Proton decay and lattice QCD

Proton decay rates in grand unified theories are calculated by using numerical results obtained by Monte Carlo simulation in lattice QCD. The decay rates are calculated in such a way that they are independent on the renormalization point. By comparing the theoretical and experimental results on p→${\pi }^0$ $e^{+}$ decay, we conclude that the simple SU(5) model is excluded as a realistic model.