Massless preheating with full Einstein gravity
Author(s)
Szmigiel, Mariusz
Type
Thesis
Abstract
Cosmic microwave background (CMB) radiation fills the universe almost uniformly
and it has imprints of the primordial curvature perturbations. Observations
of the CMB showed that to a large extent they are Gaussian [1]. However,
there are hints of some non-Gaussianity in the CMB that is within the reach of
experiments such as the Planck satellite. Different models of inflation predict
different levels of non-Gaussianity. Comparison with the experiments could be
used to falsify some models and single out the one describing the physics of
inflation most correctly [2].
It has been found that preheating can produce substantial levels of non-
Gaussianity in the massless model in the FRW backgroud [28]. In my thesis
I present a detailed description of a refined calculation, which does not assume
an FRW Universe but allows for the subhorizon inhomogeneous metric
perturbations to interact with the scalar fields in a fully non linear fashion.
Including the subhorizon metric perturbations in the dynamics is a physically
much more accurate calculation. It allows for increasing the lattice size at will
and therefore allows for including in the dynamics even those modes whose
wavelengths are equal to or greater than the size of the horizon.
I combined the lattice simulations with the separate universe approximation
[5, 40]. The latter states that points in space separated by more than
one Hubble distance cannot interact with each other and therefore evolve independently.
The numerical integration of the Einstein Equations uses the BSSN scheme [7], a technique used to solve initial value problems in the 3+1
formulation of numerical relativity.
I found that it is indeed possible to compute the superhorizon curvature
perturbations at a constant density hypersurface including full metric perturbations.
However, I also identified that accuracy improvements are needed to
compare my results to the literature. I identified and successfully implemented
a number of the improvements and presented some suggestions for the future
research.
and it has imprints of the primordial curvature perturbations. Observations
of the CMB showed that to a large extent they are Gaussian [1]. However,
there are hints of some non-Gaussianity in the CMB that is within the reach of
experiments such as the Planck satellite. Different models of inflation predict
different levels of non-Gaussianity. Comparison with the experiments could be
used to falsify some models and single out the one describing the physics of
inflation most correctly [2].
It has been found that preheating can produce substantial levels of non-
Gaussianity in the massless model in the FRW backgroud [28]. In my thesis
I present a detailed description of a refined calculation, which does not assume
an FRW Universe but allows for the subhorizon inhomogeneous metric
perturbations to interact with the scalar fields in a fully non linear fashion.
Including the subhorizon metric perturbations in the dynamics is a physically
much more accurate calculation. It allows for increasing the lattice size at will
and therefore allows for including in the dynamics even those modes whose
wavelengths are equal to or greater than the size of the horizon.
I combined the lattice simulations with the separate universe approximation
[5, 40]. The latter states that points in space separated by more than
one Hubble distance cannot interact with each other and therefore evolve independently.
The numerical integration of the Einstein Equations uses the BSSN scheme [7], a technique used to solve initial value problems in the 3+1
formulation of numerical relativity.
I found that it is indeed possible to compute the superhorizon curvature
perturbations at a constant density hypersurface including full metric perturbations.
However, I also identified that accuracy improvements are needed to
compare my results to the literature. I identified and successfully implemented
a number of the improvements and presented some suggestions for the future
research.
Version
Open Access
Date Issued
2013-03
Date Awarded
2013-07
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Rajantie, Arttu
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)