Extra dimensions -> power law lowering unification?

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Discussion Overview

The discussion revolves around the implications of extra dimensions on the unification scale of fundamental forces, particularly whether such dimensions can lower the unification scale to the TeV scale. Participants explore the relationship between extra dimensions and experimental detection possibilities at the LHC, as well as the theoretical underpinnings related to string theory and gravity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest that the existence of extra dimensions could lower the unification scale to the TeV scale, which would make it detectable at the LHC.
  • Others clarify that the size of the extra dimensions is critical, with a specific radius needed for unification at the TeV scale.
  • There is a discussion about the implications of larger dimensions affecting experimental results at the LHC, with the possibility of hiding smaller dimensions.
  • Some participants question whether forces like gravity spread through these extra dimensions, with responses indicating that gravity does indeed interact with them.
  • There is a model-building aspect mentioned, where the circumference of extra dimensions can be chosen to address specific problems.
  • One participant raises a point about the early universe and the unification of forces, suggesting that gravity would unify with other forces at Planck scales due to the mass of gravitons.
  • Another participant discusses the concept of energy and frequency in relation to the size of dimensions, proposing that smaller dimensions would correspond to higher frequencies of waves.
  • There is confusion regarding the scales of GeV and TeV in the context of unification, with references to specific papers that discuss these concepts.

Areas of Agreement / Disagreement

Participants express differing views on the implications of extra dimensions for unification scales and the specifics of how these dimensions interact with fundamental forces. There is no clear consensus on the interpretations of the scales involved or the implications for experimental verification.

Contextual Notes

The discussion includes assumptions about the nature of extra dimensions, the relationship between gravity and other forces, and the mathematical frameworks involved, which remain unresolved. The dependency on specific models and interpretations of theoretical physics is evident.

karnten07
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Is it true that the existence of extra dimensions can lower the unification scale to the GeV scale? Does this mean that the LHC would be in range to detect a unification of couplings if this were true?
 
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Well, I think you mean (?) TeV, not GeV. And this is highly dependent on the size of the extra dimensions.

So, for example, to have unification at the TeV scale, the extra dimensions have to have radius of an inverse TeV (multiply by hbar and c, and appropriate powers of 10 to get meters). If you believe that string theory is correct, then you also need 5 other dimensions that have Planck length radius, and you also have to explain this new hierarchy.

But, assuming you can explain WHY the dimension has a TeV radius (or, if you don't care), then there ARE definite consequences for the LHC, and it IS experimentally verifiable.
 
BenTheMan said:
Well, I think you mean (?) TeV, not GeV. And this is highly dependent on the size of the extra dimensions.

So, for example, to have unification at the TeV scale, the extra dimensions have to have radius of an inverse TeV (multiply by hbar and c, and appropriate powers of 10 to get meters). If you believe that string theory is correct, then you also need 5 other dimensions that have Planck length radius, and you also have to explain this new hierarchy.

But, assuming you can explain WHY the dimension has a TeV radius (or, if you don't care), then there ARE definite consequences for the LHC, and it IS experimentally verifiable.

Are you saying: the bigger the dimension, the more we tend to notice it?
 
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Yes. The larger the dimension, the more it effects the experiments that we'll preform at LHC. We can also hide the extra dimension partially or completely by making it small enough.
 
does this assume that forces like gravity spread through these extra dimensions?
 
BenTheMan said:
Yes. The larger the dimension, the more it effects the experiments that we'll preform at LHC. We can also hide the extra dimension partially or completely by making it small enough.

Thanks, Ben, though I don't quite follow--the circumference of these dimensions can be changed?

I'm a bit curious about gravity as well, but in another way. It seems that in the early universe where the spatial dimensions are at Planck scales, gravity would unify with the other forces, but only because the gravitons would have to be far massive to fit. Is this right?
 
granpa said:
does this assume that forces like gravity spread through these extra dimensions?

Gravity is always spread through the other dimensions. This scenario assumes that the regular particles (electrons, quarks, etc.) can live in the extra dimensions.
 
Phrak said:
Thanks, Ben, though I don't quite follow--the circumference of these dimensions can be changed?

This is a model building issue. You usually pick the circumference of the extra dimensions to solve some problem.

I'm a bit curious about gravity as well, but in another way. It seems that in the early universe where the spatial dimensions are at Planck scales, gravity would unify with the other forces, but only because the gravitons would have to be far massive to fit. Is this right?

I don't quite understand the question. What does "Far too massive to fit" mean?
 
BenTheMan said:
This is a model building issue. You usually pick the circumference of the extra dimensions to solve some problem.

Thanks, though I had hoped you'd droped a bombshell: dimensions of variable size.

I don't quite understand the question. What does "Far too massive to fit" mean?

I should have said 'energetic'--higher frequency. If space were small, the limited number of wavelengths that would fit would be higher frequencies. Does that make sense?
 
  • #10
Phrak said:
Thanks, though I had hoped you'd droped a bombshell: dimensions of variable size.

Sorry :) I'm not sure how this would work. I've thought about it for about ten minutes, and couldn't convince myself that I had any kind of an answer.

I should have said 'energetic'--higher frequency. If space were small, the limited number of wavelengths that would fit would be higher frequencies. Does that make sense?

Yeah I understand now. Probably the answer is that the Plank length takes care of this. The radius of the compact directions is the Plank length, and the masses are quantized in units of the Planck Mass, which is 1/Planck Length. For a 2-d example, think about waves in a fishbowl, or something. If you set up a standing wave, there are exactly an integer number of waves in the fishbowl. You can think of the Planck mass resonances in terms of this---the lowest lying massive state corresponds to one wave in the fishbowl, etc.
 
  • #11
BenTheMan said:
Well, I think you mean (?) TeV, not GeV. And this is highly dependent on the size of the extra dimensions.

So, for example, to have unification at the TeV scale, the extra dimensions have to have radius of an inverse TeV (multiply by hbar and c, and appropriate powers of 10 to get meters). If you believe that string theory is correct, then you also need 5 other dimensions that have Planck length radius, and you also have to explain this new hierarchy.

But, assuming you can explain WHY the dimension has a TeV radius (or, if you don't care), then there ARE definite consequences for the LHC, and it IS experimentally verifiable.


Yes, i was just checking if it was at the GeV or TeV scale because this is really the issue i am confused about. The text says TeV which makes sense. But then for example in a paper by Dienes, Dudas and Gia Dvali where they discuss this accelerated power law, there is a graph showing the power law. But the scale is in GeV. Or does the TeV scale refer to unity which includes gravity by lowering the Planck scale?
 
  • #12
I don't know offhand. Can you post a link to the paper?

I'm familiar with Dienes, Dudas, and Gherghetta, but not Dienes, Dudas and Dvali.
 
  • #13
BenTheMan said:
I don't know offhand. Can you post a link to the paper?

I'm familiar with Dienes, Dudas, and Gherghetta, but not Dienes, Dudas and Dvali.

I'm sorry, i think that's who i meant. I think i get it now though, because unification is predicted to occur at 10^6 GeV which is 10^2 TeV? So with large extra dimensions unification occurs at the TeV scale. I think i was getting confused because the graphs were logarithmic. Thanks for the help though guys

Karnten07
 

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