Coupled and Extended Quintessence: theoretical differences and structure formation

TL;DR

This paper compares coupled and extended quintessence models, analyzing their theoretical differences and impacts on structure formation, highlighting distinct behaviors in linear perturbations and implications for N-body simulations.

Contribution

It elucidates the relation between coupled and extended quintessence models and provides a practical framework for incorporating their effects into N-body simulations.

Findings

Enhanced clustering in coupled quintessence models.

Slower structure growth in extended quintessence models.

Specific corrections for N-body simulations provided.

Abstract

The case of a coupling between dark energy and matter (Coupled Quintessence) or gravity (Extended Quintessence) has recently attracted a deep interest and has been widely investigated both in the Einstein and in the Jordan frames (EF, JF), within scalar tensor theories. Focusing on the simplest models proposed so far, in this paper we study the relation existing between the two scenarios, isolating the Weyl scaling which allows to express them in the EF and JF. Moreover, we perform a comparative study of the behavior of linear perturbations in both scenarios, which turn out to behave in a markedly different way. In particular, while the clustering is enhanced in the considered CQ models with respect to the corresponding Quintessence ones where the coupling is absent and to the ordinary cosmologies with a Cosmological Constant and Cold Dark Matter (LCDM), structures in EQ models may grow slower. This is likely to have direct consequences on the inner properties of non-linear structures, like cluster concentration, as well as on the weak lensing shear on large scales. Finally, we specialize our study for interfacing linear dynamics and N-body simulations in these cosmologies, giving a recipe for the corrections to be included in N-body codes in order to take into account the modifications to the expansion rate, growth of structures, and strength of gravity.