Magnetic monopoles in Yang-Mills-Higgs theory with impurities

TL;DR

This paper explores how impurities affect monopole solutions in Yang-Mills-Higgs theory, revealing new structures and behaviors, including modifications to monopole interactions and potential extensions to dyon solutions.

Contribution

It introduces a detailed analysis of scalar and nonabelian impurities in BPS monopole models, including new coupling mechanisms, effects on gauge symmetry, and numerical solutions with novel features.

Findings

Impurities alter monopole asymptotics and interactions.

New impurity-induced internal structures in monopoles.

Numerical solutions demonstrate novel monopole features.

Abstract

In this work, BPS models built from the coupling of Yang-Mills-Higgs Lagrangian to impurities are investigated. We first consider scalar impurities, which in the BPS limit generate monopoles similar to those obtained in a previously considered class of $\mathrm{SU(2)}\times\mathrm{Z}_2$ or $\mathrm{SU(2)}\times\mathrm{SU(2)}$ models. We then focus on coupling with nonabelian impurities, defined as fixed backgrounds produced from fields transforming under the adjoint representation of SU(2), with a coupling chosen to preserve half of the BPS sectors. The nature of this coupling, the ensuing Bogomol'nyi bound and BPS equations, as well as the effect of these impurities in the abelianization that leads to the emergence of a U(1) gauge group are investigated. We study in greater detail impurities with spherical symmetry, and examine the manner in which impurity coupling changes the asymptotic behavior and range of monopole interactions. Moreover, we introduce a method that can be used to approximate solutions with the use of small perturbations around the Prasad-Sommerfield monopole, and discuss the possibility of extending the aforementioned results to dyons. In order to exemplify the most important properties of the theory, several specific impurity models are presented, with the respective monopole solutions are found numerically. These solutions present novel internal structure and multiple features that would not be possible in the original theory.