# BSM¶

## How do I disable decay modes in BSM models?¶

The decay modes for the new physics models do not exist prior to the Herwig++ read step, so they cannot be simply commented out of a file.

There is a mechanism so that specified decay modes will not be created. The mechanism is universal in that if a decay table is read in with a SUSY model and a decay mode from this is specified, it will also be disabled.

Using this new mechanism simply requires adding information to the .in file. As an example we take the MUED model where we wish to disable the decay modes

• KK1_u_L -> KK1_gamma,u
• KK1_Z0 -> KK1_e_R-,e+

In the relevant .in file the lines

insert /Herwig/NewPhysics/DecayConstructor:DisableModes 0 KK1_u_L->KK1_gamma,u;
insert /Herwig/NewPhysics/DecayConstructor:DisableModes 1 KK1_Z0->KK1_e_R-,e+;


should be added where the ordering of the decay products does not matter as this is taken care of by the code. Please note that each string should be terminated with a ;. In addition, the two characters following the parent particle are a dash(-) and a greater-than symbol(>).