image: The reconstructed dark-energy equation-of-state parameter w(z).The black curve denotes the mean value, while the light blue shaded zones indicate the allowed regions at 1σ confidence level.
Credit: ©Science China Press
An international team led by Professor Yi-Fu Cai from the Department of Astronomy at the University of Science and Technology of China used the latest baryon acoustic oscillation (BAO) data released by the Dark Energy Spectrometer (DESI), combined with previous observational data, to reconstruct the background evolution of the universe under the framework of dynamic dark energy by using Gaussian reconstruction method. The reconstructed dark energy equation-of-state parameter shows the dynamic behavior of quintom-B, which can be realized by modified gravity theory. This study is helpful to deepen people's understanding of the accelerated expansion of the universe in the late period. The results, entitled "Quintom cosmology and modified gravity after DESI 2024", were published in the internationally renowned academic journal Science Bulletin (English edition).
In 1998, observations of distant Type Ia supernovae revealed the existence of dark energy who drove the accelerating expansion of the universe, putting together the final piece of the puzzle of the current standard Model of cosmology. In the standard Model of cosmology, visible matter accounts for only 5% of the total energy of the universe; Dark matter accounts for 27%, while the remaining 68% is dark energy. The physical nature and dynamical characteristics of dark energy are one of the major puzzles in physics and the main scientific objectives of the Dark Energy Spectrometer project.
In April 2024, the Dark Energy Spectrometer team released the results of its first year of observations, creating the largest three-dimensional map of the universe with the most accurate measurements to date, measuring the late expansion history of the universe with an accuracy of more than 1%, giving us the best way to study the evolution of the universe. At the same time, the observational results show that dark energy, which dominates the late acceleration of the universe, may not be a cosmological constant in the traditional sense, but may have a dynamic evolutionary feature.
Based on the latest DESI observation data, this study reconstructed the evolution of the equation-of-state parameter of dark energy over time by using the Gaussian process method, and compared it with some widely studied modified gravity models. The analysis in this study shows that the reconstructed equation-of-state parameter supported the quintom dark energy model proposed by Zhang Xinmin's research team in 2004, in practically "Quintom-B". As the universe expands, the dark energy equation-of-state parameter will cross -1 from phantom to quintessence regime as the universe expands.
In order to further discuss how this dynamic feature can be interpreted through theories, this study specially considers three different modified gravity theories as specific examples, namely f(R), f(T), f(Q) gravity theories, and reconstructs the gravitational action. The result shows that certain modified gravity can exhibit the quintom dynamics and fit the recent DESI data efficiently, and for all cases the quadratic deviation from the LCDM scenario is mildly favored.
Although what dark energy corresponds to is still a mystery to us, but the latest DESI data suggest that it may not be a cosmological constant in the traditional sense. Therefore, it is very important to study the dynamic characteristics of dark energy from a phenomenological or theoretical point of view. It is hoped that this study will play a role in attracting more and more young people to participate in the study of this basic problem in the future.
Journal
Science Bulletin