The propagator of a quantum system is defined by $$\mathcal{K}(t,x;\,t_{0},x_{0})\,\equiv\,\left\langle x\right|\hat{U}(t,\,t_{0})\left|x_{0}\right\rangle.$$ In this notation, the unitarity demands that \begin{equation}\begin{split} &\hat{U}^{\dagger}(t,\,t_{0})\,\hat{U}(t,\,t_{0})\,=\,\left(\lef...

I'm an EE, not a physicist, so please forgive if this question is dumb. I learned a bit of magnetics when I took motors 20 years ago, but I don't remember much. I'm reaching out to the physics community because finding EE's who know the answer to this question can be tough. (Take me, for example....

I am using Series function in Mathematica on $(1/z)(-k^2)^z$. Up to $z^0$, the function gives me $1/z + \log[-k^2]$. But in the standard textbook on QFT, it turns out the expansion should give $1/z + \log[k^2/\mu^2] -i\pi $ up to $z^0$ in the series. Could you explain the reason behind such discr...

Given the spatial overlap of nucleon wave functions within the nucleus, why is the bonding of nucleons only the result of pion exchange and not of gluon interactions between quarks in different nucleons?