All Questions
4
questions
1
vote
0
answers
83
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Cross-sections at zero temperature and high temperature for a process and its reverse
If the Feynman amplitude for a $2-2$ forward scattering $ab\to cd$ is denoted by $\mathcal{M}_{ab\to cd}$ and that of the reverse scattering process, $cd\to ab$, is denoted by $\mathcal{M}_{cd\to ab}$...
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2
votes
1
answer
73
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Guessing the temperature dependence of a decay rate $\Gamma(A\to B+B)$
For a two-body decay of the form $$A\to B+B$$ if the interaction strength controlling the decay is $\lambda$, the Feynman amplitude $\mathcal{M}$ will contain a factor of $\lambda$ from the vertex ...
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0
votes
1
answer
250
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Physical understanding of the change in scattering cross-sections at finite temperatures
I am familiar with the computation of scattering cross-sections in zero temperature quantum field theory.
How does a scattering cross-section typically behave at temperature $T$?
Let the cross-...
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3
votes
1
answer
249
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How did dark matter become a relic?
Why did the decay rate of the dark matter particles fall when the temperature of the Universe $T_U$ dropped below dark matter mass $M_{DM}$?
In particular, why can it not decay into lighter particles ...
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