Why is the TeV scale important in predicting new physics?

[A/4]

When the LHC comes online in the near future, it's expected that we'll see a whole new realm of HEP. I'm curious why we actually believe this is true. For example, Kaluza-Klein inspired theories use the TeV scale as an a priori condition for their phenomenological predictions. The recent surge of unparticle physics papers does likewise. There is no obvious reason to set this scale, however.

What theories (SUSY, string-inspired, LQG, etc...), aside from Higgs, conclusively pinpoint the TeV scale as the place to look for new physics (in the same way that the W and Z were successfully predicted to appear)?

 

[arivero]

What theories (SUSY, string-inspired, LQG, etc...), aside from Higgs, conclusively pinpoint the TeV scale as the place to look for new physics (in the same way that the W and Z were successfully predicted to appear)?

Partial wave analysis.

It is said (I can not confirm the historicity of the process) that the discovery of W was done in two steps: First, partial wave analisys (or unitarity) predicted new physics at 100 GeV, then the W was predicted.

 

[Haelfix]

Google for LHC no lose theorems, they state under fairly easy to believe assumptions that something has to be seen at the LHC that modifies or completes the EW sector. You can actually see this based not only on unitarity bounds, but also vacuum stability arguments.

As for SuSY, well its detailed and somewhat model dependant. But on naturalness arguments, (especially with a light higgs), they tend to have their lightest superpartners somewhere in that range as well. The heavier the higgs is, the amount of finetuning goes up as a powerlaw and the hierarchy solution becomes worse and worse (it receives radiative corrections from the stop mass)

 

[BenTheMan]

A/4 a couple of reasons.

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.

The motivation for SUSY is to keep the higgs mass low, which is a thread all to itself!

 

[arivero]

http://www.hep.lu.se/atlas//thesis/egede/thesis-node21.html

http://www.hep.lu.se/atlas//thesis/egede/thesis-img175.gif