# C3 - Dark Energy - Dark Matter Interaction

## Summary

Theoretical ideas for explaining the physical origin of Dark Energy often involve effective field theories like quintessence, non-linear extensions of general gravity (e.g. f(R)-gravity), or higher-dimensional gravity theories (e.g. Dvali-Gabadadze-Porrati, DGP, gravity and its variants). It seems well possible that some of these theories help to resolve small-scale challenges that have arisen in standard ΛCDM, or conversely, that they produce non-linear structures that are readily in conflict with observational data. Numerical simulations that directly follow structure growth far into the non-linear regime provide a powerful tool to predict in detail the outcome of interesting candidate theories. This project aims to identify scenarios for which a detailed numerical study appears promising. It also develops the necessary simulation tools, and compares the results to standard ΛCDM and to observations, thereby providing constraints on the viability of these physical scenarios. A particular emphasis is put on achieving quantitatively reliable results that reach the fiducial 1% target accuracy for the matter power spectrum required by planned Dark Energy missions such as Euclid. This also necessitates a joint consideration of modified gravity and baryonic effects, which we plan to pioneer in this project. We will also extend previous simulation work on coupled Dark Energy – Dark Matter to account for spatial inhomogeneities in the effective Dark Energy field.

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