Andre Walker-Loud

Scalar strange content of the nucleon from lattice QCD

The scalar strange-quark matrix element of the nucleon is computed with lattice QCD. A mixed-action scheme is used with domain-wall valence fermions computed on the staggered MILC sea-quark configurations. The matrix element is determined by making use of the Feynman-Hellmann theorem which relates this strange matrix element to the change in the nucleon mass with respect to the strange-quark mass. The final result of this calculation is m_s = 49 +-10 +- 15 MeV and, correspondingly f_s = m_s / m_N = 0.051 +- 0.011 +- 0.016. Given the lack of a quantitative comparison of this phenomenologically important quantity determined from various lattice QCD calculations, we take the opportunity to present such an average. The resulting conservative determination is f_s = 0.043 +- 0.011.

Precise determination of the I=2 pi pi scattering length from mixed-action lattice QCD

The

Broken symmetries from minimally doubled fermions

I=2

The Electromagnetic Self-Energy Contribution to M_p - M_n and the Isovector Nucleon Magnetic Polarizability

\ensuremath{\pi}\ensuremath{\pi}

Two-Nucleon Higher Partial-Wave Scattering from Lattice QCD

scattering length is calculated in fully dynamical lattice QCD with domain-wall valence quarks on the asqtad-improved coarse MILC configurations (with fourth-rooted staggered sea quarks) at four light-quark masses. Two- and three-flavor mixed-action chiral perturbation theory at next-to-leading order is used to perform the chiral and continuum extrapolations. At the physical charged pion mass, we find

Extracting Nucleon Magnetic Moments and Electric Polarizabilities from Lattice QCD in Background Electric Fields

{m}_{\ensuremath{\pi}}{a}_{\ensuremath{\pi}\ensuremath{\pi}}^{I=2}=\ensuremath{-}0.043\text{ }30\ifmmode\pm\else\textpm\fi{}0.000\text{ }42

Extracting electric polarizabilities from lattice QCD

, where the error bar combines the statistical and systematic uncertainties in quadrature.

Kaon Condensation with Lattice QCD

Novel chirally symmetric fermion actions containing the minimum amount of fermion doubling have been recently proposed in the literature. We study the symmetries and renormalization of these actions and find that in each case, discrete symmetries, such as parity and time-reversal, are explicitly broken. Consequently, when the gauge interactions are included, these theories radiatively generate relevant and marginal operators. The restoration of these symmetries and the approach to the continuum limit thus require the fine-tuning of several parameters. With some assumptions, we show that this behavior is expected for actions displaying minimal fermion doubling.

Search for fermion actions on hyperdiamond lattices

The masses of the spin-3/2 baryons are calculated to next-to-next-to-leading order in heavy baryon chiral perturbation theory and partially quenched heavy baryon chiral perturbation theory. The calculation is performed for three light flavors in the isospin limit. These results are necessary for extrapolating QCD and partially quenched QCD lattice calculations of the decuplet baryon masses.