CosmoCoffee Forum Index CosmoCoffee

 
 FAQFAQ   SearchSearch  MemberlistSmartFeed   MemberlistMemberlist    RegisterRegister 
   ProfileProfile   Log inLog in 
Arxiv New Filter | Bookmarks & clubs | Arxiv ref/author:

What is exactly the drag epoch?
 
Post new topic   Reply to topic    CosmoCoffee Forum Index -> Cosmological Model
View previous topic :: View next topic  
Author Message
YinZhe Ma



Joined: 09 Oct 2008
Posts: 6
Affiliation: University of British Columbia

PostPosted: December 02 2011  Reply with quote

Hi Guys,

I don't quite understand the meaning of drag epoch. In Komatsu 2009 paper, it says:

the drag epoch zd and the decoupling epoch z*:

They would be equal only when the energy density of photons and that of baryons were equal at the decoupling epoch more precisely, they would be equal only when R=3ρb/4ργ=1 at z=z*?

What does this mean?

And why does the low density of baryon leads to later of drag epoch?

Thank you!
Back to top
View user's profile [ Hidden ]
Ben Gold



Joined: 25 Sep 2004
Posts: 97
Affiliation: University of Minnesota

PostPosted: December 07 2011  Reply with quote

The decoupling epoch is when the photon optical depth is one.

The drag epoch is when the baryon optical depth is one.

Since there are many more photons than baryons, the photons "decouple" (stop noticing the baryons) before the baryons stop noticing the photons.
Back to top
View user's profile [ Hidden ] Visit poster's website
Display posts from previous:   
Post new topic   Reply to topic    CosmoCoffee Forum Index -> Cosmological Model All times are GMT + 5 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group. Sponsored by WordWeb online dictionary and dictionary software.