Stable bimaximal neutrino mixing pattern

The data from the various neutrino experiments indicate a bimaximal mixing among three neutrino generations. The atmospheric neutrino puzzle requires a near maximal mixing between a pair of neutrinos [1]. The solar neutrino puzzle has various possible solutions but the large angle MSW solution is favoured [2]. As the mass squared difference required for these two solutions differ by about few orders of magnitude, we must have two different pairs with large mixing. The CHOOZ experiment constrain one of the mixing angles to be small [3]. So out of three mixing angles two are large and one is small indicating a bimaximal structure. The large mixing in neutrino is in sharp contrast to the very small mixing in the quark sector. Flavor symmetries may generate bimaximal mixing structure in neutrino masses [4]. But such structure generated at the high scale may not be stable under renormalisation group evolution to low scale if neutrino masses are quasi degenerate [5,6]. Alternatively renormalisation Group evolution from high scale to the present scale have been proposed as a mechanism to generate large mixing from a small mixing [7]. But in these mechanism enhancement of the mixing angle is scale dependent and hence may be unstable and fine tuned. [8]. We do a three generation analysis and find that large mixing can be a stable fixed point of renormalisation group evolution in certain region of experimentally allowed parameter space. We consider a quasi degenerate mass structure with one of the state in an opposite CP phase to the other two.