  We propose an algebraic Riemann-Roch formula for moving flat bundles on
contant families in characteristic zero with values in the ring of algebraic
differential characters. This formula lifts Grothendieck-Riemann-Roch formula
in the Chow groups and Bismut-Lott formula in the odd dimensional Betti
cohomology with $\C/\Z$ coefficients over the field of complex numbers.
