Analysis of solar neutrino problem by means of N\"{o}tzold and   Nakagawa's approach including the interference term- Hyperbolic-tangent   profile for electron density in the sun and exact solution -
  Using an exact solution with the hyperbolic-tangent profile for the electron density in the sun, which is developed by N\"{o}tzold and later modified by Nakagawa, we have analyzed the solar neutrino problem. An interference term in their approach is correctly taken into account. Combining the hyperbolic-tangent profile with the BP2000, we obtain a phenomenological fitting in the analytic form. Combining recent observed results for survival probability $P(\nu_e \to \nu_e)$ by the SNO, SK, SAGE, Gallex, GNO and Homestake Collaborations, we obtain a large mixing angle (LMA) whose figure is looking like a shoulder. 
Masahiro Kaneyama, Minoru Biyajima