Title: The approximate tale of cosmological collider signals

Speaker: Xi Tong (University of Cambridge)

Time: 13:30 pm, June 12 (Thursday) 2025

Venue: Room W260, Physics Building

Abstract: The soft limits of cosmological correlators often exhibit kinematic singularities in the form of the so-called cosmological collider signals, a smoking gun towards massive fields during inflation. Over the past decade, various exact solutions have been found at tree level, thanks to advances in the computational techniques of cosmological correlators. However, despite gaining full analytical control, the physical picture remains concealed by tedious mathematics. It is, for instance, mysterious why the signal strength should be suppressed by rational powers of the Boltzmann factor. In this talk, I will embark on an approximate quest to obtain cosmological collider signal waveforms that are only roughly correct, but whose physical interpretation becomes transparent. This approximation method gives us a clear understanding of signal strength and lead to a classification of cosmological collider signals in general theories with boost-breaking dispersion relations.

Bio: Dr. Xi Tong is currently a postdoctoral research associate in the Department of Applied Mathematics and Theoretical Physics in the University of Cambridge. He earned his PhD in Physics from The Hong Kong University of Science and Technology in 2023 and his Bachelor’s degree in physics from University of Science and Technology of China in 2018. Dr. Tong's research interest lies at the intersection of quantum field theory and gravity, notably primordial cosmology, black hole physics and holography. His past work encompasses topics such as cosmological collider physics, primordial non-Gaussian correlators, primordial black holes and black hole superradiance.