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RBC Collaboration

Publications and source records attributed to RBC Collaboration.

13 recordsLinked to original sources
arXiv2012

Domain Wall QCD with Near-Physical Pions

We present physical results for a variety of light hadronic quantities obtained via a combined analysis of three 2+1 flavour domain wall fermion ensemble sets. For two of our ensemble sets we used the Iwasaki gauge action with beta=2.13 (a^-1=1.75(4) GeV) and beta=2.25 (a^-1=2.31(4) GeV) and lattice sizes of 24^3 x 64 and 32^3 x 64 respectively, with unitary pion masses in the range 293(5)-417(10) MeV. The extent L_s for the 5^th dimension of the domain wall fermion formulation is L_s=16 in these ensembles. In this analysis we include a third ensemble set that makes use of the novel Iwasaki+DSDR (Dislocation Suppressing Determinant Ratio) gauge action at beta = 1.75 (a^-1=1.37(1) GeV) with a lattice size of 32^3 x 64 and L_s=32 to reach down to partially-quenched pion masses as low as 143(1) MeV and a unitary pion mass of 171(1) MeV, while retaining good chiral symmetry and topological tunneling. We demonstrate a significant improvement in our control over the chiral extrapolation, resulting in much improved continuum predictions for the above quantities. The main results of this analysis include the pion and kaon decay constants, f_\pi=127(3)_{stat}(3)_{sys} MeV and f_K = 152(3)_{stat}(2)_{sys} MeV respectively (f_K/f_\pi = 1.199(12)_{stat}(14)_{sys}); the average up/down quark mass and the strange-quark mass in the MSbar-scheme at 3 GeV, m_{ud}(MSbar, 3 GeV) = 3.05(8)_{stat}(6)_{sys} MeV and m_s(MSbar, 3 GeV) = 83.5(1.7)_{stat}(1.1)_{sys}; the neutral kaon mixing parameter in the MSbar-scheme at 3 GeV, B_K(MSbar,3 GeV) = 0.535(8)_{stat}(13)_{sys}, and in the RGI scheme, \hat B_K = 0.758(11)_{stat}(19)_{sys}; and the Sommer scales r_1 = 0.323(8)_{stat}(4)_{sys} fm and r_0 = 0.480(10)_{stat}(4)_{sys} (r_1/r_0 = 0.673(11)_{stat}(3)_{sys}). We also obtain values for the SU(2) ChPT effective couplings, \bar{l_3} = 2.91(23)_{stat}(7)_{sys}$ and \bar{l_4} = 3.99(16)_{stat}(9)_{sys}.

hep-lat↗
arXiv2006

Light meson masses and non-perturbative renormalisation in 2+1 flavour domain wall QCD

We present results for the light meson masses, the bare strange quark mass and preliminary non-perturbative renormalisation of B_K in 2+1 flavour domain wall QCD. The ensembles used were generated with the Iwasaki gauge action and have a volume of 16^3 x 32 with a fifth dimension size of 16 and an inverse lattice spacing of 1.6 GeV. These ensembles have u and d masses as low as one quarter of the strange quark mass. All data were generated jointly by the UKQCD and RBC collaborations on QCDOC machines.

hep-lat↗
arXiv2005

Light meson masses and decay constants in 2+1 flavour domain wall QCD

We present results for light meson masses and psedoscalar meson decay constants in 2+1 flavour domain wall QCD with the DBW2 and Iwasaki gauge actions, using lattices with linear sizes in the range 1.6 to 2.2fm and $u$ and $d$ quark masses as low as one quarter of the strange quark mass. All data were generated on the QCDOC machines at the University of Edinburgh and Brookhaven National Laboratory. Despite large residual masses and a limited number of sea quark mass values with which to perform chiral extrapolations, our results agree with experiment and scale within errors.

hep-lat↗
arXiv2003

Calcutation of kaon matrix elements in quenched domain-wall QCD with DBW2 gauge action

We give a progress report of our new $a^{-1}\approx 3$ GeV quenched calculation of kaon matrix elements with domain-wall fermion and DBW2 gauge action. Our smaller lattice spacing allows us to address the effect of charmed quark on the lattice. We show preliminary results of $B_K$ renormalized non-perturbatively and $K\toπ$ matrix elements.

hep-lat↗
arXiv2003

Pion electromagnetic form-factor with domain wall fermions

Motivated by recent measurements at J-Lab, the pion electromagnetic form-factor is investigated with quenched domain wall fermions and a renormalization group improved gauge action called DBW2. We see that quark mass dependence of the form-factor with finite momentum transfers is rather small.

hep-lat↗
arXiv2002

Effective Potential for Polyakov Loops in Lattice QCD

Toward the derivation of an effective theory for Polyakov loops in lattice QCD, we examine Polyakov loop correlation functions using the multi-level algorithm which was recently developed by Luscher and Weisz.

hep-lat↗
arXiv2002

Lattice QCD with dynamical domain wall quarks

We study lattice QCD with two flavors of dynamical domain wall quarks. With renormalization group motivated actions, we find chiral symmetry can be preserved to a high degree at lattice cut off of a^{-1} \sim 2 GeV even for fifth dimension size as small as L_s = 12. In addition two new steps are introduced to improve the performance of the hybrid Monte Carlo simulation.

hep-lat↗
arXiv2002

Nucleon matrix elements with domain wall fermions

We present the status of our calculation of the first few moments of the nucleon structure functions. Our calculations are done using domain wall fermions in the quenched approximation with the DBW2 gauge action at 1.3GeV inverse lattice spacing.

hep-lat↗
arXiv2002

Kaon Matrix Elements and CP-violation from Quenched Lattice QCD: (I) the 3-flavor case

We report the results of a calculation of the K --> pi pi matrix elements relevant for the $\DIhalf$ rule and $\epe$ in quenched lattice QCD using domain wall fermions at a fixed lattice spacing $a^{-1} \sim 2$ GeV. Working in the three-quark effective theory, where only the u, d and s quarks enter and which is known perturbatively to next-to-leading order, we calculate the lattice K --> pi and K --> |0> matrix elements of dimension six, four-fermion operators. Through lowest order chiral perturbation theory these yield K --> pi pi matrix elements, which we then normalize to continuum values through a non-perturbative renormalization technique. For the ratio of isospin amplitudes |A_0|/|A_2| we find a value of $25.3 \pm 1.8$ (statistical error only) compared to the experimental value of 22.2, with individual isospin amplitudes 10-20% below the experimental values. For $\epe$, using known central values for standard model parameters, we calculate $(-4.0 \pm 2.3) \times 10^{-4}$ (statistical error only) compared to the current experimental average of $(17.2 \pm 1.8) \times 10^{-4}$. Because we find a large cancellation between the I = 0 and I = 2 contributions to $\epe$, the result may be very sensitive to the approximations employed. Among these are the use of: quenched QCD, lowest order chiral perturbation theory and continuum perturbation theory below 1.3 GeV. We have also calculated the kaon B parameter, B_K and find $B_{K,\bar{MS}}(2 {\rm GeV}) = 0.532(11)$. Although currently unable to give a reliable systematic error, we have control over statistical errors and more simulations will yield information about the effects of the approximations on this first-principles determination of these important quantities.

hep-lat↗
arXiv2001

Im$A_0$, Im$A_2$, and $ε^\prime$ from quenched lattice QCD

We present results for the imaginary parts of the I=0 and 2 $K\toππ$ decay amplitudes, Im$A_{0,2}$, and the ratio of CP violation parameters, $ε^\prime/ε$. Our calculation is done in the quenched approximation at $a^{-1}\approx 2$ GeV, lattice size $16^3\times 32$, using domain wall fermions with $L_s=16$. We study the three flavor case (charm is not an active flavor) and find $ε^\prime/ε$ is small and slightly negative.

hep-lat↗
arXiv2001

Re $A_0$ and Re $A_2$ from Quenched Lattice QCD

We have used domain wall fermions to calculate $K \to π$ and $K \to 0$ matrix elements which can be used to study the $ΔI = 1/2$ rule for K decays in the Standard Model. Nonlinearities in the $ΔI = 3/2$ matrix elements due to chiral logarithms are explored and the subtractions needed for the $ΔI = 1/2$ matrix elements are discussed. Using renormalization factors calculated using non-perturbative renormalization then yields values for real $A_0$ and $A_2$. We present the details of our quenched $16^3 \times 32 \times 16$, $β= 6.0$, $M_5 = 1.8$ simulation, where a previous calculation showed that the finite $L_s$ chiral symmetry breaking effects are small ($m_{\rm res} \approx 4 \rm MeV$).

hep-lat↗
arXiv2001

Chiral properties of domain wall fermions with improved gauge actions

We study the chiral properties of quenched domain wall fermions with several gauge actions. We demonstrate that the nearly translationally invariant modes in the fifth dimension that dominate the residual mass for Wilson gauge action can be substantially suppressed using improved gauge actions. In particular, we study the Symanzik action, the Iwasaki action, the DBW2 action and compare them to the Wilson action.

hep-lat↗