TT Deformation of Quantum Field Theories

We review the basic properties of the TT deformation for general Quantum Field Theories. In particular we focus on the results by Zamolodchikov on the deformed energy spectrum and those of Cardy on the geometrical interpretation of the deformation via an Hubbard-Stratonovich transformation.

We finally try to clarify in which sense, if the undeformed theory was integrable, the deformed theory remains solvable.