## Wednesday, June 25, 2008

### MSSM in string theory: review

Hans Peter Nilles et al. review known stringy backgrounds that reproduce the Minimal Supersymmetric Standard Model, including the following constraints:
1. Exact MSSM spectrum below the unification scale
2. R-parity
3. Hierarchical Yukawa couplings with nonzero mixings
4. Solution to the mu problem
5. See-saw suppressed neutrino masses
It's amazing but even with these huge constraints, people have found diverse models that satisfy them.

The authors review these models. Because string theory offers us a very different toolkit and a very different kind of freedom in model building than field theory, I think it is a highly nontrivial observation that string theory is able to naturally reproduce all these desirable phenomenological features.

The folks who don't think that it is likely that string theory is the right description of fundamental physics are just being utterly unreasonable, if I have to use an extremely diplomatic description.