1. Standard Model of Particles
SPACE
TIME
Strong Interaction
E&M Interaction
The standard model consists of spin 1/2 quarks and leptons which interact through the interchange of gauge bosons.
The electromagnetic force is mediated by the massless photon, which is the only stable boson.
Thus the range is infinite.
The coupling is very small, and so the electromagnetic interaction can be calculated perturbatively to a very high precision.
The weak interaction is more like the electromagnetic than the strong interaction.
It also has a weak coupling, but the W and Z are very heavy, which limits its range to about .2% of the radius of the neutron.
The other property is that the W boson caries electric charge,
and thus can convert an ‘up’ quark into a ‘down’ or a ‘strange’,
and same for the leptons.
The strong interaction is mediated by gluons with three separate charges labeled by color.
The gluon does not interact with leptons, but does with quarks and even other gluons.
so what you end up with is that even the ground state
is a messy tangle of gluons and quark- anti-quark pairs called the ‘sea’.
This multiplies the force and strongly confines quarks and gluons inside of the nucleon.
So if both the strong and weak forces are short-range, how do neutrons interact?
By the exchange of quark - anti-quark pairs or mesons, which has the range of 1-2 fm.
The interesting physics happens at the vertex, which can involve weak or strong interactions.
That is what we will be discussing today.
Now, besides their obvious quantum mechanical differences fermions are a lot like cars,
so let me take you on an auto-mechanical tour of the standard model.
Weak Interaction
Hadronic Interaction
(residual nuclear force)

2. Symmetries Continuous Symmetries
space-time translation
rotational invariance
Lorentz boosts
gauge invariance
Noether’s Theorem continuous symmetries correspond to conserved quantities
energy-momentum
angular momentum
center-of-momentum
electric charge
Discrete Symmetries
parity P : x  -x
time T : t  -t
charge C : q  -q
particle P12: x1  x2 exchange
Discrete Theorems
spin-statistics theorem
CPT theorem
position symmetry
conserved momentum