Cheeger-Chern-Simons theory and differential String classes

Abstract

We introduce certain relative differential characters which we call Cheeger-Chern-Simons characters. These combine the well-known Cheeger-Simons characters with Chern-Simons forms. In the same way as the Cheeger-Simons characters generalize Chern-Simons invariants of oriented closed manifolds, the Cheeger-Chern-Simons characters generalize Chern-Simons invariants of oriented manifolds with boundary. Using Cheeger-Chern-Simons characters, we introduce the notion of differential trivializations of universal characteristic classes. Specializing to the class 1/2 $p_1\in H^4(B{\mathrm{Spin}}_n;\mathbb{Z})$ this yields a notion of differential String classes. Differential String classes turn out to be stable isomorphism classes of geometric String structures.

v3: enlarged version; references added