Abstract

We study the axion strings with the electroweak gauge flux in the DFSZ axion model and show that these strings, called the electroweak axion strings, can exhibit superconductivity without fermionic zeromodes. We construct three types of electroweak axion string solutions. Among them, the string with W-flux can be lightest in some parameter space, which leads to a stable superconducting cosmic string. We also show that a large electric current can flow along the string due to the Peccei-Quinn scale much higher than the electroweak scale. This large current induces a net attractive force between the axion strings with the same topological charge, which opens a novel possibility that the axion strings form Y-junctions in the early universe.

Highlights

  • A domain wall at the QCD phase transition

  • We study the axion strings with the electroweak gauge flux in the DFSZ axion model and show that these strings, called the electroweak axion strings, can exhibit superconductivity without fermionic zeromodes

  • We show that a large electric current can flow along the string due to the Peccei-Quinn scale much higher than the electroweak scale

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Summary

DFSZ axion model

The particle contents and the charge assignments under the SM gauge group and the U(1)PQ are shown in table 1. In order for Vmix to be invariant under the U(1)PQ symmetry, the U(1)PQ charges in table 1 should satisfy the relation 2Xs − X1 + X2 = 0. If m22 = α3 = α4 = 0, and κ1S = κ2S, the scalar potential is invariant under the custodial transformation This symmetry makes the two VEVs be equal, tan β = 1. The gauge bosons and scalars become massive due to the above VEVs. The masses of the weak gauge bosons are given by mW gvEW , 2. One of the massless eigenvector is (cos β, sin β, 0) which corresponds to the longitudinal mode of the Z boson Another zero eigenvector is given by (X1v1, X2v2, Xsvs) as long as 2Xs−X1+X2 = 0 is satisfied.

Electroweak axion strings
Axion string in DFSZ model
Type-B string with Z-flux
Type-C string with W -flux
String tensions
Superconducting DFSZ string
Zero modes along the string
Current quenching and string interaction
Y-junction formation
Conclusion
A Derivation of the linearized EOMs

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