Flavor diagonal tensor charges of the nucleon from 2+1+1 flavor lattice QCD

TL;DR

This paper provides precise lattice QCD calculations of the flavor diagonal tensor charges of the nucleon, which are crucial for understanding CP violation and electric dipole moments in particle physics.

Contribution

The study presents the most accurate lattice QCD results for nucleon tensor charges, including both connected and disconnected contributions, with systematic uncertainties addressed.

Findings

Tensor charge of up quark: 0.784(28)(10)

Tensor charge of down quark: -0.204(11)(10)

Tensor charge of strange quark: -0.0027(16)

Abstract

We present state-of-the-art results for the matrix elements of flavor diagonal tensor operators within the nucleon state. The calculation of the dominant connected contribution is done using eleven ensembles of gauge configurations generated by the MILC Collaboration using the highly improved staggered quark (HISQ) action with 2+1+1 dynamical flavors. The calculation of the disconnected contributions is done using seven (six) ensembles for the strange (light) quarks. These high-statistics simulations allowed us to address various systematic uncertainties. A simultaneous fit in the lattice spacing and the light-quark mass is used to extract the tensor charges in the continuum limit and at $M_\pi=135$ MeV. Results for the proton in the $\overline{MS}$ scheme at 2~GeV are: $g_T^u = 0.784(28)(10)$, $g_T^d = -0.204(11)(10)$ and $g_T^s = -0.0027(16)$. Implications of these results for constraining the quark electric dipole moments and their contributions to the neutron electric dipole moment are discussed.