| dc.description.abstract | Measurement of anisotropies in the cosmic microwave background (CMB) can give a wealth of information about the period of inflation that is assumed to have occurred in the early universe. The perturbations that cause these anisotropies are predominantly Gaussian, but there is the freedom for small non-Gaussianity, which is directly represented in the bispectrum (three-point function) of the perturbations. The non-Gaussianities can encode information on the underlying theory of inflation, but measuring these is hard, so theoretical work on the shape of the bispectrum is required. We will discuss how the bispectrum is typically calculated in single-field scalar models using slow-roll approximations. We calculate for the canonical scalar field model the contribution of an interaction term at next-to-leading order,
not coming from coupling to gravity but from self-coupling. This term is proportional to $\epsilon\dot\eta$, using Hubble slow-roll parameters. We find that the contribution diverges and needs to be compensated by a boundary term in time that is commonly ignored in literature and we conclude that the slow-roll combination $\epsilon\dot\eta$ is not present in the bispectrum. | |
