# Higgs Coupling - Fifth Force [duplicate]

To which of the four forces of nature does the coupling of the Higgs scalar field to other quantum fields ultimately belong to, if any? If it doesn't fall into any of the four known categories of forces, does that imply a fifth "force" of nature, or have I misunderstood the definition of force?

## marked as duplicate by lemon, John Rennie, Qmechanic♦Oct 28 '16 at 9:49

• Hi Optimus Prime. Bearing in mind this is a site for (and I quote from the tour) active researchers, academics and students of physics we expect people posting questions to have done at least some research. In this case the most obvious search would have immediately answered your question. – John Rennie Oct 28 '16 at 8:16
• The Higgs is in the electroweak sector. As neutral it couples only with the weak coupling constant. (when a model appears which unifies gravity at the quantum mechanical level with the other three forces, it will also couple with the gravitational constant) – anna v Nov 2 '16 at 4:52

The fields in the Standard model can be put into three categories:

1. Matter fields (quarks, leptons).

a) Massless at the 'fundamental' level. Massive after aquireing mass via Higgs mechanism.

b) Fermions

c) Interact with each other only via other fields, e.g.

2. Mediators of the interactions (gauge bosons). These are responsible for the presence of the 'forces'.

a) Massless at the 'fundamental' level. W&Z bosons become massive after aquireing mass via Higgs mechanism. Photons and gluons are massless.

b) Bosons

c) Photons do not self-interact, others do. Note: yes, there is such thing as photon-photon scattering, but it only goes via other fields, not directly (as, say, in gluon-gluon case).

3. Higgs boson

a) Massive

b) Boson

c) Couples (interacts with) directly to the matter fields, providing them with masses. This type of interaction is named after Yukawa.

d) Couples to electroweak gauge bosons, providing W&Z with masses.

Now you see how special the Higgs field is. It is a boson which is not a mediator of interactions. It couples (directly!) to both matter fields and electroweak bosons. Typically people refer to d) as to the Higgs mechanism.

Interactions in e) and d) are typically not called 'forces' because they are not due to the presence of gauge bosons; see the discussion here.

• By 2.a, do you mean to say that all mediators are massless? Where then would the W's and Z fall? – Optimus Prime Oct 28 '16 at 8:48
• Ooooops my bad :) All the mediators (including W and Z) are massless at the more fundamental level, i.e. prior to acquiring masses via Higgs mechanism. I suggest to take a look at wiki articles about the Higgs mechanism, W&Z bosons, and also here. – mavzolej Oct 30 '16 at 23:45
• By that rationale, you should also revise 1a an 1b , as your fermions would also be massless prior to symmetry breaking. Right? – Optimus Prime Nov 1 '16 at 6:55
• Yep! Exactly like this. Also, check out this thread. – mavzolej Nov 1 '16 at 18:09
• Since when are vector bosons ($W^\pm$, $Z$, $\gamma$, and gluons) not bosons? – Sean E. Lake Nov 2 '16 at 8:02