Infrared behavior of Closed Superstrings in Strong Magnetic and Gravitational Fields

TL;DR

Kiritsis and Kounnas construct a class of four-dimensional supersymmetric closed-string ground states with a mass gap and study their exact spectra under covariantly constant chromo-magnetic and gravitational backgrounds using marginal deformations of the worldsheet CFT. By replacing flat ${ m If R}^4$ with curved ${W_k}$ backgrounds and turning on magnetic and gravitational perturbations, they derive explicit background fields $(G,B, ext{Φ})$, reveal a maximal magnetic field $H_{ m max} o M_{ m Planck}^2/ ext{const}$ beyond which charged states decouple, and identify tachyonic instabilities at intermediate fields that are mitigated by backreaction as $H$ approaches $H_{ m max}$. The conformal-field-theory description yields modular-invariant partition functions with a doubling of the GSO projection, and the flat-space limit recovers a field-theory-like spectrum modified by gravity; overall, the work clarifies how stringy backreaction shapes the stability and spectrum of backgrounds with strong magnetic and gravitational fields, with potential implications for early-universe cosmology and vacuum selection in string theory.

Abstract

A large class of four-dimensional supersymmetric ground states of closed superstrings with a non-zero mass gap are constructed. For such ground states we turn on chromo-magnetic fields as well as curvature. The exact spectrum as function of the chromo-magnetic fields and curvature is derived. We examine the behavior of the spectrum, and find that there is a maximal value for the magnetic field $H_{\rm max}\sim M_{\rm planck}^2$. At this value all states that couple to the magnetic field become infinitely massive and decouple. We also find tachyonic instabilities for strong background fields of the order ${\cal O}(μM_{\rm planck})$ where $μ$ is the mass gap of the theory. Unlike the field theory case, we find that such ground states become stable again for magnetic fields of the order ${\cal O}(M^2_{\rm planck})$. The implications of these results are discussed.