The general MSSM has more than 100 free parameters which makes any systematic study impossible.
One way to reduce this degree of arbitrariness is to assume universality assumptions at the Grand Unification (GUT) scale.
A most commonly used example of such model is the CMSSM (or mSUGRA) which assumes at the GUT scale that:
– all the scalar particles have the same mass: called m0
– all the gauginos (partners of gauge bosons) have the same mass: called m1/2
– all the trilinear couplings of the particles are the same: called A0
and the last free parameter is tan β which is the ratio of the vacuum expectation values of the Higgs doublets.
The sign of the higgsino mass term μ is also not fixed and can be either positive or negative.