Coupled quintessence and the halo mass function

Abstract

A sufficiently light scalar field slowly evolving in a potential can account for the dark energy that presently dominates the Universe. This quintessence field is expected to couple directly to matter components, unless some symmetry of a more fundamental theory protects or suppresses it. Such a coupling would leave distinctive signatures in the background expansion history of the Universe and on cosmic structure formation, particularly at galaxy cluster scales. Using semianalytic expressions for the cold dark matter (CDM) halo mass function, we make predictions for halo abundance in models where the quintessence scalar field is coupled to cold dark matter, for a variety of quintessence potentials. We evaluate the linearly extrapolated density contrast at the redshift of collapse using the spherical collapse model and we compare this result to the corresponding prediction obtained from the nonlinear perturbation equations in the Newtonian limit. For all the models considered in this work, if there is a continuous flow of energy from the quintessence scalar field to the CDM component, then the predicted number of CDM haloes can only lie below that of ÃCDM, when each model shares the same cosmological parameters today. In the last stage of our analysis we perform a global MCMC fit to data to find the best fit values for the cosmological model parameters. We find that for some forms of the quintessence potential, coupled dark energy models can offer a viable alternative to ÃCDM in light of the recent detections of massive high-z galaxy clusters, while other models of coupled quintessence predict a smaller number of massive clusters at high redshift compared to ÃCDM.

Future weak lensing constraints in a dark coupled universe

“…Future experiments may therefore include also coupled cosmologies as possible scenarios when fitting their data. Finally we conclude noting that, as recently outlined by [51], coupled quintessence is expected to have a distinctive impact on the formation of structures at galaxy clusters scales. In our work we limited our analysis to linear scales, but for the analysis of real future data, it will be necessary a precise modeling of the effects of coupled quintessence on non-linear scales.…”

Reconciling CMB and structure growth measurements with dark energy interactions

“…In coupled dark energy models that exhibit both energy and momentum exchange, like the coupled quintessence model with Q = α 0φρc [17], the growth rate depends on two terms: a fifth-force contribution ∝ α 2 0 , and a friction term ∝ α 0φ , whose sign is determined by the sign of the coupling parameter α 0 and the quintessence potential through theφ dependence. In general, getting suppression of growth is highly non-trivial, and often requires potentials with more than one free parameters in order to make the friction term dominate over the competing fifth-force term, which tends to give growth increase for positive and negative coupling values (see [39] for details and further discussion).…”

The halo mass function in interacting dark energy models

“…Interacting DE models have been widely discussed and investigated in the literature in the last years (see e.g. Amendola 2000, 2004; Farrar & Rosen 2007; Amendola, Baldi & Wetterich 2008; Pettorino & Baccigalupi 2008; Koyama, Maartens & Song 2009; Honorez et al 2010; Baldi 2011b; Clemson et al 2012; Tarrant et al 2012) and a new detailed presentation of these cosmological scenarios would be superfluous in the present paper. We therefore refer the interested reader to the above‐mentioned literature for a thorough description of cDE models and the derivation of their main equations.…”

“…A semi‐analytic study of the HMF for coupled DE (cDE) models has been recently carried out by Tarrant et al (2012). Using the expressions for a universal ΛCDM HMF, they computed the variations in the cluster counts induced by the modification in the spherical collapse model induced by the DE coupling to CDM.…”