Question

(a) Explain what it means for a particle to be "off-shell". [1] (b) In a scattering experiment, an electron and positron are elastically scattered off each other. Show that there are two tree-level Feynman diagrams that contribute to this process, with photons as the exchange particle. [2] (c) By considering the conservation of energy and momentum, show that the exchange particle in both of your Feynman diagrams must be off-shell. (Hint: work in the centre of mass frame.) [4] (d) There are two other tree-level Feynman diagrams for the above scattering process, with a different exchange particle. What are these diagrams and why can their contribution to the scattering be neglected when compared with the photon diagrams? [3] 3

Answer 1

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My dear student your question comes under the category of multiple question type so as per guidlines given by HomeworkLib here i am giving u the answer of very first question .

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be a particle an an are Ans(a): An off-state of a may defined instance of a Quantum state that cloes not satisfy the physical constraints of Theory Physical Constraints conscvation of quantities like momotunes energy etc. This is off-shell state of don't eneiqy/ momentum that's why it is referred Unphysical 7 angular particle consure CSscanned with CamScanner