Minimal Supersymmetric Standard Model

The minimal supersymmetric standard model ( MSSM ) is the smallest possible particle content with respect to the election, the existing standard model of particle physics (SM ) to a supersymmetric physics model to expand.

In the extension of the SM to the MSSM field content is extended by an additional Higgs doublet and then assigned to each field / particle exactly a super affiliate. Since the gauge symmetries with respect to the SM remain unchanged, the calibration interactions are defined in the MSSM for the newly emerging particles already by the SM.

In addition, however, a large number of interaction terms exist that do not originate from a gauge symmetry. The existence and strength of these terms is initially unknown, so that the MSSM the most general case is a model with many new and unknown parameters.

• 2.1 interaction eigenstates
• 2.2 mass eigenstates

Interactions

The MSSM has the same gauge interactions as the SM, ie. Since up to the new Higgs doublet, whose charges are required, the charges of all fields are already known from the SM, the gauge interactions of all particles (even the new super affiliates ) is already determined by the SM. To be a realistic physics model, including the MSSM has to break the electroweak symmetry group for the electromagnetic symmetry. This is done as in the SM spontaneously through non-vanishing vacuum expectation values ​​of the Higgs fields.

Another possible non- calibration interactions ( engl.: non -gauge interactions ) can use the calibration interactions also occur, especially terms that give the particles their mass. These terms have initially unknown factors that are in the MSSM, however, all - with the exception of R- parity violating terms ( see below) - allowed as long as they are physically meaningful in terms of a renormalizable gauge theory. Due to the new terms, the number of independent parameters of the theory with respect to the SM increased by more than one hundred (! ). The MSSM is thus minimal, in the sense that the number of particles present in the theory for the minimum possible increased, but the maximum, in the sense that many theoretically allowed new interactions are taken into account.

Masses of the superpartners

The superpartners of the Standard Model particles initially have the same mass as the original particles. But until today, for example, no bosonic electron was discovered, it is assumed that the super affiliates have a much higher mass: ~ (1 TeV / c ² ); for comparison, the mass of the proton is 0.94 GeV / c ². This leads to restriction of the corresponding first parameter in the interaction terms.

There are approaches to inform the masses of the occurring in the MSSM particles to each other. These are advanced physics models (Grand unified theory, superstring theories ) that in the limit of low energies ( "low" is here to be relative, it should at least include the TeV / c ² - energy ) as the MSSM behave.

R- parity conservation

Some interaction processes with an odd number of superpartners allow the spontaneous decay of free protons. As this process has not been observed in various experimental search, the associated parameters must be very small. Often processes are simply banned with an odd number of super partners by defining a new sustaining quantum number. In this case one speaks of R- parity conservation.

The parity R is a discrete, multiplicative symmetry and is defined as

With B = baryon number, lepton number L =, s = particle spin.

The R- parity is 1 for Standardmodellteilchen (3B L 2 s straight) and -1 for supersymmetric particles (3B L 2 s odd).

In models with R- parity conservation, the lightest supersymmetric particle (LSP ) is stable. Since such a particle has not been observed, it can only be a weakly interacting, electrically neutral particles, which is why it is also considered as a possible candidate for dark matter.

Eigenstates

Interaction eigenstates

The field content of the MSSM (the set of existing species of particles in interaction picture ) arises from the field content of the SM by the following steps:

• The set of fields is extended by a Higgsdublett, which has revealed the existence of four additional Higgs boson result (see below mass eigenstates ). These additional fields are considered standard model -like, because they are not caused by supersymmetry transformations.
• The gauge group ( the group of gauge interactions / local symmetries ) remains unchanged.
• The global transformation of the space -time components is extended by a set of supersymmetry transformations. This increases the number of existing model in the fields, because each SM -like field a super affiliate is assigned, the first differs only by the spin from the original field.

For the names of the many new fields following convention: the corresponding conventional bosons fermions ending in - ino ( Wino, Bino, gluino and Higgsino ), which received the corresponding fermions bosons at the beginning of an S- ( selectron to electron, according to squarks quarks ).

Based on the MSSM the coupling constants of the three fundamental forces can extrapolate for high energies. This unification is calculated at an energy of about 1016 GeV.

Mass eigenstates

The mass eigenstates ( observable momentum eigenstates ) can - as in the SM - be respectively mixed from various interaction eigenstates. The mixed particles have to wear after the breaking of the electroweak symmetry identical spin and identical electric and color charge.

The concrete mixture ratios depend on the choice of the free parameters, in particular, the mixing ratio for standard model -like and supersymmetric particle be different. Therefore, it is no longer possible to maintain the above-described simple nomenclature. The resulting mass eigenstates are numbered partially by ascending mass.

• In the breaking of the electroweak symmetry are only three degrees of freedom of the Higgs fields absorbed by the gauge bosons as in the SM. This has the consequence that in the MSSM over the SM not only a single ( scalar ) Higgs particle remains as a mass eigenstate, but a total of five different: a relatively light scalar Higgs particle, which is similar to the Higgs boson of the SM,
• A heavy scalar Higgs particle,
• A heavy pseudoscalar Higgs particle and
• A pair of charged Higgs and.

• The electrically neutral Wino ( partner ), the Bino ( partner ) and the two electrically neutral Higgsinos mix with the neutralinos.

• The electrically charged Winos (partner of the charged W fields W ±) and the charged Higgsinos mix to charginos.

• When the quarks it comes also to blend their superpartners, the squarks, each quark has two: a partner for the right-handed spinor component and a left-handed for. Because of the small mass of the quarks of the first two generations (up / down, charm / strange ) mix their super affiliates fields to mass eigenstates without a name.
• The superpartners of the heavy quark top and bottom may be due to their large mass distinguished from these. Here, however, there is a significant ' left-right mix ' of the right - and left-handed stops and Sbottoms. For the stop so you have:

• The superpartners of the leptons are called sleptons. Just as with the quarks there are two scalar superpartners for each lepton. For the left-right mix makes for super partner of the heaviest lepton tau, the traffic jam. The above relationship applies here mutatis mutandis.

Targeted experimental evidence

An important class of experiments in the search for supersymmetry make experiments on future particle accelerators is, especially at the Large Hadron Collider ( LHC) at the European Nuclear Research Centre ( CERN). The most frequently studied supersymmetric model is the MSSM.

To obtain before the experiments information on what one hopes to see the experiments with Monte Carlo event generators are pre- simulated ( eg PYTHIA ). However, since it is virtually impossible to examine the entire 105- dimensional space of the parameters of the additional MSSM, enhanced models are commonly used with less free parameters, see benchmark scenario. In order to compare the simulations, we have agreed to certain parameter points ( Snowmass Points and Slopes, PLC), each characteristic for certain parameter regions of the enlarged models and so are supposed to represent the entire possible parameter space well.

Studies show that one can prove supersymmetric particles should be good, if they exist in the mass range up to about 1 TeV / c ² (2006 ).

It is ( in most models ) assume that the lightest supersymmetric particle (LSP ) is stable and the detector leaves undetected. This would signal to the typical missing energy perpendicular lead to incoming particle ( the energy component parallel to the particle beam for technical reasons, are often not determined ). A typical process is shown in the above Feynman diagram.

Extension: NMSSM

Non- Minimal Super Symmetric Standard Model, English: Next- to- Minimal Supersymmetric Standard Model or non -minimal supersymmetric SM

To some difficulties of the MSSM ( μ - problem, see Engl WP:. Mu problem) to eliminate, leading to an additional chiral superfield singlet N Ñ with Super Affiliates. This is necessary especially in GUT models. The physical Higgs bosons, so come add a scalar (s0 ) and a pseudoscalar (a0) singlet.