Abstract
In the search for understanding the initial conditions of the universe, it is crucial describe with high precision the evolution of the matter density in the universe on large scales as a function of time. The Effective Field Theory of Large Scale Structure (EFT of LSS) provides exactly this: it is a consistent perturbation theory of the evolution of the density on large scales, that parametrizes analytically unknown short scale behavior such as galaxy formation.
In this thesis we discuss the inclusion of particular initial conditions – primordial nonGaussianity (PNG) – in the EFT of LSS. It turns out that the evolution equations have to be modified slightly to capture the fact that for statistically nonGaussian initial conditions, short scale physics in one place can be related to large scale physics in some other place. This forces us to introduce new, fluidlike parameters in the theory on top of the standard speed of sound, viscosity, and related parameters.
We show how the EFT of LSS outperforms Standard Perturbation Theory (SPT), which does not properly take into account the backreaction from short scales, in allowing us to extract information about PNG, and forecast the constraints nearfuture galaxy surveys could put on PNG. We also comment on the relevance and subtleties involved in properly accounting for inevitable theoretical errors in forecasts.
Finally we investigate the reach of any standard perturbative treatment to the evolution of the matter density field. We do this by means of a study in one spatial dimension, for which some exact results are known. We show that perturbation theory converges for a range of Fourier space observables, but find that it is asymptotic for at least some real space observables such as the two point correlation function. We argue that this asymptotic behavior is related to the theory’s inability to describe the evolution of statistically rare events in which the density field is very large even on large scales. This suggests that there might be a floor to how well any perturbative treatment can perform. We provide a tentative estimate of the size of this floor as a function of scale.
In this thesis we discuss the inclusion of particular initial conditions – primordial nonGaussianity (PNG) – in the EFT of LSS. It turns out that the evolution equations have to be modified slightly to capture the fact that for statistically nonGaussian initial conditions, short scale physics in one place can be related to large scale physics in some other place. This forces us to introduce new, fluidlike parameters in the theory on top of the standard speed of sound, viscosity, and related parameters.
We show how the EFT of LSS outperforms Standard Perturbation Theory (SPT), which does not properly take into account the backreaction from short scales, in allowing us to extract information about PNG, and forecast the constraints nearfuture galaxy surveys could put on PNG. We also comment on the relevance and subtleties involved in properly accounting for inevitable theoretical errors in forecasts.
Finally we investigate the reach of any standard perturbative treatment to the evolution of the matter density field. We do this by means of a study in one spatial dimension, for which some exact results are known. We show that perturbation theory converges for a range of Fourier space observables, but find that it is asymptotic for at least some real space observables such as the two point correlation function. We argue that this asymptotic behavior is related to the theory’s inability to describe the evolution of statistically rare events in which the density field is very large even on large scales. This suggests that there might be a floor to how well any perturbative treatment can perform. We provide a tentative estimate of the size of this floor as a function of scale.
Original language  English 

Awarding Institution 

Supervisors/Advisors 

Award date  4 Jun 2018 
Publisher  
Publication status  Published  4 Jun 2018 
Keywords
 Cosmology
 largescale structure
 primordial nonGaussianity
 effective field theory