Direct image for multiplicative and relative $K$-theories from transgression of the families index theorem, part 2

Abstract

This is the sequel of the first part math.DG/0611281. Here, the procedure of transgressing the families index theorem (the so-called $η$-form) is adapted to take in account the case of Dirac type operators with kernels of varying dimension. The constructed form is then used to define the direct image under proper submersions of the ``free multiplicative'' $K$-theory which was defined in the first part, the behaviour of the characteristic classes on free multiplicative $K$-theory under submersion is studied. Some universal caracterisation of the forms is provided. Finally, combining our result with Bismut and Lott's results on direct images of flat vector bundles yields a ``Grothendieck-Riemann-Roch'' theorem for Nadel-Chern-Simons classes on relative $K$-theory for flat vector bundles which was defined in the first part.