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In Standard Model, there are vertex with 3 legs (example : $W l\nu$), with 4 legs (example : $WWWW$).
Is there a fundamental reason why in the Standard Model, there is no Feynman rule/diagram with more than 4 external legs ?
Are there possible in Beyond-Standard-Model theories ?
It is well known that to give a liftoff a rocket, we use the momentum principle: The momentum of the gases emitted by a rocket and the rocket's momentum is equal to zero. So why is it not enough to emit any gas quickly to impart a rocket's velocity without burning it? What is the contribution of ...
On the whole, the entropy of the universe is always increasing. There are far more possible states of "high" entropy than there are of "low" entropy. The example I've seen most often is an egg$-$ there is only one way for an egg to be whole (the low-entropy state), but many possible high-entropy ...
If you go through the definitions of phonon or for an explanation of phonon, Most of the text or article give the analogy to photons.
A photon is a discrete quantum of light.
A phonon is a discrete quantum of vibration.
Further, in this text, The author says, Phonon as being a particle (as wi...
