Calculation of fermion loops for $\eta^\prime$ and nucleon scalar and electromagnetic form factors

TL;DR

This paper presents a GPU-accelerated method for precisely calculating disconnected fermion loops relevant to meson masses and nucleon form factors, comparing stochastic techniques with exact computations.

Contribution

It introduces an efficient GPU-based approach and evaluates various noise reduction and stochastic methods for calculating disconnected diagrams in lattice QCD.

Findings

GPU technology enables exact evaluation of disconnected diagrams.

Different stochastic methods and noise reduction techniques are compared.

Number of noise vectors needed varies with operator insertion.

Abstract

The exact evaluation of the disconnected diagram contributions to the flavor-singlet pseudoscalar meson mass, the nucleon sigma term and the nucleon electromagnetic form factors, is carried out utilizing GPGPU technology with the NVIDIA CUDA platform. The disconnected loops are also computed using stochastic methods with several noise reduction techniques. Various dilution schemes as well as the truncated solver method are studied. We make a comparison of these stochastic techniques to the exact results and show that the number of noise vectors depends on the operator insertion in the fermionic loop.