Improved lattice computation of proton decay matrix elements

Abstract

We present an improved result of lattice computation of the proton decay matrix elements in N f = 2 + 1 QCD. In this study, the significant improvement of statistical accuracy by adopting the error reduction technique of All-mode-averaging, is achieved for relevant form factor to proton (and also neutron) decay on the gauge ensemble of N f = 2 + 1 domain-wall fermions in m π = 0.34-0.69 GeV on 2.7 fm 3 lattice as used in our previous work [1]. We improve total accuracy of matrix elements to 10-15% from 30-40% for p → πe + or from 20-40% for p → Kν. The accuracy of the low energy constants α and β in the leading-order baryon chiral perturbation theory (BChPT) of proton decay are also improved. The relevant form factors of p → π estimated through the "direct" lattice calculation from three-point function appear to be 1.4 times smaller than those from the "indirect" method using BChPT with α and β. 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.

The role of Lattice QCD in searches for violations of fundamental symmetries and signals for new physics

“…At the lowest order, the BNV effective interactions can be written as dimension-6 three-quark-single-lepton operators inducing the decay of the proton to a pseudoscalar meson, such as pion, kaon and η, and an antilepton [11,51,52]. The effective Lagrangian consists of these interactions accompanied by the corresponding Wilson coefficients, computed perturbatively within a given high-scale model, and renormalized (customarily within the M S scheme) at µ = 2 GeV where the corresponding operators can be renormalized nonperturbatively using LQCD [53][54][55]. This procedure provides a physical scale-independent cross section, which along with the experimental constraints on the rate, leads to constraints on the parameters of BNV models.…”

“…Figure 12: Summary of matrix elements obtained in our study; "W 0 , W µ " which are evaluat from "direct" method and "W α,β 0 , W α,β µ " which are evaluated "indirect" method, including systematic error as discussed in text. [55] using "direct" (blue) and "indirect" (green) methods with 2+1 flavor dynamical domain-wall fermions with Iwasaki gauge action generated by RBC and UKQCD collaborations [56]. W µ is a given linear combination of W 0 and W 1 form factors, see Ref.…”

“…Progress report: Since 1980s, LQCD has come a long way to compute the MEs relevant to proton decay [53][54][55][57][58][59][60]. Uncontrolled systematic uncertainties in early calculations arising from the"quenched approximation", chiral-symmetry violation, quark-mass extrapolation, and reliance on leading-order baryon χPT have been accounted for in state-of-the-art present-day calculations.…”

Connection between νn→ν¯n¯ reactions and n−Hao1 2020Phys. Rev. D3010View full textAdd to dashboardCite

“…Here, ψ q (0) is the quark wave function at the origin and |ψ q (0)| 2 0.0144(3)(21) GeV 3 [45] is given by the lattice QCD calculations, with the numbers in parenthesis being statistical and systematic uncertainties. G b is the effective coupling constant and will be discussed in more detail in the following sections.…”

Origin of a two-loop neutrino mass from SU(5) grand unification

“…(5.91) is taken from Ref. [47]: | π 0 |(ud) R u L |p | = −0.118. In the gauge coupling unification analysis presented below, we will demonstrate few different scenarios and estimate the corresponding proton lifetime using Eq.…”