Abstract: |
One of the most fundamental ingredients for our "Physics and Mathematics of the Universe" is the Yang-Mills theory, a quantum field theory based on a non-Abelian gauge group. In this colloquium, I will discuss the effects of the topological theta term in the Yang-Mills theories. This problem remains unsettled despite decades-old literature, and I will tackle this problem by combining both analytical and numerical methods. Our discussion has implications for the possible role of the axions in the Universe, for example, in the context of inflation and dark energy. |