DISPERSIVE DERIVATION OF THE TRACE ANOMALY

We present a simple derivation of the one-loop trace anomaly in spinor QED through dispersion relations, avoiding completely any ultraviolet regularization. The anomaly can be expressed as a convergent sum rule for the imaginary part of a relevant formfactor. In the massless limi t, the imaginary part produces a delta-function singularity at zero ex ternal momentum squared. Such a treatment reveals an ''infrared face'' of the trace anomaly, in striking similarity with the well-known case of the axial anomaly.