arXiv subjects

Robert D. Mawhinney

Publications and source records attributed to Robert D. Mawhinney.

26 records · Page 2Linked to original sources

arXiv1997

Lattice QCD with 0, 2 and 4 quark flavors

We have done simulations of lattice QCD with different numbers of light dynamical quarks. Since we cannot reach the continuum limit with our current computers, we have done comparisons with 0 (quenched), 2 and 4 light quark flavors with the physical volume and lattice spacing constant, when these are determined from the mass of the rho. We find a 7% (2 standard deviation) difference in the nucleon to rho mass ratio for 2 and 4 quarks. More importantly, the effects of chiral symmetry breaking are dramatically decreased for the case of 4 light quarks.

hep-lat↗

arXiv1997

Dependence of QCD hadron masses on the number of dynamical quarks

We have studied the hadron spectrum while varying the number of light dynamical quarks when the physical lattice spacing and volume are held fixed relative to the rho mass. For two and zero flavors of staggered fermions, we find the nucleon to rho mass ratios (extrapolated to zero valence quark mass) are very similar. However, for four flavors the ratio is 7% (2 standard deviations) above the two flavor result.

hep-lat↗

arXiv1997

QCDSP: The first 64 nodes

We present a summary of the progress on QCDSP in the last year. QCDSP, Quantum Chromodynamics on Digital Signal Processors, is an inexpensive computer being built at Columbia that can achieve 0.8 teraflops for three million dollars.

hep-lat↗

arXiv1997

Evidence for pronounced quark loop effects in QCD

We have measured the hadron spectrum in lattice QCD, using staggered fermions, for 0 (the quenched approximation), 2 and 4 light degenerate dynamical quarks. In addition to earlier results involving extrapolations in valence quark masses for fixed dynamical mass, we also report results where we extrapolate in the dynamical mass for 4 flavors. We see a marked difference in the hadron spectrum for 2 and 4 flavors; the hadron spectrum is nearly parity doubled for 4 flavors, indicating smaller effects of chiral symmetry breaking. This pronounced effect in the hadron spectrum cannot be removed by a simple change in scale as the number of light quark flavors is changed. Further simulations at larger volume are needed to rule out finite volume effects.

hep-lat↗

arXiv1996

Finite Volume Effects and Quenched Chiral Logarithms

We have measured the valence pion mass and the valence chiral condensate on lattice configurations generated with and without dynamical fermions. We find that our data and that of others is well represented by a linear relationship between $m_π^2$ and the valence quark mass, with a non-zero intercept. For our data, we relate the intercept to finite volume effects visible in the valence chiral condensate. We see no evidence for the singular behavior expected from quenched chiral logarithms.

hep-lat↗

arXiv1995

A Class of Saddle-point Configurations in three-dimensional SU(2) Lattice Gauge Theory

We discuss a class of saddle-point configurations in SU(2) lattice gauge theory in three Euclidean dimensions. These configurations are smooth on the scale of the lattice and have an action density exhibiting localized peaks, as has been seen in cooled and extremized Monte Carlo generated lattices. Large Wilson loops centered on the action peaks show a unit of Z(2) flux. We discuss the generation of these configurations and measurements of the Creutz ratios on them.

hep-lat↗

arXiv1994

The status of US Teraflops-scale projects

The current status of United States projects pursuing Teraflops-scale computing resources for lattice field theory is discussed. Two projects are in existence at this time: the Multidisciplinary Teraflops Project, incorporating the physicists of the QCD Teraflops Collaboration, and a smaller project, centered at Columbia, involving the design and construction of a 0.8 Teraflops computer primarily for QCD.

hep-lat↗

arXiv1992

Lattice QCD with 8 Light Quark Flavors

QCD with eight flavors is studied on $16^3\times N_t$ lattices with $N_t=4$, 6, 8, 16 and 32, a dynamical quark mass $ma=0.015$ and lattice coupling $β=6/g^2$ between 4.5 and 5.0. For $N_t=16$ and 32, hadron masses and screening lengths are computed for a variety of valence quark masses. The previously observed, strong, first-order transition for $N_t=4$, 6 and 8 is seen, for $N_t=16$, to become a $β$-independent, zero-temperature transition characterized by a factor of $\approx 3$ change in lattice scale. This strong, first-order transition restores chiral symmetry, at least for $N_t=4$, 6 and 8, producing a chirally symmetric, weak-coupling phase. However, as $N_t$ increases to 16, the chiral symmetry properties of the weak-coupling side of the zero-temperature transition are unclear and offer a hint of a normal, finite-temperature, chiral symmetry breaking transition in the weak-coupling phase.

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