Cosmological Models of Dark Sector Interactions

The dark sector, comprising dark matter and dark energy, remains one of the most profound enigmas of modern cosmology. Standard ΛCDM treats these components as non-interacting fluids minimally coupled to gravity, yet persistent discrepancies in the Hubble constant and the amplitude of matter fluctuations (S8) have motivated the exploration of dynamical interactions between dark matter and dark energy. Cosmological models of dark sector interactions employ scalar fields, vector mediators or modified gravity to introduce energy and momentum exchange, with the aim of addressing cosmic tensions and offering an underlying field-theoretic foundation. Lagrangian formalisms have been developed to characterise coupling functions that respect stability conditions and observational bounds, while phenomenological frameworks quantify momentum transfer and evaluate its impact on expansion history and structure growth. Advances in perturbation theory and N-body simulations have enabled precise predictions for the cosmic microwave background, baryon acoustic oscillations and large-scale structure, facilitating stringent tests of coupling strengths. These models not only strive to reconcile diverse data sets but also carry implications for the nature of fundamental interactions beyond the Standard Model and guide the design of future surveys targeting the late-time Universe.

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Cosmological Models of Dark Sector Interactions publication trend

The graph below shows the total number of articles in cosmological models of dark sector interactions across all publications each year (not limited to Nature Index journals).

Technical terms

Lagrangian: A function that encodes the dynamics of a physical system, yielding equations of motion via the principle of least action.

Scalar field: A field characterised by a single value at each point in space and time, often used to model dark energy or mediators of interaction.

Dark radiation: A hypothetical relativistic component of the Universe’s energy density, distinct from photons and neutrinos, that interacts only with dark matter or dark energy.

Hubble tension: The discrepancy between measurements of the Universe’s expansion rate from the early Universe (e.g. CMB) and local distance-ladder methods.

S8 tension: The observed mismatch in the amplitude of matter fluctuations between large-scale structure surveys and predictions based on early-Universe observations.

Momentum exchange: Transfer of momentum between dark matter and dark energy that can alter the growth of cosmic structures without necessarily exchanging energy.

References

1. Interacting ultralight dark matter and dark energy and fits to cosmological data in a field theory approach. Journal of Cosmology and Astroparticle Physics (2024).
2. Ruling out strongly interacting dark matter–dark radiation models from joint observations of cosmic microwave background and quasar absorption spectra. Monthly Notices of the Royal Astronomical Society: Letters (2023).
3. Momentum transfer models of interacting dark energy. Journal of Cosmology and Astroparticle Physics (2022).