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A Focused Review of Quintom Cosmology: From Quintom Dark Energy to Quintom Bounce

Tao-tao Qiu, Yifu Cai, Yang Liu, Si-Yu Li, Jarah Evslin, Xinmin Zhang

TL;DR

This work surveys Quintom cosmology as a dynamical dark energy scenario that crosses the $w=-1$ boundary and applies it to non-singular bouncing and cyclic universes. It covers three realizations of quintom bounces—two-field scalar models, higher-derivative (Lee–Wick) fields, and modified gravity constructions—and one cyclic model using coupled scalar fields, detailing background dynamics and perturbations. Across these models, the authors examine conditions for a successful bounce, how perturbations evolve through contraction, bounce, and expansion, and whether scale-invariant curvature spectra can be achieved, often finding signatures such as bounce-induced wiggles or blue-tilted tensor spectra. The discussion highlights potential observational signatures and the role of DESI DR2 in supporting dynamical dark energy scenarios, with implications for early-universe cosmology and cyclic models.

Abstract

The recently released data of DESI DR2 favors a dynamical dark energy theory, with the equation of state crossing the cosmological constant boundary $w=-1$. In this paper, we briefly review quintom cosmology, especially the quintom bounce. We will give three examples of a quintom bounce and one example of a cyclic universe with quintom matter.

A Focused Review of Quintom Cosmology: From Quintom Dark Energy to Quintom Bounce

TL;DR

This work surveys Quintom cosmology as a dynamical dark energy scenario that crosses the boundary and applies it to non-singular bouncing and cyclic universes. It covers three realizations of quintom bounces—two-field scalar models, higher-derivative (Lee–Wick) fields, and modified gravity constructions—and one cyclic model using coupled scalar fields, detailing background dynamics and perturbations. Across these models, the authors examine conditions for a successful bounce, how perturbations evolve through contraction, bounce, and expansion, and whether scale-invariant curvature spectra can be achieved, often finding signatures such as bounce-induced wiggles or blue-tilted tensor spectra. The discussion highlights potential observational signatures and the role of DESI DR2 in supporting dynamical dark energy scenarios, with implications for early-universe cosmology and cyclic models.

Abstract

The recently released data of DESI DR2 favors a dynamical dark energy theory, with the equation of state crossing the cosmological constant boundary . In this paper, we briefly review quintom cosmology, especially the quintom bounce. We will give three examples of a quintom bounce and one example of a cyclic universe with quintom matter.

Paper Structure

This paper contains 6 sections, 75 equations, 11 figures.

Table of Contents

  1. Bounce with two scalar fields
  2. Large field potentials
  3. Small field potential
  4. Bounce with a higher-derivative field
  5. Bounce with modified gravity
  6. Beyond a bounce: Cyclic scenarios

Figures (11)

  • Figure 1: Results for the posterior distributions of $w_0$ and $w_a$, from fits of the $w_0w_aCDM$ model to DESI in combination with CMB and DESY5 datasets as labelled. Quintom-A: $w$ evolves from Quintessence to Phantom; Quintom-B: from Phantom to Quintessence.
  • Figure 2: Plot of evolution of EoS $w$ in a double-field quintom bounce with large field potential. The figure is taken from Ref. Cai:2007zv.
  • Figure 3: The evolution of perturbation wavelengths with different comoving wavenumbers $k$ as well as the Hubble radius $|H^{-1}|$. The figure is taken from Ref. Cai:2007zv.
  • Figure 4: Plot of evolution of EoS $w$ in a double-field quintom bounce with small field potential. The figure is taken from Ref. Cai:2008qb.
  • Figure 5: The evolution of perturbation wavelengths with different comoving wavenumbers $k$ as well as Hubble radius $|H^{-1}|$. The figure is taken from Ref. Cai:2008qb.
  • ...and 6 more figures