Effective Field Theory of Infrared Gravity:
Emil Mottola (Los Alamos (USA))

General Relativity receives quantum corrections relevant at macroscopic distance scales and near event horizons. These arise from the conformal scalar degrees of freedom generated by the trace anomaly. I will review the role of anomalies and their importance for determining the low energy effective action in gauge theories and two dimensional gravity. The effective action for the trace anomaly in four dimensions is constructed and shown to lead to additional scalar degrees of freedom in low energy gravity not present in Einstein's general relativity. At event horizons the conformal anomaly scalar degrees of freedom can have macroscopically large effects on the geometry, potentially removing the classical event horizon of black hole and cosmological spacetimes, replacing them with a quantum boundary layer where the effective value of the gravitational vacuum energy density can change. In the effective theory, the cosmological term becomes a dynamical condensate, and a running coupling whose value depends upon boundary conditions near the horizon.
The observed dark energy of our universe likewise may be a macroscopic finite size effect whose value depends not on microphysics but on the cosmological horizon scale. This infrared renormalization effect could be studied by the methods of the Exact Renormalization Group.