Using the CMB to explore inflationary models presenting features in the potential.

Inflation is now believed to be the theory describing the first instants of the universe. It consists on a period of very rapid (exponential) expansion of the universe. Despite being very well established as the theory describing the very early universe, since it solves several problems (it provides an explanation for the flatness, and homogeneity of the universe, and it predicts the generation of perturbations from this homogeneous background), the mechanism driving inflation is still unknown. One of our best ways to explore possible mechanisms that drive inflation is to look for anisotropies in the cosmic microwave background (CMB), the radiation coming from the epoch of recombination, which has recently been measured to extreme accuracy. The most accurate measurement of these anisotropies comes from the Planck satellite, and it is the data that I am using on my project.

My project consists on exploring models in which a scalar field, whose potential presents features, drives inflation. These potentials lead to very characteristic power functions, which can be compared to the data obtained from the Planck satellite. The objective is to use a Monte Carlo parameter estimation, comparing the theoretically and the observed two point function (and potentially higher point functions) to look for models presenting features that are favoured by the data. In case I find models that agree with the anisotropies observed by Planck, I will try to look for a theoretical explanation that would generate this inflationary mechanism (features could be caused, for example, by phase transitions in fields coupled to the inflaton)

The first part consists on using the Planck data to perform a Monte Carlo parameter estimation on models called axion monodromy inflation. These models are motivated from String Theory, and just like the models that I am interested in, they present very characteristic point functions. Although they are not favoured by the CMB data, the Planck collaboration already published in their official papers the parameter searches for these models, so I am using them to test that everything is working correctly in my Monte Carlo simulation, before I try to use it on new models.

At the moment that I am writing this, this test on axion monodromy models is looking very promising, and I am obtaining very similar results to those published by the Planck collaboration, so I will soon start testing new models that present features.