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.
Highlights
Stochastic backgrounds of cosmological origin have been suggested more than forty years ago [1,2,3] as a genuine general relativistic effect in curved space-times
The backgrounds of cosmic gravitons are analyzed in terms of the spectral energy distribution in critical units, conventionally denoted by Ωgwðν; τ0Þ where τ0 is the present value of the conformal time coordinate and ν is the comoving frequency whose numerical value coincides with the value of the physical frequency
The target sensitivity to detect the stochastic background of inflationary origin should correspond to a chirp amplitude hc 1⁄4 Oð10−29Þ and to a spectral energy distribution in critical units h20Ωgw 1⁄4 Oð10−16Þ
Summary
Stochastic backgrounds of cosmological origin have been suggested more than forty years ago [1,2,3] as a genuine general relativistic effect in curved space-times. Since the evolution of the tensor modes of the geometry is not Weylinvariant [1], the corresponding classical and quantum fluctuations can be amplified in an anisotropic metric and in conformally flat background geometries [2,3] (see [4]) For this reason, backgrounds of relic gravitons are expected, with rather different properties, in a variety of cosmological scenarios and, in particular, during an isotropic phase of quasi–de Sitter expansion [5]. The target sensitivity to detect the stochastic background of inflationary origin should correspond to a chirp amplitude hc 1⁄4 Oð10−29Þ (or smaller) and to a spectral energy distribution in critical units h20Ωgw 1⁄4 Oð10−16Þ (or smaller) These orders of magnitude estimates directly come from the amplitude of the quasiflat plateau produced in the context of single-field inflationary scenarios; in this case the plateau encompasses the mHz and the audio bands with basically the same amplitude.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
