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Pion multiplet spectrum with improved staggered fermions

Presenter: Taegil Bae — Seoul National University

David H. Adams, Taegil Bae, Chulwoo Jung, Jongjeong Kim, Weonjong Lee, and Stephen R. Sharpe

We study the quantitative impact of using HYP-smeared improved staggered fermions on the size of taste breaking. We first calculate the pion spectrum using unimproved and HYP-smeared staggered fermions on quenched lattices with a≈0.1fm, using quark masses in the range msphys/5–msphys. For unimproved staggered fermions, we find, consistent with previous work, that taste symmetry breaking effects (which are of O(a2)) are large and comparable to the O(p2)∼O(m) contributions for the lighter quark masses. We also find that O(a2p2) effects are substantial enough to be seen. With HYP-smeared fermions, we find that taste symmetry breaking is very substantially reduced (numerically by a factor of 4–7), so that for our mass range the appropriate power-counting is O(a2)≪O(p2). We next compare HYP-smeared valence fermions to asqtad valence fermions on unquenched 2 + 1 flavor lattices generated with asqtad sea quarks and a≈0.125fm. Here both types of valence fermion have tree-level taste-breaking removed. We find that taste-breaking in the pion spectrum is reduced by 2.5–3 using HYP-smeared fermions. For both types of fermions, there are no indications of substantial O(a2p2) effects for our range of quark masses.