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Is a virtual particle necessary an off-shell particle? Could a virtual particle be on-shell?

Urb
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Mathieu Krisztian
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1 Answers1

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A virtual particle, by definition, is an internal line in a Feynman diagram. In most cases, it is off-shell. In some special cases, e.g. when studying factorization channels of the $S$-matrix, it can be taken on-shell.

Prahar
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