Quantcast
  • 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.

News

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

Attributions

(propose a free ad)

Site Statistics

205 submissions , 163 unreviewed
5,082 questions , 2,232 unanswered
5,353 answers , 22,789 comments
1,470 users with positive rep
820 active unimported users
More ...

  The difference between The Dilaton and The Radion?

+ 5 like - 0 dislike
1073 views

I have read this question on the Dilaton, but I am a little confused with the distinction between the Dilaton and the Radion.

I definitely have the feeling that these two scalar fields are different particles.

I am fimiliar with the Diliton being related to the coupling constant in String Perturbation Theory.

$$g_s = e^{\langle \phi\rangle}$$

Moreover, the Dilaton is related to the size of a compactificated dimension. This was covered in our Bosonic String Theory lectures (I cannot link from outside the network).

On the other hand, the Radion is usually the name given to the $g_{55}$ (or $g_{zz}$ in the notes referenced) component of the metric tensor in a Kaluza-Klein theory, and too is related to the size of the compactified dimension

$$ \hat{g}_{zz} = \exp(2 \beta \phi) $$

giving a four-dimensional effective field theory

$$ \mathcal{L} = \sqrt{-\hat{g}}\hat{\mathcal{R}} = \sqrt{-g}\left(\mathcal{R} - \frac{1}{2}(\partial \phi)^2 \frac{-1}{4} \exp \left(-2 (D-1) \alpha \phi \right) \mathcal{F}^2 \right) $$

Furthermore, in Randal-Sundrum model I have seen the scalar field called a Radion, even though here we explicitly avoid compactification.

Finally, in the Cyclic Model of the Universe I have heard the moduli scalar field which 'measures' the distance of seperation between the two branes the Radion.

I have been studying the original paper on the Alternative to Compactification and a review on the Cyclic Model of the universe, as well the lecture notes on Kaluza-Klein Theory by C. Pope to try to learn about these things.

User1504 mentions that they are the same in M-Theory and Type IIA string theory, but I am afraid that I have not studied Superstring theory or beyone yet.

So to reiterate, my question is, can anyone give me a discription of the difference between the Dilaton and the Radion?

This post imported from StackExchange Physics at 2014-04-15 05:21 (UCT), posted by SE-user Flint72
asked Apr 14, 2014 in Theoretical Physics by Flint72 (120 points) [ no revision ]

1 Answer

+ 2 like - 0 dislike

The Dilaton, more commonly called the Radion, in Kaluza -Klein theory is similar to the Dilaton in String Theory. In the Type IIA Superstring Theory, for example, the Dilaton Field, together with the Metric Tensor and the Neveu-Schwarz B-field (analogous to the Electromagnetic Field), can be found in the Neveu-Schwarz Neveu-Schwarz sector. 

It is important to notice this, that the graviton, the "photon", and the dilaton are all found in the same sector of Type IIA string theory. The NS-NS sector of the Type IIA superstring theory is actually the sector that gives rise to the Kaluza-Klein theory.  

answered Apr 15, 2014 by dimension10 (1,985 points) [ no revision ]

This whole thread makes me feel pinged, even though I have no yellow dot in my inbox :-). I never encountered before that the $g_{55}$ in KK theory is called a radion ...

The Kaluza-Klein scalar field is usually called a radion; the term dilaton is more common in string theory etc. Actually the only use of the word "dilaton" in Kaluza-Klein that I remember is in the "also known as" brackets : )   

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:
p$\varnothing$ysicsOverflow
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
...