At the very end of February, I published my first paper. In this post, I want to provide a brief, non-technical overview of what we* were doing in this work and the results we found. The manuscript is currently under review at MNRAS but you can view the preprint here:

http://www.arxiv.org/abs/1902.10694.

The aim of this work was to test the viability of a dark energy model known as the interacting vacuum scenario. In this scenario, the vacuum (i.e. the energy associated with empty space) is free to exchange energy with dark matter (the invisible matter present in the Universe that helps structures such as galaxies form and grow). We wanted to see if such a scenario can be ruled in or out using the latest observational datasets.

The motivation for such a study is that the current standard model of dark energy (known as the cosmological constant model) is fairly unsatisfactory, and fails to explain an important observational phenomenon: that the amount of dark energy in the Universe seems to be increasing. To address this, it seems natural to investigate the possibility that the vacuum is gaining energy from dark matter.

To test this idea, we used the numerical codes CAMB and CosmoMC. CAMB computes all the physics that goes on in the cosmological model you want to test, and CosmoMC is a statistical inference code that allows you to estimate the values of model parameters using observational data. We modified these codes to include our particular interacting dark energy scenario, then tested some variations on that theme.

We found that this model is not ruled out by observational data, but it is fairly strongly constrained. The data also seem to favour the standard cosmological constant case. Consequently, while this model has the potential to explain the observed discrepancies in the amount of dark energy, it fails to capitalise on that potential.

However, this isn’t the end of the road. There is still plenty of work to be done on the theoretical side, particularly on theory of perturbations (i.e. how small fluctuations in matter density evolve over time) in the interacting vacuum. We are also interested in examining the case of a time-varying interaction more closely, as from a physical standpoint this would seem to be more “natural”.

Please feel free to comment below or email me if you have any questions about our work!

*”we” refers to my collaborators Matteo Martinelli and Simone Peirone, my supervisors Marco Bruni and David Wands, and myself.