Listening to Spacetime: Phase Space Harmonics and EFT

by Brian Henning (Kavli Institute for Theoretical Physics/UCSB)

Wednesday Mar 5, 2025, 3:30 PM → 4:30 PM Pacific/Honolulu

Room 417A (Watanabe Hall)

High-energy physics experiments measure distributions of relativistic events across phase space, yet traditionally phase space has served merely as a calculational backdrop. In this seminar, I propose a paradigm shift: viewing phase space as a dynamic, geometric entity deeply entwined with the underlying physics. By treating phase space as a manifold with its own intrinsic structure, we can reveal how its geometry encodes the kinematics of effective field theories (EFTs).

This approach enables a systematic construction of the complete EFT operator basis—a longstanding open problem. In particular, I will show how the manifold structure of phase space naturally organizes the allowed interactions via harmonic decompositions. For massless particles, I introduce a generalized N-particle helicity group that not only organizes the operator basis but also gives rise to new quantum numbers, unearthing hidden symmetries in the scattering data.

These advances bridge formal theory and phenomenology. As searches for physics beyond the Standard Model demand ever greater precision and complexity, a refined understanding of phase space offers novel strategies for data analysis, yielding powerful event discriminators. In the talk, I will illustrate these ideas with concrete examples and discuss their implications for both theoretical constructions and experimental observables.

Ultimately, by “listening” to the harmonics of phase space, we reveal a unified framework for EFT that equips us to confront the precision and complexity of modern high-energy physics.