Conformal anomaly free CGHS model
The Russo–Susskind–Thorlacius model[1] or RST model in short is a modification of the CGHS model to take care of conformal anomalies and render it analytically soluble. In the CGHS model, if we include Faddeev–Popov ghosts to gauge-fix diffeomorphisms in the conformal gauge, they contribute an anomaly of -24. Each matter field contributes an anomaly of 1. So, unless N=24, we will have gravitational anomalies.
To the CGHS action
- , the following term
is added, where κ is either or depending upon whether ghosts are considered. The nonlocal term leads to nonlocality.
In the conformal gauge,
- .
It might appear as if the theory is local in the conformal gauge, but this overlooks the fact that the Raychaudhuri equations are still nonlocal.