# Is there a SQCD gluino string, similar to the gluon string?

A gluon string is a particular kind of open string terminated in two particles which are the sources for the field. Is it possible to have a similar arrangement with gluinos? At first glance, it seems to me that such object could not exist, or at least not as an extended object: you need bosons to mediate between the two sources, and you need bosons to build a classical field extended in space. On other hand, the fact that in the world-sheet such structure is just an object with fermionic coordinates --and without bosonic coordinates-- could be telling that you can build it, but it is not extended in space, just a point. But I have never read of such description, so surely intuition is failing here.

-
Good question, I'm curious about this myself. – David Z Aug 2 '11 at 21:03

## 1 Answer

In SQCD, you can get "gluino hadrons", mesons and baryons in which the gluino is one of the constituent fermions. (Also a gluinoball, a glueball with some gluinos mixed in.) So you could have a "gluino string", but in the opposite sense to what you want: it's two gluinos, at the ends of a gluon string.

Another possibility would be a topological defect in a gluino condensate. Maybe you could get this in N=2 SQCD, with monopoles at the ends.

But what you're looking for is a "fermionic meson", two quarks connected by the "gluino string". Well, you can define this as an operator, a fermionic Wilson line. The only place I can find such an entity playing a role is in holographic approximations to QCD like the Sakai-Sugimoto model. In holographic QCD, you typically have color branes and flavor branes. A gluon is a string between color branes, a quark is a string between a color brane and a flavor brane, a meson is a string between flavor branes, and a baryon is a brane connected by strings to flavor branes (these strings are the valence quarks). These strings and branes all live in AdS space, and QCD lives on the boundary. Also, these are usually supersymmetric models - the exact, nonsupersymmetric holographic dual to QCD has yet to be determined.

In superstring theory, you do have fermionic strings, and they are extended in space; the Fermi statistics come from the fermionic fields on the worldsheet. And the meson strings in holographic QCD do have mesino superpartners. See section 3.3.2 here. They are discussing mesino operators in the worldvolume theory of a flavor brane. One is a quark-squark composite, but the other is a quark and an antiquark connected by a gluino (the adjoint fermion). So we had to go into anti de Sitter space to find it, but there it is, the fabled fermionic gluino string. :-)

-
Still, I am not sure if mesinos are extended in space time, and even so, is there some non-extended solution... This should be, when the world-sheet bosonic field is constant, shouldnt it? – arivero Aug 6 '11 at 18:44
Sure, you can have a zero-length fermionic string, but you can also have a zero-length bosonic string. Also, the strings in this case live in the AdS space, which you might regard as unphysical compared to the boundary space. Though in an orthodox braneworld theory, you would say that the space near the brane was quite physical and that it was approximated by AdS. – Mitchell Porter Aug 10 '11 at 8:56
Just to clarify: the Sakai-Sugimoto model is not supersymmetric. – Frederic Brünner Apr 12 '14 at 4:40
Just to clarify the clarification... Sakai-Sugimoto is based on a supersymmetric theory (Type IIA string theory), but SUSY is broken by boundary conditions in one of the compact dimensions. cc: @Frederic Brünner – Mitchell Porter Apr 13 '14 at 5:27
That is correct. – Frederic Brünner Apr 13 '14 at 10:37