What is the current status of susy and string theory?

[potato123]

I heard that the LHC was supposed to do some testing on supersymmetry but i didn't hear anything from them and is string theory still possible or not.

 

[mfb]

String theory is out of the energy reach of the LHC.
It does test supersymmetry. So far, no supersymmetric particles have been found (it would be impossible to miss that), so the exclusion limits were improved. We now know better where supersymmetry is not.

 

[MathematicalPhysicist]

@mfb but does the LHC can confirm or disprove supersymmetry?

 

[mfb]

It has a chance to confirm it, if supersymmetry exists and if the scale is not too high.

It can disprove specific models and parameter ranges, but not all possible models of supersymmetry everywhere. On the other hand, if the LHC does not find supersymmetry, many of the theoretical advantages of supersymmetry go away. It loses significant motivation then.

 

[MathematicalPhysicist]

What are the theoretical advantages and what is the 'significant motivation'?
I wonder if it's to my interest to learn supersymmetry and supergravity, obvoiously as a mathematical theory there's no harm in learning it, but from the physical ground, if the LHC doesn't find supersymmetry is it still worthwhile to learn?

 

[mfb]

if the LHC doesn't find supersymmetry is it still worthwhile to learn?

Depends on who you ask. There is still a lot of interest in it, but if we don't find something in the next 5 years more and more groups will look for other things I guess.

Precision experiments at lower energy can extend the searches beyond the energy reach of the LHC for some models.

Supersymmetry with particle masses of the order of 1 TeV reduces the required fine-tuning of the Higgs mass and makes a unification of the strong interaction with the electroweak interaction more plausible. It also offers a natural candidate for dark matter. All those arguments get weaker if the particle masses are around 10 TeV or even higher.

 

[kodama]

is it true electron EDM measurements means LHC most likely will not see SUSY?

 

[mfb]

Jester covered it. "Most likely" depends on your prior expectation for SUSY parameters. In particular, if you don't expect large CP violation, it does not exclude anything.

 

[kodama]

Jester covered it. "Most likely" depends on your prior expectation for SUSY parameters. In particular, if you don't expect large CP violation, it does not exclude anything.

ok i'll read it.

if LHC doesn't find any SUSY how will that affect string theory research and LQG?

 

[newjerseyrunner]

I was under the impression that the next run of LHC was about to delve into some of the lower limits of predictions made by string theory? I've heard that the next run is above the lower energy limits of creating a micro black hole depending on the number of dimensions?

 

[mfb]

For some models with tiny extradimensions, it can be possible to test them. For others, it is not. That was true in run 1 as well.
That does not exclude string theory, the extra dimensions could be too small, or the interactions could behave differently in those extra dimensions.