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Asymptotic Infrared Fractal Structure of the Propagator for a Charged Fermion
It is well known that the long-range nature of the Coulomb interaction makes
the definition of asymptotic ``in'' and ``out'' states of charged particles
problematic in quantum field theory. In particular, the notion of a simple
particle pole in the vacuum charged particle propagator is untenable and should
be replaced by a more complicated branch cut structure describing an electron
interacting with a possibly infinite number of soft photons. Previous work
suggests a Dirac propagator raised to a fractional power dependent upon the
fine structure constant, however the exponent has not been calculated in a
unique gauge invariant manner. It has even been suggested that the fractal
``anomalous dimension'' can be removed by a gauge transformation. Here, a gauge
invariant non-perturbative calculation will be discussed yielding an
unambiguous fractional exponent. The closely analogous case of soft graviton
exponents is also briefly explored.Comment: Updated with a corrected sign error, longer discussion of fractal
dimension, and more reference