Speaker
Description
Interacting Dark Energy (IDE) models, where dark matter and dark energy interact through a non-gravitational coupling, have recently regained attention as late-time cosmic tensions persist and new datasets hint at possible dynamical dark energy and deviations from ΛCDM.
In this talk, we will present observational constraints on a broad class of linear and non-linear IDE models using some of the newest late-time datasets: DESI DR2 BAO, Pantheon+ supernovae, Cosmic Clocks, and BBN. These IDE models, each of which admits exact analytical solutions for the Hubble parameter H(z), allow us to directly explore features such as the possible direction of energy transfer, the presence of negative energy densities, and effective phantom-crossing behaviour.
We show that several IDE models provide improved fits to the combined DESI and Pantheon+ data compared to ΛCDM, even after accounting for the additional model parameters. A consistent pattern emerges across many models: the data mildly prefer a small but non-zero energy transfer in the dark sector, typically from dark matter to dark energy at early times, with a possible switch in the direction of energy transfer at later epochs. Furthermore, for all interactions considered, where possible, we find a phantom-divide crossing for the effective equation of state of dark energy, with the density of dark energy decreasing at present and at low redshift, while increasing in the past at high redshift.
However, these results must be interpreted with caution, as many models predict negative energy densities in the past or future, or exhibit early-time instabilities at the perturbation level, which may be unphysical. A complete assessment requires the inclusion of CMB and other early-universe probes, as well as a dedicated stability analysis, which will be considered in future work.
| Stream | Science or Engineering |
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