GR Dynamics of Stochastic Inflation

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This PhD project will advance the early universe theory of inflation, which explains the origin of galaxies and large-scale structure in the Universe, by merging stochastic inflation methods with fully nonlinear General relativistic evolution to make quantitative statistical predictions from inflationary models. Non-Gaussian signatures are inherently present in primordial fluctuations due to the nonlinearities produced by both general relativity and the fact that the potential responsible for driving inflation may be interacting. The goal of this project is to analytically and numerically model nonlinear inflationary dynamics in order to make bispectrum (three-point) and other higher-order correlator predictions which encompass a much broader range of inflationary scenarios (including those with multiple fields); this is an important discriminant between competing inflation models that can be used to distinguish them observationally. This will be achieved by exploiting the new GRChombo numerical relativity pipeline to compute these nonlinear effects using full 3D general relativistic simulations, augmenting it by the inclusion of quantum fluctuations that get amplified during Inflation. The latter will be implemented as stochastic source terms to be integrated within the GRChombo evolution routines and which, in turn, will be determined via perturbative analytic computations from effective field theory. DAMTP cosmologists, led by the PhD supervisor Shellard, have been able to constrain a wide range of inflationary scenarios by using innovative separable techniques (the MODAL pipeline) to extract and reconstruct the temperature and polarization bispectra from Planck satellite maps of the cosmic microwave background (CMB); this is now being applied to new observational data sets from both CMB experiments (Simons Observatory) and galaxy surveys (SDSS, DES and beyond). The resulting 3D fields of the stochastic nonlinear GR simulations from this PhD project will be directly amenable to analysis by these techniques, advancing the detailed confrontation of inflationary theory with cosmological data