By studying NIM-representations we show that the Fibonacci category and its
tensor powers are completely anisotropic; that is, they do not have any
non-trivial separable commutative ribbon algebras. As an application we deduce
that a chiral algebra with the representation category equivalent to a product
of Fibonacci categories is maximal; that is, it is not a proper subalgebra of
another chiral algebra. In particular the chiral algebras of the Yang-Lee
model, the WZW models of G2 and F4 at level 1, as well as their tensor powers,
are maximal.
We give a characterization of Drinfeld centers of fusion categories as
non-degenerate braided fusion categories containing a Lagrangian algebra.
Further we study the quotient of the monoid of non-degenerate braided fusion
categories modulo the submonoid of the Drinfeld centers and show that its
formal properties are similar to those of the classical Witt group.
We apply the full centre construction, defined in arXiv:0908.1250, to
algebras in and module categories over categories of representations of Hopf
algebras. We obtain a compact formula for the full centre of a module algebra
over a Hopf algebra.