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The Standard Model

  1. Nov 15, 2004 #1
    Would it be safe to say that according to the standard model of particle physics all that actually exists at the most fundamental level are leptons, quarks, and bosons?
     
  2. jcsd
  3. Nov 15, 2004 #2

    dextercioby

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    Safe and correct.Fermions:quarks and leptons.Bosons:scalar,vector (massive and not massive).
    But the gravitational interraction between such particles is TOTALLY NEGLECTED.ABSENT,IF U LIKE.
     
  4. Nov 15, 2004 #3
    Ok. But wasn't there some talk about including gravity in the model as a boson called a graviton?

    Has that been ruled out? Or is there still some expectation that a graviton might be discovered some day that could fit into this model?
     
  5. Nov 15, 2004 #4

    dextercioby

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    Copy of a post in another thread:
    Treating GR as an ordinary field theory encountered in the SM is practically useless,because the quantum theory obtained is not renormalizable.
    Hilbert-Einstein action describes at quantum level a theory of SELFINTERRACTING gravitons,quanta of gravitational field i.e.particles with spin two.
    Other attempts have been made of finding something else instead of the HE action.The linearized theory of gravity (developed by Einstein in 1916) is basically "good" when it comes to quantum behavior (i analyzed this theory using standard BRST antiparanthesis-antifield forrmalism (developed frankly by Batalin&Vilkovisky,but it's usually called Lagrangian BRST (cf.the Hamiltonian approach found independently by Becchi,Rouet,Storra and Tyiutin))),but it has the disadvantage of working with the gauge-fixed Pauli-Fierz action which describes the FREE (i.e.NONSELFINTERRACTING) GRAVITONS.In fact,these gravitons interract with ghost fields.Other attempt was the so-called Weyl gravity (i.e. gravity based not on the Riemann curvature tensor (of the curved manifold called spacetime),but on the conformal Weyl tensor,un ugly (still 4-th order) tensor).This theory is excellent at quantum level (i.e.renormalizable) but the classical (nonrelativistic) limit of the unquantized action gives you 4-th order LODE of motion (cf.2-nd order LODE of motion in the Newtonian limit of Einstein GR).
    A step forward was made by Elie Cartan who developed the so called "Einstein-Cartan GR" which used other fields (called vierbeins,usually seen as vielbeins) for describing the gravitational field.This theory is good because it allows coupling with spinor and scalar matter fields in a theory called SUPERGRAVITY.If i'm not mistaking,these theories of Sugra (apud Supergravity),though allow an unifying theory of all 4 fundamental interractions,are,at quantum evel,still nonrenormalizable.I mean,if they were (it doesn't matter how many supemultiplets of particles it envolved),why would ST and LQG be alive today??
    And then,ST,the final (??) frontiere.It is said to give a satisfactory behavior of gravitational interraction at the quantum level (this time there are no point-particles like in SM anf SUGRA,but strings,10-dimensional objects).

    This a plainy simple and incomplete (probably incorrectas well,at least in its final lines) review on the the work that's been done by theorists worldwide in the last 70 years or so in the field of Quantum Gravidynamics (the name i give for the theory of QG in agreement with common names used in the SM).

    Daniel.
     
  6. Nov 15, 2004 #5
    So, in other words, you're basically saying that it's been ruled out.

    I can buy that.

    But then we'd have to conclude that the Standard Model of particle physics does not describe all that actually exists.

    Is that a fair conclusion?

    Edited to add:
    I should have said that SM cannot describe all that actually exists then. Not merely "does not". Right?
     
    Last edited: Nov 15, 2004
  7. Nov 15, 2004 #6

    dextercioby

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    Yes,that's why theoretical HEP is still alive these days,either in the presence of strings or not.Incidentally or not,we don't even know,at this present,that all predictions of the SM are correct or not.This,together with the fact that it does not incorporate GR,make us,theorists,live,breathe and probably be able to multiply... :tongue2:
     
  8. Nov 15, 2004 #7

    dextercioby

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    Else,we would have been dead like Mr.Max Born said 76 years ago...
     
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