Form factors of the tricritical three-state Potts model in its scaling limit

We compute the form factors of the order and disorder operators, together with those of the stress-energy tensor, of a two-dimensional three-state Potts model with vacancies along its thermal deformation at the critical point. At criticality, the model is described by the non-diagonal partition function of the unitary minimal model M6,7 of conformal field theories and is accompanied by an internal S 3 symmetry. The off-critical thermal deformation is an integrable massive theory that is still invariant under S 3. The presence of infinitely many conserved quantities, whose spin spectrum is related to the exceptional Lie algebra E 6, allows us to determine the analytic S-matrix, the exact mass spectrum and the matrix elements of local operators of this model in an exact non-perturbative way. We use the spectral representation series of the correlators and the fast convergence of these series to compute several universal ratios of the renormalization group.