Notes on Obstructions in the Hyperbolic Clifford Algebra Bundle Structure

Starting from a general analysis of obstruction classes, we develop the investigation of obstructions associated with the bundle structure of the hyperbolic Clifford algebra. By taking into account particularities arising from the Whitney sum, it is shown that, unlike classical tangent bundle cases, the hyperbolic frame bundle of an oriented manifold admits lifting without any topological obstruction; that is, it admits a structure of the connected double covering of GL+(2m,R), and the hyperbolic tangent bundle carries a Spinm,me structure (with m=dimM), whatever the value of w2(M). These conclusions are known from the work of Karoubi and Gualtieri, and the point of this note is that they follow from the Whitney product formula alone, or from the additivity formula of Whitney sums with an explicit covering group, without recourse to Karoubi’s criterion for indefinite signature. We also describe the spinor bundles involved, which are bundles of differential forms and not Dirac spinor bundles, and we show that orientability is needed for the covering of the full linear group.