-non-perturbative Four-Dimensional String Cosmology
نویسندگان
چکیده
Starting from an exact (in the Regge slope α ′ ) functional method for a bosonic stringy σ-model, we investigate four-dimensional cosmological string solutions in graviton, dilaton and antisymmetric tensor backgrounds, compatible with world-sheet conformal invariance, and valid beyond perturbative expansions in powers of α ′ . The antisymmetric tensor field, playing the rôle of an axion in the four-dimensional target space time, leads to spatial anisotropies of the emergent Robertson-Walker expanding Universe, and, upon coupling the system to the electromagnetic field, it results in non-trivial optical activity. Some estimates of the corresponding effects are made and their relevance to current cosmology is briefly discussed.
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