Isocurvature perturbations during two-field inflation and reheating

We use Hamilton–Jacobi formalism to study the curvature and isocurvature perturbations during inflation. This formalism is suitable for going beyond slow roll regime. We solve the equation of fields’ perturbations for some two-field models, and calculate their spectra. We next use δN\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\delta N$$\end{document} formalism to calculate the curvature and isocurvature non-Gaussianity for a non-separable form of the Hubble expansion rate. Finally, using the sudden decay approximation, we obtain the link between the perturbations during inflation and after reheating for noninteracting fields.