Cosmological Moduli and the Post-Inflationary Universe: A Critical Review

TL;DR

This review discusses how cosmological moduli from string theory influence the post-inflationary universe, affecting matter domination, dark matter, and cosmic structure, with implications for theory and observations.

Contribution

It provides a comprehensive review of the role of moduli in post-inflationary cosmology, emphasizing non-thermal histories and their observational consequences.

Findings

Moduli decay before Big Bang Nucleosynthesis, avoiding conflicts with its predictions.

Non-thermal histories offer a robust alternative to thermal scenarios in early universe models.

Moduli influence baryogenesis, dark matter production, and large-scale structure formation.

Abstract

We critically review the role of cosmological moduli in determining the post-inflationary history of the universe. Moduli are ubiquitous in string and M-theory constructions of beyond the Standard Model physics, where they parametrize the geometry of the compactification manifold. For those with masses determined by supersymmetry breaking this leads to their eventual decay slightly before Big Bang Nucleosynthesis (without spoiling its predictions). This results in a matter dominated phase shortly after inflation ends, which can influence baryon and dark matter genesis, as well as observations of the Cosmic Microwave Background and the growth of large-scale structure. Given progress within fundamental theory, and guidance from dark matter and collider experiments, non-thermal histories have emerged as a robust and theoretically well-motivated alternative to a strictly thermal one. We review this approach to the early universe and discuss both the theoretical challenges and the observational implications.