Recent content by Abrain

Nobody knows anything about this? [= UP]

Do somebody knows anything about the Dirca's identity? \begin{equation} \label{Dirac} \frac{\partial^2}{\partial x_{\mu}\partial x^{\mu}} \delta(xb_{\mu}xb^{\mu}) = -4\pi \delta(xb_0)\delta(xb_1)\delta(xb_2)\delta(xb_3) \end{equation} here xb, is the 4-vector $x-b$ in Minkowsky spacetime...

...Up!

Hi everybody! I'd like to understand the physical meaning of the Feynman's vector potential definition: $ A_{m}^{(b)}(x) = e_b \int \delta (xb_{\mu}xb^{\mu})db_m(b), \qquad m=0,1,2,3 $ (component m of the vector potential of the particle b at the point x) Here - the integration is done over...

This could be... the book does'n say exactly what dS is. However dS = -dx-dy-dz+cdt is a 4-volume, isn't it? But,if you are right, the equality is holding only because of the Gauss law? This sound pretty correct

Oh thank you! I feel so stupid about this... :-p

It doesn't seem to work neither with [tex] or [itex]

I'd like to understand why \int{\rho}dV = \frac{1}{c} \int{j^0}dV = \frac{1}{c} \int{j^i}dS_i (the second equality), where j^i = \rho \frac{dx^i}{dt} is the current density 4-vector \mathbf{j} = \rho \mathbf{v} is the current density 3-vector j^i = (c\rho, \mathbf{j}) \rho is...