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---
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title: Decay calculation with SPheno
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permalink: /Decay_calculation_with_SPheno/
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---
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[Category:Outputs](/Category:Outputs "wikilink") [Category:SPheno](/Category:SPheno "wikilink")
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Decays calculated by SPheno
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---------------------------
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The calculation of decays widths and branching ratios can be done by using the interface between SARAH and SPheno. SPheno modules created by SARAH calculate all two-body decays for SUSY and Higgs states as well as for additional gauge bosons. In addition, the three-body decays of a fermion into three other fermions and of a scalar into another scalar and two fermions are included.
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In the Higgs sector, possible decays into two SUSY particles, leptons and massive gauge bosons are calculated at tree-level. For two quarks in the final state the dominant QCD corrections due to gluons are included . [The loop induced decays into two photons and gluons are fully calculated at leading-order (LO) with the higher order corrections known from the SM/MSSM](/Diphoton_and_digluon_vertices_with_SPheno "wikilink"). For the LO contributions all charged and coloured states in the given model are included in the loop, i.e. new contributions rising in a model beyond the MSSM are fully covered at one-loop. In addition, in the Higgs decays also final states with off-shell gauge bosons (*Z**Z*<sup>\*</sup>, *W**W*<sup>\*</sup>) are included. The only missing piece is the *γ**Z* channel. The corresponding loops are not yet derived by SARAH and the partial width is set to zero.
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Setting up the list of decaying particles
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-----------------------------------------
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One can set the lists of particles for which the two- and three-body decays shall be calculated via
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ListDecayParticles=...
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ListDecayParticles3B=...
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with the following possibilities and conventions
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1. `ListDecayParticles` defines the list of particles for which the two-body decays are to be calculated. There are two possibilities:
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- A list of particles is given
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- The keyword `Automatic` is used. In that case, the widths of all particles not defined as standard model particles as well as for the top quark are calculated. Note, `Automatic` is not possible for [a low scale SPheno version](/Low_or_High_scale_SPheno_version "wikilink").
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2. `ListDecayParticles3B` defines the list for three body decays. Also here two options are possible:
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- A list of particles and the corresponding file name is given
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- The keyword `Automatic` is used. In that case, the widths of all particles not defined as standard model particles as well as for the top quark are calculated. Note, `Automatic` is not possible for [a low scale SPheno version](/Low_or_High_scale_SPheno_version "wikilink").
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#### Example
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1. All two-body decays for SUSY states, the Higgs states and the top in the MSSM are included via
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ListDecayParticles = {Sd,Su,Se,hh,Ah,Hpm,Chi,Cha,Glu};
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This would give the same output as just
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ListDecayParticles=Automatic;
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2. The three body decays of SUSY fermions in the MSSM are included via
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ListDecayParticles3B = {{Chi,"Neutralino.f90"},
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{Cha,"Chargino.f90"},
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{Glu,"Gluino.f90"}};
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If instead
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ListDecayParticles3B=Automatic;
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would be used, also three-body decays of scalars are included. The auto generated file names are the [OutputName](/particles.m "wikilink") of each field.
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The parameters used in the decays
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---------------------------------
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In contrast to other spectrum generators, SPheno modules by SARAH can perform a RGE running to the mass scale of the decaying particle. This should give a more accurate prediction for the decay width and branching ratios. However, the user can also turn off this running and use always the parameters as calculated at the renormalisation scale *Q* in all decays as this is done by other codes.
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Important flags in the Les Houches file
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---------------------------------------
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- `11` if `1`, the branching ratios of the SUSY and Higgs particles are calculated; default is `1`
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- `12` defines minimum value for a branching ratios to be included in output; default is 10<sup>−4</sup>
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- `13` adjusts the three-body decays: `0`: no three-body decays are calculated; `1` only three-body decays of fermions are calculated; `2` only three-body decays of scalars are calculated; `3` three-body decays of fermions and scalars are calculated; default is `1`
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- `14` if `1`, the running parameters at the mass scale of the decaying particle are calculated. Otherwise, the parameters at the standard renormalization scale are used; default is `1`
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See also
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-------- |
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\ No newline at end of file |