Cosmological meaning of the gravitational gauge group

It is shown that among the (R+beta S^{abc}S_{abc}) models, only the one with (beta =1/2) has nonvanishing torsion effect in the Robertson–Walker universe filled with a spin fluid, where (S_{abc}) denotes torsion. Moreover, the torsion effect in that model is found to be able to replace the big-bang singularity by a big bounce. Furthermore, we find that the model can be obtained under a Kaluza–Klein-like ansatz, by assuming that the gravitational gauge group is the de Sitter group.