Astrophysics

We have great certainty on how gravity works around our solar system: General Relativity (GR) has been found to be very accurate at these small scales. On large scales though, we still have a considerable lack of understanding about the evolution of the universe, and its constituents. While the LCDM model is in good agreement with cosmological data, this might change in the future. For this reason, we need to test GR on these scales.

There are a number of proposals on how to characterize deviations from GR on larges scales, by parametrizing different cosmological evolutions of the universe - the PPF, EFT and EA approaches. The objective is to use experimental data to constrain these parameters, and thus identify the most accurate cosmological model. In this talk I will show an alternative, systematic and general, parametrization method, in which we construct the most general quadratic action for linear cosmological perturbations, given some field content and gauge symmetries. I will show the example of linearly diffeomorphism-invariant scalar-tensor theories, in which case the parametrization encompasses well-known theories such as Horndeski and Beyond Horndeski. The method can straightforwardly be applied to any gravity theory with any fields and gauge symmetries.

I will discuss how we constrain properties of the universe using two
tracers of large scale structure measured by the BOSS (Baryon
Oscillations Spectroscopic Experiment): galaxies and Lyman-alpha
forest. I will show recent results from baryonic acoustic oscillations
measured in both tracers and discuss cosmological implications. I
will briefly mention other measurements and consider forecasts for
quasar-forest bispectrum to constrain primordial non-Gaussianity.