# Calculation of disconnected quark loops in lattice QCD

• Calculation of disconnected quark loops in lattice QCD is very time consuming. Stochastic noise methods are generally used to estimate these loops. However, stochastic estimation gives large errors in the calculations of disconnected diagrams. We use the symmetric multi-probing source (SMP) method to estimate the disconnected quark loops, and compare the results with the $Z(2)$ noise method and the spin-color explicit (SCE) method on a quenched lattice QCD ensemble with lattice volume $12^{3}\times24$ and lattice spacing $a\approx0.1$ fm. The results show that the SMP method is very suitable for the calculation of pseudoscalar disconnected quark loops. However, the SMP and SCE methods do not have an obvious advantage over the $Z(2)$ noise method in the evaluation of the scalar disconnected loops.
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Zhen Cheng, Jian-Bo Zhang and Guang-Yi Xiong. Calculation of disconnected quark loops in lattice QCD[J]. Chinese Physics C, 2020, 44(3): 033104. doi: 10.1088/1674-1137/44/3/033104
Zhen Cheng, Jian-Bo Zhang and Guang-Yi Xiong. Calculation of disconnected quark loops in lattice QCD[J]. Chinese Physics C, 2020, 44(3): 033104.
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沈阳化工大学材料科学与工程学院 沈阳 110142

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## Calculation of disconnected quark loops in lattice QCD

###### Corresponding author: Guang-Yi Xiong, xionggy@zju.edu.cn
• Department of Physics, Zhejiang University, Hangzhou 310027, China

Abstract: Calculation of disconnected quark loops in lattice QCD is very time consuming. Stochastic noise methods are generally used to estimate these loops. However, stochastic estimation gives large errors in the calculations of disconnected diagrams. We use the symmetric multi-probing source (SMP) method to estimate the disconnected quark loops, and compare the results with the $Z(2)$ noise method and the spin-color explicit (SCE) method on a quenched lattice QCD ensemble with lattice volume $12^{3}\times24$ and lattice spacing $a\approx0.1$ fm. The results show that the SMP method is very suitable for the calculation of pseudoscalar disconnected quark loops. However, the SMP and SCE methods do not have an obvious advantage over the $Z(2)$ noise method in the evaluation of the scalar disconnected loops.

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