Neutron Electric Dipole Moment and Tensor Charges from Lattice QCD

TL;DR

This paper reports on lattice QCD calculations of neutron tensor charges, including systematic extrapolations, to better understand the neutron electric dipole moment and constrain new physics models beyond the Standard Model.

Contribution

First simultaneous extrapolation of lattice QCD results for neutron tensor charges to the physical point, improving accuracy and reducing uncertainties.

Findings

Tensor charge estimates with all systematics included

Disconnection contributions are negligible within errors

Updated bounds on neutron EDM in BSM scenarios

Abstract

We present Lattice QCD results on the neutron tensor charges including, for the first time, a simultaneous extrapolation in the lattice spacing, volume, and light quark masses to the physical point in the continuum limit. We find that the "disconnected" contribution is smaller than the statistical error in the "connected" contribution. Our estimates in the $\bar{\text{MS}}$ scheme at $2$ GeV, including all systematics, are $g_T^{d-u}=1.020(76)$, $g_T^d = 0.774(66)$, $g_T^u = - 0.233(28)$, and $g_T^s = 0.008(9)$. The flavor diagonal charges determine the size of the neutron electric dipole moment (EDM) induced by quark EDMs that are generated in many new scenarios of CP-violation beyond the Standard Model (BSM). We use our results to derive model-independent bounds on the EDMs of light quarks and update the EDM phenomenology in split Supersymmetry with gaugino mass unification, finding a stringent upper bound of $d_n < 4 \times 10^{-28} \, e$ cm for the neutron EDM in this scenario.