Singular BPS Saturated States and Enhanced Symmetries of Four-Dimensional N=4 Supersymmetric String Vacua

TL;DR

This paper investigates special BPS saturated solutions in four-dimensional N=4 string vacua that become massless at certain moduli points, potentially leading to gauge and supersymmetry enhancements, with a focus on singular dyonic configurations.

Contribution

It characterizes singular BPS solutions in N=4 string vacua and explores their role in gauge and supersymmetry enhancement at special moduli points.

Findings

Massless states occur at specific moduli points.

Purely electric/magnetic solutions preserve half supersymmetry.

Dyonic solutions can enhance local supersymmetry.

Abstract

A class of supersymmetric (BPS saturated), static, spherically symmetric solutions of four-dimensional effective N=4 supersymmetric superstring vacua, which become massless at special points of moduli space, is studied in terms of the fields of the effective heterotic string theory compactified on a six-torus. Those are singular four-dimensional solutions corresponding to $O(6,22,Z)$ orbits of dyonic configurations (with zero axion), whose left-moving as well as right-moving electric and magnetic charges are orthogonal (light-like in the $O(6,22,Z)$ sense), while the $O(6,22,Z)$ norms of both the electric and magnetic charges are negative. Purely electric [or purely magnetic] and dyonic configurations preserve $1\over 2$ and $1\over 4$ of N=4 supersymmetry, respectively, thus belonging to the vector and the highest spin $3\over 2$ supermultiplets, respectively. Purely electric [or purely magnetic] solutions (along with an infinite tower of $SL(2,Z)$ transformed states) become massless at a point of the corresponding ``one-torus'', thus may contribute to the enhancement of non-Abelian gauge symmetry, while dyonic solutions become simultaneously massless at a point of the corresponding two-torus, and thus may in addition contribute to the enhancement of the local supersymmetry there.