Speaker
Description
Axions are among the most compelling candidates for dark matter and arise naturally in theories of fundamental physics. Their cosmological behavior, however, depends on assumptions about the underlying theory that are often taken for granted. One such assumption concerns the geometry associated with the fields describing the axion, which is usually assumed to be flat. In this talk, I will explore what happens when this geometry is instead curved—specifically, when it has a hyperbolic structure of the kind that can arise in theories such as string theory, SUGRA and other UV complete theories. We will see that this change can dramatically alter the evolution of the axion in the early universe. It can lead to efficient production of axion particles and generate fluctuations that are very small on the enormous scales probed by the cosmic microwave background, yet much larger on scales comparable to galaxies. This mechanism has several implications such as for DM isocurvature, tachyonic production to name a few. This provides an example of how the geometry underlying a fundamental theory can leave potentially observable signatures in our universe.