Observing the big bounce with tensor modes in the cosmic microwave background: Phenomenology and fundamental loop quantum cosmology parameters

Cosmological models where the standard big bang is replaced by a bounce have been studied for decades. The situation has, however, dramatically changed in the past years for two reasons: first, because new ways to probe the early Universe have emerged, in particular, thanks to the cosmic microwave background, and second, because some well grounded theories-especially loop quantum cosmology-unambiguously predict a bounce, at least for homogeneous models. In this article, we investigate into the details the phenomenological parameters that could be constrained or measured by next-generation B-mode cosmic microwave background experiments. We point out that an important observational window could be opened. We then show that those constraints can be converted into very meaningful limits on the fundamental loop quantum cosmology parameters. This establishes the early Universe as an invaluable quantum gravity laboratory.