Cut routines
Here is an overview of the cutting routines supported by the code.
Gluon fields can be computed from the logarithm or approximation to the logarithm of the SU(NC)-valued parallel transport matrices. By default the code uses the normal lattice approximation but can also use the logarithmic definition although for NC > 3, this becomes slow and unstable as series expansions are used to compute this thing.
A gluon propagator in momentum space is defined as
In Landau gauge
The Landau gauge condition in configuration space is
In momentum space this becomes
I define the lattice momentum in the usual manner,
Where n_\mu is an integer Fourier mode,
The factor of e^{iaq_\mu/2} comes from the gauge fields being well approximated by lying halfway between the lattice sites.
We can define projectors for the transverse and longitudinal components,
Because of the Landau condition in momentum space, the longitudinal component is zero as is the second term in the transverse component, so this expression just leaves a Kronecker delta.
We write out the transverse component in Big Endian binary format.
Coulomb gauge propagators are different. I use indices i and j to define indices running only in the spatial directions. The Coulomb condition is simply,
We can define both spatial and temporal propagators
