What is vector-like matter?

[meha]

What is "vector-like" matter?

Hi,
can someone please tell me what vector-like matter is?

meha

 

[tom.stoer]

can you tell us where you found the term "vector-like matter"?

 

[meha]

Sure, one place I encountered it is here:
http://arxiv.org/abs/1001.1129

 

[tom.stoer]

Unfortunately they do not write down the kinetic part of the Lagrangian.

I suspected that it has something to do with spin, but w/o the Lagrangian it's hard to tell. In addition they talk about a scalar superpartner, but the superpartner to a spin-1object is not spin-0.

 

[Parlyne]

It looks like they're using the term to imply that the new (fermionic) matter has vector-like couplings to all standard model gauge fields. This is to be contrasted with ordinary standard model fermions, which have chiral SU(2)xU(1) couplings.

 

[meha]

Thanks. According to the reference hep-th/9903387 vector-like is used synonymously with non-chiral. Which means that left and right components transform differently under SU(2) x U(1). But what if these groups are not present? What would be the distinction between chiral and non-chiral matter for SU(5) or SO(10)?

 

[tom.stoer]

Just to make sure: "chiral" means that there is a gamma matrix projector in the Dirac kinetic term, whereas "vector" means it looks like in QED w/o such a projector?

 

[meha]

Thanks for all your thoughts.

 

[arivero]

Probabli the best translation is tom's "like in QED".

Historically, the problem of GUT models has been to avoid vector-like interactions. Actually, vector-like *matter* is a misnomer; it refers to *interactions*

 

[meha]

Now I am confused. In susy theories there are chiral superfields as well as vector superfields, completely independent of interactions. (http://en.wikipedia.org/wiki/Supersymmetric_gauge_theory). Chiral fields are defined by $$\bar{D} \Phi=0$$. Vector fields one the other hand are identical to their hermitian adjoints $$V = V^{\dagger}$$. Am I intermingling different concepts here?

 

[tom.stoer]

Yes, the concepts are different and the name vector-like matter is misleading.

As far as we understand the paper the situation is as follows: one uses spinors (!) to construct either bilinear vectors (like the el.-mag. current from the fermion field) or bilinear axial vector (like the left-handed neutrino current in el.-weak theory). The currents are coupled to other fields, in these examples the photon field or the Z- and W-field.

If the current is a vector, the matter is called vector-like even if the matter field itself is a spinor. (this is my interpretation of the discussion)

 

[Parlyne]

Yes, the concepts are different and the name vector-like matter is misleading.

As far as we understand the paper the situation is as follows: one uses spinors (!) to construct either bilinear vectors (like the el.-mag. current from the fermion field) or bilinear axial vector (like the left-handed neutrino current in el.-weak theory). The currents are coupled to other fields, in these examples the photon field or the Z- and W-field.

If the current is a vector, the matter is called vector-like even if the matter field itself is a spinor. (this is my interpretation of the discussion)

Strictly, the neutrino current is left chiral, not axial. A left chiral current is vector minus axial vector (or V-A); and a right chiral current is V+A.

 

[tom.stoer]

Strictly, the neutrino current is left chiral, not axial. A left chiral current is vector minus axial vector (or V-A); and a right chiral current is V+A.

You are right.