1. weak
interactions

2. weak decays
beta decay of
neutron

3. e n neutrino p direct interaction of four fermions
Enrico Fermi, ~1936

4. Enrico
Fermil

7. 1964 ===>
gauge theory
electroweak

8. 1957
weak bosons W
J. Schwinger

9. ( Glashow, Salam, Weinberg )-
gauge theory
of the
electroweak
interactions
( Glashow, Salam, Weinberg )

10. Glashow Salam Weinberg

11. weak and
electromagnetic
interactions
partial unification

12. gauge group
SU(2)xU(1)

13. S U (2) x U (1)
weak
interaction
electromagnetic
interaction

14. SU(2) x U(1)
gauge bosons
photon
Z W(+) W(-)

15. SU(2)xU(1)
weak
interactions
electromagnetism
neutral current

16. SU(2)xU(1)
neutral current
CERN 1972

17. photon: superposition
of SU(2) and
U(1) – gauge boson
Why photon massless?
Why W – boson massive?

18. by spontaneous symmetry breaking
mass generation
by spontaneous symmetry breaking
( “ Higgs “ – mechanism)

19. Minimal electroweak theory
Gauge group:
SU(2) x U(1)

20. SU(2)
U(1)
fermions

23. symmetry breaking:
SU(2) and U(1) are broken,
but the electric
charge is unbroken

27. neutral current interaction
parity violation

28. neutral current interaction
parity violation
observed in atomic physics

30. weak
interactions

31. weak decays
beta decay of
neutron

32. e n neutrino p direct interaction of four fermions
Enrico Fermi, ~1936

34. Minimal electroweak theory
Gauge group:
SU(2) x U(1)

37. symmetry breaking:
SU(2) and U(1) are broken,
but the electric
charge is unbroken

40. M(W) = 80.4 GeV
M(Z)= 91.2 GeV
CERN, 1984 =>

42. The masses of the weak bosons are predicted,
once the weak angle is measured.
The electron mass cannot be predicted
( the coupling constant g is unknown ).

43. electroweak theory: QCD: mass generation by SSB mass generation
problem: mass generation
electroweak theory:
mass generation by SSB
QCD:
mass generation
by confinement

44. hypothetical Higgs boson

45. limit on mass of
Higgs boson from LEP:
114 GeV

46. L3 I
ATLAS
CMS
LHCb
Alice
LEP - LHC

48. muon
H===> Z Z
LHC
Higgs particle

49. W W M(W)~100 MeV - other possibility to generate the
masses for the weak bosons:
W =>pion=>W
pion W W
M(W)~100 MeV

50. W =>technipion=>W-
technicolor
W =>technipion=>W
technipion W W
M(W)~100 GeV

51. composite weak bosons, leptons and quarks
other possibility:
composite weak bosons,
leptons and quarks