What is meant by the breakdown of unitarity at TeV-scale

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In summary: This is due to the Higgs self-coupling going to zero as the Higgs mass goes to infinity. This is why people say that the SM becomes non-perturbative at some energy.In summary, the Standard Model predicts that at energies above 1 TeV, the probability for WW scattering will increase to a point where it is greater than one, breaking the principle of unitarity in quantum mechanics. This means that new physics, such as a Higgs-like mechanism, must be present to maintain unitarity. If the Higgs mass is above 1 TeV, its width becomes too large, making the SM non-perturbative at high energies.
  • #1
guimauve
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I read a statement that there is a breakdown of unitarity in the Standard Model at 1 TeV. What exactly is meant by that?
 
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http://en.wikipedia.org/wiki/Unitarity_(physics )
I couldn't get my head round this, might try later. Some one else can probably explain it to you if you don't understand it either.

*Edit*
Just realized that even if you know what Unitarity is, you might not under stand what it means when it breaks down.
 
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  • #3
If the time evolution isn't described with unitary operators, then probability isn't conserved and quantum mechanics breaks down.

As for breakdown at TeV-scale ... I don't see why this would be. Can you site the paper? Is it in the context of what it would mean if no Higgs-like mechanism was found?
 
  • #4
https://www.physicsforums.com/archive/index.php/t-187870.html

"If one looks at WW scattering, it is pretty easy to see that the process scales as energy squared (sometimes called s). This means that as energy increases, the probability for WW to scatter increases. At some point, this probability is greater than one, which doesn not make sense. ALL of quantum mechanics is based on probabilities being less than or equal to one.

The energy scale where WW scattering breaks unitarity is at 1 TeV. This means that we HAVE to see something happening at this energy scale, or our theory is not unitary, which would be an absolute disaster. SOME new physics (maybe just a single higgs) MUST come into save unitarity."

So this would be the context of no Higgs below 1 TeV which means no SM Higgs.
 
  • #5
guimauve said:
So this would be the context of no Higgs below 1 TeV which means no SM Higgs.
No. You need the Higgs mass to be less than approximately 1 TeV in the SM. Otherwise, its width becomes too large compared to its mass. But that's definitely the SM Higgs.
 
  • #6
@humanino

Why does the width become too large compared to it's mass?
 
  • #7
guimauve said:
Why does the width become too large compared to it's mass?
Take a look at Fig4. It's log-log but the scales are different : the width blows up.
 

What is meant by the breakdown of unitarity at TeV-scale?

The breakdown of unitarity at TeV-scale refers to a theoretical prediction in particle physics that suggests that the fundamental principles of quantum mechanics, specifically unitarity, may not hold true at very high energies, specifically at the TeV (teraelectronvolt) scale. This means that the probability of certain particle interactions occurring may exceed 100%, which goes against the principles of unitarity.

How does the breakdown of unitarity impact our understanding of particle physics?

The breakdown of unitarity challenges our current understanding of particle physics and the Standard Model. It suggests that there may be new, unknown physics at play at high energies that we have yet to discover. This presents an exciting opportunity for scientists to explore and expand our knowledge of the fundamental building blocks of the universe.

What evidence supports the possibility of unitarity breaking down at the TeV-scale?

There is currently no direct experimental evidence for the breakdown of unitarity at the TeV-scale. However, certain theoretical models, such as string theory, suggest that at very high energies, the rules of quantum mechanics may need to be modified. Additionally, the discovery of the Higgs boson at the Large Hadron Collider (LHC) has opened up the possibility for new physics beyond the Standard Model at the TeV-scale.

What implications does the breakdown of unitarity have for the LHC and other particle accelerators?

The breakdown of unitarity has significant implications for the LHC and other particle accelerators because it suggests the possibility of discovering new particles and phenomena at the TeV-scale. This is why the LHC is currently being upgraded to reach even higher energies, in hopes of discovering new physics and understanding the breakdown of unitarity.

Are there any potential consequences of the breakdown of unitarity at the TeV-scale?

One potential consequence of the breakdown of unitarity is that it could lead to inconsistencies in the mathematical equations used to describe particle interactions. This could have far-reaching implications for our understanding of the universe and could potentially require a major overhaul of our current theories and models.

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