Comments on anomaly cancellations by pole subtractions and ghost instabilities with gravity

We investigate some aspects of anomaly cancellation realized by the subtraction of an anomaly pole, stressing on some of its properties in superspace. In a local formulation, these subtractions can be described in terms of a physical scalar, an axion and related ghosts. The subtraction of these anomaly poles appears necessary for the unitarization of the theory in the ultraviolet, but it may generate an infrared instability of the corresponding effective action, signalled by ghost condensation. In particular, the significance of the subtraction of the superanomaly multiplet by a pole in superspace is dubious, due to the different nature of the chiral and conformal anomalies. In turn, this may set more stringent constraints on the coupling of supersymmetric theories to gravity.