Generalised chiral null models and rotating string backgrounds

TL;DR

The paper extends conformal chiral null models to include simultaneous left and right couplings, probing non-BPS rotating string backgrounds. By constructing a generalised CNM and analyzing both flat and curved transverse sectors in six dimensions, it shows that two independent rotation parameters generally preclude asymptotically flat, non-singular backgrounds; the regular short-distance limit becomes a twisted $SL(2,\mathbb{R}) \times SU(2)$ WZW throat. The results reveal that only non-asymptotically flat, two-parameter rotating solutions exist in the generic case, with a supersymmetric or quantised-twist regime recovered under special conditions. This work connects exact string theory constructions of rotating backgrounds to WZW CFT descriptions and potential D-brane interpretations, highlighting fundamental constraints on smoothness and asymptotics for non-BPS solutions.

Abstract

We consider an extension of a special class of conformal sigma models (`chiral null models') which describe extreme supersymmetric string solutions. The new models contain both `left' and `right' vector couplings and should correspond to non-BPS backgrounds. In particular, we discuss a conformal six-dimensional model which is a combination of fundamental string and 5-brane models with two extra couplings representing rotations in orthogonal planes. If the two rotational parameters are independent the resulting background is found to be either singular or not asymptotically flat. The non asymptotically flat solution has a regular short distance limit described by a `twisted' product of SL(2,R) and SU(2) WZW theories with two twist parameters mixing the isometric Euler angles of SU(2) with a null direction of SL(2,R).