Improved lattice computation of proton decay matrix elements

We present an improved result for the lattice computation of the proton decay matrix elements in N₅=2+1 QCD. In this study, by adopting the error reduction technique of all-mode-averaging, a significant improvement of the statistical accuracy is achieved for the relevant form factor of proton (and also neutron) decay on the gauge ensemble of N₅=2+1 domain-wall fermions with m_=0. 34--0. 69 GeV on a 2. 7 fm^3 lattice, as used in our previous work 1. We improve the total accuracy of matrix elements to 10--15% from 30--40% for pe^+ or from 20--40% for p. The accuracy of the low-energy constants and in the leading-order baryon chiral perturbation theory (BChPT) of proton decay are also improved. The relevant form factors of p estimated through the ``direct'' lattice calculation from the three-point function appear to be 1. 4 times smaller than those from the ``indirect'' method using BChPT with and. It turns out that the utilization of our result will provide a factor 2--3 larger proton partial lifetime than that obtained using BChPT. We also discuss the use of these parameters in a dark matter model.