Infrared divergence

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In physics, an infrared divergence is a situation in which an integral, for example a Feynman diagram, diverges because of contributions of objects with very small energy approaching zero, or, equivalently, because of physical phenomena at very long distances.

The infrared (IR) divergence usually appears in theories with massless particles, and it means that we have asked an incorrect question. They represent a legitimate effect that a complete theory often implies. One way to deal with it is to impose an infrared cutoff and take the limit as it approaches zero and/or refine the question.

[edit] See also

• Soft photons
• Cutoff
• Renormalization
• Renormalization group
• Ultraviolet divergence