Astrophysics Seminar

Curvature perturbations act as the seed for structure formation as well as the temperature fluctuations of the universe observed today. A light scalar field during inflation develops significant quantum fluctuations on super-horizon scales. If the amount by which space expands depends on the local value of the light field, then its quantum fluctuations are converted into curvature perturbations. 

Furthermore, if the expansion of space is a non-linear function of the light field, which is generally the case when the field modulates some non-equilibrium phenomenon, then the curvature perturbations will also be significantly non-Gaussian. This non-Gaussianity is measured by cosmological experiments. I will present general methods to estimate the non-Gaussianity arising from vacuum transition during inflation and preheating after inflation. The calculation for vacuum transition proceeds by finding the instanton solution in de Sitter space, while for preheating it involves lattice simulations. I will illustrate the methods by applying them to realistic alpha-attractor and Higgs inflation models.