Form factors in the massless coset models su(2)k+1⊗su(2)k/su(2)2k+1

Massless flows between the coset model su(2)k+1⊗su(2)k/su(2)2k+1 and the minimal model Mk+2 are studied from the viewpoint of form factors. These flows include, in particular, the flow between the tricritical Ising model and the Ising model. Form factors of the trace operator with an arbitrary number of particles are constructed, and numerical checks on the central charge are performed with four-particle contribution. Large discrepancies with respect to the exact results are observed in most cases.