Resonance

:This article is about resonance in physics. For other senses of this term, see resonance (disambiguation).

Quantum field theory

In quantum field theory, resonance is an unstable particle/bound state. It is characterized by a complex pole off the real line in the S-matrix (which happens to be analytic). A sharp resonance is a resonance with a sharp peak in the S-matrix (which corresponds to a long lifetime compared to the reciprocal of its mass) while a broad resonance is a resonance with a spread out peak (which corresponds to a short lifetime relative to the reciprocal of its mass). If a resonance is too broad, it might not be considered as a particle at all even if it has a complex pole (far from the real line).

Related Topics:
Quantum field theory - Unstable particle - Bound state - Complex pole - S-matrix - Analytic - Lifetime

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See also relativistic Breit-Wigner distribution

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If the resonance happens to be a "fundamental particle" (i.e. described by a "fundamental field" of its own), it shows up as a complex pole off the real line in the 2-point connected correlation function (i.e. the propagator).

Related Topics:
Fundamental particle - Fundamental field - Connected correlation function - Propagator

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