## Information

• 官方介绍: https://theoreticalminimum.com/courses/particle-physics-2-standard-model/2010/winter
• 把主要内容整理一下.

## Lecture 1: Particles, Fields & Forces

Any particle can be exchanged in some context or another. So every kind of particle in one way or another produces a force.

Example: Covalent bounds: sharing an electron Coulomb: exchange photons
 Name Symbol Type Charge B number Mass Photon $\gamma, A$ Boson $0$ $0$ $0$ Electron $e^{\pm}, \psi_e$ Fermion $-1$ $0$ $.51$ MeV Quark $q, \psi_q$ F $\frac{1}{3}$ down $-\frac{1}{3}$ $10$ MeV up $\frac{2}{3}$ $5$ MeV strange $-\frac{1}{3}$ $100$ MeV charm $\frac{2}{3}$ $1$ GeV bottom $-\frac{1}{3}$ $5$ GeV top $\frac{2}{3}$ $170$ GeV

## Lecture 2: Quantum Chromodynamics

Gluons interact with each other forces between gluons.

## Lecture 5: Gauge Fields and Symmetry

Anytime that has conserved quantity analogous to electric charge which functions as the source of photon like field, that called a gague theory. Gauge theories are always based on symmetries.

## Lecture 6: The Weak Interaction

Why weak interactions give such slow decay rates?

## Lecture 7: Spontaneous Symmetry Breaking & Goldstone Bosons

How a particle like the photon can get a mass from something called spontaneous symmetry breaking?

How if the symmetry group associated with the photon were broken spontaneously how it would give the photon of mass.

How gauge bosons like the photon get a mass when spontaneous symmetry breaking?

what is the symmetry incidentally when I say you associated with photon? There's a conserved quantity which is the charge. Conserved quantities always go with symmetries. What's the symmetry that's connected with the conservation of electric charge? It's thing which multiplies the charged fields by a phase.

Example of the Higgs phenomenon: Superconductor Photon get a mass and the $U(1)$ symmetry is spontaneously broken.

Not the same as photon in prism!

\begin{align} E = \hbar \omega \\ p = \hbar k \\ \omega = c k \end{align}

if $\omega = 0$ , then $k = 0$ , we call massless.

$E = \sqrt{p^{2} + m^2}$ , if $p = 0$ , the energy is not zero, that's the mass.

Oscillations of a field when it is homogeneous when is has infinite wavelength those are the things we call mass. The Goldstone boson got eaten by the gauge boson resulting in giving the Higgs boson a mass. ## Lecture 8: The Higgs Field

Gauge invariance is a symmetry which prohibits the photon from having a mass.

## Lecture 9: The Higgs Field & Fermions

 massless photons Higgs massive photon massless Goldstone bosons $\Longrightarrow$ no Goldstone boson massive Higgs bosons phenomenon massive Higgs bosons

Mass stands for energy at rest, but it also stands for energy associated with uniform homogeneous shifts of fields.

Moving the plus charges relative to the minus charges -> plasma. Plamas have mass, phonons do not.

$\beta$ decay: mirror, discreate, not a symmetry of weak interaction.

Mass term is a thing which turns left handed to right handed.

Mass is always for fermions, it always left hand, trun into the right hand, right hand ...

## Lecture 10: Running of Coupling Constant

Condense: which means the field for this field of particle gets shifted.

## Self-Examination Questions

• How to describe weak interaction? Which particles?
• How to describe strong interaction? Which particles?
• What is a gague theory?
• How strong interaction different from others?
• Why weak interactions give such slow decay rates?
• How a particle like the photon can get a mass from something called spontaneous symmetry breaking?
• How fermions get their mass?
• How to understanding the meaning of mass?
• What is Majorana fermion?