Browsing by Author "Albert Young, Committee Member"

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Application of Perturbative and Lattice Techniques to the Analysis of Nuclear Matter.
(2010-08-09) Thomson, Richard; Chueng Ji, Committee Chair; Albert Young, Committee Member; Dean Lee, Committee Member; Thomas Schaefer, Committee Member; Sarah Ash, Committee Member
Physical Constraints on Causality-violating Spacetimes in General Relativity
(2007-04-11) Janca, Andrew Joseph; Arkady Kheyfets, Committee Co-Chair; J. David Brown, Committee Chair; Nancy Mitchell, Committee Member; Ronald Fulp, Committee Member; Albert Young, Committee Member
The theoretical possibility of global causality violation has long been a problem within general relativity, for there exists a large number of model spacetimes known to admit closed timelike curves, trajectories allowing a timelike observer to return to some point in her own past. However, nearly all such known models have some unphysical feature. These physicality issues rendered causality-violation to the status of an interesting but safely theoretical problem until twenty years ago, when the appearance of a new type of causality-violating model spacetime and the subsequent proliferation of new models admitting closed timelike curves forced the attention of the community to the issue, and made causality violation and its possible physical consequences an active area of research within general relativity. This paper focuses on some of the older causality-violating spacetimes which model matter sources with cylindrical symmetry. By describing how cylindrically-symmetric solutions can be embedded within a spatially bounded and physically realistic body which outwardly has the symmetry of a torus or ring, it is shown that the chief problem of physical plausibility which these older solutions possess can be resolved. The intention is to make these models active candidates for consideration in future experiments to test general relativity's prediction that causality violation is a phenomenon that could be observed in the real world. Attending chapters describe physical systems other than rotating objects that can alter a local observer's experience of time to a substantial extent, including an electrically-charged massive shell slowing time in its interior (though not affecting causality) and a class of trajectories in the Reissner-Nordström background that could in principle allow a timelike observer to reverse her personal arrow of time relative to other observers in the spacetime as a whole. The paper concludes with a discussion of one of the plausibility problems with the `consistency conjectures' which attempt to address some of the apparently paradoxical consequences of time travel.
QCD Coulomb Gauge Approach to Exotic Hadrons
(2006-12-19) General, Ignacio Jose; Albert Young, Committee Member; Ronald Fulp, Committee Member; Dean Lee, Committee Member; Stephen Cotanch, Committee Chair
The Coulomb Gauge Hamiltonian (CGH) model, a field theoretical, relativistic, many-body approach to Quantum Chromodynamics (QCD),is developed, which describes the vacuum through a Bogoliubov-Valatin transformation. This transformation also dresses the bare quarks and gluons, producing quasi-particles with constituent masses and quark and gluon condensates. This framework is then applied, using the variational principle, to the hybrid meson and tetra-quark problems, where exotic quantum numbers can be generated; light u-ubar-g, strange s-sbar-g and charmed c-cbar-g hybrid meson spectra are calculated and found to agree reasonably well with lattice and Flux Tube predictions. The light tetra-quark spectra is also calculated, along with the charmed tetra-quark structures likely to be the X(3872) and Y(4262) particles. The lowest 1-+ hybrid meson mass is found to be just above 2.2 GeV while the lightest tetra-quark state mass with these exotic quantum numbers is predicted around 1.4 GeV. These theoretical formulations all indicate the observed 1-+ pi 1(1600) and, more clearly, pi 1(1400) are definitely not hybrid states but could be tetra-quark states, with a molecular type, meson-meson structure.