Recent content by smileii

OK, the Lagragian should be Lorentz invariant if $phi$ and $J$ are scalr classical fields. Now, when only \phi is quantized, \phi's Lorentz transformation rule is still the same. So, to keep the Lorent invariance of this "new" Lagragian, I require that $J$ transforms in the same way as $\phi$...

To meopemuk: I think the external source makes sense in some cases. For example, if we consider the scattering of electron by some electroganetic field, usually, the electron field is quantized, but not the EM field. This half-second- quantization is for calculation simplicity.

Some friend asked me the following question: For a real scalar field \phi, assume that H = H_free - \int d^3 x\ J \phi. J(x, t) is just some real number, source, or background field, without second quantization. Now, what is the amplitude \psi(x, t) for finding a particle at time t(before...