Mikheyev-Smirnov-Wolfenstein Effect for Linear Electron Density
  When the electron density is a linear function of distance, it is known that the MSW equations for two neutrino species can be solved in terms of known functions. It is shown here that more generally, for any number of neutrino species, these MSW equations can be solved exactly in terms of single integrals. While these integrals cannot be expressed in terms of known functions, some of their simple properties are obtained. Application to the solar neutrino problem is briefly discussed. 
Harry Lehmann (Hamburg), Per Osland (Bergen) and Tai Tsun Wu (Harvard   and CERN)