Stability Conditions and Branes at Singularities

I use Bridgeland's definition of a stability condition on a triangulated category to investigate the stability of D-branes on Calabi-Yau cones given by the canonical line bundle over a del Pezzo surface. In this context, I prove the existence of the decay of a D3-brane into a set of fractional branes. This is an important aspect of the derivation of quiver gauge theories from branes at singularities via the technique of equivalences of categories. Some important technical aspects of this equivalence are discussed. I also prove that the representations corresponding to skyscraper sheaves supported off the zero section are simple.Comment: 22 pages, uses utarticle.cls, dcpic.sty, v2: published versio

Dipoles, Twists and Noncommutative Gauge Theory

T-duality of gauge theories on a noncommutative $T^d$ can be extended to include fields with twisted boundary conditions. The resulting T-dual theories contain novel nonlocal fields. These fields represent dipoles of constant magnitude. Several unique properties of field theories on noncommutative spaces have simpler counterparts in the dipole-theories.Comment: 20pp LaTeX, amsfonts and amssymb, JHEP format and ref adde

A Note on Intersecting and Fluctuating Solitons in 4D Noncommutative Field Theory

We examine the intersections, fluctuations and deformations of codimension two solitons in field theory on noncommutative $R^4$, in the limit of large noncommutativity. We find that holomorphic deformations are zero modes of flat branes, and we show that there is a zero mode localized at the intersection of two solitons.Comment: 19pp LaTeX, refs adde

Moduli spaces for Bondal quivers

Given a sufficiently nice collection of sheaves on an algebraic variety V, Bondal explained how to build a quiver Q along with an ideal of relations in the path algebra of Q such that the derived category of representations of Q subject to these relations is equivalent to the derived category of coherent sheaves on V. We consider the case in which these sheaves are all locally free and study the moduli spaces of semistable representations of our quiver with relations for various stability conditions. We show that V can often be recovered as a connected component of such a moduli space and we describe the line bundle induced by a GIT construction of the moduli space in terms of the input data. In certain special cases, we interpret our results in the language of topological string theory.Comment: 17 pages, major revisio

Moduli Spaces for D-branes at the Tip of a Cone

For physicists: We show that the quiver gauge theory derived from a Calabi-Yau cone via an exceptional collection of line bundles on the base has the original cone as a component of its classical moduli space. For mathematicians: We use data from the derived category of sheaves on a Fano surface to construct a quiver, and show that its moduli space of representations has a component which is isomorphic to the anticanonical cone over the surface.Comment: 8 page

The architectural impact of using ground-source heat pumps in commercial buildings in Las Vegas

A series of parametric studies evaluate the architectural impacts on the design and long term performance of ground-coupled heat pump systems over a fixed period of time. The results are applied to a commercial office building in order to assess the net impact of combining various energy efficiency strategies. The conclusion of the comprehensive study is that energy efficient design strongly contributes to a reduction in the required size of a ground-coupled heat pump system. A comparative life-cycle cost analysis validates these results by using the same commercial office building design to evaluate a ground-coupled heat pump system against two other commonly used HVAC systems for commercial building applications; The analysis indicates that ground-coupled heat pump systems perform competitively against other systems in terms of life-cycle costs. The impact on the ground temperature at the ground-loop in such a system rises significantly over the simulation period of 25 years. This condition strongly suggests that ground-coupled heat pump systems that do not incorporate a secondary means of heat disposal such as a cooling tower or absorption chiller may not be the most suitable HVAC system type for commercial office buildings in Las Vegas. (Abstract shortened by UMI.)