Astrophysics

Perturbative calculations with light and polynomially self-interacting scalar fields in de Sitter spacetime are commonly plagued by infrared divergences as the scalar fluctuations become strongly coupled on large scales. Using techniques familiar from stochastic inflation, we treat super-Hubble fluctuations non-perturbatively through a probability distribution featuring composite operators of the light scalar. We find that these composite operators behave like late-time conformal primaries and admit a power-law four-point function in position space that is strikingly simple. We attribute physical meaning to these composite operators and conjecture that light interacting scalars in de Sitter in the stochastic picture hadronize into a tower of composite scalars on superhorizon scales. We further investigate whether these composite scalars can be described by a weakly-coupled effective field theory.

Two puzzling periods of accelerated expansion are thought to bookend the timeline of our Universe: cosmic inflation in the beginning, and dark energy domination in recent times. New observations from experiments such as DESI and the Simons Observatory are enabling unprcedented insights into both of these epochs. In this talk, I will highlight the critical and cross-cutting role of gravitational lensing in realizing this scientific promise, focusing on recent joint analyses of CMB lensing and galaxy clustering in redshift space, as well as delensing of CMB B-mode polarization. Along the way, I will discuss several enabling methodological developments, including a new understanding of extragalactic CMB foregrounds, fingers-of-god, pixel-free estimators, and more.