Multifield Cosmology and the Dark Universe

Abstract

Multifield models, arising from multiple scalars interacting with gravity, provide a rich theoretical framework for addressing fundamental problems in modern cosmology. A key role in this regard is played by the so called rapid turn regime, which is characterized by background solutions with strongly non-geodesic field-space trajectories. We review the implications of this regime for a number of problems relevant for cosmological inflation, dark matter and dark energy. We focus, in more detail, on a class of exact rapid-turn solutions that give a model of dynamical dark energy. In this model, the sound speed of the dark energy perturbations is reduced compared to the speed of light, which leads to observational differences from a cosmological constant even for an equation-of-state parameter very close to -1. Furthermore, this model holds promise for the simultaneous alleviation of two prominent cosmological tensions.

arXiv comment9 pages, contribution to the proceedings of the 29th international conference on Integrable Systems and Quantum Symmetries (ISQS-29), Prague, 2025; references added