Stable charged cosmic strings

TL;DR

This paper demonstrates that in a simplified standard model, charged cosmic strings can be stabilized by heavy fermions without requiring extremely large fermion masses, with the most stable configuration being a narrow Higgs vev trough.

Contribution

It shows that stable charged cosmic strings can form with fermion masses less than twice the top quark mass, challenging previous assumptions about the need for very heavy fermions.

Findings

Charged strings become stable with fermions less than twice the top quark mass.

The most favorable string profile is a narrow Higgs vev trough of about 10^{-18} meters.

Neutral strings are not energetically favored, ensuring vacuum stability.

Abstract

We study the quantum stabilization of a cosmic string by a heavy fermion doublet in a reduced version of the standard model. We show that charged strings, obtained by populating fermionic bound state levels, become stable if the electro--weak bosons are coupled to a fermion that is less than twice as heavy as the top quark. This result suggests that extraordinarily large fermion masses or unrealistic couplings are not required to bind a cosmic string in the standard model. Numerically we find the most favorable string profile to be a simple "trough" in the Higgs vev of radius $\approx 10^{-18}\,\mathrm{m}$. The vacuum remains stable in our model, because neutral strings are not energetically favored.