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arXiv · 1511.03129

The hemispherical asymmetry from a scale-dependent inflationary bispectrum

Christian T. Byrnes·Donough Regan·David Seery·Ewan R. M. Tarrant
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Abstract

If the primordial bispectrum is sufficiently large then the CMB hemispherical asymmetry may be explained by a large-scale mode of exceptional amplitude which perturbs the zeta two-point function. We extend previous calculations, which were restricted to one- or two-source scenarios, by providing a method to compute the response of the two-point function in any model yielding a 'local-like' bispectrum. In general, this shows that it is not the reduced bispectrum fNL which sources the amplitude and scale-dependence of the mode coupling but rather a combination of 'response functions'. We discuss why it is difficult to construct successful scenarios and enumerate the fine-tunings which seem to be required. Finally, we exhibit a concrete model which can be contrived to match the observational constraints and show that to a Planck-like experiment it would appear to have |fNL-local| ~ |fNL-equi| ~ |fNL-ortho| ~ 1. Therefore, contrary to previous analyses, we conclude that it is possible to generate the asymmetry while respecting observational constraints on the bispectrum and low-ell multipoles even without tuning our location on the long-wavelength mode.

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Christian T. Byrnes, Donough Regan, David Seery, Ewan R. M. Tarrant. 2016-06-24. The hemispherical asymmetry from a scale-dependent inflationary bispectrum. https://doi.org/10.1088/1475-7516%2F2016%2F06%2F025

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