8 Beyond the Standard Model
497
The model, as written, has 178 independent parameters. Their number could
be reduced if they had their origin in an underlying microscopic theory. In some
present versions the matrices of parameters denoted above by c ij are set to zero
thus reducing by fiat the number of free parameters to 124. This is but the tip of an
iceberg, one proceeds from versions of the MSSM and derives the mass spectrum of
the supersymmetric particles while ensuring to preserve the known properties of the
standard model particles as well as a variety of experimental bounds. The bounds
range from cosmological ones to bounds on rare decays. We hope that in the not
too distant future the fog will disperse and one will be able to write a rather concise
item in a physics encyclopedia which would select the relevant physical components
of this effort. As mentioned any model for SUSY breaking should respect present
experimental constraints. Many models of spontaneous SUSY breaking fail to do
this as a result it was suggested to add to the yet to be seen superpartners of the
standard model particles also a hidden sector. In such models SUSY is to be broken
in the hidden sector and its effects are supposed to be mediated to the “seen” sector.
The agents or messengers which couple the two sectors vary. In some models the
coupling is by the gravitational force at tree level, in others the coupling occurs first
only at the one loop level and is called anomaly (Weyl anomaly) mediated. There are
models in which the coupling is done through gauge interactions, they have a lower
energy scale than the gravity mediated interactions. Each of these models has some
advantages as well as disadvantages and are at this stage an active area of research.
We will end the section with a short glossary of terms currently used in describing
MSSM features which were not mentioned above.
Short Glossary:
• Chargino—Charged supersymmetric partner of a charged standard model particle.
• Gaugino—Spin one half supersymmetric partner of a standard model gauge
particle.
• LSP—Lightest supersymmetric partner of a standard model particle. It is long
lived in many models.
• μ term—Term coupling the two different Higgs chiral supermultiplets.
• Neutralino—Neutral supersymmetric partner of a neutral standard model particle.
• squark—Spin zero supersymmetric partner of a standard model quark.
• slepton—Spin zero supersymmetric partner of a standard model lepton.
• tan(β)—Ratio of the expectation values of the two Higgs fields.
497
The model, as written, has 178 independent parameters. Their number could
be reduced if they had their origin in an underlying microscopic theory. In some
present versions the matrices of parameters denoted above by c ij are set to zero
thus reducing by fiat the number of free parameters to 124. This is but the tip of an
iceberg, one proceeds from versions of the MSSM and derives the mass spectrum of
the supersymmetric particles while ensuring to preserve the known properties of the
standard model particles as well as a variety of experimental bounds. The bounds
range from cosmological ones to bounds on rare decays. We hope that in the not
too distant future the fog will disperse and one will be able to write a rather concise
item in a physics encyclopedia which would select the relevant physical components
of this effort. As mentioned any model for SUSY breaking should respect present
experimental constraints. Many models of spontaneous SUSY breaking fail to do
this as a result it was suggested to add to the yet to be seen superpartners of the
standard model particles also a hidden sector. In such models SUSY is to be broken
in the hidden sector and its effects are supposed to be mediated to the “seen” sector.
The agents or messengers which couple the two sectors vary. In some models the
coupling is by the gravitational force at tree level, in others the coupling occurs first
only at the one loop level and is called anomaly (Weyl anomaly) mediated. There are
models in which the coupling is done through gauge interactions, they have a lower
energy scale than the gravity mediated interactions. Each of these models has some
advantages as well as disadvantages and are at this stage an active area of research.
We will end the section with a short glossary of terms currently used in describing
MSSM features which were not mentioned above.
Short Glossary:
• Chargino—Charged supersymmetric partner of a charged standard model particle.
• Gaugino—Spin one half supersymmetric partner of a standard model gauge
particle.
• LSP—Lightest supersymmetric partner of a standard model particle. It is long
lived in many models.
• μ term—Term coupling the two different Higgs chiral supermultiplets.
• Neutralino—Neutral supersymmetric partner of a neutral standard model particle.
• squark—Spin zero supersymmetric partner of a standard model quark.
• slepton—Spin zero supersymmetric partner of a standard model lepton.
• tan(β)—Ratio of the expectation values of the two Higgs fields.