Kantowski-Sachs String Cosmologies
John D. Barrow, Mariusz P. Dabrowski

TL;DR
This paper derives new exact solutions for string cosmologies with Kantowski-Sachs geometry, involving non-zero dilaton and axion fields, highlighting anisotropic models with space-dependent axion fields that do not isotropize.
Contribution
It introduces novel exact solutions to string equations with non-zero dilaton and axion fields in Kantowski-Sachs backgrounds, including cases with space-dependent axion fields.
Findings
Solutions include time-dependent dilaton and axion fields.
Space-dependent axion fields lead to anisotropic models.
Models do not isotropize due to distinguished spatial directions.
Abstract
We present new exact solutions of the low-energy-effective-action string equations with both dilaton and axion fields non-zero. The background universe is of Kantowski-Sachs type. We consider the possibility of a pseudoscalar axion field () that can be either time or space dependent. The case of time-dependent reduces to that of a stiff perfect-fluid cosmology. For space-dependent there is just one non-zero time-space-space component of the axion field , and this corresponds to a distinguished direction in space which prevents the models from isotropising. Also, in the latter case, both the axion field and its tensor potential () are dependent on time and space yet the energy-momentum tensor remains time-dependent as required by the homogeneity of the cosmological model.
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