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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.

**^**Russo, Jorge; Susskind, Leonard; Thorlacius, Lárus (15 Oct 1992). "The Endpoint of Hawking Evaporation".*Physical Review*. D.**46**(8): 3444–3449. arXiv:hep-th/9206070. Bibcode:1992PhRvD..46.3444R. doi:10.1103/PhysRevD.46.3444. PMID 10015289. S2CID 184623.