Almost-Goldstone Bosons from Extra-Dimensional Gauge Theories

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Abstract
A mechanism is presented through which very light scalar degrees of freedom obeying the nonlinear sigma model equation can emerge in spontaneously broken gauge theories. The mechanism operates in extra-dimensional theories in which (a) there are massless gauge fields present in the theory prior to compactification, and (b) the extra dimensions are inhomogeneous in such a way that symmetry breaking Higgs fields acquire vacuum expectation values only at very localized points on the manifold. These conditions are naturally fulfilled in orbifold compactifications of string theory. Possible applications include cosmic texture, axions, and family symmetry.