Improved Semileptonic Form Factor Calculations in Lattice QCD

TL;DR

This paper compares stochastic methods to the traditional Sequential Propagator Method in Lattice QCD for calculating semileptonic form factors, finding that stochastic approaches can be more efficient despite added noise.

Contribution

The study introduces and evaluates a stochastic propagator method as an alternative to the Sequential Propagator Method in Lattice QCD calculations of semileptonic form factors, demonstrating its competitiveness.

Findings

Stochastic propagator method becomes competitive or superior to the Sequential Propagator Method.

The 'one-end trick' is less efficient in this context.

The stochastic method successfully extracts form factors on two gauge ensembles.

Abstract

We investigate the computational efficiency of two stochastic based alternatives to the Sequential Propagator Method used in Lattice QCD calculations of heavy-light semileptonic form factors. In the first method, we replace the sequential propagator, which couples the calculation of two of the three propagators required for the calculation, with a stochastic propagator so that the calculations of all three propagators are independent. This method is more flexible than the Sequential Propagator Method but introduces stochastic noise. We study the noise to determine when this method becomes competitive with the Sequential Propagator Method, and find that for any practical calculation it is competitive with or superior to the Sequential Propagator Method. We also examine a second stochastic method, the so-called ``one-end trick", concluding it is relatively inefficient in this context. The investigation is carried out on two gauge field ensembles, using the non-perturbatively improved Wilson-Sheikholeslami-Wohlert action with N_f=2 mass-degenerate sea quarks. The two ensembles have similar lattice spacings but different sea quark masses. We use the first stochastic method to extract ${\mathcal O}(a)$-improved, matched lattice results for the semileptonic form factors on the ensemble with lighter sea quarks, extracting f_+(0).