IAS-PHYS Fundamental Physics Seminar Series - Tracing out Massive Fields in Cosmology

Abstract

Cosmological correlators are calculated through the in-in formalism in (quasi-)de Sitter background. Their effective description is best represented by a reduced density matrix. In this talk, the speaker will first review the differences between the usual EFT used in scattering amplitude calculations and the Schwinger-Keldysh EFT for correlators. He will then discuss the reduced density matrix for a light field at finite time, obtained by tracing out a massive field in a quasi-single-field model with non-linear couplings. The trace generates branch-mixing terms which are generally present in the Schwinger-Keldysh formalism. Explicit calculations of the effective description and the bispectrum will be shown for a conformally coupled massive field. He will then discuss how a local effective field theory is obtained through a large mass expansion of the exact non-local effective description. Finally, the speaker will study the symmetry and Schwinger-Keldysh constraints on the reduced density matrix.


About the Speaker

Dr. SUN Guanhao is currently a Hongshen Young Researcher at Chongqing University. He was a postdoc in the physics department of the University of California, San Diego. He obtained his PhD in physics from Columbia University in 2022, and his Bachelor's degree from The Hong Kong University of Science and Technology in 2016. Dr. Sun's research focuses on the application of effective field theories in cosmology and condensed matter systems. His works span a variety of topics, including inflationary physics, effective field theory of condensed matter systems, formal QFT, and black hole superradiance.


About the Center for Fundamental Physics

For more information, please refer to https://iascfp.hkust.edu.hk/.


For Attendees' Attention

Seating is on a first come, first served basis.