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What do you guys think of the new non-background independent Chamseddine and Connes paper?
atyy said: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 !marcus said:The symmetry group is U(1)xSU(2)xSU(3).
atyy said: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.bcrowell said:"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.bcrowell said: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_Modelbcrowell said:What is a "doublet Higgs?"
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.
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.hamster143 said: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 canmarcus said:Blue: 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.
"Death to background independence" is a phrase used in the field of theoretical physics, specifically in the study of quantum gravity. It refers to the idea that the concept of a fixed background space-time, as described by general relativity, should be discarded in favor of a more fundamental, background-independent theory.
Background independence is important because it allows for a more complete and unified understanding of the universe. In traditional theories, such as general relativity, the background space-time is treated as fixed and unchanging. However, in reality, space-time is constantly evolving and interacting with matter and energy. A background-independent theory would be able to account for these interactions and provide a more accurate understanding of the universe.
One of the main challenges in developing a background-independent theory is the mathematical complexity involved. The concept of a fixed background space-time is often used as a simplifying assumption in theories, and removing it can make the mathematics significantly more difficult. Additionally, there is currently no consensus on what a background-independent theory would look like, so researchers are still exploring different approaches and ideas.
Yes, there have been various theories proposed that aim to be background-independent, such as loop quantum gravity, causal set theory, and spin networks. However, these theories are still in the early stages of development and have not been fully tested or accepted by the scientific community.
A successful background-independent theory could have a significant impact on our understanding of the universe by providing a unified framework for understanding gravity and other fundamental forces. It could also potentially resolve some of the current conflicts and limitations of existing theories, such as the incompatibility of general relativity and quantum mechanics. Additionally, a background-independent theory could lead to new insights and discoveries about the nature of space and time.