Standard Model particle spectrum from String Theory


by Kalimaa23
Tags: model, particle, spectrum, standard, string, theory
marcus
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#19
Oct25-05, 11:43 AM
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Quote Quote by Mike2
As I understand it, mass is the only property that generates and responds to gravity. So it would seem that we are not going to understand where mass comes from until we understand gravity (spacetime) itself.
hadn't thought of it exactly like that, could be true.
what you said makes a lot of sense
Mike2
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#20
Oct25-05, 02:18 PM
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Quote Quote by marcus
hadn't thought of it exactly like that, could be true.
what you said makes a lot of sense
Is there any form of energy not dependent on mass (not really, E=mc^2). How about the potential energy derived from the separation of electrically charge particles? As I understand it charge is derived from some sort of spacetime symmetry of the particles. And other kinds of spacetime symmetry give rise to the Strong force and the Weak force. So if symmetry gives rise to force and thus energy which is equal to mass, then is mass a measure of symmetry, or a different kind of symmetry, etc?
marcus
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#21
Oct25-05, 02:55 PM
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Quote Quote by Mike2
Is there any form of energy not dependent on mass (not really, E=mc^2). How about the potential energy derived from the separation of electrically charge particles? ...
really should wait for sA or someone else to reply

two electrons which have been forced close to each other have more mass, as a combined system, than the two weighed separately


an electron and a proton, close together, have less mass than they would have if they were farther apart other things being equal.

I think the answer "is there any form" is probably "no" as long as an equation like E=mc^2 makes sense it will apply. if someone knows of an exception, would be happy to have it explained to me
mccrone
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#22
Oct25-05, 04:11 PM
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You guys are missing the point. It is like Sherlock Holmes and the dog that didn't bark. The fact that particle masses don't fall into a neat and tidy hierarchy of multiples seems a significant constraint on any theories about the nature of mass (or gravity).

There are a lot of things we don't know. But one of the things we definitely know is that particle masses are not neat and tidy. Perhaps they are even random in their distribution (has the analysis been done?). So this seems a big clue. What other more everyday physical systems can replicate this kind of behaviour?

There are plenty of models for why masses would come in a series of steps.
The Higgs mechanism and symmetry breaking. Strings winding around the holes of CY space. Particles and their cumulative self-interactions. The inertial drag of the vacuum.

But all these are saying that behind the variety of particle rest masses, there is one common mechanism. Are there any models that address the other face of the rest mass story - the reason why a common mechanism would seem to generate random output?

Self-adjoint says - "one extra particle-antiparticle pair. The interaction of these with the ordinary Higgs bosons could introduce some variation in the mass-conveying Higgs mechanism..."

This seems like the kind of approach that would help. Perhaps there are more remnant modes flying about than are normally modelled in symmetry breaking stories. WIMPs or suchlike that only show their presence by the way they mess up what might otherwise be a neat and tidy progression of resonances for the "fundamental" particles.

In this view, much larger symmetry groups may be needed to see all the hidden contributions to the particular rest mass levels of the known particles.

SU5, or whatever, might already be dismissed on the grounds that the ragged particle masses suggest it is too simple.
selfAdjoint
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#23
Oct25-05, 07:58 PM
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I don't know that quark masses are so untidy. They do follow the pattern that u and d are lighter than s and c, which are lighter than t and b. And each pair has a lighter particle and a heavier one. And this pattern is repeated with the leptons.
mccrone
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#24
Oct25-05, 08:37 PM
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Quote Quote by selfAdjoint
I don't know that quark masses are so untidy. They do follow the pattern that u and d are lighter than s and c, which are lighter than t and b. And each pair has a lighter particle and a heavier one. And this pattern is repeated with the leptons.
What kind of a response is that? I take it you are merely teasing me here.

We agree there is a pattern of three generations and other regularities. But consider again the steps between generations (note these are not exact numbers as only good approximations are available for some particles).

The up quark sequence steps up in multiples of 1/600/283.

The down quark sequence goes 1/16/42.

The electron sequence goes 1/20/170.

The neutrino sequence goes 1/15000/133.

Again, these are rough figures, especially the neutrino. All I was interested in was the accepted wisdom as to why we don't see a more regular pattern.
Kea
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#25
Oct25-05, 10:21 PM
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John (mccrone)

How can you say there isn't a pattern when the only way to see a pattern is to understand completely what we don't understand?

Juan R.
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#26
Oct29-05, 08:22 AM
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Quote Quote by Dimitri Terryn
It seems that a group of researchers has constructed a Calabi-Yau compactification that reproduces that particles of the standard model.
A bit exagerated the claim!

1) There is no possibility for deriving the compactification from firts principles. In fact, string theory cannot predict anything.

2) Nobody has obtained the full standard model. As far i know only partial ideas like hypotetical relations of CY holes with the asumed number of families, etc. This work appears to be based in some topological 'conjetures', etc.

3) The only physical states in string theory are masless supersimmetric states. Experiments claim just the contrary. Even if in the future high-energy experiment (e.g. HLC), supersimmetry is found, that does NOT imply that string theory was correct -in fact, supersimmetry is previous to string hype and appears in several alternative theories- . Since the standard model continues to be non-superssimetric and with no massless particles -and this is independent of future experiments-, string theory continues to be wrong.

P.S.1: Any theory predicting contrary to experiment is wrong.

P.S2: The CY is not the last 'geometry' of string theory. The CY is only valid as approximation in the asymptotic regimes of the 'branescan' just when 'string theory general relativity' does not hold -string theory is background dependent, GR is NOT-. In M-theory -the full quantum gravity regime-, the manifold is still unknown, but some people is researching in G2 manifolds.


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