Non-thermal moduli production during preheating in $\alpha$-attractor inflation models

TL;DR

This paper investigates how non-thermal production of light moduli during preheating in $eta$-attractor inflation models can affect Big Bang Nucleosynthesis, establishing bounds on model parameters to ensure cosmological consistency.

Contribution

It provides a detailed analysis of moduli production via parametric resonance in $eta$-attractor models, highlighting the dependence on the parameter $eta$ and its implications for inflationary energy scales.

Findings

Moduli production is suppressed for small $eta$ values.

An upper bound on $eta$ is established as $eta \,\lesssim 10^{-8} m_{\rm Pl}^2$.

Constraints on inflationary energy scale and reheating temperature are derived.

Abstract

Production of gravitationally coupled light moduli fields must be suppressed in the early universe, so that its decay products do not alter Big Bang Nucleosynthesis (BBN) predictions for light elements. On the other hand, the moduli quanta can be copiously produced non-thermally during preheating after the end of inflation. In this work, we study the production of moduli in the $\alpha$-attractor inflationary model through parametric resonances. For our case, where the inflationary potential at its minimum is quartic, the inflaton field self-resonates, and subsequently induces large production of moduli particles. We find that this production is suppressed for small values of $\alpha$. Combining semi-analytical estimation and numerical lattice simulations, we infer the parametric dependence on $\alpha$ and learn that $\alpha$ needs to be $\lesssim 10^{-8}\,m_{\rm Pl}^2$ to be consistent with BBN. This in turn predicts an upper bound on the energy scale of inflation and on the reheating temperature.