Quintom cosmology and modified gravity after DESI 2024

Area of Science:

• Cosmology
• Astrophysics
• Theoretical Physics

Background:

• The nature of dark energy remains a primary enigma in modern cosmology.
• Understanding its equation-of-state parameter, w(z), is crucial for deciphering cosmic evolution.
• Dynamical dark energy models offer potential explanations beyond the standard cosmological constant (ΛCDM).

Purpose of the Study:

• To reconstruct the cosmological background evolution under dynamical dark energy scenarios.
• To investigate the behavior of the dark energy equation-of-state parameter, w(z).
• To explore the theoretical underpinnings of observed dark energy dynamics within modified gravity frameworks.

Main Methods:

• Utilizing the Gaussian process approach for cosmological background reconstruction.
• Incorporating the latest Dark Energy Spectroscopic Instrument (DESI) baryon acoustic oscillation (BAO) data.
• Combining DESI BAO data with other relevant cosmological observations.
• Reconstructing actions for modified gravity theories: f(R), f(T), and f(Q) gravity.

Main Results:

• The reconstructed dark energy equation-of-state parameter, w(z), exhibits "quintom-B" behavior.
• This quintom-B behavior signifies a transition across w = -1, from a phantom to a quintessence-like regime.
• Certain modified gravity models successfully reproduce this quintom dynamics and align with DESI data.
• A mild preference for quadratic deviations from the standard ΛCDM model was observed across all investigated cases.

Conclusions:

• The universe's expansion may be driven by a dynamical dark energy component exhibiting complex behavior.
• Modified gravity theories, specifically certain f(R), f(T), and f(Q) gravity models, provide viable explanations for the observed dark energy dynamics.
• The findings suggest that extensions to the standard ΛCDM model are potentially favored by current observational data, particularly from DESI.