lecture 3 1 2 3 4 5 Dirac
- Slides: 72
lecture 3 1
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Dirac 1927: search for a wave equation, in which the time derivative appears only in the first order ( Klein- Gordon equation: second time derivate is needed ) 6
electron proton ? 7
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positron 11
Dirac equation 12
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. Suppose that the proton is a collection of 3 quarks (zero binding energy). The proton mass is the sum of the three quark masses: mass (quark ) = M(proton)/3 =>one obtains the correct magnetic moment of the proton 21
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The vector current and the axial vector current can be measured by the electromagnetic and by the weak interactions. The tensor, the scalar and the pseudoscalar densities cannot be measured. 25
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M. Faraday ~ 1850 electric and magnetic fields 27
electric and magnetic fields 28
1826 conversion of magnetism into electricity 29
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Quantum physics 31
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Lagrangian of a free Dirac field 35
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field strength 37
Dirac equation with interaction of electron and photon Maxwell equation 38
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e 40
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gauge theory 46
Intrinsic connection between charged fields and space-time
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Arnold Sommerfeld, 1916 49
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fine-structure constant =0. 00729735253 51
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refdn dd Kl renormalization of the electron mass kl 12 56
renormalization of the electric charge dd Kl refdn kl 12 57
Quantum Field Theory: Finestructure constant becomes function of energy or scale due to quantum fluctuations of electron-positron pairs => partial screening of bare charge of the electron at distances less than the compton wavelength of the electron 58
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ALEPH L 3 OPAL DELPHI 62
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Non-Abelean gauge theories 64
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Pauli did not publish his theory, since he did not know, how to introduce the masses for the gauge bosons. 66
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Yang and Mills did not mention the letter of Pauli in their paper, published in Phys. Rev. They disregarded the problem how to introduce the masses of the gauge bosons. ( In QCD no masses are needed. ) 68
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Abelean gauge theory ( e. g. QED): The gauge boson interacts only with the fermions. Non-Abelean gauge theory ( e. g. QCD): The gauge bosons interact with the fermions and with the gauge bosons (e. g. in QCD: gluon-gluon scattering ). 72