Right-handed neutrino mass and bottom-tau ratio in strong coupling unification

The recent results of neutrino experiments indicate the existence of the right-handed neutrinos with masses around intermediate scale, which affects the prediction of the bottom-tau mass ratio. In the minimal supersymmetric standard model, this effect largely depends on the right-handed neutrino mass scale and then may severely limit its lower bound. In this letter, we show that in the case of strong coupling unification the bottom-tau mass ratio is little affected by the presence of the right-handed neutrinos. This is because of the infrared fixed-point behavior of Yukawa couplings, which is a common feature of this kind of model.