Higgs particle is 'found': Scientists at CERN expected to announce on Wednesday

jcsd

What do people make of this?: [new paper on possible Higgs imposters]

http://arxiv.org/abs/1207.1093

jcsd

One question I have about the Higgs mechanism is, would the Goldstone bosons, the hypercharge gauge boson, etc be observable as individual particles in suitbaly high energy regimes?

tom.stoer

For a global symmetry: at high energies the broken symmetry is restored and therefore no Goldstone boson does exist.

For a gauge theory: there is no Goldstone boson at all b/c it's an unphysical d.o.f. The excitation which would be represented by the so-called "would-be" Goldstone is "pure gauge", i.e. can be absorbed in a local gauge transformation.

eXorikos

Can you explain me why?

tom.stoer

If the 3*3 matrix U is non-unitary, this means that a forth generation is missing which fixes the non-unitarity; i.e. a 4*4 matrix U' which contains U may be unitary again.

eXorikos

That I know, but why does unitarity not prove the impossibility of a fourth generation?

If the CKM matrix is unitary, how can there be a fourth generation that mixes with the three known generations?

mfb

You always have measurement uncertainties - while the measurements can be consistent with (3x3) unitarity, they cannot prove it. The other option would be no mixing with the 4th generation at all, but that looks odd.

If mixing with a 4th generation exists, it has to be small, otherwise it would have been detected in loops (similar to the top-quark). And the high required neutrino mass is extremely odd, given that the known three neutrinos have a mass of at least 1-2 eV (using the upper limit for the electron neutrino and the mixing measurements).

PAllen

References to the following paper are beginning to make the rounds, so thought I'd post here (though all differences from SM in the recent LHC data are 2 sigma or less, of course people will jump on the hints):

http://arxiv.org/abs/1207.1445

tom.stoer

As said: "It doesn't, and indeed, it cannot. Non-unitarity of the 3x3 CKM can require a 4th generation, but unitarity cannot forbid one."

If the 3*3 CKM matrix is not unitary this may (or must?) be fixed by adding a forth generation. If the 3*3 CKM matrix is unitary there may be a forth generation w/o CKM mixing. I am not even sure whether a 'putative unitary' 3*3 CKM matrix with experimental uncertainties taken into account does rule out a small 4*4 mixing.

EDIT: just saw mfb's reply ...