Lectures on Inflation

TL;DR

The notes present inflation as the leading framework for the early universe, motivated by the flatness and horizon problems of the standard Big Bang cosmology. They develop the slow-roll scalar-field mechanism and connect its quantum fluctuations to the nearly scale-invariant, Gaussian curvature perturbations observed in the CMB, while outlining how tensors could reveal the inflationary energy scale. A unifying EFT of Inflation is introduced, recasting inflation as the dynamics of a Goldstone boson and enabling systematic predictions for the two-point function and possible non-Gaussianities. The text further explores extensions (DBI, Ghost inflation), the in-in formalism for higher-point functions, and the speculative regime of eternal inflation, highlighting both the predictive power and the open questions in early-universe cosmology.

Abstract

Planning to explore the beginning of the Universe? A lightweight introductory guide to the theory of Inflation.

Figures (22)

• Figure 1: Propagation of signals in the $\tau-\chi$ plane.
• Figure 2: The naive horizon $H^{-1}$ at the time of recombination (among the two purple arrows), is much smaller than the scale over which we see statistical homogeneity.
• Figure 3: How inflation solve the horizon problem: in the past, there is much more time than what there would have naively been without inflation.
• Figure 4: A simple inflationary model.
• Figure 5: A 'large-field' inflationary model.