Multifield inflation beyond N_field=2: non-Gaussianities and single-field effective theory

Abstract In this article, we study in detail the linear dynamics and cubic interactions for any number N field of scalar fields during inflation, directly terms observable curvature perturbation ? -1 entropic fluctuations, a choice that is more suitable analytical works. equations motion perturbations, uncover rich geometrical effects beyond involving just space, come from non-canonical kinetic structure when dimension space larger than two. Moreover, show fast rotation local basis can result negative eigenvalues mass matrix, potentially destabilising background ? 3. We also explain how to render manifest sizes between adiabatic extending previous work ours interacting fields. As first application our generic formalism, derive effective single-field theory perturbations up order all fluctuations are heavy enough be integrated out. slow-varying limit, recover action expected but with prediction usual Wilson coefficients multifield parameters, thus proposing new interpretation bispectrum context.