I'm struggling to understand the Bose enhancement in reheating. I've read that:

- At the end of inflation, the inflaton field, $\phi$, is something like a condensate with excitations of a single momentum, say $p^\mu=(m_\phi,0)$ in the rest frame.
- The inflatons decay into pairs of bosons, say $bb$, with $q^{\mu}=(m_\phi/2,\pm\vec p)$, with $\vec p$ fixed by conservation of energy.
- The Fock space of the $b$ field is filled with states of momentum $\vec p$.
- This results in "Bose enhancement" of the decay $\phi\to bb$.

Why do the large occupation numbers for the final state $b$ enhance the decay rate $\phi\to bb$? Also, why can we assume that the inflaton field is like a condensate with excitations of the same momenta?

I've seen some arguments with matrix elements,
$$
|\langle n_\phi -1, n_k+1, n_{-k}+1 | a^\dagger_k a^\dagger_{-k} a_\phi | n_\phi, n_k, n_{-k} \rangle |^2 \propto n_k n_{-k}
$$
but I find them surprising. Is there a physical/intuitive way to understand the enhancement? Is it reasonable to think of the $CPT$ process? I suppose I find it intuitive that $bb\to\phi$ with $\phi$ at threshold could be enhanced by high occupation numbers for the correct $b$ momenta.

This post imported from StackExchange Physics at 2014-04-13 14:41 (UCT), posted by SE-user innisfree