Cobimaximal neutrino mixing from A4 and its possible deviation

It has recently been shown that the phenomenologically successful pattern of cobimaximal neutrino mixing ($\theta_{13} \neq 0$ , $\theta_{23} = \pi/4$ , and $\delta_{CP} = \pm \pi/2$ ) may be achieved in the context of the non-Abelian discrete symmetry A 4 , if the neutrino mass matrix is diagonaized by an orthogonal matrix ${\cal O}$ . We study how this pattern would deviate if ${\cal O}$ is replaced by a unitary matrix.