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

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

145 submissions , 122 unreviewed
3,930 questions , 1,398 unanswered
4,862 answers , 20,637 comments
1,470 users with positive rep
502 active unimported users
More ...

Does string theory have a notion of vacuum?

+ 7 like - 0 dislike
92 views

Does string theory have a notion of vacuum? If yes, what is known about it?

This post imported from StackExchange Physics at 2014-04-04 16:40 (UCT), posted by SE-user Arnold Neumaier
asked May 24, 2012 in Theoretical Physics by Arnold Neumaier (12,385 points) [ no revision ]
Most voted comments show all comments
I suspect the question may be a bit too general to be easily answered. String theory isn't a field theory (String Field Theory exists, but I don't think it's well understood) but string theorists do have a concept of a vacuum. Indeed there's a group studying string vacua. Google "string vacuum project" for more info.

This post imported from StackExchange Physics at 2014-04-04 16:40 (UCT), posted by SE-user John Rennie
Hm Arnold certainly knows about these vacua the project is about; maybe the question asks about an even more "vacuous" vacuum that has not even spacetime in it ...?

This post imported from StackExchange Physics at 2014-04-04 16:40 (UCT), posted by SE-user Dilaton
@Dilaton: I know much about QFT and CFT but very little about string theory itself. In particular, I don't have a good conceptual grasp of what goes on. That's why I ask her sometimes questions in the hope of getting information that is not too technical but connects to what I know.

This post imported from StackExchange Physics at 2014-04-04 16:40 (UCT), posted by SE-user Arnold Neumaier
@JohnRennie: "string vacuum project" returned a conference web page, but none of the talks contains the word ''vacuum'' in the title. Thus I guess I need a much more basic source that tells me how the subjects discussed there are related to my question.

This post imported from StackExchange Physics at 2014-04-04 16:40 (UCT), posted by SE-user Arnold Neumaier
Isn't it similar to the notion in QFT?

This post imported from StackExchange Physics at 2014-04-04 16:40 (UCT), posted by SE-user MBN
@MBN: It is said that string theory is not a QFT. Thus I do not know which of the QFT notions extend, and how.

This post imported from StackExchange Physics at 2014-04-04 16:40 (UCT), posted by SE-user Arnold Neumaier
@ArnoldNeumaier: I am sure I know less about it than you, so my question was really more a question than a statement. ST is not a QFT in the sense that the string to be quantized is not a field, it is not defined on all of space time, but the quantization is analogous, is it not? Fourier expansion, creation and anihilation operators, vacuum state, excited states and so on. This is also a question.

This post imported from StackExchange Physics at 2014-04-04 16:40 (UCT), posted by SE-user MBN

2 Answers

+ 7 like - 0 dislike

As I recall from Susskind's course, there is no actual vacuum in string theory. There are some pieces of information, which can be helpful, like terminology developed for 2 decades. Please, note the dates.

String theory is believed to have a huge number of vacua — the so-called string theory landscape.

Terminology starting from almost nothing:

"In discussing compactifications of string theory, we will discuss only vacuum states that can be described as the propagation of strings in a background space-time. It is quite conceivable that more complex, "inherently stringy" vacuum states should be considered, but a workable approach to considering them does not appear to exist at present."

Candelas, P., Horowitz, G. T., Strominger, A., and Witten, E.Vacuum congurations for superstrings. Nucl. Phys., B258, 46. 1985

Developed to more specific ideas:

"The vacuum structure of the theory, called the string theory landscape (or the anthropic portion of string theory vacua), is not well understood. String theory contains an infinite number of distinct meta-stable vacua, and perhaps 10520 of these or more correspond to a universe roughly similar to ours — with four dimensions, a high planck scale, gauge groups, and chiral fermions. Each of these corresponds to a different possible universe, with a different collection of particles and forces",

de Sitter Vacua in String Theory, by Shamit Kachru, Renata Kallosh, Andrei Linde, Sandip P. Trivedi, 2003.

"Flux compactications typically give very many possible vacua, since the fluxes can take many difrent discrete values, and there is no known criterion for choosing among them. These vacua can be regarded as extrema of some potential, which describes the string theory landscape."

String Theory and M-Theory: A Modern Introduction, by Katrine Becker, Melanie Becker, 2007, p.477

"Gukov, Vafa and Witten (2001) made it evident that Flux compactications can lead to a solution of the moduli-space problem, since a nonvanishing potential for the moduli elds is generated. This led to the introduction of the string theory landscape, which describes a huge number of possible string theory vacua, in Susskind (2003)."

  • Gukov, S., Vafa, C., and Witten, E. (2001). CFT's from Calabi{Yau four-folds. Nucl. Phys., B584, 69. Erratum { ibid. B608, 477. E-print hep-th/9906070.

  • Susskind, L. (2003). The anthropic landscape of string theory. E-print hep-th/0302219.

String Theory and M-Theory: A Modern Introduction, by Katrine Becker, Melanie Becker, 2007, p.715

Can't find any other notions dated after 2007. Hope this was helpful.

This post imported from StackExchange Physics at 2014-04-04 16:40 (UCT), posted by SE-user Sigrlami
answered Nov 9, 2012 by Sigrlami (70 points) [ no revision ]
300 to you. Also, your pic makes you look like Malcolm in the middle.

This post imported from StackExchange Physics at 2014-04-04 16:40 (UCT), posted by SE-user NiftyKitty95
Thank you. Loved this show when I was young, maybe unconscious intention or coincidence =)

This post imported from StackExchange Physics at 2014-04-04 16:40 (UCT), posted by SE-user Sigrlami
+ 4 like - 0 dislike

In the string theory literature, the term "vacuum" is usually synonymous with "perturbative string background", i.e. a target space of a 2d CFT with the right central charge. This target space comes equipped with a metric satisfying the Einstein equations, as well as a host of other background fields, dilaton, B-field, and whatnot, all satisfying the equations implied by conformal invariance on the worldsheet.

Given any such background, you can use the machinery of perturbative string theory to add excitations. A standard (but not terribly rigorous) argument indicates that adding these new excitations is equivalent to deforming the background fields. Which means that the new state with excitations is also a string background. So any string theory state is a string background, and hence in some sense, a vacuum state.

It seems reasonable to think that any string background is a coherent state, built up by adding arbitrarily many strings to a state with no strings at all. This hypothetical no-string state would be a better analogy to the usual sort of QFT vacuum. But it's never been defined. We don't understand what string theory is well enough to say if this true vacuum exists, or if all we can do is dial around through non-trivial backgrounds.

Similar comments apply to other corners of string theory, like matrix models and AdS/CFT.

This post imported from StackExchange Physics at 2014-04-04 16:40 (UCT), posted by SE-user user1504
answered Nov 9, 2012 by user1504 (1,100 points) [ no revision ]

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).
To avoid this verification in future, please log in or register.




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

Your rights
...