Modular Inflation Observables and $j$-Inflation Phenomenology

TL;DR

This paper explores the dynamics and observable predictions of modular inflation, a class of two-field inflation models with a conformally flat target space, emphasizing the role of modular forms and comparing $j$-inflation phenomenology with recent CMB data.

Contribution

It provides a detailed analysis of modular inflation's perturbations and observables, highlighting the impact of modular form derivatives and comparing $j$-inflation predictions with observational constraints.

Findings

Modular inflation observables are constructed from almost holomorphic modular forms.

$j$-inflation's phenomenology aligns with Planck and BICEP2/Keck data.

Nonmodular derivatives of modular forms influence CMB predictions.

Abstract

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.