# Are W and T gauge bosons?

1. Jul 28, 2010

### Timo

I've left particle physics after my diploma a few years ago so I am not familiar with all of the slang, anymore. My question is pretty simple:

How common is it to call the W and the Z boson "gauge bosons" in professional physics.

Is it pretty much not used and seen as a sign of the person doing so not having understood the Higgs Mechanism? Is it used well knowing that it's just lazy talk? Or is the name "gauge bosons" really established for the W and Z? Did I simply not understand the Higgs mechanism? Something completely different?

As for the background of my question: Some time ago I was surprised seeing the Wikipedia article "gauge boson" listing the photon, gluons, W and Z as the gauge bosons of the Standard Model. What I learned is that gauge fields are the fields that are required to keep the action invariant under a local gauge, the SM gauge fields being the massless gluons, photons, W and B fields. I would then expect that a "gauge boson" is just the quantized field (maybe this is where I go wrong). However, I've never seen anyone else than me wondering about calling the massive W and Z, mixtures of gauge fields and Higgs fields, "gauge boson" so I am a bit confused. My question on Wikipedia was left unanswered for about half a year now.

Comments by actual particle physicists (please remember that I am interested in the professional usage, not usage on forum discussions), both from theory and experiment, would be very welcome.

EDIT: On the German keyboard, T and Z are next to another. I meant the Z, of course. Maybe some moderator can correct the thread title.

2. Jul 29, 2010

### Meir Achuz

W and Z are gauge bosons. The problem is that gauge bosons are supposed to be massless. The Higg's mechanism is hoped to produce the mass of the originally massless W and Z by spontaneously breaking the symmetry that required they be massless.

3. Jul 29, 2010

### nrqed

Professional particle physicists do refer to them as gauge bosons.
I think your misconception is in the last sentence above. The massive W and Z are *not* mixtures of gauge fields and Higgs field. The $W^{+}, W^{-}$ and Z are linear combinations of various components of the original $W^{\mu}$ and $B^\mu$. The Higgs field does not appear in these linear combinations. There are interactions between the gauge fields and the Higgs and upon spontaneous symmetry breaking these interactions lead to mass terms for the massive gauge bosons, but the Higgs field does not appear in the definition of the $W^{+}, W^{-}$ and Z.

Hope this helps.

4. Jul 30, 2010

### Timo

Absolutely, nrqed. I'll have a look in one of my books to reread the symmetry breaking in that light, but assuming you are correct (no reason to assume otherwise), that answer is more than I was hoping for. So thanks a lot to both of you (though I must admit I do not fully understand Meir's answer in the context of my question).

5. Jul 30, 2010

### nrqed

You are welcome Timo. You will see that the mass terms arise from interaction terms containing the Higgs field and two gauge boson fields. Upon SSB, the Higgs field is replaced by $H + v$ where v is the vacuum expectation value. But if you look at the definition of the W+, W- and Z, you will see that they are linear combinations of the components of the $W^{\mu}$ and $B^{\mu}$ only, no Higgs there.

Tschuss!

Patrick