Radiative improvement of spin and Darwin terms in the NRQCD action

TL;DR

This paper reports on the calculation of radiative corrections to various terms in the lattice NRQCD action, improving the accuracy of heavy quark simulations, especially for hyperfine splittings.

Contribution

It provides updated radiative corrections for spin-dependent terms and first results for spin-independent terms in the NRQCD action, addressing previous limitations.

Findings

Radiative corrections significantly affect hyperfine splitting calculations.

Spin-dependent terms show notable impact on bottomonium and heavy-light mesons.

Challenges remain in evaluating spin-independent terms due to lattice artifacts and IR divergences.

Abstract

We present updated results for the radiative improvement of the \sigma.B term and the spin-dependent four-fermion terms in the lattice NRQCD action, and first results for the radiative corrections to the NRQCD Darwin term and spin-independent four-fermion terms. The spin-dependent terms have significant impact on getting the correct hyperfine splitting for both bottomonium and heavy-light mesons, while the spin-independent terms suffer from a conspiracy between lattice artifacts and severe IR divergences that complicates their evaluation.