2025/11/21 by S. Willenbrock, Willenbrock, Scott
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #High Energy Physics - Lattice (hep-lat) #High Energy Physics - Phenomenology (hep-ph) #Quantum Electrodynamics and Casimir Effect #Quantum Mechanics and Applications #Quantum and Classical Electrodynamics
paper · pdf · doi:10.48550/arxiv.2511.16941
openalex publication_date 2025/11/21 · openalex created_date 2025/11/25 · openalex updated_date 2026/07/28
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.