Macroscopic Effects of Quantum Anomalies and the Effective Field Theory of Gravity

Abstract: Quantum anomalies arise when two invariances of classical physics turn out to be incompatible in quantum theory. Originally discovered in perturbation theory by methods devised to control and remove UV divergences in QED, it eventually became clear that this incompatibility is fundamental, in fact of infrared origin, and independent of UV physics. For this reason anomalies can affect low energy processes in Effective Field Theory (EFT), even non-perturbatively. Reviewing first the infrared origin of the chiral anomaly of QED and QCD, I will discuss the extension to the conformal anomaly in curved spacetime, and the Wess-Zumino (WZ) action of the conformal anomaly. This WZ action and EFT describes a Nambu-Goldstone (NG) boson of broken conformal invariance, a new long range massless scalar degree of freedom in gravity, in addition to the metric degrees of freedom of classical general relativity. The NG scalar has consequences for macroscopic gravity both in the vicinity of black hole event horizons and final state, and for cosmological dark energy, where it allows the effective value of vacuum energy to change in space and time, also predicting the existence of scalar gravitational waves, which can be tested in forthcoming observations.