Linked Questions

1
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1answer
537 views

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 $e^+e^-$ ?
1
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0answers
112 views

Pair production in empty space [duplicate]

Why can't the pair production process occur in empty space? I have read that a nucleus must exist and this is how it is useful: that the photon turns into virtual loops of e+ e- and one of them ...
22
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8answers
23k views

Why can't a single photon produce an electron-positron pair?

In reading through old course material, I found the assignment (my translation): Show that a single photon cannot produce an electron-positron pair, but needs additional matter or light quanta. My ...
10
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3answers
3k views

Can an object falling in vacuum generate electricity by itself?

When an object falls through vacuum, gravitational potential energy is converted to kinetic energy. Is there some way to get electrical energy out of the equation by itself (i.e. somehow convert the ...
25
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4answers
5k views

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 ...
4
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2answers
6k views

Pair production - mathematically?

Allover the web i am only seeing a statement similar to this: Pair production is not possible in vaccum, 3rd particle is needed so that conservation of momentum holds. Well noone out of many ...
6
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1answer
1k views

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 ...
3
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2answers
2k views

Pair production kinematics

In the process $A\rightarrow B+C$ If we know the energy and momentum four vectors of B and C, then how can we find the momentum three vector of A. The particular proces I have in mind is pair ...
0
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2answers
1k views

Particle anti-particle annihilation and photon production

This is just a conceptual question I guess. The annihilation of a particle with a finite mass and its anti-particle cannot lead to the emission of only one photon, and this is due to the conservation ...
3
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2answers
920 views

Electron/Positron pair production in free space?

Is it true that both linear momentum and energy cannot be conserved if the production of an electron-positron pair via photon annihilation were to occur in free space?
2
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1answer
585 views

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 ...
0
votes
2answers
868 views

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 ...
0
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1answer
91 views

momentum conservation in particle-antiparticle creation

It's understood that the PRESENCE of a heavy nucleus is necessary for conservation of linear momentum in pair creation. What I can't understand is why it must occur in ADJACENCY of the nucleus. Is ...