Gravitational anomaly

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Anomalies in the usual 4 spacetime dimensions arise from triangle Feynman diagrams

In theoretical physics, a gravitational anomaly is an example of an anomaly: it is an effect of quantum mechanics - usually a one-loop diagram - that invalidates the general covariance of a theory of general relativity combined with some other fields. The adjective "gravitational" is derived from the symmetry of a gravitational theory, namely from general covariance.

The anomaly usually appears as a Feynman diagram with a chiral fermion running in the loop (a polygon) with n external gravitons attached to the loop where $n = 1 + D / 2$ where $D$ is the spacetime dimension. Anomalies occur only in even spacetime dimensions. General covariance is a very important symmetry for the consistency of the whole theory, and therefore all gravitational anomalies must cancel out.

[edit] See also

For a different concept in geodesy and geophysics, dealing with differences between observed values of gravity and theoretical values for that location, see gravity anomaly.