Thomas Blum

We review the lattice QCD calculation of nuetron (and proton) electric dipole moment, and show the recent lattice calculation in dynamical fermion configurations.

We report the recent study of neutron and proton electric dipole moment (EDM) from lattice QCD. We use the domain-wall fermion (DWF) in N f = 2 + 1 in 24 3 × 64 lattice at a-1 = 1.73 GeV, which has been generated by RBC/UKQCD collaboration. DWF is suitable to control the chiral symmetry on the lattice especially near light mass. We also employ the AMA algorithm which is recently developed in order to reduce the statistical error, and as a result we obtain the finite value of neutron EDM in 300 Mev pion mass.

After a brief self-contained introduction to the muon anomalous magnetic moment, (g-2), we review the status of lattice calculations of the hadronic vacuum polarization contribution and present first results from lattice QCD for the hadronic light-by-light scattering contribution. The signal for the latter is consistent with model calculations. While encouraging, the statistical error is large and systematic errors are mostly uncontrolled. The method is applied first to pure QED as a check.

We demonstrate the new class of variance reduction techniques for hadron propagator and nucleon isovector form factor in the realistic lattice of N f = 2 + 1 domain-wall fermion. All-mode averaging (AMA) is one of the powerful tool to more effectively reduce the statistical noise of various observables rather than low-mode averaging (LMA). We adopt this technique into the two-point function and three-point function, and comparing with LMA and traditional source-shift method in the same ensembles we see AMA has much advantage of performance for these observables.

The exciting possibility of direct observation of QCD instantons in heavy-ion collisions has recently been proposed by Kharzeev. The underlying phenomenon, known as the chiral magnetic effect, may have been observed recently at RHIC, and a first principles calculation is needed to confirm and understand the results. The chiral magnetic effect is thought to be visible in the symmetric phase, at temperatures above the QCD critical temperature, and in the presence of an external magnetic field. We report on first 2+1 flavor, domain wall fermion, QCD+QED dynamical simulations above the critical temperature, in a fixed topological sector(s), which are used to study the electric charge separation produced by the effect.

We discuss Quantum Chromodynamics calculations using the lattice regulator. The theory of the strong force is a cornerstone of the Standard Model of particle physics. We present USQCD collaboration results obtained on Argonne National Lab's Intrepid supercomputer that deepen our understanding of these fundamental theories of Nature and provide critical support to frontier particle physics experiments and phenomenology.

At stronger gauge-field couplings, the domain wall fermion (DWF) residual mass, a measure of chiral symmetry breaking, grows rapidly. This measure is largely due to near zero fermion eigenmodes of logarithm of the 4D transfer matrix along the fifth dimension, and these eigenmodes increase rapidly at strong coupling. To suppress these eigenmodes, we have added to the DWF path integral a multiplicative weighting factor consisting of a ratio of determinants of Wilson-Dirac fermions having a chirally twisted mass with a large negative real component and a small imaginary chiral component. Numerical results show that this weighting factor with an appropriate choice of twisted masses significantly suppresses the residual mass while allowing adequate topological tunneling.