Potting, Robertus (2012), "Kallen-Lehmann representation for Lorentz-violating field theory", PHYSICAL REVIEW D, 85, 4.
Abstract: We consider field-theoretic models, one consisting purely of scalars,
the other also involving fermions, that couple to a set of constant
background coupling coefficients transforming as a symmetric observer
Lorentz two-tensor. We show that the exact propagators can be cast in
the form of a Kallen-Lehmann representation. We work out the resulting
form of the Feynman propagators and the equal-time field commutators,
and derive sum rules for the spectral density functions.
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