Magnetic monopoles in Yang-Mills-Higgs theory with impurities

Abstract In this work, BPS models built from the coupling of the 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 SU(2) × Z2 or SU(2) × SU(2) models. We then focus on the coupling to non-Abelian impurities, defined as fixed backgrounds produced by 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 on the abelianization that leads to the emergence of a U(1) gauge group are investigated. We also verify that these impurity models can be derived as effective theories from a homogeneous $\rm {SU(2)}\times \widetilde{\rm {SU}}(2)$ Yang-Mills-Higgs parent model with a bridge field. In this interpretation, the SU(2) impurities of the effective impurity-doped theory are produced by frozen antimonopoles from the $\widetilde{\rm {SU}}(2)$ sector. 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. In order to exemplify the most important properties of the theory, several specific impurity models are presented, and the corresponding monopole solutions are found numerically. These solutions present novel internal structure and multiple features that would not be possible in the original theory.