• Register
PhysicsOverflow is a next-generation academic platform for physicists and astronomers, including a community peer review system and a postgraduate-level discussion forum analogous to MathOverflow.

Welcome to PhysicsOverflow! PhysicsOverflow is an open platform for community peer review and graduate-level Physics discussion.

Please help promote PhysicsOverflow ads elsewhere if you like it.


PO is now at the Physics Department of Bielefeld University!

New printer friendly PO pages!

Migration to Bielefeld University was successful!

Please vote for this year's PhysicsOverflow ads!

Please do help out in categorising submissions. Submit a paper to PhysicsOverflow!

... see more

Tools for paper authors

Submit paper
Claim Paper Authorship

Tools for SE users

Search User
Reclaim SE Account
Request Account Merger
Nativise imported posts
Claim post (deleted users)
Import SE post

Users whose questions have been imported from Physics Stack Exchange, Theoretical Physics Stack Exchange, or any other Stack Exchange site are kindly requested to reclaim their account and not to register as a new user.

Public \(\beta\) tools

Report a bug with a feature
Request a new functionality
404 page design
Send feedback


(propose a free ad)

Site Statistics

205 submissions , 163 unreviewed
5,075 questions , 2,226 unanswered
5,347 answers , 22,749 comments
1,470 users with positive rep
818 active unimported users
More ...

  Understanding Bose enhancement in reheating

+ 0 like - 0 dislike

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
asked Apr 6, 2014 in Theoretical Physics by innisfree (295 points) [ no revision ]
A comment on your last question: Mukhanov has a good discussion of this in his book Principles of Physical Cosmology, in chapter 5, I believe.

This post imported from StackExchange Physics at 2014-04-13 14:42 (UCT), posted by SE-user Danu
@danu I didn't find Muhkanov that helpful. "...an oscillating homogenous field can be thought of as a condensate of massive scalar particles with zero momentum". That's not obvious to me :s

This post imported from StackExchange Physics at 2014-04-13 14:42 (UCT), posted by SE-user innisfree
I remember reading it as well and being confused, only later understanding that he was referring back to something he derived earlier. I will try to take a look at it

This post imported from StackExchange Physics at 2014-04-13 14:42 (UCT), posted by SE-user Danu

Your answer

Please use answers only to (at least partly) answer questions. To comment, discuss, or ask for clarification, leave a comment instead.
To mask links under text, please type your text, highlight it, and click the "link" button. You can then enter your link URL.
Please consult the FAQ for as to how to format your post.
This is the answer box; if you want to write a comment instead, please use the 'add comment' button.
Live preview (may slow down editor)   Preview
Your name to display (optional):
Privacy: Your email address will only be used for sending these notifications.
Anti-spam verification:
If you are a human please identify the position of the character covered by the symbol $\varnothing$ in the following word:
Then drag the red bullet below over the corresponding character of our banner. When you drop it there, the bullet changes to green (on slow internet connections after a few seconds).
Please complete the anti-spam verification

user contributions licensed under cc by-sa 3.0 with attribution required

Your rights