The Higgs field: so gravitational field by itself cannot confer mass?

[bananan]

the Higgs field: so gravitational field by itself cannot confer mass to elementary particles? What properties of a particle determine how it interacts with the Higgs field in such a way that it gains mass (whereas others, such as photons, remain massless)?

 

[Severian]

I don't know of any low energy theories where gravity creates mass (string theory sort of does of course). It only acts on it (in the non-relativistic limit). In GR, gravity acts on the energy (actually the stress-energy tensor) and it is just that for a non-relativistic particle, the energy is mainly in the mass, so it looks like it is acting on the mass.

The Higgs couplings to various particles are just Yukawa interactions put in by hand - there is really no predictive power here since the Yukawa couplings are just put into give the right (ie. observed) masses. However, the photon being massless is a prediction of the theory, because it is protected from having a mass by the U(1) symmetry which is left over after electroweak symmetry breaking.

 

[Haelfix]

Its interesting to note*, that only with supersymmetry do Higgs fields give predictive power (at the cost of course of adding a ton of extra degrees of freedom).

*im excluding various other models like little higgs, technicolor and so forth*

 

[Severian]

Its interesting to note*, that only with supersymmetry do Higgs fields give predictive power (at the cost of course of adding a ton of extra degrees of freedom).

That is not really fair. The Higgs mechanism relates the W/Z mass ratio to the Weinberg angle, and predicts that the masses are all proportional to the their coupling to the Higgs. Then there are all the Higgs modifications to precision tests. So the SM Higgs is still predictive, though not as predictive as in the MSSM.

(I presume your objection is that the Higgs mass is free in the SM? Even that is not quite true, since we need the Higgs lighter than about 700GeV to avoid unitarity violation.)

 

[Haelfix]

Yes I know that the W and Z are related to the weak mixing angle via the Higgs mechanism, and yes my objection is the Higgs is a free parameter. I'm just reiterating what you said in your previous post basically.

Unitarity bounds are evadable with extra field content, but yes things become nonminimal.

As far as the MSSM Higgs for those that are interested, the mass scale is set by it quartic self coupling and it cannot be accounted for or swallowed by a soft supersymmetry breaking term or redefinition, hence it is not a free parameter. And should be naively on the order of the Z mass. Radiative corrections will enhance this b/c of supersymmetry breaking, and push the mass up somewhat (particularly from heavy quark/squark diagrams). But get too heavy, and the MSSM goes to hell rapidly.