On the double natured solutions to the two-temperature external soft   photon comptonized accretion disks
  We have analyzed pair production in the innermost region of a two-temperature external soft photon comptonized accretion disk. We have shown that, if the viscosity parameter is greater than a temperature and r dependent critical value, the solution to the disk equation is double valued: one, advection dominated and the other, radiation dominated. When the viscosity parameter is below this critical value, the accretion rate has to be confined within a region limited by a minimum and a maximum accretion rates in order to have two steady state solutions. These critical accretion rates are shown to be dependent on r, on the temperature and on the viscosity parameter . Depending on the combination of the parameters, the advection dominated solution may not be physically consistent. 
Cesar Meirelles Filho