Predictions in multifield models of inflation

TL;DR

This paper develops an analytic method to determine the density functions of observables in multifield inflation models, revealing a sharp peak that is robust against initial condition variations, exemplified by spectral index predictions.

Contribution

It introduces an analytic approach for density functions in multifield inflation, showing robustness of predictions and extending applicability beyond sum-separable potentials.

Findings

Density functions generally have a sharp peak.

Peak location is mildly sensitive to initial conditions.

Predicted spectral index and running match observational data.

Abstract

This paper presents a method for obtaining an analytic expression for the density function of observables in multifield models of inflation with sum-separable potentials. The most striking result is that the density function in general possesses a sharp peak and the location of this peak is only mildly sensitive to the distribution of initial conditions. A simple argument is given for why this result holds for a more general class of models than just those with sum-separable potentials and why for such models, it is possible to obtain robust predictions for observable quantities. As an example, the joint density function of the spectral index and running in double quadratic inflation is computed. For scales leaving the horizon 55 e-folds before the end of inflation, the density function peaks at n_{s}=0.967 and \alpha=0.0006 for the spectral index and running respectively.