The implications of dark matter and dark energy on cosmological models.

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Implications of Dark Matter and Dark Energy on Cosmological Models

Introduction to Dark Matter and Dark Energy

Dark matter and dark energy are two of the most enigmatic components of the universe, constituting approximately 95% of its total energy density. Despite their prevalence, their exact nature remains elusive, posing significant challenges to modern cosmology . Dark matter is believed to be a new type of particle that has not yet been detected in laboratory settings, while dark energy is associated with the energy of empty space, driving the accelerated expansion of the universe.

Interactions Between Dark Matter and Dark Energy

Theoretical Challenges and Observational Signatures

Models proposing interactions between dark matter and dark energy have been developed to address the coincidence problem, which questions why the densities of dark matter and dark energy are of the same order of magnitude today. These interactions can influence the background dynamics of the universe and modify the evolution of linear perturbations. Current observational data supports the compatibility of these interaction models with astronomical and cosmological observations.

Multi-Interacting Dark Energy Models

Multi-interacting dark energy models introduce interaction channels between dark energy and both dark matter and photons. These models aim to modify the expansion history of the universe to resolve tensions between early- and late-time observations, such as the $S_8$ and $H_0$ tensions. However, while these models can reduce the significance of these tensions, they do not completely resolve them and still favor the $\Lambda$CDM model in statistical analyses.

Alternative Cosmological Models

Negative-Mass Cosmology

An alternative model proposes that both dark matter and dark energy can be explained by a single fluid of negative mass. However, this model faces significant challenges, including discrepancies with the observed shape and density of galactic dark matter halos and the presence of a large-scale "runaway effect" that would result in galaxies moving at nearly the speed of light. These issues make the negative-mass cosmology model less viable.

Dynamical Space-Time Cosmology

The Dynamical Space-Time Cosmology (DSC) model unifies dark matter and dark energy through a Lagrange multiplier coupled to the energy momentum tensor and a scalar field. This model can lead to cosmic acceleration and stable late-time attractors under certain conditions. Observational data from low-redshift probes show that DSC models are in good agreement with current data, although they exhibit small deviations from the $\Lambda$CDM model.

Modified Gravity and Dark Energy

Interacting Modified QCD Ghost Dark Energy

In the framework of dynamical Chern-Simons modified gravity, interacting modified QCD ghost dark energy models are explored. These models investigate cosmological parameters such as the Hubble parameter, deceleration parameter, and equation of state. The results indicate that these models can explain the accelerated expansion of the universe and are compatible with observational data.

Dynamical Dark Energy

Recent observations have revealed tensions between various cosmological probes, such as the Lyman-α forest measurement of baryon acoustic oscillations and the Hubble constant. These tensions suggest that dark energy may not be constant but could evolve over time. Dynamical dark energy models, which allow for this evolution, have been shown to relieve these tensions and are preferred over the $\Lambda$CDM model based on improvements in fit alone. Future surveys, such as the Dark Energy Spectroscopic Instrument, are expected to provide decisive evidence for or against these models.

Conclusion

The study of dark matter and dark energy continues to be a central focus in cosmology, with various models and theories being proposed to explain their nature and interactions. While interaction models and alternative cosmological theories offer potential solutions to existing tensions in observational data, the $\Lambda$CDM model remains the most statistically favored. Future observational data from upcoming surveys will be crucial in further understanding the implications of dark matter and dark energy on cosmological models.