Ponente
Descripción
Although the Lambda cold dark matter model (ΛCDM) has become the best phenomenological description for the late-time accelerating phase of the Universe, the yet unsolved cosmological constant problem has driven an effort towards alternatives. We will mention two leading approaches which avoid the introduction of a cosmological constant. On the one hand, Dark Energy (DE) models where yet unobserved scalar fields would dominate the energy content at late times, avoiding fine-tuning issues as well as accelerating the Universe. On the other hand, there are Modified Gravity (MG) models that instead modify the current theory of gravity. We will demonstrate how to work out solutions to the perturbations equations in MG and DE models under the sub-horizon approximation. We will see that one can derive analytical solutions for DE perturbations and test them numerically showing that the quasi-static approximation actually performs quite well for this kind of models. Using the latter and simple modifications to the CLASS Boltzmann code, which we call EFCLASS, in conjunction to very accurate analytic approximations for the background evolution, one can obtain competitive results in a much simpler and less error-prone approach. We then use the aforementioned models to derive constraints from the latest cosmological data, including Type Ia supernovae, Baryon Acoustic Oscillations (BAO), Cosmic Microwave Background (CMB), H(z) and growth-rate data, and find they are statistically consistent to the ΛCDM model.
