About a class of exact string backgrounds

TL;DR

This paper explores exact string backgrounds, specifically the chiral null model, and examines their properties under dualities, including special solutions like Taub-NUT and black holes, revealing massless states and duality symmetries.

Contribution

It analyzes the chiral null model as an exact string background and investigates its duality properties, including S-duality and T-self-duality, with specific focus on Taub-NUT and black hole solutions.

Findings

Identification of massless black hole states at the T-self-dual point

Demonstration of S-self-dual points in Taub-NUT geometry

Correlation of H-monopoles with N_L=1 string states

Abstract

This model also known as chiral null model is a generalization of the gravitational wave and fundamental string background and is exact in the $\a'$ expansion. The reduction to 4 dimensions yields a stationary IWP solution which couples to 7 gauge fields (one gravi-photon and 6 matter gauge fields) and 4 scalars. Special cases are the Taub-NUT geometry and rotating black holes. These solutions possess a T-self-dual point where the black hole becomes massless. Discussing the S-duality we show that the Taub-NUT geometry allows an S-self-dual point and that the electric black hole corresponds to a magnetic black hole or an H-monopole. We could identify the massless black hole as $N_L=0$ and confirm the H-monopole as an $N_L=1$ string states.