  The present paper is the first in a series of papers, in which we shall
construct modular functors and Topological Quantum Field Theories from the
conformal field theory developed in [TUY].
  The basic idea is that the covariant constant sections of the sheaf of vacua
associated to a simple Lie algebra over Teichm\"uller space of an oriented
pointed surface gives the vectorspace the modular functor associates to the
oriented pointed surface. However the connection on the sheaf of vacua is only
projectively flat, so we need to find a suitable line bundle with a connection,
such that the tensor product of the two has a flat connection.
  We shall construct a line bundle with a connection on any family of pointed
curves with formal coordinates. By computing the curvature of this line bundle,
we conclude that we actually need a fractional power of this line bundle so as
to obtain a flat connection after tensoring. In order to functorially extract
this fractional power, we need to construct a preferred section of the line
bundle.
  We shall construct the line bundle by the use of the so-called $bc$-ghost
systems (Faddeev-Popov ghosts) first introduced in covariant quantization [FP].
We follow the ideas of [KNTY], but decribe it from the point of view of [TUY].
