arXiv subjects

Taegil Bae

Publications and source records attributed to Taegil Bae.

26 records · Page 2Linked to original sources

arXiv2008

Scaling behavior and sea quark dependence of pion spectrum with HYP-smeared staggered fermions

We study the pion spectrum (and in particular taste-symmetry breaking within it) using HYP-smeared valence staggered fermions on the coarse and fine MILC lattices (which have asqtad staggered sea quarks). We focus on the dependence on lattice spacing and sea-quark mass. We also update our results on source dependence. Our main conclusion is that on the MILC fine lattices the appropriate power-counting for SU(3) staggered chiral perturbation theory may have discretization errors entering at next-to-leading order rather than at leading-order.

hep-lat↗

arXiv2008

Calculating $B_K$ using HYP staggered fermions

We give an update on our calculation of $B_K$ using HYP-smeared valence staggered quarks. We have results for $B_K$ at tree-level on several coarse MILC lattices ($a\approx 0.12 $fm) and one of the fine lattices ($a\approx 0.09 $fm), using 10 light valence quarks ranging down to $m_s^{\rm phys}/10$. We have generalized staggered chiral perturbation theory to our mixed action setup, and outline the results. We explain our present fitting strategy, and give some preliminary results.

hep-lat↗

arXiv2008

Taste symmetry breaking with HYP-smeared staggered fermions

We study the impact of hypercubic (HYP) smearing on the size of taste breaking for staggered fermions, comparing to unimproved and to asqtad-improved staggered fermions. As in previous studies, we find a substantial reduction in taste-breaking compared to unimproved staggered fermions (by a factor of 4-7 on lattices with spacing $a\approx 0.1 $fm). In addition, we observe that discretization effects of next-to-leading order in the chiral expansion (${\cal O}(a^2 p^2)$) are markedly reduced by HYP smearing. Compared to asqtad valence fermions, we find that taste-breaking in the pion spectrum is reduced by a factor of 2.5-3, down to a level comparable to the expected size of generic ${\cal O}(a^2)$ effects. Our results suggest that, once one reaches a lattice spacing of $a\approx 0.09 $fm, taste-breaking will be small enough after HYP smearing that one can use a modified power counting in which ${\cal O}(a^2) \ll {\cal O}(p^2)$, simplify fitting to phenomenologically interesting quantities.

hep-lat↗

arXiv2008

$B_K$ in unquenched QCD using improved staggered fermions

We present preliminary results for $B_K$ calculated using improved staggered fermions with a mixed action (HYP-smeared staggered valence quarks and AsqTad staggered sea quarks). We investigate the effect of non-degenerate quarks on $B_K$ and attempt to estimate the ${\cal O}(a^2)$ effect due to non-Goldstone pions in loops. We fit the data to continuum partially quenched chiral perturbation theory. We find that the quality of fit for $B_K$ improves if we include non-degenerate quark mass combinations. We also observe, however, that the fitting curve deviates from the data points in the light quark mass region. This may indicate the need to include taste-breaking in pion loops.

hep-lat↗

arXiv2007

Improvement of the pion spectrum with HYP-smeared staggered fermions

We extend our previous study of taste-symmetry breaking using HYP-smeared staggered fermions in two ways. First, we improve the statistics of a comparison of unimproved and HYP-smeared staggered fermions on quenched lattices with $a\approx 0.1 $fm. This allows us to obtain a signal for all pion tastes, rather than just a subset, and thus to make a complete comparison. In addition, it allows us to differentiate between wall and local sources. Second, we compare HYP-smeared valence quarks to asqtad valence quarks on 2+1 flavor unquenched MILC lattices. We find that taste breaking is substantially reduced by HYP-smearing, bringing the size of this discretization effect (which is the dominant such effect with staggered fermions) down to the size expected generically for any fermion type.

hep-lat↗

arXiv2006

Pion spectrum using improved staggered fermions

We present results for the pion multiplet spectrum calculated using both unimproved staggered fermions and improved HYP-smeared staggered fermions. In the case of unimproved staggered fermions, we observe (consistent with previous work) that ${\cal O}(a^2)$ taste symmetry breaking effects are large and comparable to the $\approx {\cal O}(p^2)$ contributions to their masses. Higher order ${\cal O}(a^2 p^2)$ effects are also substantial enough to be seen. For HYP-smeared staggered fermions, we find that taste breaking is much reduced. The ${\cal O}(a^2)$ effects are observable, but are noticeably smaller than those obtained with AsqTad-improved staggered fermions, and much smaller than those obtained using unimproved staggered fermions, while ${\cal O}(a^2 p^2)$ effects are suppressed to such a level that we cannot observe them given our statistical errors. From this numerical study, we conclude that HYP staggered fermions are significantly better that AsqTad fermions from the perspective of taste symmetry breaking.

hep-lat↗

arXiv2005

Calculating $B_K$ using a mixed action

We present preliminary results of $B_K$ calculated using improved staggered fermions with the mixed action (valence quarks = HYP staggered fermions and sea quarks = AsqTad staggered fermions). We analyze the data based upon the prediction by Van de Water and Sharpe. A hint of consistency with the prediction is observed. We also present preliminary results of $B_8^{(3/2)}$ and $B_7^{(3/2)}$.

hep-lat↗

arXiv2005

Non-degenerate quark mass effect on $B_K$ with a mixed action

We investigate the effect of non-degenerate quarks on $B_K$. This effect is noticeably large for $B_K$ (significantly larger than statistical uncertainty). Hence, it is important to include this effect in order to determine $B_K$ with higher precision. We also observe that the quality of fitting for $B_K$ gets better when we include non-degenerate combinations to fit to the prediction by Van de Water and Sharpe. However, this effect on $B_7^{(3/2)}$ and $B_8^{(3/2)}$ turns out to be relatively small.

hep-lat↗