The duality of quantum Liouville field theory

It has been found empirically that the Virasoro center and three-point functions of quantum Liouville field theory with the potential exp(2bϕ(x)) and the external primary fields exp(αϕ(x)) are invariant with respect to the duality transformations ℏα→q−α, where q=b−1+b. The steps leading to this result (via the Virasoro algebra and three-point functions) are reviewed in the path-integral formalism. The duality occurs because the quantum relationship between the α and the conformal weights Δα is two-to-one. As a result, the quantum Liouville potential can actually contain two exponentials (with related parameters). In the two-exponential theory, the duality appears naturally, and an important previously conjectured extrapolation can be proved.