Heterotic strings in a uniform magnetic field

TL;DR

This paper presents an exact conformal model of heterotic strings in a uniform magnetic field, revealing that even small magnetic fields induce infinite tachyonic excitations, affecting the string spectrum.

Contribution

It provides an explicit solution for heterotic strings in a magnetic background and analyzes the resulting spectrum for various embeddings of the magnetic U(1) subgroup.

Findings

Small magnetic fields cause infinite tachyonic excitations.

Charged vector states become tachyonic at the massless level.

Higher spin and charge states are also affected by the magnetic field.

Abstract

An exact conformal model representing a constant magnetic field background in heterotic string theory is explicitly solved in terms of free creation/annihilation operators. The spectrum of physical states is examined for different possible embeddings of the magnetic U(1) subgroup. We find that an arbitrarily small magnetic field gives rise to an infinite number of tachyonic excitations corresponding to charged vector states of the massless level and to higher level states with large spins and charges.