Recent content by George Wu

I encounter a function that I don‘t know in the calculation of Relativistically invariant 2-body phase space integral: in this equation, ##s##is the square of total energy of the system in the center-of-mass frame(I think) I don't know what the function ##\lambda^{\frac{1}{2}}## is. There are...

Thanks for your explanation，I think I get the spirit.

This question arise when I try to understand the equation (4.68) : In order to understand the factor ##e^{-i\mathbf{b}\cdot \mathbf{k}_B}##： I use the so-called "spatial wavefunction": if$$\phi _B(\mathbf{k}_B)=\int{d^3\mathbf{x}}\phi _B(\mathbf{x})e^{-i\mathbf{k}_B\cdot \mathbf{x}}$$...

My understanding is: $$\phi (\mathbf{k})=\int{d^3}\mathbf{x}\phi (\mathbf{x})e^{-i\mathbf{k}\cdot \mathbf{x}}$$ But what is ##\phi (\mathbf{x})## in Qft? In quantum mechanics, $$|\phi \rangle =\int{d^3}\mathbf{x}\phi (\mathbf{x})\left| \mathbf{x} \right> =\int{d^3}\mathbf{k}\phi...

I have found a great answer: Prahar (https://physics.stackexchange.com/users/8821/prahar), Time ordering of integral, URL (version: 2022-12-17): https://physics.stackexchange.com/q/741494 $$T\int_{t_0}^t{d}t_1\cdots dt_nH_I\left( t_1 \right) \cdots H_I\left( t_n \right)$$ is defined to equal to...

In Peskin P85: It says the Time-ordered exponential is just a notation，in my understanding, it means $$\begin{aligned} &T\left\{ \exp \left[ -i\int_{t_0}^t{d}t^{\prime}H_I\left( t^{\prime} \right) \right] \right\}\\ &\ne T\left\{ 1+(-i)\int_{t_0}^t{d}t_1H_I\left( t_1 \right)...