Engineering topics
Roberts, Craig D
Publications and source records attributed to Roberts, Craig D.
Pion and kaon valence-quark parton distribution functions.
A rainbow-ladder truncation of QCD's Dyson-Schwinger equations, constrained by existing applications to hadron physics, is employed to compute the valence-quark parton distribution functions of the pion and kaon. Comparison is made to {pi}-N Drell-Yan data for the pion's u-quark distribution and to Drell-Yan data for the ratio u{sub K}(x)/u{sub {pi}}(x): the environmental influence of this quantity is a parameter-free prediction, which agrees well with existing data. Our analysis unifies the computation of distribution functions with that of numerous other properties of pseudoscalar mesons.
QCD Phase Diagram Using Dyson-Schwinger Equations
We describe briefly the Dyson-Schwinger equation approach of QCD and the study of the QCD phase diagram in this approach. The phase diagram in terms of the temperature and chemical potential, and that in the space of coupling strength and current-quark mass are given.
T(r)opical Dyson-Schwinger Equations
We provide a glimpse of recent progress in hadron physics made using QCD's Dyson-Schwinger equations, reviewing: the notion of in-hadron condensates and a putative solution of a gross problem with the cosmological constant; the dynamical generation of quark anomalous chromo- and electro-magnetic moments, and their material impact upon the proton's electric/magnetic form factor ratio; a computation that simultaneously correlates the masses of meson and baryon ground- and excited-states; and a prediction for the x{yields}1 value of the ratio of neutron/proton distribution functions.
Quark Spectral Function above T{sub c}
The maximum entropy method is used to calculate the dressed-quark spectral density from the self-consistent solution of the rainbow-truncated gap equation of QCD at temperatures above T{sub c}, the critical temperature for chiral symmetry restoration. We find that, besides the normal and plasmino modes, the spectral function exhibits an essentially nonperturbative zero mode at the temperatures above but near T{sub c}. In the vicinity of T{sub c}, this long-wavelength mode contains the bulk of the spectral strength. So long as this mode persists, the system may reasonably be described as a strongly-coupled state of matter.
Phase Diagram and Critical End Point for Strongly Interacting Quarks
We introduce a method based on chiral susceptibility, which enables one to draw a phase diagram in the chemical-potential-temperature plane for strongly interacting quarks whose interactions are described by any reasonable gap equation, even if the diagrammatic content of the quark-gluon vertex is unknown. We locate a critical end point at ({mu}{sup E},T{sup E}){approx}(1.0,0.9)T{sub c}, where T{sub c} is the critical temperature for chiral-symmetry restoration at {mu}=0, and find that a domain of phase coexistence opens at the critical end point whose area increases as a confinement length scale grows.