Unstable Particles in Quantum Field Theory
High Energy Physics - Phenomenology
2025-12-17 v2 High Energy Physics - Experiment
High Energy Physics - Lattice
Abstract
In honor of Dave Roper's 90th birthday, I present a pedagogical introduction to our modern understanding of unstable particles in Quantum Field Theory, based on the analytic structure of the propagator, with occasional remarks on the Roper resonance. I discuss the mass and decay rate of unstable particles, Breit-Wigner resonance formulae and width, poles and branch cuts, and pole trajectories.
Keywords
Cite
@article{arxiv.2511.16941,
title = {Unstable Particles in Quantum Field Theory},
author = {Scott Willenbrock},
journal= {arXiv preprint arXiv:2511.16941},
year = {2025}
}
Comments
12 pages, 7 figures. Minor changes