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In the Minimal Supersymmetric Standard Model, the chiral fermion fields (the Higgsinos) don't have any soft SUSY breaking mass terms and soft SUSY breaking trilinear interactions while their scalar superpartners (the Higgs bosons) have so, whereas naively it should have been the other way around, in order to explain the fact that the superpartners have higher masses than their counterparts in the Standard Model. e.g The gauginos have soft SUSY breaking mass terms and intuitively obey this naive expectation.

  1. Why do the chiral fields have such a distinctive feature as mentioned above? Why don't gauginos share the same feature?
  2. Why do the scalar Higgs get contributions instead?
  3. Also how do we calculate the coupling parameters of the $L_{soft}$ terms starting from first principles? Or are these parameters arbitrary?

EDIT : As pointed out in an existing answer, starting with soft terms for chiral fermionic components is possible but redundant. But precise details are not given there. The third part of the question is answered well enough, but I need necessary details for the first and the second part. I am following arxiv.org/abs/hep-ph/9709356 where these questions are not addressed.

Bruce Lee
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  1. One could write soft terms for the fermionic component of the chiral Supermultiplet for sure, but it's redundant. This terms could be reabsorbed into the other terms of the lagrangian by a field redefinition. Finally one has to decide to write down soft masses for chiral fermions or for it's superpartners. This is not the case for the gauginos since are part of a vector supermultiplet, are the superpartners of a gauge bosons and do not appear in the superpotential.

  2. The scalar higgs is the scalar part of the higgs chiral supermultiplet, so has scalar soft couplings in equal footage respect to other scalar particles.

  3. The general understanding is that some mechanism breaks SUSY spontaneously in some secluded sector, and it's effects are transmitted to the visible sector by some high scale mechanism (supergravity interactions, gravitational anomalies, gauge interactions at GUT scale ,and many other proposals in the market). The soft terms just give and effective description at low energy. Since the structure of the resulting terms depends strongly on the SUSY breaking mechanism, typically one consider this as free parameters in some "natural" range. Where natural means that could be justified by some SUSY breaking scenario.

Iñaki Lara
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