Post-inflationary thermal histories and the refractive index of relic gravitons

Abstract

We investigate the impact of the post-inflationary thermal histories on the cosmic graviton spectrum caused by the inflationary variation of their refractive index. Depending on the frequency band, the spectral energy distribution can be mildly red, blue or even violet. Wide portions of the parameter space lead to potentially relevant signals both in the audio range (probed by the advanced generation of terrestrial interferometers) and in the mHz band (where space-borne detectors could be operational within the incoming score year). The description of the refractive index in conformally related frames is clarified.

36 pages, 9 figures

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• Inflation, the Hubble Tension and Early Dark Energy: an alternative overview
• Towards a reliable calculation of relic radiation from primordial gravitational waves
• Inflationary Potential as seen from Different Angles: Model Compatibility from Multiple CMB Missions
• Post-inflationary phases stiffer than radiation and Palatini formulation
• Tracking the Multifield Dynamics with Cosmological Data: A Monte Carlo approach
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• Polarized backgrounds of relic gravitons
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