### An Investigation of a Dark Matter-Dark Energy Interaction Model to Explain Discrepancies in Hubble Rate Measurements

By Angela Zhou

Intermediate Category (Grades 9-10)

Innovation | Physics

One of the many goals of cosmology is to accurately model the universe. Cosmological models try to quantitatively predict the values of many parameters in the universe, as well as how they evolve over time. Examples of such parameters include the densities of the universe’s contents and the rate at which the universe is expanding (the Hubble Rate). Throughout the past century, there has been much dispute over what the correct model is, beginning with Einstein’s addition and subsequent removal of a “cosmological constant” in his Einstein Field Equations. The current standard model for density evolutions in the universe, the Lambda-CDM model, includes this cosmological constant because observations have indicated that the universe is expanding at an accelerating rate. While this model correctly predicts a lot of data gathered from satellites and sky surveys, some independent measurements of the Hubble Rate contradict what the model predicts, leading to the idea that new physics is going on.

My project, conducted at SFU, aims to investigate one potential area of “new physics” – interactions between dark matter and dark energy. The evolution equations were modified so that dark matter decayed into dark energy at a rate that depends on the density of dark matter. Then, a Markov chain Monte Carlo sampling algorithm was used to determine the probability distributions and best-fit values for different densities and the Hubble Rate. The results for some datasets support the modified model, as well as the idea that dark energy density is increasing.