Anomaly flow by an Aharonov-Bohm phase

TL;DR

This paper investigates how an Aharonov-Bohm phase in gauge-Higgs unification causes continuous transformation of chiral fermions into vectorlike fermions and affects gauge anomalies in flat and warped extra-dimensional spaces.

Contribution

It demonstrates the smooth variation of chiral anomalies with the AB phase in RS space and clarifies the behavior in the flat spacetime limit, revealing novel anomaly phenomena.

Findings

Chiral fermions become massive at $ heta_H = \pi$

Anomalies vary smoothly with $ heta_H$ in RS space

Anomalies depend on warp factor but not on bulk mass parameter

Abstract

In gauge-Higgs unification (GHU), gauge symmetry is dynamically broken by an Aharonov-Bohm (AB) phase, $\theta_H$, in the fifth dimension. We analyze $SU(2)$ GHU with an $SU(2)$ doublet fermion in flat $M^4 \times (S^1/Z_2)$ spacetime and in the Randall-Sundrum (RS) warped space. With orbifold boundary conditions the $U(1)$ part of gauge symmetry remains unbroken at $\theta_H = 0$ and $\pi$. The fermion multiplet has chiral zero modes at $\theta_H = 0$, which become massive at $\theta_H = \pi$. In other words chiral fermions are transformed to vectorlike fermions by the AB phase $\theta_H$. Chiral anomaly at $\theta_H = 0$ continuously varies as $\theta_H$ and vanishes at $\theta_H=\pi$. We demonstrate this intriguing phenomenon in the RS space in which there occurs no level crossing in the mass spectrum and everything varies smoothly. The flat spacetime limit is singular as the AdS curvature of the RS space diminishes, and reproduces the result in the flat spacetime. Anomalies appear for various combinations of Kaluza-Klein excitation modes of gauge fields as well. Although the magnitude of anomalies depends on $\theta_{H}$ and the warp factor of the RS space, it does not depend on the bulk mass parameter of the fermion field controlling its mass and wave function at general $\theta_H$.