delta M-v, 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) similar or equal to 10 degrees, 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-v)(22) = (delta M-v)(33) is a key condition for theta(23) similar or equal to 45 degrees.