Power spectrum of inflationary attractors

Inflationary attractors predict the spectral index and tensor-to-scalar ratio to take specific values that are consistent with Planck. An example is the universal attractor for models with a generalized nonminimal coupling, leading to Starobinsky inflation. In this paper we demonstrate that it also predicts a specific relation between the amplitude of the power spectrum and the number of $e$-folds. The length and height of the inflationary plateau are related via the nonminimal coupling: in a wide variety of examples, the observed power normalization leads to at least 55 flat $e$-foldings. Prior to this phase, the inflationary predictions vary and can account for the observational indications of power loss at large angular scales.

Figure 1

Potential (16) with $n=1,2,8$ (black, blue, red from right to left). Higher $n$ require lower $\xi$ if one seeks just 55 flat $e$-folds. The dashed line depicts the potential without corrections.