Can string theory include fermions without supersymmetry?

[petergreat]

I'm taking an introductory string theory course which focuses on bosonic string theory. The lecturer says to include fermions supersymmetry must be included (aka. superstrings). If we face the event that the LHC fails to find any supersymmetry at TeV scale and the physics community lose faith in supersymmetry, are there any alternative ways of dealing with fermions in string theory? My knowledge is still very limited (basic QFT), but what comes into my mind is the following: is it possible to quantize the string action using anti-commutation relations? Or maybe this is wrong because string theory gives rise to gravitons with spin 2 which is not spin half?

 

[humanino]

There are means not have supersymmetry realized on our worldsheet, although existing in the entire target space.

How Strings Make Do without Supersymmetry: An Introduction to Misaligned Supersymmetry

 

[humanino]

It occurred to me, rather independently of the above, there are models of "hidden sectors" where supersymmetry is hard to find at the LHC essentially because of a proliferation of channels, the signal gets diluted. I'm not sure the original question points in this direction, and I have little familiarity with this, so I will not point to a reference, but "hidden sector" is the keyword if you want to google it.

 

[tom.stoer]

Are there hints why SUSYshould exist at the TeV scale? If the LHC does not find SUSY,does this rule out string theory (and MSSM, SUGRA etc.) or isn't it simply possible to "shift" SUSY to higher energies?

 

[humanino]

Are there hints why SUSYshould exist at the TeV scale?

There are discussions about the use of "naturalness" in model building, especially with historical perspective we would be foolish to put all our apples in the same basket. With this grain of salt, yes it is much more natural to have supersymmetry come in the game around the electroweak scale. But as above, it could be hidden.

If the LHC does not find SUSY,does this rule out string theory (and MSSM, SUGRA etc.) or isn't it simply possible to "shift" SUSY to higher energies?

It is always possible to push it where we can't see it, but it is also possible that the LHC would not be "clean" enough (because of the difficulties to understand backgrounds, in particular hadronic) with so-called hidden sectors.

 

[arivero]

There is also the joke I was doing in the other thread. If you take that the fermions are the quarks but the bosons are the terminated gluon sector, in the spirit (and probably exactly as) of http://dx.doi.org/10.1016/0370-2693(71)90028-1 , then you can use my hep-ph/0512065 to get a pair of equations for the number of generations, the number of light UP quarks and the number of light DOWN quarks:

$$D U = 2N$$

$$D(D + 1)/2 = 2N$$

So at least in this sense a quark/gluon dual model is realistic. Problem is, that this supersymmetry does not seem to control the Higgs, because the scalar partners are the usual mesons and diquarks, which do not couple to it.

Edit: note the simplest solutions of the above pair, from 2 U = D +1, are D=3, U=2. If you add the matching conditions for mesons too, you get an (bit ad hoc, but argued in later papers) extra equation for the count of the neutrino sector, 4 N = U^2 + D^2 -1, fixing the answer. Even without the fix, you can discard the next solution in terms of ugliness: D=7 U=4 N=14.