Direct CP asymmetry of b -> s gamma and b -> d gamma in models beyond the Standard Model

We study the direct CP asymmetry of the decays b -> s gamma and b -> d gamma in the context of two models: i) a supersymmetric (SUSY) model with unconstrained SUSY phases, and ii) a model with a single generation of vector quarks. In both the above models we show that b -> d gamma can sizeably influence the combined asymmetry (i.e. that of a sample containing both b -> s gamma and b -> d gamma), and in case (ii) may in fact be the dominant contribution.