# How can string theory work without supersymmetry?

This question is inspired from reading Mitchell Porter's nice answer here to a question asking why supersymmetry should be expected naturally. Among other things, he explains that since weak scale supersymmetry comes a bit under pressure now, theorists could in the future be lead to consider rather high scale suppersymmetry or even string theory without supersymmetry at all.

This last bit gives me quite a pause, I always thought string theory needs supersymmetry to be consistant? And now it seems that there can be string vacua in the landscape that have no supersymmetry at all? Or would they be in something I have heared about which is called the "swamp land" (I dont know exactly what this is)?

So can somebody explain how string theory would work and look like without supersymmetry?

• – user1504 May 15 '13 at 23:28
• Thanks for the link @user1504, I like your question and Lumo's answer there :-) – Dilaton May 15 '13 at 23:49
• Along with the type 0 string, arxiv.org/abs/hep-th/9707148 is another example. – Mitchell Porter May 16 '13 at 1:11
• Actually, the SO(16) x SO(16) string in that paper might already be an example of the type 0 string? Anyway, one thing to note is that some of these "nonsusy strings" still have a type of susy somewhere, e.g. on the worldsheet but not in spacetime. – Mitchell Porter May 16 '13 at 2:01
• There is a possibly related paper about non supersymmetric F-Theory compactifications discussed in the first part of this blog post. – Dilaton Jul 24 '13 at 23:48

## 2 Answers

If you spend some time looking in detail at the arguments that string theory requires supersymmetry, you'll find that they are not watertight. (How could they be, since we still can't say/don't know precisely what string theory is?)

Basically, some string theorists argue that that the usual classification depends too strongly on choosing nearly trivial boundary conditions and backgrounds, and that weirder things ought to be allowed -- like type 0 strings, Liouville backgrounds, gravitational duals of randomly-chosen CFTs, miscellaneous higher spin gauge theories, bosonic string tachyon condensation, strings above Hagedorn temperature. The experts differ on how believable these arguments are, and in whether the various bizarre things you get this way really should be thought of as part of string theory.

What this means is that no one can quite answer your question. No one knows for sure that SUSY is required. No one knows for sure that it isn't. This is why it is a very good idea to a) not believe most things you read in the popular literature, and b) not believe most things you read in the scientific literature.

• Thanks for this nice answer, do you have some explanatory links to the different possibilities? Quite some time ago I have stopped reading too popular stuff about these topics for some reason ;-) – Dilaton May 16 '13 at 10:46

i think that the superstrings need not of supersymetry or better.all occur into of tolpology of smooth 4-dimension manifolds containing infinity families of smoth with differents metrics curvatures