Seminar: Nonanalyticity and On-Shell Factorization of Inflation Correlators

ABSTRACT

The dynamics of quantum fields during cosmic inflation can be probed through their late-time boundary correlators. The analytic structure of these boundary correlators contains rich physical information about bulk dynamics and their relationship to cosmological collider observables. In this talk, I will focus on a distinctive nonanalytic behavior known as the nonlocal signal, which emerges at the boundary of the physical region. To facilitate analytic calculations, I will first introduce the partial Mellin Barnes representation (PMB), which allows us to study this type of nonanalyticity at both the tree and loop levels. With the utility of PMB, we propose a signal-detection algorithm to identify all potential sources of nonlocal signals in arbitrary graphs and provide an "on-shell" factorization theorem for the leading signal. Additionally, we derive a "cutting rule" for the nonlocal signal as a byproduct, applicable to arbitrary graphs. I should emphasize that our theorem can be understood from a boundary OPE viewpoint, but is also applicable to dS-boost-breaking cases. Finally, I will present several examples up to 2-loop to illustrate our theorem. Notably, for certain simple yet nontrivial loop graphs, such as the 4pt triangle and box diagrams, we are able to derive analytic expressions for the leading nonlocal signal and easily extend the calculations to higher orders of squeezeness.  

Reference:

(1) Z. Qin and Z.-Z. Xianyu, "Helical inflation correlators: partial Mellin-Barnes and bootstrap equations," JHEP 04 (2023) 059, arXiv:2208.13790 [hep-th]; (2) Z. Qin and Z.-Z. Xianyu, "Inflation correlators at the one-loop order: nonanalyticity, factorization, cutting rule, and OPE," JHEP 09 (2023), 116, arXiv:2304.13295 [hep-th]; and (3) Z. Qin and Z.-Z. Xianyu, "Nonanalyticity and On-Shell Factorization of Inflation Correlators at All Loop Orders," arXiv: 2308.14802 [hep-th].

BIOGRAPHY

Mr. Zhehan Qin is a third-year PhD student in the Department of Physics at Tsinghua University, China. He obtained his bachelor's degrees in both physics, and mathematics and applied mathematics from Tsinghua University in 2021. His research mainly focuses on quantum field theories in de Sitter spacetime, in particular the perturbative calculations of late-time boundary correlators within the inflation background. He is also interested in the phenomenology of cosmological collider physics.