  We give a new proof of the Jantzen sum formula for integral representations
of Chevalley schemes over Spec Z. This is done by applying the fixed point
formula of Lefschetz type in Arakelov geometry to generalized flag varieties.
Our proof involves the computation of the equivariant Ray-Singer torsion for
all equivariant bundles over complex homogeneous spaces. Furthermore, we find
several explicit formulae for the global height of any generalized flag
variety.
