Fibre inflation and precision CMB data
  Generic features of models of inflation obtained from string
compactifications are the correlations between the model parameters and the
postinflationary evolution of the universe. Thus, the postinflationary
evolution depends on the inflationary model parameters and accurate
inflationary predictions require that this be incorporated in the evolution of
the primordial spectrum. The fibre inflation model is a promising model of
inflation constructed in type IIB string theory. This model has two interesting
features in its postinflationary evolution. The reheating temperature of the
model is directly correlated with the model parameters. The model also
necessarily predicts some dark radiation, which can be sizable for certain
choices of discrete parameters in the model. We analyze this model in detail
using publicly available codes - ModeChord and CosmoMC with the latest
Planck+BICEP2/Keck array data to constrain the model parameters and $N_{\rm
pivot}$ (the number of $e$-foldings between horizon exit of the CMB pivot mode
and the end of inflation). We also carry out the same analysis using the
publicly available code Cobaya. We find the results of both the analysis to be
in agreement. Our analysis provides the basic methods necessary to extract
precise inflationary prediction in string models incorporating correlations
between model parameters and postinflationary evolution.
