Trying to relate string and inflation

In summary, Inflation is not allowed in the most well understood class of semi-realistic type IIA string compactifications: Calabi-Yau compactifications with only standard NS-NS 3-form flux, R-R fluxes, D6-branes and O6-planes at large volume and small string coupling.
  • #1
marcus
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http://arxiv.org/abs/0709.0002
Searching for Inflation in Simple String Theory Models: An Astrophysical Perspective
Mark P. Hertzberg (MIT), Max Tegmark (MIT), Shamit Kachru (Stanford), Jessie Shelton (Rutgers), Onur Ozcan (MIT)
24 pages, 5 figs
(Submitted on 3 Sep 2007 (v1), last revised 3 Sep 2007 (this version, v2))

"...We analyze three explicit string models from the recent literature, each containing an infinite number of "vacuum" solutions. Our numerical investigation of some natural candidate inflatons, the so-called "moduli fields", fails to find inflation. We also find in the simplest models that, after suitable field redefinitions, vast numbers of these vacua differ only in an overall constant multiplying the effective inflaton potential, a difference which affects neither the potential's shape nor its ability to support slow-roll inflation. This illustrates that even having an infinite number of vacua does not guarantee having inflating ones. This may be an artifact of the simplicity of the models that we study. Instead, more complicated string theory models appear to be required, suggesting that explicitly identifying the inflating subset of the string landscape will be challenging." http://space.newscientist.com/article/dn12628-can-string-theory-accommodate-inflation.html
Can string theory accommodate inflation?
 
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  • #2
Hello marcus,
I see what you are getting at and it seams to sound like a simple thing, even i find myself wondering 'Why don't they just use M-theory', isn't m-theory the string theory, so to speak, isn't it the "one" string theory? Why don't they use that! But still, they have made a good point buy using type 2(a) string theories because it is even more compelling evidence that that typical string theory can be swept to the side (the other evidence being the incompatibility with dark-matter). This is quite a good thing, the only problem is that the mathematics is unimaginably complex. The more complex the string theory, the harder the mathematics!
 
  • #3
kurt.physics said:
Hello marcus,
I see what you are getting at...

Hi Kurt, actually I am not sure how to interpret this paper and I'm hoping to learn by seeing how other people respond. Your response already helps clarify it for me, so thanks.

Something I noticed is that Shamit Kachru is one of the most highly cited string theorists less than, say 40 years old. If you look at papers since 2000, say, he is one of the stars.

Another thing I noticed is the quotes in the New Scientist article. I normally don't read NewSci because of its careless over-sensational style, but this article seemed better journalism than usual for them and the quotes were quite interesting----for instance from Paul Steinhardt.

And from the lead author Mark Hertzberg.

Another thing is the article SAYS up front that it has a definite political/pedagogical agenda of inducing more real astrophysicists, more mainstream working cosmologists, to look at stringy stuff. It says that it is a LANGUAGE barrier that has been keeping conventional astronomy people from taking string seriously and it declares that its purpose is to show by example how to get over that barrier.

But actually the example they present would seem to have something of the opposite effect. And their "dictionary" is almost funny. So here we have a paper by among other prominent people a young star of string, Kachru, that SAYS up front that it has a definite agenda, but that doesn't seem to go according. It even seems to put string public relations (with other fields like astro) at risk. So at first look, I am baffled.
 
  • #4
The first paper was accepted for publication in Physical Review D.
A second Hertzberg et al paper came out today about the same stuff, the difficulty of having an inflationary stage in cosmology in the context of certain models

http://arxiv.org/abs/0711.2512
Inflationary Constraints on Type IIA String Theory
Mark P. Hertzberg (MIT), Shamit Kachru (Stanford), Washington Taylor (MIT), Max Tegmark (MIT)
(Submitted on 16 Nov 2007)

"We prove that inflation is forbidden in the most well understood class of semi-realistic type IIA string compactifications: Calabi-Yau compactifications with only standard NS-NS 3-form flux, R-R fluxes, D6-branes and O6-planes at large volume and small string coupling. With these ingredients, the first slow-roll parameter satisfies epsilon >= 27/13 whenever V > 0, ruling out both inflation (including brane/anti-brane inflation) and de Sitter vacua in this limit. Our proof is based on the dependence of the 4-dimensional potential on the volume and dilaton moduli in the presence of fluxes and branes. We also describe broader classes of IIA models which may include cosmologies with inflation and de Sitter vacua. The inclusion of extra ingredients, such as NS 5-branes and geometric or non-geometric NS-NS fluxes, evades the assumptions used in deriving the no-go theorem. We focus on NS 5-branes and outline how such ingredients may prove fruitful for cosmology, but we do not provide an explicit model. We contrast the results of our IIA analysis with the rather different situation in IIB."

There was another related thread, not specifically about inflation but about rolled-up dimensions being unstable.
https://www.physicsforums.com/showthread.php?t=197056
 
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1. How does string theory relate to inflation?

String theory is a theoretical framework that aims to unite all the fundamental forces of nature, including gravity, into a single framework. Inflation theory, on the other hand, is a concept in cosmology that explains the rapid expansion of the universe in the first fraction of a second after the Big Bang. While there is currently no definitive answer, some scientists believe that string theory could provide a possible explanation for the underlying mechanisms of inflation.

2. Can string theory explain the origin of inflation?

This is a highly debated question in the scientific community. While string theory does offer potential mechanisms for inflation, it is still a developing theory and there is not yet enough evidence to definitively link it to the origin of inflation. More research and experimentation is needed to fully understand the relationship between string theory and inflation.

3. Are there any observable consequences of string theory on inflation?

String theory is a highly theoretical and complex subject, making it difficult to test directly. However, some scientists have proposed that certain signatures in the cosmic microwave background radiation (CMB) could potentially provide evidence for the influence of string theory on inflation. Other researchers are also exploring the possibility of detecting gravitational waves or other cosmological phenomena that could be linked to both string theory and inflation.

4. How does the concept of extra dimensions in string theory impact inflation?

String theory proposes that there are more than the traditional four dimensions (three spatial dimensions and one time dimension) that we experience in our everyday lives. These extra dimensions could have played a role in the dynamics of inflation and the expansion of the universe. Some scientists believe that the shape and size of these extra dimensions could have influenced the strength and duration of inflation, potentially leading to different observable consequences in the CMB.

5. What current research is being done to better understand the relationship between string theory and inflation?

Scientists are constantly conducting experiments and developing new theories to better understand the relationship between string theory and inflation. Some researchers are using data from the Large Hadron Collider (LHC) to search for evidence of supersymmetry, a key component of string theory. Others are using advanced mathematical models and simulations to explore the potential implications of string theory on the dynamics of inflation. Overall, there is ongoing effort to bridge the gap between these two fundamental theories in order to gain a deeper understanding of the early universe.

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