Observational bounds on the recent expansion of the universe and extended theories of gravity using a model-independent q(z) reconstruction
Intervenant : Mariana Penna
The description of the recent accelerated expansion of the universe includes different propositions for dark energy models and modified gravity theories. To establish their features in order to discriminate between them or even rule out part of these models, using observational data, is a fundamental issue in cosmology. Assuming only that the spacetime is homogeneous and isotropic and described by a metric theory, in this presentation we will discuss a model-independent method to reconstruct directly the deceleration function via a piecewise function. We will then apply this approach to study the recent evolution of the universe (z < 2.4), without specifying its matter content nor any theory of gravitation, using type Ia supernovae, baryon acoustic oscillations and H(z) data. Subsequently, we will derive energy condition bounds for a class of extended theories of gravity (ETGs), and put observational constraints on these bounds. We also obtain an additional bound imposing that the strong energy condition applies only to the ordinary matter. The main result of this work is a set of bounds that every considered ETG must fulfill given the aforementioned assumptions. Using them, we also verify the fulfillment/violation of the energy conditions in the context of general relativity. For instance, the strong energy condition is violated, corresponding to an accelerated expansion, with more than 5.22σ confidence interval considering the whole reconstruction interval. Finally, we will show how these bounds can restrict the dynamics of the ETGs by imposing general restrictions on the ETG effective energy density and equation of state. In this case, we found a larger allowed region for a phantom-like dark energy (dark energy with equation of state w < -1).