Jongjeong Kim

Taste symmetry breaking with hypercubic-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_equal}0.1 fm). In addition, we observe that discretization effects of next-to-leading order in the chiral expansion (O(a{sup 2}p{sup 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 O(a{sup 2}) effects. Our results suggest that, once one reaches a lattice spacing of a{approx_equal}0.09 fm, taste-breaking will be small enough after HYP smearing that one can use a modified power counting in which O(a{sup 2})<<O(p{sup 2}), simplify fitting to phenomenologically interesting quantities.

Improved determination of B-K with staggered quarks

obtained using improved staggered fermionson a much enlarged set of MILC asqtad lattices. Compared to our previous publication, which wasbased largely on a single ensemble at each of the three lattice spacings aˇ0:09 fm, 0:06 fm and0:045 fm, we have added seven new ne and four new super ne ensembles, with a range of valuesof the light and strange sea-quark masses. We have also increased the number of measurementson one of the original ensembles. This allows us to do controlled extrapolations in the light andstrange sea-quark masses, which we do simultaneously with the continuum extrapolation. Thisreduces the extrapolation error and improves the reliability of our error estimates. Our nal resultis B^

Properties of light pseudoscalars from lattice QCD with HISQ ensembles

We fit lattice-QCD data for light-pseudoscalar masses and decay constants, from HISQ configurations generated by MILC, to SU(3) staggered chiral perturbation theory. At present such fits have rather high values of χ2/d.o.f., possibly due to the lack of ensembles with lighter-than-physical sea strange-quark masses. We propose solutions to this problem for future work. We also perform simple linear interpolations near the physical point on two ensembles with different lattice spacings, and obtain the preliminary result ( fK/ fπ) = 1.1872(41) in the continuum limit. XXIX International Symposium on Lattice Field Theory July 10 16 2011 Squaw Valley, Lake Tahoe, California

Kaon semileptonic decay form factors with HISQ valence quarks

+ (0) on the asqtad Nf = 2+ 1 MILC configurations, discuss the chiral-continuum extrapolation, and give a preliminary estimate of the total error. We also present a more preliminary set of results for the same form factor but with the sea quarks also simulated with the HISQ action; these results include data at the physical light quark masses. The improvements that we expect to achieve with the use of the HISQ configu rations and simulations at the physical quark masses are briefly discussed.

One-loop matching factors for staggered bilinear operators with improved gauge actions

We present results for one-loop perturbative matching factors using bilinear operators composed of improved staggered fermions, using unimproved (Wilson) and improved (Symanzik, Iwasaki, and DBW2) gluon actions. We consider two fermions actionschar22{}HYP/

Non-perturbative Renormalization of Four-fermion Operators Relevant to B_K with Staggered Quarks.

overline{mathrm{Fat}7}

Flavored pion and kaon masses at next-to-leading order in mixed-action staggered chiral perturbation theory

-smeared and asqtad. The former is being used in calculations of electroweak matrix elements, while the latter have been used extensively by the MILC collaboration. We observe that using the improved gluon action leads to small reductions in the perturbative corrections, but that these reductions are smaller than those obtained when moving from the tadpole-improved naive staggered action to either HYP-smeared or asqtad action.

HISQ fermions and physical light quark masses

We present preliminary results of matching factors of the four-fermion operators relevant to

Finite Volume Effects in B_K with improved staggered fermions

B_K

One loop matching factors for improved staggered four-fermion operators with improved glue

, which are obtained using the non-perturbative renormalization (NPR) method in the RI-MOM scheme with HYP-smeared improved staggered fermions. We use the MILC asqtad coarse (