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### Why during annihilation of an electron and positron 2 gamma rays are produced instead of 1? [duplicate]

$1 \gamma \rightarrow 1 e^- + 1 e^+$ (pair production) Then why $1 e^- + 1 e^+ \rightarrow 2 \gamma$ (annihilation of matter) instead of $1 e^- + 1 e^+ -> 1 \gamma$ ?
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### Why electron-positron annihilation releases two gamma photons? [duplicate]

I have heard that a gamma photon can convert into an electrons positron pair( I don't know how that works), but see when the reverse thing happens shouldn't a single photon be release but in books it ...
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### Why are two photons created in annihilation? [duplicate]

My textbook says it is because momentum has to be conserved but I don't see how photons can have momentum since they have zero mass (according to my book).
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### Showing the annihilation of an electron-positron pair [duplicate]

How to show that the annihilation of an electron-positron pair under emission of one real photon (mass zero) is forbidden by energy-momentum conservation, the emission of two photons is allowed?
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### Why are there two photons in pair production Feynman diagram? [duplicate]

Given I wonder why are there two photons entering in a) pair production? Isn't it one photon resulting in $e^+e^-$ ?
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### Decay of massless particles

We don't normally consider the possibility that massless particles could undergo radioactive decay. There are elementary arguments that make it sound implausible. (A bunch of the following is ...
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### Spontaneous pair production?

So I've been looking into particle-antiparticle pair production from a gamma ray and don't understand one thing. Let's say I have a 1,1 MeV photon and it hits a nucleus - electron-positron pair with ...
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### Why is a nearby nucleus required for Pair Creation?

I was recently studying Pair Production and Annihilation. The author mentions that a nearby nucleus is required when the photon materialises into a particle and an anti-particle. The explanation given ...
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### In QED, why is the $e^- + e^+\leftrightarrow\gamma$ process forbidden on-shell?

QED has a vertex that couples a single photon to two fermions. This vertex describes the annihilation of an electron-positron pair into a photon. Why is this process forbidden for all three particles ...
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### Why does a particle-antiparticle collision produce $2$ photons instead of $1$?

In one of the questions that I did, it asked: What is produced when an electron and positron collides with each other? The answer is $2$ photons. Why doesn't it merge into one? After all, the photon ...
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### QED: basic process which violates energy-momentum conservation

Why is the following process not possible? My book says it's because it violate energy and momentum conservation. Can someone explain me explicitly why? Why couldn't an energetic electron not ...
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### Pair production and energy conservation?

Consider the question whether a photon can decay, in the free space, into an electron and a positron - a pair production event. Such an event I don't think is possible, because both energy and ...
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### Particle-antiparticle annihilation

In the book - The Elegant Universe In quantum field theory, a particle and its antiparticle can momentarily annihilate one another, producing a photon. Subsequently, this photon can give rise to ...
When we consider process like $e^- e^- \to e^- e^-$ in QED, we see that from exchanges of one photon (tree-level diagrams) one can obtain Coulomb's law, while loop-diagrams give quantum corrections ...