  The Standard Model of the theory of elementary particles is based on the
$U(1)\times SU(2)\times SU(3)$ symmetry. In the presence of a gravitation
field, i. e. in a non-flat space-time manifold, this symmetry is implemented
through three special vector bundles. Connections associated with these vector
bundles are studied in this paper. In the Standard Model they are interpreted
as gauge fields.
