How can string theory work without supersymmetry?

Question

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?

Comments

related: physics.stackexchange.com/q/30703

This post imported from StackExchange Physics at 2014-03-30 15:50 (UCT), posted by SE-user user1504

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Thanks for the link @user1504, I like your question and Lumo's answer there :-)

This post imported from StackExchange Physics at 2014-03-30 15:50 (UCT), posted by SE-user Dilaton

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Along with the type 0 string, arxiv.org/abs/hep-th/9707148 is another example.

This post imported from StackExchange Physics at 2014-03-30 15:50 (UCT), posted by SE-user Mitchell Porter

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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.

This post imported from StackExchange Physics at 2014-03-30 15:50 (UCT), posted by SE-user Mitchell Porter

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There is a possibly related paper about non supersymmetric F-Theory compactifications discussed in the first part of this blog post.

This post imported from StackExchange Physics at 2014-03-30 15:50 (UCT), posted by SE-user Dilaton

Answer 1

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.

This post imported from StackExchange Physics at 2014-03-30 15:50 (UCT), posted by SE-user user1504

Comments

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 ;-)

This post imported from StackExchange Physics at 2014-03-30 15:50 (UCT), posted by SE-user Dilaton

Answer 2

p-adic strings or the adelic approach created by B.Dragovich don't require SUSY at all. At least, not the usual SUSY symmetry...

Non-critical string theory, the so-called Liouville theory, is based on the hypothesis of non-imposing the condition that critical strings with fermions (superstrings) impose on the space-time dimension due to internal consistency.

This post imported from StackExchange Physics at 2014-03-30 15:50 (UCT), posted by SE-user riemannium

Comments

Speaking as a user (as opposed to a moderator), concerning the first claim in the answer (v1), i.e., that $p$-adic (quantum) string theory doesn't need SUSY at all, it might be good idea to at least give a heuristic physical reason, or point to a reference.

This post imported from StackExchange Physics at 2014-03-30 15:50 (UCT), posted by SE-user Qmechanic

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Search for Branko Dragovich papers in the arxiv or his talks. p-adic string theory and the adelic approach references were also studied by Arefeva and the russian school (not only the serbian physicists like Dragovich and collaborators). Do you mean I should post some concrete reference? By the way, Witten, Freund and some other people studied p-adic amplitudes during the eighties of the past century...I am amazed that they abandoned that approach. After all, it does not require (a priori) extra new particles, only to understand what is a p-adic worldsheet (unsolved problem to my knowledge).

This post imported from StackExchange Physics at 2014-03-30 15:50 (UCT), posted by SE-user riemannium

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Some concrete references would be nice, if you know them.

This post imported from StackExchange Physics at 2014-03-30 15:50 (UCT), posted by SE-user Dilaton

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projecteuclid.org/… and references therein...

This post imported from StackExchange Physics at 2014-03-30 15:50 (UCT), posted by SE-user riemannium

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Most interesting to see p-adics cropping up in physics. Wonderful in one sense, perhaps not too surprising in another (Ostrowsky's theorem). I studied them a long time ago (late eighties) as part of a maths degree and applications to physics were spoken of but I never got around to looking up what they were.

This post imported from StackExchange Physics at 2014-03-30 15:50 (UCT), posted by SE-user WetSavannaAnimal aka Rod Vance

Answer 3

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

This post imported from StackExchange Physics at 2014-03-30 15:50 (UCT), posted by SE-user Rosy Mota