= Infrared regularization
An infrared regulator suppresses the small-<momentum> region responsible for an <infrared divergence>. Examples are a small positive <mass> or a finite volume. It must be distinguished from an <ultraviolet cutoff>: setting external <momenta> and <masses> to zero to extract an <ultraviolet divergence> can introduce a spurious <infrared divergence>. Keep a positive auxiliary <mass> until the divergent local coefficients have been separated, then take the desired limit in infrared-safe quantities.
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