David Schaich

Novel phase in SU(3) lattice gauge theory with 12 light fermions

We study the phase structure of SU(3) lattice gauge theory with

Lattice Simulations and Infrared Conformality

{N}_{f}=12

Exploring strange nucleon form factors on the lattice

staggered fermions in the fundamental representation, for both zero and finite temperature at strong gauge couplings. For small fermion masses we find two transitions at finite temperature that converge to two well-separated bulk phase transitions. The phase between the two transitions appears to be a novel phase. We identify order parameters showing that the single-site shift symmetry of staggered fermions is spontaneously broken in this phase. We investigate the eigenvalue spectrum of the Dirac operator, the static potential and the meson spectrum, which collectively establish that this novel phase is confining but chirally symmetric. The phase is bordered by first-order phase transitions, and since we find the same phase structure with

Scale-dependent mass anomalous dimension from Dirac eigenmodes

{N}_{f}=8

Strongly interacting dynamics and the search for new physics at the LHC

fermions, we argue that the novel phase is most likely a strong-coupling lattice artifact, the existence of which does not imply IR conformality.

Nonperturbative β function of eight-flavor SU(3) gauge theory

We examine several recent lattice-simulation data sets, asking whether they are consistent with infrared conformality. We observe, in particular, that for an SU(3) gauge theory with 12 Dirac fermions in the fundamental representation, recent simulation data can be described assuming infrared conformality. Lattice simulations include a fermion mass m which is then extrapolated to zero, and we note that this data can be fit by a small-m expansion, allowing a controlled extrapolation. We also note that the conformal hypothesis does not work well for two theories that are known or expected to be confining and chirally broken, and that it does work well for another theory expected to be infrared conformal.

Improving the continuum limit of gradient flow step scaling

We discuss techniques for evaluating sea quark contributions to hadronic form factors on the lattice and apply these to an exploratory calculation of the strange electromagnetic, axial, and scalar form factors of the nucleon. We employ the Wilson gauge and fermion actions on an anisotropic 24^3 x 64 lattice, probing a range of momentum transfer with Q^2 _0. We discuss the unique systematic uncertainties affecting the latter quantity relative to the continuum, as well as prospects for improving future determinations with Wilson-like fermions.

Toward TeV Conformality

A bstractWe investigate the eigenmodes of the massless Dirac operator to extract the scale-dependent fermion mass anomalous dimension γm(μ). By combining simulations on multiple lattice volumes, and when possible several gauge couplings, we are able to measure the anomalous dimension across a wide range of energy scales. The method that we present is universal and can be applied to any lattice model of interest, including both conformal or chirally broken systems. We consider SU(3) lattice gauge theories with Nf = 4, 8 and 12 light or massless fermions. The 4-flavor model behaves as expected for a QCD-like system and demonstrates that systematic effects are manageable in practical lattice calculations. Our 12-flavor results are consistent with the existence of an infrared fixed point, at which we predict the scheme-independent mass anomalous dimension

Parity Doubling and the S Parameter below the Conformal Window

\gamma_m^{*}=0.32(3)

Finite size scaling of conformal theories in the presence of a near-marginal operator

. For the 8-flavor model we observe a large anomalous dimension across a wide range of energy scales. Further investigation is required to determine whether Nf = 8 is chirally broken and walking, or if it possesses a strongly-coupled conformal fixed point.