Celia Escamilla-Rivera

A tensor instability in the Eddington inspired Born-Infeld Theory of Gravity

In this paper we consider an extension to Eddingtons proposal for the gravitational action. We study tensor perturbations of a homogeneous and isotropic space-time in the Eddington regime, where modifications to Einstein gravity are strong. We find that the tensor mode is linearly unstable deep in the Eddington regime and discuss its cosmological implications.

Nonparametric reconstruction of the cosmic expansion with local regression smoothing and simulation extrapolation

In this work we present a nonparametric approach, which works on minimal assumptions, to reconstruct the cosmic expansion of the Universe. We propose to combine a locally weighted scatterplot smoothing method and a simulation-extrapolation method. The first one (Loess) is a nonparametric approach that allows to obtain smoothed curves with no prior knowledge of the functional relationship between variables nor of the cosmological quantities. The second one (Simex) takes into account the effect of measurement errors on a variable via a simulation process. For the reconstructions we use as raw data the Union2.1 Type Ia Supernovae compilation, as well as recent Hubble parameter measurements. This work aims to illustrate the approach, which turns out to be a self-sufficient technique in the sense we do not have to choose anything by hand. We examine the details of the method, among them the amount of observational data needed to perform the locally weighted fit which will define the robustness of our reconstruction. In view of our results, we believe that our proposal offers a promising alternative for reconstructing global trends of cosmological data when there is little intuition on the relationship between the variables and we also think it even presents good prospects to generate reliable mock data points where the original sample is poor.

Interacting closed string tachyon with modified Chaplygin gas and its stability

In this paper, we have considered closed string tachyon model with a constant dilaton field and interacted it with Chaplygin gas for evaluating cosmology parameters. The model has been studied in

Status on Bidimensional Dark Energy Parameterizations Using SNe Ia JLA and BAO Datasets

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The rise of a tensor instability in Eddington-inspired gravity

-dimensional that its

THE CLOSED STRING TACHYON AND ITS RELATIONSHIP WITH THE EVOLUTION OF THE UNIVERSE

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Nonparametric Reconstruction of the Om Diagnostic to Test ΛCDM

-dimensional is related to compactification on an internal non-flat space and its other

Unveiling the tachyon dynamics in the Carrollian limit

4

Cosmological analysis of a DGP stable model with

-dimensions is related to FLRW metric. By taking the internal curvature as a negative constant, we obtained the closed string tachyon potential as a quartic equation. The tachyon field and the scale factor have been achieved as functional of time evolution and geometry of curved space where the behaviour of the scale factor describes an accelerated expansion of the universe. Next, we discussed the stability of our model by introducing a sound speed factor, which one must be, in our case, a positive function. By drawing sound speed against time evolution we investigated stability conditions for non-flat universe in its three stages: early, late and future time. As a result we shall see that in these cases remains an instability at early time and a stability point at late time.

H(z)

Using current observations of forecast type Ia supernovae (SNe Ia) Joint Lightcurve Analysis (JLA) and baryon acoustic oscillations (BAO), in this paper we investigate six bidimensional dark energy parameterizations in order to explore which has more constraining power. Our results indicate that for parameterizations that contain z 2 -terms, the tension (σ-distance) between these datasets seems to be reduced and their behaviour is <1σ compatible with the concordance model (ΛCDM). Also, the results obtained by performing their Bayesian evidence show a striking evidence in favour of the ΛCDM model, but only one parameterization can be distinguished by around 1 % from the other models when the combination of datasets are considered.