Abstract
We examine the possibility that the strong problem is solved by string-theoretic axions in the strong-coupling limit of the heterotic string theory theory). We first discuss some generic features of gauge kinetic functions in compactified theory, and examine in detail the axion potential induced by the explicit breakings other than the QCD anomaly of the nonlinear symmetries of string-theoretic axions. It is argued based on supersymmetry and discrete gauge symmetries that if the compactification radius is large enough, there can be a symmetry whose breaking other than the QCD anomaly, whatever its microscopic origin is, is suppressed enough for the axion mechanism to work. Phenomenological viability of such a large radius crucially depends upon the quantized coefficients in gauge kinetic functions. We note that the large radius required for the axion mechanism is viable only in a limited class of models. For instance, for compactifications on a smooth Calabi-Yau manifold with a vanishing field strength, it is viable only when the quantized flux of the antisymmetric tensor field in theory has a minimal nonzero value. It is also stressed that this large compactification radius allows the QCD axion in theory to be cosmologically viable in the presence of a late time entropy production.
- Received 26 June 1997
DOI:https://doi.org/10.1103/PhysRevD.56.6588
©1997 American Physical Society