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Understanding Dark Energy: Background and Interactions
Introduction to Dark Energy and Dark Matter
Dark energy and dark matter are the primary components driving the evolution of the late universe. They are detected indirectly through their gravitational effects, and there is a possibility of interaction between them without violating observational constraints1. The universe's accelerated expansion is a direct indicator of dark energy, while cosmic microwave background (CMB) anisotropy measurements provide indirect evidence3.
Observational Evidence and Theoretical Models
Cosmic Microwave Background and Supernovae Observations
The presence of dark energy is strongly supported by observations of the large-scale structure at low redshift and the CMB. The angular scale of acoustic oscillations in the CMB supports a nearly flat universe, while low-redshift cosmology suggests a matter density around 25% of the critical density4. Supernova Ia results corroborate these findings, providing a robust observational framework for dark energy4.
Early Dark Energy Models
New early dark energy (NEDE) models have been developed to reconcile the CMB with higher Hubble constant values inferred from supernovae observations. NEDE introduces a phase transition mechanism triggered by a subdominant scalar field, improving upon older models by naturally explaining the decay of the extra energy component5.
Dark Energy and Dark Matter Interactions
Coupling Mechanisms
Several models propose interactions between dark matter and dark energy to address the coincidence problem. These interactions influence the background dynamics and modify the evolution of linear perturbations. Current observational data supports the compatibility of these interactions with astronomical and cosmological observations6.
Scalar Field Models
Scalar field models, such as quintessence, K-essence, and phantom models, are extensively studied to explain dark energy. These models emphasize the importance of cosmological scaling solutions and the evolution of cosmological perturbations, which can be compared with CMB and large-scale structure observations8.
Phenomenological Approaches
Phenomenological models introduce interactions between dark matter and dark energy by modifying matter conservation equations while keeping Einstein equations unchanged. These models suggest that dark sector coupling could introduce new terms in gravitational dynamics, such as bulk dissipative pressure, which affects structure formation at small scales9.
Probing Dark Energy
Methods and Strategies
Various methods are employed to probe dark energy, including magnitude-redshift (Hubble) diagrams, galaxy and cluster number counts, and CMB anisotropy. Type Ia supernovae are particularly useful for constraining cosmological parameters, with future data sets expected to provide even more precise measurements3.
Thermal Dark Energy
A novel source of dark energy, motivated by hidden sectors in string theory models, involves thermal effects that hold a light hidden sector scalar at a non-minimum point in field space. This leads to an effective cosmological constant with an equation of state ( w = -1 ), matching the observed dark energy density10.
Conclusion
Dark energy remains one of the most enigmatic components of the universe, with its nature still largely unknown. Observational evidence from CMB, supernovae, and large-scale structure provides strong support for its existence. Theoretical models, including scalar field and phenomenological approaches, offer potential explanations and mechanisms for dark energy and its interaction with dark matter. Future observational data and refined models will continue to enhance our understanding of this mysterious force driving the accelerated expansion of the universe.
Sources and full results
Most relevant research papers on this topic
Dynamics of dark energy with a coupling to dark matter
A new form of dark sector coupling, involving exponential quintessence and simple energy exchange, leads to a more complex dynamical phase space and better physical motivation than previous couplings.
Highly CitedDark matter and background light
Dark matter is most likely to be weakly interacting massive particles (WIMPs) or higher-dimensional sources, affecting the night sky's light patterns.
Highly CitedPROBING DARK ENERGY: METHODS AND STRATEGIES
Supernovae and number counts have the most potential to probe dark energy, with CMB anisotropy providing the first measurements and supernovae and number counts providing the most potential for constraining cosmological parameters.
Highly CitedObserving dark energy
Dark energy is strongly supported by large-scale structure observed at low redshift and in the cosmic microwave background, supporting a nearly flat universe and a matter density around 25% of the critical density.
Hot new early dark energy
Hot new early dark energy (NEDE) explains the cosmic microwave background with a higher Hubble constant, based on a vacuum first-order phase transition triggered by thermal corrections in a dark gauge sector.
Dark matter and dark energy interactions: theoretical challenges, cosmological implications and observational signatures
Dark matter and dark energy interactions are compatible with current astronomical data and will be further supported by future observational data sets.
Highly CitedModels of dark matter coupled to dark energy
Three distinct types of models of dark energy in the form of a scalar field coupled to dark matter are presented, and their cosmology is investigated using cosmic microwave background and matter power spectra calculations.
Highly CitedDynamics of dark energy
Dark energy models can explain the accelerating universe and can potentially be used to reconstruct the equation of state of dark energy using Supernovae Ia data.
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