Byrnes, Christian T, Regan, Donough, Seery, David and Tarrant, Ewan R M (2016) The hemispherical asymmetry from a scale-dependent inflationary bispectrum. Journal of Cosmology and Astroparticle Physics, 2016 (06). 025. ISSN 1475-7516

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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.

Item Type:	Article
Schools and Departments:	School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects:	Q Science > QB Astronomy > QB0980 Cosmogony. Cosmology
Depositing User:	David Seery
Date Deposited:	13 Jun 2016 06:01
Last Modified:	11 Jun 2017 22:58
URI:	http://sro.sussex.ac.uk/id/eprint/61311

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