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arXiv · 2511.16941

Unstable Particles in Quantum Field Theory

Scott Willenbrock
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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.

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Scott Willenbrock. 2025-11-21. Unstable Particles in Quantum Field Theory. https://arxiv.org/abs/2511.16941

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