Observable non-gaussianity from gauge field production in slow roll inflation, and a challenging connection with magnetogenesis

By N. Barnaby, R. Namba, Marco Peloso. 2012

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In any realistic particle physics model of inflation, the inflaton can be expected to couple to other fields. We consider a model with a dilaton-like coupling between a U(1) gauge field and a scalar inflaton. We show that this coupling can result in observable non-gaussianity, even in the conventional regime where inflation is supported by a single scalar slowly rolling on a smooth potential: the time dependent inflaton condensate leads to amplification of the large-scale gauge field fluctuations, which can feed-back into the scalar/tensor cosmological perturbations. In the squeezed limit, the resulting bispectrum is close to the local one, but it shows a sizable and characteristic quadrupolar dependence on the angle between the shorter and the larger modes in the correlation. Observable non-gaussianity is obtained in a regime where perturbation theory is under control. If the gauge field is identified with the electromagnetic field, the model that we study is a realization of the magnetogenesis idea originally proposed by Ratra, and widely studied. This identification (which is not necessary for the non-gaussianity production) is however problematic in light of a strong coupling problem already noted in the literature. PACS numbers:

Subfields: Astronomy and Astrophysics, Oceanography

View Paper: https://www.semanticscholar.org/paper/2aaee6e3dc55de007bca9d5c4c204f53275c7180

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Citations in the corpus

Planck 2018 results. IX. Constraints on primordial non-Gaussianity (2019, background): “…term I2(ϕ)F2, where Fµν = ∂µAν − ∂νAµ and the coupling I2(ϕ)F2 can allow for scale invariant vector fluctuations to be generated on superhorizon scales (Barnaby et al. 2012; Bartolo et al. 2013a).4 Primordial magnetic fields sourcing curvature perturbations can also generate a…”
Magnetogenesis from axion inflation (2016, background): “It is generally very hard to produce the required amplitude of seed magnetic fields in the context of the Ratra model without producing significant non-Gaussianities in the cosmic microwave background, or suffering from the strong coupling problem [38].”
Gauge fields and inflation (2012, background): “Another possibility for generating sizable non-Gaussianity from gauge fields discussed in the literature is through the gauge kinetic term [80, 81].”
Planck 2015 results. XVII. Constraints on primordial non-Gaussianity (2015, unknown): “Recently, the possibility of observable tensor bispectra has been vigorously discussed in a model where the inflaton couples to a pseudoscalar field (Barnaby et al. 2012a; Cook & Sorbo 2013; Ferreira & Sloth 2014).”