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.