Gauged NonAbelian Vortices: Topology and Dynamics of a Coupled 2D-4D Quantum Field Theory

Nonabelian vortices - vortex solutions carrying nonabelian continuous orientational zero modes - have been extensively investigated in the last decade, revealing many interesting features. Typically they occur in a system in the color-flavor locked phase, i.e. systems in which the gauge symmetry is broken by a set of scalar condensates that, however, leave a color-flavor diagonal symmetry intact. Color-flavor locked systems appear to be quite ubiquitous in Nature. Standard QCD at zero temperature exhibits some characteristic features of this sort. They occur in the infrared effective theories of many N=2 supersymmetric theories softly broken to N=1 and may carry important hints about the mechanism responsible for quark confinement. In particular they could shed light on the mysteries of nonabelian monopoles. They are realized in high-density QCD in the color superconductor phase, which may well be realized in the interiors of neutron stars. In the present thesis, a generalization of the standard nonabelian vortex studied in the literature is investigated. In the case of the standard nonabelian vortex, vortices are due to the symmetry breaking G->H, where the residual symmetry group H is realized globally. The low-energy theory is fully higgsed and no massless fields propagate in the 4D bulk around the vortex. At the same time, the existence of an intact nonabelian group H, surviving the symmetry breaking, endows the vortex with nonabelian orientational moduli, describing the orientation of the enclosed flux in group space. Such orientational modes are confined to propagate on the string worldsheet and once excited give rise to finite-energy excitations. The new vortices arise when H is realized locally. In our benchmark model, obtained from the bosonic truncation of an N=2 super Yang-Mills theory, this is achieved through a gauging of the flavor group. As soon as the flavour symmetry is gauged, however, massless fields appear and infrared divergences immediately ensue. The massless gauge bosons of the 4D bulk interact nontrivially with the internal orientational modes supported by the string and change their dynamics dramatically. In addition, with the gauging of the flavor group, all sorts of global effects, reminiscent of the exotic Alice strings, make their appearance. Such global effects, which include a nonabelian version of the Aharonov-Bohm effect and a kind of topological interaction between vortices, are deeply intertwined with the dynamics of the orientational modes