Add $\gamma_0 \gamma_i$ correlators in rho-pi-pi scattering

[yannickdengler]

Compiled and ready for cluster :)

[fzierler]

What is this comment referring to?

[fzierler]

It appears to be working correctly on the cluster where I tested it. We should write some documentation for the used functions in general.

[fzierler]

I have looked at the $\gamma_0\gamma_i-\gamma_i$ cross-correlators in the free theory. The result is:
$C_{V-T}(\vec P, t-t') = +\frac{4i}{L^6 T^2} \sum_{q_0, p_0, \mathbf p} e^{+i(p_0 - q_0) (t-t')} \frac{\left( \hat m(q_0,\vec P+\vec p) \sin(p_0) - \hat m(p) \sin(q_0) \right)}{N(p)N(q_0,\vec P+\vec p)}$
with
$\hat m(p) = m + \sum_\mu \left[ 1 - \cos \left( p_\mu \right)\right]$
$N(p) = \hat m(p)^2 + \sum_\mu \sin^2 \left( p_\mu \right)$
I will do the same calculation for the triangle diagrams. We should then implement tests for the diagrams you have added.

[yannickdengler]

Added a input option to measure axialvector.
Added the cross-correlator for gi to g0gi for P=0
Also added the contractions gi to gj for i!=j (Not sure if this one contains physics)