Improved lattice computation of proton decay matrix elements

We present an improved result for the lattice computation of the proton decay matrix elements in N-f = 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 N-f = 2 + 1 domain-wall fermions with m(pi) = 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 p -> pi e(+) or from 20-40% for p -> K nu. The accuracy of the low-energy constants alpha and beta in the leading-order baryon chiral perturbation theory (BChPT) of proton decay are also improved. The relevant form factors of p -> pi 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 BChPTwith alpha and beta. 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.