Our Universe is spatially homogeneous and isotropic on large scales. This high symmetry of the Universe enables us to systematically investigate various possibilities of cosmological scenarios using the powerful tool from high-energy physics, namely, effective field theory (EFT). In this approach, the difference in field contents is translated into the difference in symmetry-breaking patterns,...
Effective field theory techniques provide an efficient way to enumerate the allowed operators in various physical systems based on their symmetries. Moreover, they allow for a systematic classification of these operators in decreasing order of relevance based on a derivative expansion. These tools are powerful in guiding us towards the construction of a realistic inflationary scenario with few...
I will give an introduction to the effective field theory (EFT) of open systems aimed at cosmologists. After motivating why open systems are relevant in cosmology, I will discuss Brownian motion as the simplest illustrative example. I will then present the EFT construction for open systems with spontaneous symmetry breaking and in the presence of gravity, with cosmological applications in mind.
