Pi-K Scattering in Full QCD with Domain-Wall Valence Quarks

We calculate the pi+ K+ scattering length in fully-dynamical lattice QCD with domain-wall valence quarks on MILC lattices with rooted staggered sea-quarks at a lattice spacing of b=0.125 fm, lattice spatial size of L =2.5 fm and at pion masses of m_pi=290, 350, 490 and 600 MeV. The lattice data, analyzed at next-to-leading order in chiral perturbation theory, allows an extraction of the full pi K scattering amplitude at threshold. Extrapolating to the physical point gives m_pi a_3/2 = -0.0574 (+- 0.0016)(+0.0024 -0.0058) and m_pi a_1/2 = 0.1725 (+- 0.0017)(+0.0023 -0.0156) for the I=3/2 and I=1/2 scattering lengths, respectively, where the first error is statistical and the second error is an estimate of the systematic due to truncation of the chiral expansion.Comment: 14 pages, 9 figure

SU(4) lattice gauge theory with decuplet fermions: Schr\"odinger functional analysis

We complete a program of study of SU(N) gauge theories coupled to two flavors of fermions in the two-index symmetric representation by performing numerical simulations in SU(4). The beta function, defined and calculated via the Schr\"odinger functional, runs more slowly than the two-loop perturbative result. The mass anomalous dimension levels off in strong coupling at a value of about 0.45, rendering this theory unsuitable for walking technicolor. A large-N comparison of this data with results from SU(2) and SU(3) reveals striking regularities.Comment: 15 pages, 15 figure

Session 1: The Legal Landscape

This is the transcript from a symposium on copyright exceptions for libraries and section 108 reform done in cooperation with the U.S. Copyright Office

A note on the power divergence in lattice calculations of ΔI=1/2\Delta I = 1/2 K→ππK\to\pi\pi amplitudes at MK=MπM_{K}=M_{\pi}

In this note, we clarify a point concerning the power divergence in lattice calculations of $\Delta I = 1/2$ $K\to\pi\pi$ decay amplitudes. There have been worries that this divergence might show up in the Minkowski amplitudes at $M_{K}=M_{\pi}$ with all the mesons at rest. Here we demonstrate, via an explicit calculation in leading-order Chiral Perturbation Theory, that the power divergence is absent at the above kinematic point, as predicted by CPS symmetry.Comment: 5 pages, 2 figure

Finite-Volume Two-Pion Amplitudes in the I=0 Channel

We perform a calculation in one-loop chiral perturbation theory of the two-pion matrix elements and correlation functions of an I=0 scalar operator, in finite and infinite volumes for both full and quenched QCD. We show that major difficulties arise in the quenched theory due to the lack of unitarity. Similar problems are expected for quenched lattice calculations of $K \to \pi \pi$ amplitudes with $\Delta I=1/2$. Our results raise the important question of whether it is consistent to study $K\to\pi\pi$ amplitudes beyond leading order in chiral perturbation theory in quenched or partially quenched QCD.Comment: Version to appear on Phys. Lett. B, with only very minor and stylistic change

On the effects of (partial) quenching on penguin contributions to K-> pi pi

Recently, we pointed out that chiral transformation properties of strong penguin operators change in the transition from unquenched to (partially) quenched QCD. As a consequence, new penguin-like operators appear in the (partially) quenched theory, along with new low-energy constants, which should be interpreted as a quenching artifact. Here, we extend the analysis to the contribution of the new low-energy constants to the K^0 -> pi^+ pi^- amplitude, at leading order in chiral perturbation theory, and for arbitrary (momentum non-conserving) kinematics. Using these results, we provide a detailed discussion of the intrinsic systematic error due to this (partial) quenching artifact. We also give a simple recipe for the determination of the leading-order low-energy constant parameterizing the new operators in the case of strong $LR$ penguins.Comment: 17 pages, 1 figure, minor correction