Main Question or Discussion Point
What do you guys think of the new non-background independent Chamseddine and Connes paper?
I think this prediction was already in "why the standard model" and "A dress for standard model the beggar" but it is disputed. It was not a strict requirement, but rather the simplest ansatz. I do not expect that has improved, but I have not studied the paper yet. With this word of caution, I too am very glad he is (they are) back in business !The symmetry group is U(1)xSU(2)xSU(3).
It would seem so. And the new Connes Chamseddine paper will put additional energy into the LQG program. The synergy between the approaches is strong. You may recall that Chamseddine gave a plenary talk at the main Loops conference of 2008--organized by John Barrett at Nottingham.I guess background independence is still alive...
That's not correct. Look at QCD: its classical action is scale-free, no dimensionful parameter. But due to the renormalization group calculations in the effective, quantum mechanical action a new scale often called LambdaQCD is generated. Otherwise you would have no preferred mass or energy scale for nucleons yand you could find protons and neutrons aof all sizes and masses."Top quark mass of 170-175 Gev." ... You clearly can't predict a dimensionful quantity directly unless your theory has some scale built into it already.
The top quark mass is just too heavy in the standard model. It is expected that there is something special simply because it does not fit into the overall quark mass scale.What's so special about the top quark in their model?
There are several possibilities how can can build Higgs-based models. It is not required that there is just one Higgs boson. Especially in SUSY-based models there can be families of Higgs bosons, the simplest possibility in the MSSM are two Higgs doublets: http://en.wikipedia.org/wiki/Minimal_Supersymmetric_Standard_ModelWhat is a "doublet Higgs?"
You can't do renormalization group calculations without fixing the value of coupling at a certain value of energy.That's not correct. Look at QCD: its classical action is scale-free, no dimensionful parameter. But due to the renormalization group calculations in the effective, quantum mechanical action a new scale often called LambdaQCD is generated. Otherwise you would have no preferred mass or energy scale for nucleons yand you could find protons and neutrons aof all sizes and masses.
Page 25, last two paragraphs. Looks like they are picking values for two parameters out of the thin air and then saying "look, if this parameter has this value and this parameter has this value, our theory predicts Higgs of 170 GeV and top quark of 179 GeV".Flipping through the article casually, I didn't have much luck finding where this was discussed. You clearly can't predict a dimensionful quantity directly unless your theory has some scale built into it already. Are they really retrodicting the dimensionless ratio of the top quark mass to the Planck mass?
I agree. This is essentially the way how quantization and renormalization generate a mass scale which is absent in classical physics. The scale is not "built in" but emergent.You can't do renormalization group calculations without fixing the value of coupling at a certain value of energy.
Once you do that, you're no longer scale free.
I think the Tevatron is in trouble, because they tried to get more from their data than they canBlue: I think this particular version of Connes Standard Model ran into trouble because experiment seemed to rule out Higgs around 170. Please correct me if I am mistaken.
However, Connes' model relies on the "big desert" hypothesis.We update the theoretical predictions for the production cross sections of the Standard Model Higgs boson at the Fermilab Tevatron collider, focusing on the two main search channels, the gluon-gluon fusion mechanism [tex]gg \to H[/tex] and the Higgs-strahlung processes [tex]q \bar q \to VH[/tex] with [tex]V=W/Z[/tex], including all relevant higher order QCD and electroweak corrections in perturbation theory. We then estimate the various uncertainties affecting these predictions: the scale uncertainties which are viewed as a measure of the unknown higher order effects, the uncertainties from the parton distribution functions and the related errors on the strong coupling constant, as well as the uncertainties due to the use of an effective theory approach in the determination of the radiative corrections in the [tex]gg \to H[/tex] process at next-to-next-to-leading order. We find that while the cross sections are well under control in the Higgs--strahlung processes, the theoretical uncertainties are rather large in the case of the gluon-gluon fusion channel, possibly shifting the central values of the next-to-next-to-leading order cross sections by more than [tex]\approx 40[/tex]%. These uncertainties are thus significantly larger than the [tex]\approx 10[/tex]% error assumed by the CDF and D0 experiments in their recent analysis that has excluded the Higgs mass range [tex]M_H=[/tex]162-166 GeV at the 95% confidence level. These exclusion limits should be, therefore, reconsidered in the light of these large theoretical uncertainties.