What is the hand that rocks the "cradle” of the accelerating universe?

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Interacting 3-form dark energy models: distinguishing interactions and avoiding the Little Sibling of the Big Rip

Publication . Morais, João; Bouhmadi Lopez, Mariam; Kumar, K. Sravan; Marto, João; Tavakoli, Yaser

In this paper we consider 3-form dark energy (DE) models with interactions in the dark sector. We aim to distinguish the phenomenological interactions that are defined through the dark matter (DM) and the DE energy densities. We do our analysis mainly in two stages. In the first stage, we identify the non-interacting 3-form DE model which generically leads to an abrupt late-time cosmological event which is known as the little sibling of the Big Rip (LSBR). We classify the interactions which can possibly avoid this late-time abrupt event. We also study the parameter space of the model that is consistent with the interaction between DM and DE energy densities at present as indicated by recent studies based on BAO and SDSS data. In the later stage, we observationally distinguish those interactions using the statefinder hierarchy parameters {S3(1),S4 (1)},{S3 (1),S5 (1)} . We also compute the growth factor parameter ε(z) for the various interactions we consider herein and use the composite null diagnostic (CND) {S3(1), ε(z)} as a tool to characterise those interactions by measuring their departures from the concordance model. In addition, we make a preliminary analysis of our model in light of the recently released data by SDSS~III on the measurement of the linear growth rate of structure.

2017-03Journal article

Open access

3-Form Cosmology: Phantom Behaviour, Singularities and Interactions

Publication . Morais, João; Bouhmadi Lopez, Mariam; Marto, João

The latest cosmological observations by the Planck collaboration (and combined with others) are compatible with a phantom-like behaviour (w < − 1) for the dark energy equation of state that drives the current acceleration of the Universe. With this mindset, we look into models where dark energy is described by a 3-form field minimally coupled to gravity. When compared to a scalar field, these models have the advantage of more naturally accommodating a cosmological-constant and phantom-like behaviours. We show how the latter happens for a fairly general class of positive-valued potentials, and through a dynamical system approach, we find that in such cases the 3-form field leads the Universe into a Little Sibling of the Big Rip singular event into the future. In this work, we explore the possibility of avoiding such singularity via an interaction in the dark sector between cold dark matter and the 3-form field. For the kind of interactions considered, we deduce a condition for replacing the LSBR by a late time de Sitter phase. For specific examples of interactions that meet this condition, we look for distinctive imprints in the statefinder hierarchy { S 3 ( 1 ) ; S 4 ( 1 ) } , { S 3 ( 1 ) ; S 5 ( 1 ) } , and in the growth rate of matter, e ( z ) , through the composite null diagnostic (CND).

2017Journal article

Open access

Cosmic infinity: a dynamical system approach

Publication . Bouhmadi Lopez, Mariam; Marto, João; Morais, João; Silva, César M.

Dynamical system techniques are extremely useful to study cosmology. It turns out that in most of the cases, we deal with finite isolated fixed points corresponding to a given cosmological epoch. However, it is equally important to analyse the asymptotic behaviour of the universe. On this paper, we show how this can be carried out for 3-forms model. In fact, we show that there are fixed points at infinity mainly by introducing appropriate compactifications and defining a new time variable that washes away any potential divergence of the system. The richness of 3-form models allows us as well to identify normally hyperbolic non-isolated fixed points. We apply this analysis to three physically interesting situations: (i) a pre-inflationary era; (ii) an inflationary era; (iii) the late-time dark matter/dark energy epoch.

2017-03-21Journal article

Open access