Strings without low scale supersymmetry

[atyy]

Are there stringy candidates for reproducing the SM and dark matter etc without low scale supersymmetry?

 

[fzero]

Are there stringy candidates for reproducing the SM and dark matter etc without low scale supersymmetry?

As far as I know, there isn't any concrete explanation for the SUSY breaking scale from first-principles. As you're no doubt aware, the focus on low-scale SUSY is based explaining the EWSB scale.

If you don't want low-scale SUSY, then you have a few options. You could still consider models with high-scale SUSY, maybe broken at a GUT scale. I don't think this is a particularly well-studied area, but it doesn't seem like computing spectra of particles would be a big issue. The issue is always in computing parameters and scales.

One could also look for models with no high scale SUSY. One rough class would include non-critical strings and other non-SUSY orbifold models that are studied in the context of time-dependence and cosmology, rather than from the particle phenomenology perspective. The other class would include various free-fermion models designed to exhaust the possibilities for SM-like spectra. There are various groups that have worked on the latter, but someone that's worked in this area for decades is Bert Schellekens. I don't especially follow this work, but it does seem that it is very hard to cancel tachyons and tadpoles without some amount of SUSY being forced upon you (see 0810.2267 for example). On the other hand, there are very speculative suggestions (see 0904.3498) that tachyon condensation could be related to inflation.

I think that one can formulate plenty of models without low-scale SUSY. It is probably much harder to try to compute anything without the SUSY crutch.