History 181B - Class 42

History 181B: Modern Physics

Class 42 (5/5/03)
The Standard Model and beyond

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Outline

The Standard Model (continued)
    Quantum chromodynamics
        A gauge field theory of the strong interaction
        Predicting and testing
        Permanently bound quarks

Beyond the Standard Model
    Why go beyond?
    Experimental hints: Neutrinos and muons
    Theoretical proposals
    Why unification? And some thoughts on the history
    How to test? And some thoughts on the politics

Names and terms

Primary	Secondary
quarks (flavor, color) gluons QCD (quantum chromodynamics) supersymmetry grand unified theories quantum gravity, graviton string (or superstring) theory Superconducting Supercollider (SSC, cancelled 1993) Large Hadron Collider (LHC, at CERN, expected 2007) Next Linear Collider (NLC)	leptons

Assignment

Richard D. Mattuck, selections from A Guide to Feynman Diagrams in the Many-Body Problem, 2nd ed. (New York: Dover, 1976), 1-24.

    The diagrams may look complicated, but the ideas are plainer than it may seem.
    What do the fictitious bodies (section 0.1) do? What is a quasi particle (section 0.2)?
    Then what is a collective excitation (section 0.2)?
    What is the basic strategy involved in using Feynman diagrams? Looking especially at section 1.2, put it in words. What are the propagators?
    These techniques remind us of renormalized QED and come out of elementary particle physics. But at the bottom of p. 1 Mattuck writes that the many-body problem is not limited to any one branch of physics. What is his point?
    Extra: Does the strategy described here remind you of any problem-solving approaches from ordinary life?

Extra credit: Third Nobel option due.