Could dark matter interactions be an alternative to dark energy?

Abstract

We study the global dynamics of the universe within the framework of the interacting dark matter (IDM) scenario. Assuming that the dark matter obeys the collisional Boltzmann equation, we can derive analytical solutions of the global density evolution, that can accommodate an accelerated expansion, equivalent to either the quintessence or the standard Λ models, with the present time located after the inflection point. This is possible if there is a disequilibrium between the DM particle creation and annihilation processes with the former process dominating, which creates an effective source term with negative pressure. Comparing the predicted Hubble expansion of one of the IDM models (the simplest) with observational data, we find that the effective annihilation term is quite small, as suggested by various experiments.

Observational constraints on interacting dark matter model without dark energy

“…Basilakos & Plionis (2009) phenomenologically identified two functional forms for which the previous Boltzmann equation can be solved analytically, only one of which is of interest since it indicates the dependence of the scale factor on a "∝a −3 ". We refer to Appendix B in Basilakos & Plionis (2009) for details. We assume that…”

“…where Z(t) = t t 0 a −3 e −2κC 1 (t−t 0 ) (Basilakos & Plionis 2009). At the present epoch, the density evolves according to ρ(a) C 1 + a −3 /C 2 , which is approximately equivalent to the corresponding evolution in the ΛCDM model, in which the C 1 term resembles the cosmological constant term (ρ Λ ) and the 1/C 2 term resembles the density of matter (ρ m ).…”

“…When the annihilation term is negligible (κ = 0) and the particle creation term dominates, it is straightforward to obtain the evolution of the total energy density (Basilakos & Plionis 2009) …”

“…In the framework of the Boltzmann formalism, if there is a disequilibrium between the dark matter particle creation and annihilation processes, an effective source term with negative pressure could be created. Basilakos & Plionis (2009) investigated the circumstances under which the analytical solution space within the framework of the interacting dark matter (IDM) scenario allows for a late accelerated phase of the Universe, and find that the effective annihilation term of the simplest IDM model is quite small by using the nine observational H(z) data points of Simon et al (2005). The gravitational matter creation model that is fully dominated by cold dark matter (Lima et al 2008;Basilakos & Lima 2010) is mathematically equivalent to one case of the IDM models (Basilakos & Plionis 2009).…”

“…In this paper, we use the newly revised H(z) data (Stern et al 2010;Gaztañaga et al 2009) and the Union2 set of 557 SNe Ia (Amanullah et al 2010) to constrain the relevant IDM models (Basilakos & Plionis 2009) by using the Markov chain Monte Carlo (MCMC) method. This paper is organized as follows.…”