Description
I will introduce the real determinant line bundle which characterizes the Weyl anomaly as a real-valued one-dimensional modular functor over the genus 0 moduli space of Riemann surfaces with analytically parametrized boundaries.
A universal property of such modular functors is obtained by studying the corresponding central extensions of the group of analytical circle diffeomorphisms. In particular, a cocycle using rotation numbers does not appear and hence the central extension is the Virasoro-Bott group or trivial.
