Starting from [math]E^2=m^2c^4+p^2c^2[/math], then a matrix-type root

we get Dirac equation. But here, the term pc is a kinetic term, but not for massive particle, i.e. pc is only for massless. Is it that this equation rules a field with a massive (mc^2) and a massless parts ?

Starting from [math]E^2=m^2c^4+p^2c^2[/math], then a matrix-type root

we get Dirac equation. But here, the term pc is a kinetic term, but not for massive particle, i.e. pc is only for massless. Is it that this equation rules a field with a massive (mc^2) and a massless parts ?

 

 

E=pc only applies to massless particles, but [math]E^2=m^2c^4+p^2c^2 \neq (mc^2+pc)^2[/math], so the kinetic term is not pc

If pc is not a kinetic term, what is then p, the momentum, if it does not depend on the speed ? Is it a quantum quantity proportional to h*k.?

 

In fact my question is : How do we get the term pc ?