The development of unified theory
Symmetries
In theoretical physics, symmetry is a important tool to study interactions. There are representative symmetries as below:
- C-symmetry: The symmetry of charge-conjugation transformation. Weak interaction violate C-symmetry.
- P-symmetry: The symmetry of parity transformation. Weak interaction also violate P-symmetry.
- T-symmetry: The symmetry of time reversal transformation.
- CP-symmetry: Combining C-symmetry and P-symmetry, the symmetry transforms a particle into its antiparticle and forms the mirror image of a physical system. As we describe above, weak interaction violate CP-symmetry.
- CPT-symmetry: The symmetry combines CP-symmetry with T-symmetry. Any Lorentz invariant local QFT with a Hermitian Hamiltonian have CPT-symmetry.
By the way, "chirality" is similar with "helicity", which describes right-handed and left-handed of particles. Exactly, if the direction of spin is same as the direction of motion called right-handed, if the direction of spin and motion is opposite called left-handed. However, chirality is determined by whether the particle transforms in a right- or left-handed representation of the Poincaré group.
- C-symmetry: The symmetry of charge-conjugation transformation. Weak interaction violate C-symmetry.
- P-symmetry: The symmetry of parity transformation. Weak interaction also violate P-symmetry.
- T-symmetry: The symmetry of time reversal transformation.
- CP-symmetry: Combining C-symmetry and P-symmetry, the symmetry transforms a particle into its antiparticle and forms the mirror image of a physical system. As we describe above, weak interaction violate CP-symmetry.
- CPT-symmetry: The symmetry combines CP-symmetry with T-symmetry. Any Lorentz invariant local QFT with a Hermitian Hamiltonian have CPT-symmetry.
By the way, "chirality" is similar with "helicity", which describes right-handed and left-handed of particles. Exactly, if the direction of spin is same as the direction of motion called right-handed, if the direction of spin and motion is opposite called left-handed. However, chirality is determined by whether the particle transforms in a right- or left-handed representation of the Poincaré group.
Quantum electrodynamics (QED)
QED is the theory of electromagnetic interaction. It can also derive the mass of photons, of course, it's massless. Feynman diagram, renormalization are the famous technique stemmed from QED. It's seen as a pretty theory in physics.
Quantum chromodynamics (QCD)
QCD is the theory of strong interaction, which describes the force between quarks and gluons. There are two famous phenomena as below:
- Color confinement: The phenomenon that color charged particles like quarks cannot be isolated singularly.
- Asymptotic freedom: The phenomenon that bonds between particles will become asymptotically weaker if distance decreases and energy increases.
- Color confinement: The phenomenon that color charged particles like quarks cannot be isolated singularly.
- Asymptotic freedom: The phenomenon that bonds between particles will become asymptotically weaker if distance decreases and energy increases.
Electroweak interaction
Electroweak interaction is unified theory of electromagnetic interaction and weak interaction. The force becomes single as the energy scale around 246 GeV, approximately 10^15 K.
Higgs mechanism
This is a mechanism that describes how the gauge bosons gained the mass. Under some high energy scale, the Higgs field causes spontaneous symmetry breaking and trigger Higgs mechanism.