Topological defects in the Georgi-Machacek model

Abstract

We study topological defects in the Georgi-Machacek model in a hierarchical symmetry breaking in which extra triplets acquire vacuum expectation values before the doublet. We find a possibility of topologically stable non-Abelian domain walls and non-Abelian flux tubes (vortices) in this model. In the limit of the vanishing U (1) Y gauge coupling in which the custodial symmetry becomes exact, the presence of a vortex spontaneously breaks the custodial symmetry, giving rise to S 2 Nambu-Goldstone (NG) modes localized around the vortex corresponding to non-Abelian fluxes. Vortices are continuously degenerated by these degrees of freedom, thereby called non-Abelian. By taking into account the U (1) Y gauge coupling, the custodial symmetry is explicitly broken, the NG modes are lifted, and all non-Abelian vortices fall into a topologically stable Z-string. This is in contrast to the SM in which Z-strings are non-topological and are unstable in the realistic parameter region. Non-Abelian domain walls also break the custodial symmetry and are accompanied by localized S 2 NG modes. Finally, we discuss the existence of domain wall solutions bounded by flux tubes, where their S 2 NG modes match. The domain walls may quantum mechanically decay by creating a hole bounded by a flux tube loop, and would be cosmologically safe. Gravitational waves produced from unstable domain walls could be detected by future experiments.

Non-Abelian strings and domain walls in two Higgs doublet models

“…[63,64] (and in the Georgi-Machacek model in Ref. [72]). Thus, the topologically stable strings in the 2HDM and dense QCD are very similar apart from the matrix sizes; they are both global string carrying a non-Abelian magnetic flux accompanied by the non-Abelian moduli, CP 1 ( S 2 ) and CP 2 in the 2HDM and dense QCD, respectively.…”

“…[50][51][52] as a review), color-flavor locked phase in dense QCD [53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70] (see Ref. [71] as a review), and recently in the Georgi-Machacek model [72]. As the same with these cases, a non-Abelian string in 2HDM has infinitely degenerate family, characterized by a moduli pace isomorphic to S 2 SU (2)/U (1).…”

The gravitational waves from the collapsing domain walls in the complex singlet model

“…Since the discovery of the gravitational waves (GW) by the LIGO/Virgo collaboration [5,6], it is widely believed that the further probes of various GW signals in different frequencies can provide an unprecedented window to the new physics beyond the SM. It is likely that the symmetry breaking patterns in new physics models are associated with non-trivial vacuum structure, which therefore leads to various topological defects [7][8][9][10][11][12][13]. The GWs from different topological defects during the early evolution of the Universe have been studied in many early literatures as well as recent ones, such as domain walls [14][15][16][17][18][19][20][21][22][23] and cosmic strings [3,14,15,[24][25][26][27][28][29][30][31][32].…”

Constraints on two Higgs doublet models from domain walls

“…It also admits CP domain walls [18,19] and membranes [20,21]. Topological strings are attatched by domain walls or membranes [22,23], resembling axion strings [24], axial strings in dense QCD [25] and topological Z-strings [26] in the Georgi-Machacek model [27]. When a string is attached by a single domain wall, such the domain wall can quantum mechanically decay by creating a hole bounded by the above mentioned string [8,28].…”