Electroweak theory

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imported>Pythagoras0님의 2012년 10월 29일 (월) 10:50 판
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introduction

  • Glashow-Weinberg-Salam model
  • doublets of leptons and quarks => SU(2) symmetry
  • W-boson mass causes some trouble
  • Goldston boson
  • Higgs mechanism

 

 

recipe

  • start with the local gauge symmetric SU(2) Lagrangian with massless gauge fields
  • introduce the Higgs field
  • break the local gauge symmetry in such a way by a new interaction between the Higgs field and gauge fields so as to generate terms in the Lagrangian that look like mass terms for gauge fields

 

 

adjoining U(1) symmetry

\(\begin{pmatrix}\gamma \\Z^0 \end{pmatrix} = \begin{pmatrix}\cos \theta_W & \sin \theta_W \\-\sin \theta_W & \cos \theta_W \end{pmatrix} \begin{pmatrix}B^0 \\W^0 \end{pmatrix} \)

 

 

 

weak interactions

  • massive gauge bosons 
    • W and Z bosons

 

 

consequences

  • neutral currents
  • new mesons
  • parity violating effects
  • W and Z bosons

 

 

W-boson

  • massive charged spin 1 boson

 

 

Z-boson

  • massive neutral spin 1 boson

 

 

weak force

  • neutron beta decay
  • muon decay
  • high-energy neutrino collisions with matter

 

 

three classes of weak interactions

  • leptonic reactions
  • semi-leptonic reactions
  • hadronic weak reactions

 

 

Higgs mechanism

  • Higges field
    • pervasive universal background field that modifies the simple electroweak gauge theory as the gravitational field caused by mass
  • two initial charged massless weak field W, W^{+}
    • mix with Higgs fields H^{+}, H^{-}
    • W fields get mass
  • two electrically neutral massless fields W^0, G^0
    • mix with neutral Higgs field H^0
    • Z-field massive neutral weak field
  • resulting bosons
    • W - massive charged spin 1
    • Z- massive neutral spin 1 boson
    • photon - massless spin 1
    • Higgs - massive neutral scalar spin 0

 

 

related items

 

 

books

 

 

encyclopedia

 

 

articles