Process computation

Functions for process computation:

compute_process_rcl(npr,p,order) Computes the structure-dressed helicity amplitudes and the summed squared amplitude (unless polarizations specified, see define_process_rcl()) for the process with process number npr.
compute_colour_correlation_rcl(…) Computes the colour-correlated summed squared amplitude, between particle with leg number i1 and particle with leg number i2, for the process with process number npr.
compute_spin_correlation_rcl(npr,p,j,v,order=) Computes the spin-correlated summed squared amplitude, where the polarization vector of particle j, necessarily being a gluon or photon, is is substituted for the user-defined polarization vector v.
compute_spin_colour_correlation_rcl(…) Computes the spin-colour-correlated summed squared amplitude, between particle with leg number i1 and particle with leg number i2, for the process with process number npr.
rescale_process_rcl(npr,order) Adjusts the results calculated by compute_process_rcl() for a new value of \(\alpha_\mathrm{s}\), rescaling the structure-dressed helicity amplitudes and recomputing the summed squared amplitude for the process with process number npr.
get_amplitude_rcl(…) Extracts a specific contribution to the amplitude of the process with process number npr, according to the values of pow, order, colour and hel.
get_squared_amplitude_rcl(…) Extracts the computed value of the summed squared amplitude with pow being order in the fundamental couplings at loop-order order for the process with process number npr.

Conventions for momenta

The momenta passed to Recola are standard lorentz vectors. For a \(2\to n\) process the first two momenta are considered incoming and need to have positive energy while the other \(n\) are outgoing and, thus, have to fulfill the four momentum conservation:

\[p_1^\mu + p_2^\mu = \sum_{k=3}^{n+2} p_k^\mu\]

For decay processes \(1\to n\) the four-momentum conservaion reads:

\[p_1^\mu = \sum_{k=2}^{n+1} p_k^\mu\]

Recola2 provides a RAMBO module to generate random PSP for any beam initial and final state:

set_outgoing_momenta_rcl(npr,pIn) Random phase space generation given incoming momenta.