Minimal Supersymmetric Standard Model - Problems With The MSSM

Problems With The MSSM

There are several problems with the MSSM — most of them falling into understanding the parameters.

• The mu problem: The supersymmetric Higgs mass parameter μ appears as the following term in the superpotential: μH_uH_d. It should have the same order of magnitude as the electroweak scale, many orders of magnitude smaller than that of the planck scale, which is the natural cutoff scale. The soft supersymmetry breaking terms should also be of the same order of magnitude as the electroweak scale. This brings about a problem of naturalness: why are these scales so much smaller than the cutoff scale yet happen to fall so close to each other?
• Flavor universality of soft masses and A-terms: since no flavor mixing additional to that predicted by the standard model has been discovered so far, the coefficients of the additional terms in the MSSM Lagrangian must be, at least approximately, flavor invariant (i.e. the same for all flavors).
• Smallness of CP violating phases: since no CP violation additional to that predicted by the standard model has been discovered so far, the additional terms in the MSSM Lagrangian must be, at least approximately, CP invariant, so that their CP violating phases are small.