  Starting from an abelian rigid braided monoidal category C we define an
abelian rigid monoidal category C_F which captures some aspects of perturbed
conformal defects in two-dimensional conformal field theory. Namely, for V a
rational vertex operator algebra we consider the charge-conjugation CFT
constructed from V (the Cardy case). Then C = Rep(V) and an object in C_F
corresponds to a conformal defect condition together with a direction of
perturbation. We assign to each object in C_F an operator on the space of
states of the CFT, the perturbed defect operator, and show that the assignment
factors through the Grothendieck ring of C_F. This allows one to find
functional relations between perturbed defect operators. Such relations are
interesting because they contain information about the integrable structure of
the CFT.
