Speaker: Chia-Hsien Shen, Uppsala University and National Taiwan University

Title: Positivity in EFT Renormalization: from Quantum Particles to Classical Black Holes

Abstract: Renormalization group (RG) evolution is a fundamental feature of quantum field theory, playing a pivotal role in both its formal structures and phenomenological applications in particle physics and beyond. While the framework for calculating RG flows is well established, unexpected patterns continue to emerge. In this talk, I will leverage fundamental principles—unitarity and analyticity—to constrain the direction of RG evolution in effective field theory that shares a similar spirit as the a-theorem in conformal field theory. This result can be understood as an infrared avatar of positivity bound. For phenomenological applications, I will discuss examples in chiral perturbation theory and the Standard Model Effective Field Theory. I will also discuss a similar behavior in the renormalization of the dynamical tidal Love numbers of Schwarzschild black holes. This talk is based on 2505.02910 and work in progress.