3:30–4:30 pm ERC 161
Liang Dai (UC Berkeley) "Looking for Axion Particles In the Universe"
Axion particles are a generic class of hypothetical spin-zero particles that are of great interest to a range of fundamental questions about particle physics and about the universe. In this talk, I will discuss several ideas at the intersection of particle physics and cosmology to find their signatures. An ultralight axion particle may cause the formation of a cosmic string network following spontaneous symmetry breaking in the early Universe and may rotate the polarization direction of photons through a Chern-Simons interaction with electromagnetism. I will discuss how traditional and novel statistical estimators can be employed to extract polarization rotation signatures from Cosmic Microwave Background anisotropies. Additionally, I will introduce a new idea of measuring axion-induced polarization rotation using large galaxy surveys. Furthermore, the QCD axion as a promising solution to the Strong CP Problem may constitute the dark matter, and may cluster in self-gravitating mini-halos of asteroid to planet masses. I will explain how the most extreme gravitational lensing phenomenon in the universe can be exploited to reveal the existence of such minuscule structures.
