Unphysical Poles of Domain Wall Fermions at finite $L_s$

Abstract

We investigate the origin and behavior of oscillations observed in the hadron correlators constructed from the domain wall fermion (DWF) for different parameters involved in lattice QCD simulations. This oscillatory behavior at early time slices hinders the extraction of excited states in hadron spectroscopy. Furthermore, the deviation from exponential decay may have a significant impact on fermion loop calculations performed on the lattice. We present results for several well-known implementations of the DWF actions. We extend the study of Shamir DWF action to include Bori\c{c}i and M\"{o}bius DWF actions by analyzing the poles of 4D quark propagator. For each action considered, we find an unphysical mode when analyzing the pole structure of the free DWF propagator for a finite extent of the $5^{\text{th}}$ dimension $L_s$, and we show that this mode is responsible for the oscillatory behavior observed in hadron correlators. We have performed numerical checks on these results and have found that the presence of oscillatory behavior is sensitive to the DWF parameters $a_5$, $b_5$, $c_5$ and DW height $M$. To minimize oscillations, our results suggest that one should choose $M a_5<1$ for the Shamir and Bori\c{c}i DWFs, and $M(b_5-c_5)<1$ for M\"{o}bius DWF when $M>1$. For each calculation considered, the Bor\c{c}i DWF displayed the smallest magnitude of oscillation when compared to the Shamir and M\"{o}bius DWF actions using the same input parameters.