Small field models with gravitational wave signature supported by CMB data

Understand

We study scale dependence of the cosmic microwave background (CMB) power spectrum in a class of small, single-field models of inflation which lead to a high value of the tensor to scalar ratio.

• The inflaton potentials that we consider are degree 5 polynomials, for which we precisely calculate the power spectrum, and extract the cosmological parameters: the scalar index $n_s$, the running of the scalar index $n_{\mathrm{run}}$ and the tensor to scalar ratio $r$.
• We find that for non-vanishing $n_{\mathrm{run}}$ and for $r$ as small as $r=0.001$, the precisely calculated values of $n_s$ and $n_{\mathrm{run}}$ deviate significantly from what the standard analytic treatment predicts.
• We study in detail, and discuss the probable reasons for such deviations.