Interactions in the Dark: physics of Dark Energy-Dark Matter interactions

With the backing of the amazing precision of observational data on the largest scales of the universe, the "dark energy" has established itself firmly into our thinking of fundamental theoretical physics. The current paradigm, the LCDM cosmology provides an excellent model to describe the universe, but we lack a convincing theoretical framework to accommodate the extreme fine-tuning of the dark energy density parameter to 10^(-120).

In light of this problem it is worthwile to explore alternative models and examine how these can be efficiently tested using state-of-the-art observational data. For instance, a subclass of theories have consequences on all scales by invoking a condensable dark energy field: the interactions involved can help shed light on the amazing coincidences with the mass scale of neutrinos and the scaling coefficient of the Tully-Fisher or MOND relation in galaxies. Some of these models even claim to unify the origin of dark energy, dark matter and the neutrino masses, thus providing interesting fundamental ways to extend the standard model of particle physics.

Thanks to recent observational advances, predictions on galaxy and cluster scales can be used to falsify some of these theories. Such tests are worth the attention of numerical simulators, who can facilitate the testing of exotic physics with precision astronomical tests, such as gravitational lensing of galaxies. Therefore, this workshop brings together those observers, simulators and physicists who can outline key tests, and specifically those that involve cosmological simulations for interactive dark energy theories.

The Science Questions:

1. Which theories of physics are promising to overcome the problems of finetuning of LCDM? Are there generic predictions of a condensable dark energy field in a clumpy universe? How many different corrections are needed to standard theories? (Input from Physicists mainly).

2. How can the existing standard codes be hacked to simulate a generic interaction of a dark energy field with the metric or matter or neutrino fields? Any challenges to make such simulations to yield predictions as detailed as in LCDM? (Input from Simulators mainly).

3. Which data, and on what scale are most sensitive to test these simulations? Can we establish a common benchmark data on galaxy and large scale for theories to pass? (Input from Observers mainly)