Standard model

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What is the standard model?
 
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A simple question,...no simple answer.
To start with, it is the first "Complete" system of particles that we think makes up the entire universe. It is a collection of around 60 particles, plus their antiparticles, of which 12 are particles that carry forces between the other particles (for instance gluons that carry the "colored/strong" force between the quarks, or the photon that carries the EM force between charged particles) and "spin-1 gauge boson" which is called the graviton. Besides this, it is mathematical description of a "unified" view of the four forces. The only force not included is Gravity.

You can find info about in any University textbook ("Nuclear and particle physics", W.S.C. Williams, for instance) available, or on the web (including the archives of this site).
 

Hurkyl

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and "spin-1 gauge boson" which is called the graviton.
Graviton is spin-2 and not part of the standard model. Did you mean the Higgs boson?
 
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Am I right in thinking that this model is not actually very effective and the GUT can replace it?
 
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Jack, the Standard Model is the name given to the current theory of fundamental particles and how they interact. It is something to do with strong interactions due to the color charges of quarks and gluons. A combined theory of weak and electromagnetic interaction, known as electroweak theory, that introduces W and Z bosons as the carrier particles of weak processes, and photons as mediators to electromagnetic interactions. The theory does not include the effects of gravitational interactions. These effects are tiny under high-energy Physics situations, and can be neglected in describing the experiments. Eventually, we seek a theory that also includes a correct quantum version of gravitational interactions, but this is not yet achieved.
 
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Would you like to summarise that in your own words please viper? :wink: :wink:
 

damgo

Originally posted by Jack
Am I right in thinking that this model is not actually very effective and the GUT can replace it?
There is no GUT, yet. The SM is incredibly effective and accurate, annoyingly so. Everyone is pretty sure it will be replaced eventually, but exhaustive experimental searches for differences from its predictions have turned up only hints, nothing ironclad.

Basically, it is the modern quantum field theory best modelling reality. It contains all the modern particles, their masses, various details about them (mixing matrices), and the form of the various interactions (the three forces, which are succinctly described by their symmetry groups.)

Gravity is not included in the Standard Model.
 
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Originally posted by damgo

Gravity is not included in the Standard Model.
Which is why the GUT could replace it (I meant to say could replace it as opposed to can on my previous post)
 
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Jack, It so easy the Standard Model is the name how particles interact. There is a colour change in quarks and glucons and this produces the weak electromagnetic theroy. This introduces W and Z bosons as the carrier particles of weak processes, and photons as mediators to electromagnetic interactions.
Suprised Jack, I know something you don`t?
 

marcus

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Originally posted by damgo
...It contains all the modern particles, their masses, various details about them (mixing matrices), and the form of the various interactions (the three forces, which are succinctly described by their symmetry groups.)...
Please give some idea how the three forces can be quantified thru their symmetry groups

Baez lists 26 numbers that describe the SM from which everything else can be calculated.
most of the numbers are masses (like you say) of certain key particles

but (like you say) there are also two mixing matrices, each of which is described by 4 numbers

and there are two coupling constants for symmetry groups U(1) and SU(2) and these (you indicate) must succinctly describe the coupling constants that you actually plug into the Feynmann diagrams to calculate perturbation series. What the dickens is a "symmetry group coupling constant" and how can you get a practical coupling constant from it?

These physicists with their parlor magic rabbits out of hats are a caution. Of course they know best, but there are times when
all this succinct description is too succinct. :)
 

marcus

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Originally posted by Jack
What is the standard model?
Have to take a shot. Even laymen can say words about the
standard model. Damgo who is going up the ladder (now learning QFT) will correct me if I am wrong.

There is one blindingly awesomely beautiful thing about it which is a great SIMPLIFICATION in our picture of the world.

There is only one electron field that stretches throughout the universe.

All the electrons we are made of and encounter in life are simply individual twangs or ripples in this one field.

For each basic particle----3 leptons 6 quarks etc etc----there is a field.

So basically it is not much more complicated than a 12-string guitar right (oops I dont want to suggest any connection with "string theory"!!!, this guitar I am imagining is a very ordinary metaphorical guitar)

the electron is one of those 3 leptons so somewhere on the model there is an electron-field and all the electrons we know are just individual exitations of that one electron-field. They can come into existence (by the investment of a small amount of energy) and then go out of existence (releasing the energy to be used for something else)

12 of the 26 numbers that describe the SM are masses of basic particles. The mass of a field helps to tell how that field will behave. The mass associated with the electron fields tells you, for example, how much energy you have to hit the field with in order for a new exitation to be created.

I like this SM picture because it is much more simple than the picutre that Newton or Democritus had to deal with where there are jillions of little specky atomic particles flying around each on its own trajectory. In the SM there are only a small number of basic fields and the world comes into existence by their being excited. OK damgo, or is the picture wacky?
 
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Originally posted by Viper
Jack, It so easy the Standard Model is the name how particles interact. There is a colour change in quarks and glucons and this produces the weak electromagnetic theroy. This introduces W and Z bosons as the carrier particles of weak processes, and photons as mediators to electromagnetic interactions.
Suprised Jack, I know something you don`t?
Well I would be surprised if you really did and hadn't just copied it off the internet.
 
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What proof do you have of such alligations?
 
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Originally posted by Jack
What is the standard model?
Hi Jack, The following is an abstract of a paper that presumed that the mother nucleon was the Proton from which nature supposedly creates the neutron, rather than the experimentally known natural decay of the Neutron that thus becomes a Proton. If anyone wishes I have a copy of Arne's abstract of the Neutron model:

FBO3 11 Electromagnetic structure of the proton ARNE OLSON, Argonne National Laboratory The proton's magnetic moment and charge radius are derived for an infinitely thin, unit-charged spherical shell of radius 0.94855 fm, rotating rigidly at v/c = 0.94855. This radius is in good agreement with experiment. The predicted magnetic moment is mp = +2.70150 mN, which differs from experiment by less than 3.3%. This computation of the absolute value, and sign of the proton's magnetic moment is the first known that uses no fitted parameters. Model characteristics will show that the charged shell energy, velocity, and radius are not arbitrary but are the consequence of logical constraints on the internal dynamics of the proton. It will be shown that the proton is a quantum coherent state. Inside the charge shell exist uncharged bosons (gluons), which carry the bulk of the proton’s rest mass and internal energy. The Einstein-Bose energy distribution function yields their energy. By treating the gluons as quantum vortices, stability of the proton is discovered for a unique condition. The strong force is found to be a consequence of vortex dynamics which binds the gluons: T (strong) = 2p(e3 g(.5))2/hc = 492.306 MeV/fm, where e3 g(.5) is 311.68 MeV, the energy of each of three identical gluons. The key to proton stability is that three quantum vortices with orbital angular momentum 2h/2p must rotate at precisely c/2. The proton is stable because this configuration is achieved exactly.

[NEOclassic's comment: Is Arne Olson’s abstract, presented above, really the epitome of “simplicity and beauty” promised by the late Dick Feynman some thirty five years ago? I quote the final two paragraphs of Feynman’s “The Character of Physical Law”:
“In this age people are experiencing a delight, the tremendous delight that you get when you guess how nature will work in a new situation never seen before. From experiments and information in a certain range you can guess what is going to happen in a region where no one has ever explored before. It is a little different from the regular exploration in that there are enough clues on the land discovered to guess what the land that has not been discovered is going to look like. These guesses, incidentally, are often very different from what you have already seen – they take a lot of thought.”
“What is it about nature that lets this happen, that it is possible to guess from one part what the rest is going to do? That is an unscientific question: I do not know how to answer it, and therefore I am going to give an unscientific answer. I think it is because nature has a simplicity and therefore a great beauty.”] Cheers, Jim
 

damgo

Please give some idea how the three forces can be quantified thru their symmetry groups.
SU(3)_color x SU(2) x U(1)

:smile: So these are gauge symmetry groups -- the most basic example of a gauge symmetry is the potential, in electrostatits. We all know that the electric potential is arbitrary up to a constant; this is a global gauge symmetry with gauge group R (the reals.) More generally, you may remember that you can add the gradient of an arbitrary function to the four-potential w/o changing anything. This corresponds to an arbitrary continuous local change of phase of the photon field, a local gauge symmetry with gauge group U(1).

Now it turns out -- though it's complex to show -- that by imposing local U(1) gauge invariance on the photon field and requiring renormalizability, you automatically get out the QED Lagrangian; that is, the exact form of the electromagnetic interaction.

Similarly local SU(3) color gauge symmetry -- which in effect is sorta saying that the assignment of colors is arbitrary -- gives you the strong force.

The picture is actually a little bit icky, because the SU(2)xU(1) gauge group I listed above give you four bosons -- but they are *not* the photon, W+, W-, and Z, because the latter three have mass. This is where the Higgs comes in and breaks the symmetry, mixing those four to give the physical W/Z/photon. I don't understand this at all yet.

Your post looked all good, BTW.
 

marcus

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Originally posted by damgo
SU(3)_color x SU(2) x U(1)

:smile:

Now it turns out -- though it's complex
(pun?) to show -- that by imposing local U(1) gauge invariance on the photon field and requiring renormalizability, you automatically get out the QED Lagrangian; that is, the exact form of the electromagnetic interaction.

Similarly local SU(3) color gauge symmetry -- which in effect is sorta saying that the assignment of colors is arbitrary
AAHHHH! this gives me some notion, SU(3) is doing something sensible that I can hope to understand -- gives you the strong force.

The picture is actually a little bit icky, because the SU(2)xU(1) gauge group I listed above give you four bosons -- but they are *not* the photon, W+, W-, and Z, because the latter three have mass. This is where the Higgs comes in and breaks the symmetry, mixing those four to give the physical W/Z/photon. I don't understand this at all yet.
epicycles were introduced into the ptolemaic system for the purpose---which I regard as entirely honorable---of "saving the phenomena" and so we can
all rejoice that "the Higgs comes in and breaks the symmetry" as you say so that the W and Z thanks be to Allah the merciful turn out to have mass after all!

Your post looked all good, BTW.
thanks and cheers, this is believe it or not making more and more sense
 

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