## The Klein-Gordon Propagator

1. Klein-Gordon Equation The Klein-Gordon equation is a relativistic wave equation, related to the Schrödinger equation. It is second order in space and time and manifestly Lorentz covariant. It is a quantized version of the relativistic energy–momentum relation. Its solutions include a quantum scalar or pseudoscalar field, a field whose quanta are spinless particles. The […]

## Linear Response Theory

A small perturbation act on a system in equilibrium may produce an effect related to this external field, which can be treat as a linear response up to first order approximation.

## Tensor Analysis in Special Relativity

1. Vector analysis in spetial relativity A vector in an inertial frame can be written as (1)   In another inertial frame which moving in the drirection with vecocity (2)

## Feynman Diagrams

In Coordinate Space The Green’s function of a fermion can be written as the sum of all connected diagrams

## Wick’s Theorem

Wick’s theorem is a way to reduce a time-ordered operator into the sum of normal-ordered operator and various contractions. Then, where is the time-ordered operator from? Why we need this reduction?

## Quantum Pictures

This note gives a comparison on the three quantum pictures. Also, the Dyson series are introduced with the help of time-ordering operators.

## Blackbody Radiation

1.  What is Blackbody Radiation?   All normal matter emits electromagnetic radiation when it has a temperature above absolute zero. The radiation represents a conversion of a body’s thermal energy into electromagnetic energy, and is therefore called thermal radiation. It is a spontaneous process of radiative distribution of entropy.

## Summary on Special Relativity

I didn’t really understand the special relativity, although I get to know it for many years. But I know that I should make a summary of this fabulous theory when I came to be the TA for such kind of class.

## Partition Function and Laplace Transform

Partition function is in fact the Laplace transformation of density of states.

## Boltzmann Transport Equation

Before Maxwell and Gibbs introduced ensemble theory, physicists such as Bernoulli, Herapath, Joule, Kronig, Clausius, Boltzmann and so on has constructed the kinetic theory which is the beginnings of statistical mechanics. Kinetic theory starts with the microscopic movements of all of the particles, try to find out the distribution of these particles in space. Based […]