Evaluating The Two Loop Diagram Responsible For Neutrino Mass In Babu's Model

Babu studied the neutrino spectrum obtained when one adds a charged singlet and a doubly charged singlet to the standard model particle spectrum. It was found that the neutrinos acquire a mass matrix at the two-loop level which contains one massless eigenstate. The mass matrix of Babu's model depends on an integral over the undetermined loop momenta. We present the exact calculation of this integral.