Evolution of the neutrino state inside the Sun - art. no. 013008

We reexamine the conventional physical description of the neutrino evolutio n inside the Sun. We point out that the traditional notion of resonance is a useful physical concept only in the limit of small values of the neutrino mixing angle, theta<<1. For large values of theta, the resonance condition specifies neither the point of the maximal violation of adiabaticity in th e nonadiabatic case, nor the point where the flavor conversion occurs at th e maximal rate in the adiabatic case. The corresponding correct conditions, valid for all values of theta including theta>pi /4, are presented. The ad iabaticity condition valid for all values of theta is also described. The r esults of accurate numerical computations of the level jumping probability in the Sun are presented. These calculations cover a wide range of Deltam(2 ), from the vacuum oscillation region to the region where the standard expo nential approximation is good. A convenient empirical parametrization of th ese results in terms of elementary functions is given. The matter effects i n the so-called ''quasivacuum oscillation regime" are discussed. Finally, i t is shown how the known analytical results for the exponential, 1/x, and l inear matter distributions can be simply obtained from the formula for the hyperbolic tangent profile. A new expression for the jumping probability fo r the distribution N(e)proportional to [coth(x/l)+/-1] is obtained.