Induced fermionic current by a magnetic tube in the cosmic spacetime

TL;DR

This paper investigates how a magnetic flux confined in a cylindrical tube around a cosmic string induces fermionic currents in the surrounding spacetime, analyzing three magnetic field configurations and their effects on vacuum currents.

Contribution

It provides explicit wave-functions and analyzes the induced vacuum fermionic currents for three magnetic field configurations around a cosmic string, highlighting core-induced effects.

Findings

Induced currents are azimuthal and decomposed into zero-thickness and core-induced parts.

Core-induced contributions depend on total magnetic flux and are generally non-periodic.

Zero-thickness flux contribution depends only on the fractional part of the flux ratio.

Abstract

In this paper, we consider a charged massive fermionic quantum field in the space-time of an idealized cosmic string, in the presence of a magnetic field confined in a cylindrical tube of finite radius. Three distinct configurations for the magnetic field is taken into account: (i) a cylindrical shell of radius $a$, (ii) a magnetic field proportional to $1/r$ and (iii) a constant magnetic field. In these three cases, the axis of the infinitely long tube of radius $a$ coincides with the cosmic string. Our main objective is to analyze the induced vacuum fermionic current densities outside the tube. In order to do that, we explicitly construct the wave-functions inside and outside the tube for each case. Having the complete set of normalized wave-functions, we use the summation method to develop our analysis. We show that in the region outside the tube, the induced currents are decomposed into a parts corresponding to a zero-thickness magnetic flux in addition to a core-induced contributions. The latter presents specific form depending on the magnetic field configuration considered. We also see that the only non-vanishing component of fermionic current corresponds to the azimuthal one. The zero-thickness contribution depends only on the fractional part of the ration of the magnetic flux inside the tube by the quantum one. As to the core-induced contribution, it depends on the total magnetic flux inside the tube, and consequently, in general, it is not a periodic function of the flux.