Lecture 3 1. 2 3 4 5 Dirac 1927: search for a wave equation, in which the time derivative appears...
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lecture 3
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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 ) 66
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0)( mi
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positronpositron
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Dirac Dirac equationequation
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2020
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. . Suppose that the proton is a Suppose that the proton is a collection of 3 quarks (zero binding collection of 3 quarks (zero binding
energy).energy).The proton mass is the sum of The proton mass is the sum of
the three quark masses:the three quark masses:
mass (quark ) = mass (quark ) = M(proton)/3 M(proton)/3
=>one obtains the correct =>one obtains the correct magnetic moment of the protonmagnetic moment of the proton
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The vector current and the The vector current and the axial vector current can beaxial vector current can be
measured by the measured by the electromagnetic and by the electromagnetic and by the
weak interactions.weak interactions.
The tensor, the scalar and theThe tensor, the scalar and thepseudoscalar densities cannotpseudoscalar densities cannot
be measured. be measured. 2525
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18261826conversion conversion
of of magnetismmagnetism
intointo electricity electricity
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Quantum physics
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Dirac equation with interaction of electron and photonMaxwell equation
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e
fieldphotonA
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)()( )( xex xi
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gauge theory
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Intrinsic connection between charged fields and space-time
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hce /22
Arnold Arnold Sommerfeld, Sommerfeld, 19161916
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137
12
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e
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fine-structure constant hce /22
=0.00729735253
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03599976137
1
.
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eVm
mm
e
e
511.0)(
)( 0
refdn
dd
Kl renormalization of the electron mass kl12
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refdn
ddKl renormalization of the electric charge
kl12
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)( 0
e
ee
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Quantum Field Theory:Quantum Field Theory:
Finestructure constant becomes function of Finestructure constant becomes function of energy or scale due to quantum energy or scale due to quantum fluctuations of electron-positron pairsfluctuations of electron-positron pairs
=> partial screening of bare charge of the => partial screening of bare charge of the electron at distances less than the electron at distances less than the compton wavelength of the electroncompton wavelength of the electron
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+
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3
2
( , ) ( )ln( / )
( ) ...12
r
de q e e
d q M
QED
ee
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+
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OPAL
ALEPHL3
DELPHI
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(200 )GeV
( ) 1/127.8ZM 6363
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Non-Abelean Non-Abelean gauge gauge theoriestheories
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Pauli did not publish Pauli did not publish hishis
theory, since he did theory, since he did notnot
know, how to know, how to introduceintroduce
the masses for the the masses for the gauge bosons. gauge bosons.
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Yang and Mills did not Yang and Mills did not mentionmention
the letter of Pauli in theirthe letter of Pauli in theirpaper, published in Phys. paper, published in Phys.
Rev.Rev.They disregarded the They disregarded the
problemproblemhow to introduce the masseshow to introduce the masses
of the gauge bosons.of the gauge bosons.
( In QCD no masses are ( In QCD no masses are
needed.) needed.)
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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 ).
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