Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Multifield Cosmology and the Dark Universe

Lilia Anguelova

TL;DR

The paper investigates multifield cosmologies with non-geodesic, rapidly turning field-space trajectories as a unifying framework to address inflation, dark matter, and dark energy. It develops exact rapid-turn background solutions on a hyperbolic field-space (Poincaré disk) and analyzes the resulting dark-energy perturbations, including a reduced sound speed $c_s^{DE}$ and a clustering scale $r_s^{DE}$. The results show that rapid-turn dynamics can realize inflation on steep potentials, enable primordial black hole production, and yield a dynamical dark-energy sector with $w_{DE}$ near $-1$ and $c_s^{DE} < 1$, potentially alleviating the $H_0$ and $ ext{sigma}_8$ tensions. The work discusses theoretical consistency with swampland ideas and outlines observational challenges and future directions, including confronting the model with DESI and other data sets.

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.

Multifield Cosmology and the Dark Universe

TL;DR

The paper investigates multifield cosmologies with non-geodesic, rapidly turning field-space trajectories as a unifying framework to address inflation, dark matter, and dark energy. It develops exact rapid-turn background solutions on a hyperbolic field-space (Poincaré disk) and analyzes the resulting dark-energy perturbations, including a reduced sound speed and a clustering scale . The results show that rapid-turn dynamics can realize inflation on steep potentials, enable primordial black hole production, and yield a dynamical dark-energy sector with near and , potentially alleviating the and tensions. The work discusses theoretical consistency with swampland ideas and outlines observational challenges and future directions, including confronting the model with DESI and other data sets.

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.

Paper Structure

This paper contains 12 sections, 26 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Multifield cosmological models
  3. Novel features of rapid turn models
  4. Slow roll on steep potentials
  5. Primordial black hole generation
  6. Dynamical dark energy
  7. Dynamical dark energy
  8. Multifield model of late dark energy
  9. Exact background solutions
  10. Dark energy perturbations
  11. Alleviating cosmological tensions
  12. Concluding remarks

Figures (1)

  • Figure 1: Two examples of field-space trajectories $\left(\varphi(t), \theta(t)\right)$ of the exact solutions of ADGW. (The numerical values of the relevant integration constants, used in these plots, can be found in that reference.) The solid dot at $\theta = \frac{\pi}{2}$ and $\varphi \neq 0$ denotes the starting point of the trajectories at an initial moment of time.