Thanks for your reply.
"The wave would then be a straight line."
Why would the line be straight? It appears that the matter wave of an electron wraps around in the orbitals of atoms. The matter wave would be in the direction the particle travels.
While the wavelength of a matter wave is independent of electric charge, it's path should be influenced by electric charge
In the double slit experiment, the size of a matter wave must be large enough to have some part of it go through both slits when an electron goes through one of the slits.
Two particles traveling parallel at the same velocity would appear to each other to have infinite wavelengths, but would still have constant frequencies.
I think you are playing with many particles like that at LHD, yes?
I indeed thought too fast and was focusing on the 1D case. With a period being infinite, we can see the 1D wave as a straight line. Which is what I had actually in mind.
The wave vector follows the momentum, or vice versa. So yes, somehow.
There is actually no way to answer that question. The electron passes through both slits at the same time. You may want to check some of the older posts I wrote on this.
Here you also need field theory and relativistic mechanics, but yes we do :)
Thanks