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arXiv · 1809.01159

Reheating and Dark Radiation after Fibre Inflation

Michele Cicoli·Gabriel A. Piovano
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Abstract

We study perturbative reheating at the end of fibre inflation where the inflaton is a closed string modulus with a Starobinsky-like potential. We first derive the spectral index $n_s$ and the tensor-to-scalar ratio $r$ as a function of the number of efoldings and the parameter $R$ which controls slow-roll breaking corrections. We then compute the inflaton couplings and decay rates into ultra-light bulk axions and visible sector fields on D7-branes wrapping the inflaton divisor. This leads to a reheating temperature of order $10^{10}$ GeV which requires $52$ efoldings. Ultra-light axions contribute to dark radiation even if $ΔN_{\rm eff}$ is almost negligible in the generic case where the visible sector D7-stack supports a non-zero gauge flux. If the parameter $R$ is chosen to be small enough, $n_s\simeq 0.965$ is then in perfect agreement with current observations while $r$ turns out to be of order $r\simeq 0.007$. If instead the flux on the inflaton divisor is turned off, $ΔN_{\rm eff}\lesssim 0.6$ which, when used as a prior for Planck data, requires $n_s\simeq 0.99$. After $R$ is fixed to obtain such a value of $n_s$, primordial gravity waves are larger since $r\simeq 0.01$.

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Michele Cicoli, Gabriel A. Piovano. 2019-03-25. Reheating and Dark Radiation after Fibre Inflation. https://doi.org/10.1088/1475-7516%2F2019%2F02%2F048

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