Modular Inflation Observables and $j$-Inflation Phenomenology

Understand

Modular inflation is the restriction to two fields of automorphic inflation, a general group based framework for multifield scalar field theories with curved target spaces, which can be parametrized by the comoving curvature perturbation ${\cal R}$ and the isocurvature perturbation tensor $S^{IJ}$.

• This paper describes the dynamics and observables of these perturbations and considers in some detail the special case of modular inflation as an extensive class of two-field inflation theories with a conformally flat target space.
• It is shown that the nonmodular nature of derivatives of modular forms leads to CMB observables in modular invariant inflation theories that are in general constructed from almost holomorphic modular forms.
• The phenomenology of the model of $j$-inflation is compared to the recent observational constraints from the Planck satellite and the BICEP2/Keck Array data.