Title: Compact Scalars at the Cosmological Collider

Time: 10:00 am, Nov 9 (Thursday) 2023

Location: 腾讯会议：319-394-973 https://meeting.tencent.com/dm/4H1c2V8pkc8c

Abstract: We study the dynamics of scalar fields with compact field spaces, or axions, in de Sitter space. We argue that the field space topology can qualitatively affect the physics of these fields beyond just which terms are allowed in their actions. For instance, we argue that while the free massless noncompact scalar field does not admit a two-point function that is both de Sitter-invariant and well-behaved at long distances, the massless compact scalar does. As a proof of principle, we show how the long-distance behavior, and thus the cosmological collider signal, of a heavy scalar field can be sensitive to whether or not a light scalar field it weakly interacts with has a compact field space. We find an interesting interplay between the circumference of the field space and the Hubble scale. When this circumference is much larger than Hubble, the compact field behaves similarly to a light noncompact scalar and forces the heavy field to dilute much faster than any free field can. However, depending on how much smaller the circumference is compared to Hubble, the compact field can cause the heavy scalar to dilute either faster or slower than any free field, and so there can be qualitative and observable consequences of the field space's compactness in inflationary correlation functions.

Bio: John Stout completed his PhD at Cornell University in 2017 under the supervision of Liam McAllister. He then worked as a postdoctoral researcher at Utrecht University and the University of Amsterdam, before moving to Harvard University in 2020 where he is currently a postdoctoral fellow.