Transgression forms and extensions of Chern-Simons gauge theories

A gauge invariant action principle, based on the idea of transgression forms,is proposed. The action extends the Chern-Simons form by the addition of aboundary term that makes the action gauge invariant (and not justquasi-invariant). Interpreting the spacetime manifold as cobordant to anotherone, the duplication of gauge fields in spacetime is avoided. The advantages ofthis approach are particularly noticeable for the gravitation theory describedby a Chern-Simons lagrangian for the AdS group, in which case the action isregularized and finite for black hole geometries in diverse situations. Blackhole thermodynamics is correctly reproduced using either a background fieldapproach or a background-independent setting, even in cases with asymptoticallynontrivial topologies. It is shown that the energy found from the thermodynamicanalysis agrees with the surface integral obtained by direct application ofNoether's theorem.Comment: 28 pages, no figures. Minor changes in the introduction, final comments and reference