Cosmic Strings Stabilized by Fermion Fluctuations

TL;DR

This paper explores how quantum effects from heavy fermions can stabilize cosmic strings within a simplified standard model framework, showing that realistic fermion masses can lead to stable string configurations.

Contribution

It demonstrates that fermion quantum fluctuations can stabilize cosmic strings without requiring unrealistically large fermion masses or couplings.

Findings

Fermion zero-point fluctuations contribute to string stabilization.

Strings with fermion charge can be stable if coupled to a sufficiently heavy fermion.

Neutral strings are energetically disfavored, ensuring vacuum stability.

Abstract

We provide a thorough exposition of recent results on the quantum stabilization of cosmic strings. Stabilization occurs through the coupling to a heavy fermion doublet in a reduced version of the standard model. The study combines the vacuum polarization energy of fermion zero-point fluctuations and the binding energy of occupied energy levels, which are of the same order in a semi-classical expansion. Populating these bound states assigns a charge to the string. Strings carrying fermion charge become stable if the Higgs and gauge fields are coupled to a fermion that is less than twice as heavy as the top quark. The vacuum remains stable in the model, because neutral strings are not energetically favored. These findings suggest that extraordinarily large fermion masses or unrealistic couplings are not required to bind a cosmic string in the standard model.