Katherine Benson

Zero modes of non-abelian vortices

We investigate the bosonic zero modes of cosmic strings formed in the breaking of a gauge group G → H, and find exact charge-carrying zero mode solutions. For the case of G = U(1) × U(1) we find that it is necessary to modify Wittens superconducting zero mode ansatz. In the case of non-abelian G, zero modes are generically present. Further, in the presence of a non-abelian string the embedding of H in G is angle dependent, with only a subgroup H being globally single valued. This subgroup is determined by the Wilson loop integral around the string, and depends on detailed dynamics. We find that gauge bosons associated with multivalued generators Aharonov-Bohm scatter off the string. The Alice string (H = O(2), H = Z2) has novel electrodynamics: it attracts charges, scatters the SO(2) “photon”, and a two-string system has zero modes with unlocalizable (“Cheshire”) charge. We extend this analysis to generalized Alice strings and end by considering the bosonic zero modes of domain walls.

A universe in a global monopole

We investigate brane physics in a universe with an extra dimensional global monopole and negative bulk cosmological constant. The graviton zero mode is naturally divergent; we thus invoke a physical cutoff to induce four-dimensional gravity on a brane at the monopole core. Independently, the massive Kaluza-Klein modes have naturally compactified extra dimensions, inducing a discrete spectrum. This spectrum remains consistent with four-dimensional gravity on the brane, even for a small mass gap. Extra dimensional matter fields also induce four-dimensional matter fields on the brane, with the same Kaluza-Klein spectrum of excited states. We choose parameters to solve the hierarchy problem, that is, to induce the observed hierarchy between particle and Planck scales in the effective four-dimensional universe.

Skyrmions and Semilocal Strings in Cosmology

Abstract It has been pointed out that cosmic string solutions can exist in gauge field theories with broken symmetry even when gp1(G/H) is trivial. The stability of such semilocal defects is not guaranteed by topology and depends on dynamical considerations. In the literature it has been tacitly assumed that if stable, such strings would from in the Early Universe in a manner analogous to the formation of a network of more robust topologically-stable strings. In this paper we find that except for unnaturally small values of the correlation length, a network of semilocal strings does not firm. Instead, delocalized skyrmionic string configurations, which expand with the Hubble flow, dominate.

Coaxing charge from the vacuum

Abstract We examine a U(1)-symmetric field theory for two scalar fields in which thee tree-level potential is ununded from below. We calculate the finite-temperature effective potential and demonstrate that (1) radiative corrections stabilize the theory; (2) Q-balls appear at low temperatures; and (3) the U(1) symmetry is spontaneously broken at high temperatures and restored at low temperatures. We investigate the theorys dynamics in a sector of fixed charge, focusing on the cosmological production of Q-balls as relics of the early era of broken symmetry.

QCD flux tubes as sigma model relics.

We describe flux tubes and their interactions in a low-energy sigma model induced by SU([ital N][sub [ital F]])[r arrow]SO([ital N][sub [ital F]]) flavor symmetry breaking in SO([ital N][sub [ital c]]) QCD. Gauge confinement manifests itself in the low-energy theory through flux tube interactions with unscreened sources. The flux tubes mediating confinement act as Alice strings in their cores, a phenomenon which may occur for [pi][sub 2] line defects in physically realized systems.

Toward a path integral quantization of Q-balls

Abstract Q-balls are time-dependent solitons present in many field theories with unbroken global internal symmetries. To examine the quantized energy spectrum of such objects with Lie groups as internal symmetry groups, we apply group projection techniques to a functional integbral method developed by Dashen, Hasslacher and Neveu. This analysis treats only in the internal symmetry zero modes of such field theories, discussed via their quantum mechanical analogues, since the subtleties of quantization stem largely from the internal symmetry. Examples of U(1) symmetry and SU( n ) symmetry on the internal spaces S 1 , S 2 , and SU( n ) are presented.

Growing inhomogeneities in cosmological Goldstone modes

Abstract We examine the evolution of initial inhomogeneities in a Goldstone field in an expanding Friedmann-Robertson-Walker universe. We find subhorizon inhomogeneities grow, relative to the homogeneous state. This stems not from growing fluctuations — which simply redshift — but from rapid ( ϱ ∼ a −6 ) decay of the homogeneous state. We show how Goldstone modes escape assumptions — some inapplicable, some ill-founded — underpinning conventional analyses of cosmological fluctuations. Finally, we reconcile our analysis to standard cosmology, noting that the Goldstone evolution is essentially decoupled and dynamical.