An accelerating cosmology without dark energy

Abstract

The negative pressure accompanying gravitationally-induced particlecreation can lead to a cold dark matter (CDM) dominated, accelerating Universe (Lima et al. 1996 [1]) without requiring the presence of dark energy or a cosmological constant. In a recent study, Lima et al. 2008 [2] (LSS) demonstrated that particle creation driven cosmological models are capable of accounting for the SNIa observations [3] of the recent transition from a decelerating to an accelerating Universe, without the need for Dark Energy. Here we consider a class of such models where the particle creation rate is assumed to be of the form Γ = βH+γH0, where H is the Hubble parameter and H0 is its present value. The evolution of such models is tested at low redshift by the latest SNe Ia data provided by the Union compilation [4] and at high redshift using the value of zeq, the redshift of the epoch of matter — radiation equality, inferred from the WMAP constraints on the early Integrated Sachs-Wolfe (ISW) effect [5]. Since the contributions of baryons and radiation were ignored in the work of LSS, we include them in our study of this class of models. The parameters of these more realistic models with continuous creation of CDM are constrained at widely-separated epochs (zeq ≈ 3000 and z ≈ 0) in the evolution of the Universe. The comparison of the parameter values, {β, γ}, determined at these different epochs reveals a tension between the values favored by the high redshift CMB constraint on zeq from the ISW and those which follow from the low redshift SNIa data, posing a potential challenge to this class of models. While for β = 0 this conflict is only at ≲ 2σ, it worsens as β increases from zero.