Transcript conserved in strong interactions

Quantum Electrodynamics
Dirac Equation : spin 1/2
Feynmann Diagrams
Moller Scattering
Interaction is mediated by
exchange of a photon
Bhaba Scattering
electron positron annhilation
Symmetries, Groups and Conservation laws
Closure:
R1,R2 belong to G, R1.R2 also
belongs to G
Identity: There exists element I
such that for all elements in G
IRi=RiI=Ri
Inverse: For every element there
exists an inverse element such that
RiRi-1=I
Associativity:
Symmetries and Conservation Laws
Noether's theorem: Every continuous symmetry implies a
corresponding conservation law and conversely, every
conservation law reveals a symmetry in the system.
Rotation ---- Angular momentum
Time translation ----- Energy
SU(2) Symmetry Group: Isospin
• mass of proton ~ mass of neutron
• treating proton as a different charge substrate of neutron:
Isospin (I) I=1/2. (conserved in strong interactions)
• I3 =+/- 1/2 -----> charge Q/e=1/2+ I3
• Analogous to a particle of ordinary spin 1/2
Generators of SU(2) are Pauli matrices:
SU (3) symmetry: Flavour symmetry
Generators of SU(3):Gell Mann Matrices
Charge Conjugation: C
Particle to antiparticle
Parity Operation:
P, reflects a system through the origin
right handed system to left handed system
axial system invariant under parity
C and P are conserved in EM and Strong
Interactions
Time Reversal: T . Changes the direction of motion
CPT invariance:
All interactions are invariant under combined C,P,T
Weak Interactions
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All quarks, leptons carry "weak charge"
Short range interaction
Interact via exchange of W+,W- and Z bosons (massive)
two kinds of weak interactions: charged (W bosons) and neutral (Z
boson)
• Examples :decay processes
Weak Interactions: Leptons
charged
neutral
Conservation of electron, muon, tau
numbers
Conservation laws in WI
• Conservation of charge
• Conservation of Colour
• Conservation of Baryon number
• Electron, muon, tau number
CP violation in Weak Interaction
Weak Interactions are not always CP invariant.
CP violation implies Time reversal must also be violated.