Jon
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 Dec 11 awarded Yearling Jul 1 comment Lorentz transformation of Gamma matrices $\gamma^{\mu}$ Your transformation is not enough. To keep the Lagrangian invariant, as $\psi\rightarrow e^{iS}\psi$, you will get $\gamma'=e^{-iS}\gamma e^{iS}$. For the $S$ to exist, granting in this way Lorentz invariance, you can check whatever book on QFT as e.g. Bjorken and Drell Vol.I. Apr 3 comment Space-time translations and Propagator Steven, thanks anyway. I know this is not a very simple problem and probably not much is known unless some particular forms of $\Omega(t)$ are known. But I hope someone else could help on this. Apr 3 comment Space-time translations and Propagator Yes, I would like to know if some technique is known about this, if the physics coming our from $G(t,0)$ is enough without knowing $G(t,t')$ and so on. It is also possible that no answer is known and this will be a legal answer too. Apr 3 comment Space-time translations and Propagator If you need more information on why this is so, I am happy to extend my question. Apr 3 comment Space-time translations and Propagator That's my point. How can I get back from $G(t,0)$ to $G(t,t')$? Of course, your answer is not really an answer but rather a comment of a well-known fact. Apr 3 comment Space-time translations and Propagator Apply this to the following Green function $\ddot G(t,t')+\Omega(t) G(t,t')=\delta(t-t')$. Apr 3 asked Space-time translations and Propagator Feb 26 revised Could this model have soliton solutions? Added Wikipedia link to Derrick's theorem Feb 26 answered Could this model have soliton solutions? Jan 29 comment What happens when two photons collide? See physics.stackexchange.com/questions/159320/… It is called Delbrück scattering and is a higher order effect in quantum electrodynamics. Jan 19 awarded Enthusiast Jan 14 revised If two photons collide, does the resulting particle have zero velocity? Fixed a small LaTeX problem Jan 14 comment If two photons collide, does the resulting particle have zero velocity? This is known as Delbrück scattering en.wikipedia.org/wiki/Delbr%C3%BCck_scattering and being a four vertexes effect is really small. Jan 14 suggested approved edit on If two photons collide, does the resulting particle have zero velocity? Jan 9 revised Why does the diffusion pole universally appear in the two-particle Greens function (diffuson) TeXified formulas Jan 9 suggested approved edit on Why does the diffusion pole universally appear in the two-particle Greens function (diffuson) Jan 8 answered What's the closed-form of the sum relating to the DOS of simple harmonic motion? Dec 11 awarded Yearling Nov 21 comment Scalar field in a Schwarzschild metric Thanks for pointing this out. I upvoted your answer because that lectures are very good but do not appear to fit the bill properly. The radial part of the wave equation is explicitly given without being solved. No explicit exact solution is really presented.