Jay R. Yablon said:
I guess I'd be interested in seeing mathematically how the Lorentz violation comes about in Zitterbewegung theory and how what I am doing matches up or not.
[Long post continued]
Now consider the Feynman diagram that annihilates an [tex]e_L[/tex] and creates an [tex]e_R[/tex] with momentum [tex]p_R = p_L[/tex]. This is a trivial type of Feynman diagram in that it has only one input and only one output. Add another diagram, one that does the reverse transformation. Together, these form a Zitterbewegung model for the electron.
Since we are considering the electron as a composite particle made up of a part e_L and a part e_R, we will have to have a two-component vector to model the electron. The two components of this vector will
correspond to the left and right handed parts of the electron. Since the two halves of the electron are scalar particles, we will require a vector of two complex numbers to model the electron. This is convenient because it is just the number of degrees of freedom we need.
To derive the propagator for the electron from the propagators for the e_L and e_R, we need to take into account the Zitterbewegung effect. That is, we need to take into account the interaction that converts a left-handed electron into a right-handed electron and vice-versa.
As is usual in QFT, we will need to resum the whole series of Feynman diagrams (that is, the series generated by the above two) in order to find the propagator for the electron. Fortunately, these two Feynman diagrams are particularly simple.
Let me write down the Feynman diagrams that we must resum, in order of their complexity:
[tex]e_L \to e_L[/tex]
[tex]e_R \to e_R[/tex]
[tex]e_L \to e_R[/tex]
[tex]e_R \to e_L[/tex]
[tex]e_R \to e_L \to e_R[/tex]
[tex]e_L \to e_R \to e_L[/tex]
[tex]e_R \to e_L \to e_R \to e_L[/tex]
[tex]e_L \to e_R \to e_L \to e_R[/tex]
...
To calculate these we need the usual Feynman rules. Note that since there are no loops, there is no need to do any integration. I need to specify a value to associate with the nodes, that is a probability, let us choose $im$.
Now I can resum the propagators. Note that the above series will resum not to a single propagator, but instead to 4. They will be the e_L -> e_L, the e_L -> e_R, the e_R -> e_L and the e_R -> e_R. Let's do
the e_L->e_L propagator first:
[tex]e_L \to e_L[/tex]
[tex]+ e_L \to e_R \to e_L[/tex]
[tex]+ e_L \to e_R \to e_L \to e_R \to e_L[/tex]
[tex]+ ...[/tex]
To sum these, remember the propagators defined above and that p = p_L = p_R.
[tex]L \to L =(i/p_L) + (i/p_L) I am (i/p_R) I am (i/p_L) + ...[/tex]
[tex]L \to L =(i/p) + i (m/p)^2p + i (m/p)^4 p + ...[/tex]
[tex]L \to L =(i/p)(1+(m/p)^2 + (m/p)^4 + ...[/tex]
[tex]L \to L =\frac{i/p}{1-(m/p)^2}[/tex]
[tex]L \to L =\frac{ip^2/p}{p^2-m^2}[/tex]
[tex]L \to L =\frac{ip}{p^2-m^2}[/tex]
I've left more stages in the algebra than necessary in order to hint where you will have to work harder to put the gamma matrices back in.
The p_R to p_R propagator will be similar:
[tex]L \to R =\frac{ip}{p^2-m^2}[/tex]
The p_L to p_R propagator is as follows. The Feynman diagrams are:
[tex]e_L \to e_R[/tex]
[tex]+ e_L \to e_R \to e_L \to e_R[/tex]
[tex]+ e_L \to e_R \to e_L \to e_R \to e_L \to e_R[/tex]
[tex]+ ...[/tex]
These work out to be:
[tex]L \to R =(i/p_L) I am (i/p_R) + (i/p_L) I am (i/p_R) I am (i/p_L) I am (i/p_R) + ...)[/tex]
[tex]L \to R = \frac{im}{p^2}(1 + (m/p)^2 + (m/p)^4 + ...)[/tex]
[tex]L \to R = \frac{im}{p^2(1-(m/p)^2)}[/tex]
[tex]L \to R = \frac{im}{p^2-m^2}[/tex]
Similarly, R->L works out as:
[tex]R \to L = \frac{im}{p^2-m^2}[/tex]
With all four propagators computed, we can put them together into a single equation using matrices. We assume our (spinors) consist of left-handed massless particles on the top part of a 2-vector, and right-handed massless particles on the bottom part. Then the desired resummation of the propagators is:
[tex]\left(\begin{array}{cc} L \to L \;&\; L \to R \\ R \to L \;&\; R \to R \end{array} \right)[/tex]
[tex]=\left(\begin{array}{cc} \frac{ip}{p^2-m^2} \;&\; \frac{im}{p^2-m^2} \\ \frac{im}{p^2-m^2} \;&\; \frac{ip}{p^2-m^2} \end{array} \right)[/tex]
[tex]=\frac{1}{p^2-m^2}\left(\begin{array}{cc} ip \; & \; I am \\ I am \; & ip \end{array}\right)[/tex]
Uniting the left and right handed electron fields back to the same particle, one ends up with a propagator of:
[tex]\frac{i(p+m)}{p^2-m^2}[/tex]
I tend to lose factors of i so you might check this. Also, note that the positron works out the same way and increases the size of the matrix from 2x2 to 4x4 as in the usual Dirac matrices.
Now in the above, there isn't any Lorentz violation. But if you consider an electron at rest with spin +1/2 in the z direction, for it to be composed of e_L and e_R portions, one must have that the velocities of these two subparticles be in opposite directions. This is incompatible with their momenta being identical. You can fix this by going back and making p_R = - p_L, but then you've lost conservation of momentum at the vertices of your Feynman diagrams.
Carl