# Setting parameters¶

## Couplings and masses¶

Setting parameters can be done by invoking set_parameter_rcl(). For SM-like theories Recola2 comes with dedicated functions to set certain parameters which are all listed below.

 set_parameter_rcl(pname,pvalue) Sets value for the parameter with name pname to pvalue. set_pole_mass_w_rcl(m,g) Sets the pole mass and width of the W boson. set_pole_mass_z_rcl(m,g) Sets the pole mass and width of the Z boson. set_pole_mass_h_rcl(m,g) Sets the pole mass and width of the Higgs boson. set_pole_mass_top_rcl(m,g) Sets the pole mass and width of the top-quark. set_pole_mass_bottom_rcl(m,g) Sets the pole mass and width of the bottom-quark. set_pole_mass_charm_rcl(m,g) Sets the pole mass and width of the charm-quark. set_pole_mass_strange_rcl(m) Sets the pole mass of the strange-quark. set_pole_mass_up_rcl(m) Sets the pole mass of the up-quark. set_pole_mass_down_rcl(m) Sets the pole mass of the down-quark. set_pole_mass_tau_rcl(m,g) Sets the pole mass and width of the tau. set_pole_mass_muon_rcl(m,g) Sets the pole mass and width of the muon. set_pole_mass_electron_rcl(m) Sets the pole mass of the electron.

## Renormalization of alphas¶

A running $$\alpha_\mathrm{s}$$ is implemented for various different scenarios.

1. The running is given externally (obtained from pdfs or other sources). In this case it is enough to update the value $$\alpha_\mathrm{s}(Q)$$ at the scale $$Q$$ before computing the next phase-space-point using set_alphas_rcl().
2. The running can be computed by Recola to 1 and 2-loop order via compute_running_alphas_rcl().

Computations are typically performed for different scale choices at the same time in order to give an estimate of missing higher orders. The additional scale variation can be obtained at zero cost by using the following sequence of calls:

First the a default scale is computed via the squence:

and then other scales are obtained by rescaling:

set_alphas_rcl(as,Q,Nf) Sets the values of $$\alpha_\mathrm{s}$$ to as, the renormalization scale $$\mu_\mathrm{MS}$$ to Q and the number of active quark flavours to Nf.
get_alphas_rcl()
return: Returns the value of $$\alpha_\mathrm{s}$$
compute_running_alphas_rcl(Q,Nf,lp) Computes the value for alpha_s at the scale Q employing the renormalization-group evolution at lp loops (lp can take the value lp=1 or lp=2).
set_alphas_masses_rcl(mc,mb,mt,gc=0.,gb=0.,gt=0.) Overwrites the values of the quark masses for the running of $$\alpha_\mathrm{s}$$ used in the rest of the computations.

### Renormalization of alpha¶

use_gfermi_scheme_rcl([g]) Sets the EW renormalization scheme to the gfermi scheme.
use_alpha0_scheme_rcl([a]) Sets the EW renormalization scheme to the $$\alpha_0$$ scheme.
use_alphaZ_scheme_rcl([a]) Sets the EW renormalization scheme to the $$\alpha_\mathrm{Z}$$ scheme.
get_alpha_rcl()
return: Returns the value of $$\alpha$$

## Scales¶

 set_delta_uv_rcl(d) This subroutine sets the finite part of the UV subtracted term: $$\Delta_\mathrm{UV} = \frac{1}{\epsilon} - \gamma + \log (4 \pi)$$ to d. get_delta_uv_rcl() Gets the finite part of the UV subtracted term $$\Delta_\mathrm{UV}$$. set_delta_ir_rcl(d1, d2) This subroutine sets the finite part of the IR subtracted term $$\Delta_\mathrm{IR} = \frac{1}{\epsilon} - \gamma + \log (4 \pi)$$ to d1 $$\Delta_\mathrm{IR2} = \frac{(4 \pi)^\epsilon \Gamma(1+\epsilon)}{\epsilon^2}$$ to d2. get_delta_ir_rcl() Gets the finite parts of the IR subtracted terms $$\Delta_\mathrm{IR}$$, $$\Delta_\mathrm{IR2}$$. set_mu_uv_rcl(m) Sets the UV scale $$\mu_\mathrm{UV}$$ to m. get_mu_uv_rcl() Returns the UV scale $$\mu_\mathrm{UV}$$. set_mu_ms_rcl(m) Sets the $$\overline{\mathrm{MS}}$$ scale $$\mu_{\overline{\mathrm{MS}}}$$ to m. get_mu_ms_rcl() Returns the $$\overline{\mathrm{MS}}$$ scale $$\mu_{\overline{\mathrm{MS}}}$$. set_dynamic_settings_rcl(i) Sets the dynamic_settings flag to i. set_compute_ir_poles_rcl(mode) Sets whether IR poles are computed when calling compute_process_rcl().