# Tag Info

6

I think that this question can be answered in three parts: Are there any exact solutions to any equations of the SM? Do we always have to use perturbation methods to solve anything within the SM? Are there any exact solutions beyond the SM? The answer to question 1 is: it depends on what equations you are referring to. For example, the propagators of ...

5

No. You have just named a series of unanswered questions as if the fact they're unanswered somehow invalidates the Standard Model. This is not in general how science works. For the extensive evidence for the Standard Model, please see http://arxiv.org/abs/hep-ph/9810316 among many other things.

3

Neutrino mass is not in conflict with electroweak theory. One can introduce neutrino masses by modifying the Higgs or lepton sector of the Standard Model. The simplest method, that which you propose, is introducing a right handed neutrino with a Yukawa coupling with the left handed neutrino (extending the lepton sector). The right handed neutrino, however, ...

3

Tarek (OP) e-mailed me to contribute to this thread. Here's the response that I gave him (slightly edited for clarity). I see why this was confusing, my apologies! I was perhaps too glib in the post. Iwas implicitly talking about a chiral rotation but wanted to present it somewhat more intuitively. Let me try to spell it out more carefully, and hopefully ...

3

Now that we have seen the Higgs boson, all the particles predicted by the Standard Model have been discovered. The penultimate particle to be discovered was the tau-neutrino at Fermi-Lab in 2000. The antepenultimate particle to be discovered was the top quark, also at Fermi-Lab in 1995. For a complete timeline, see e.g. this wiki page. There are, of ...

3

I agree with the answer of Quantum physicist , that zero mass for neutrinos was an input to the standard model , not a prediction, because measurements showed a mass compatible with zero. But I will add that the discovery that neutrinos must have mass does not destroy the Standard Model, just different Lagrangian for the neutrinos has to be included. ...

3

Standard model doesn't predict that neutrinos are massless. It's a "Model", where initially neutrinos are considered massless, because no mass was observed. The way we know, now, that neutrinos have masses, is through the mixing between the different neutrino types, through a matrix called the PMNS matrix (similar to the CKM matrix for quarks). This mixing ...

2

Well, after symmetry breaking, all that remains is electromagnetic $U(1)$, so the only generator that is truly a symmetry generator is $Q$. The fermions couple to the "Higgs" via the Yukawa coupling: $\mathcal{L}_y = -y_e^{ij} \bar L_{L,i} \Phi e_{R,j} - y_u^{ij} \bar Q_{L,i} \tilde{\Phi} u_{R,j} - y_d^{ij} \bar Q_{L,i} \Phi d_{R,j} + h.c.\,$ which mixes ...

1

What is in the same electroweak doublet are just left-handed components of electron and neutrino. Note that the mass of the particle can be thought of as the strength of the coupling between left-handed and right-handed components of particle's field. You have such coupling for electron (in a gauge-invariant way, via Higgs), and not for neutrino (which lacks ...

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