Supersymmetry
Supersymmetry ( SUSY ) is converted into each other a hypothetical symmetry of particle physics, bosons ( particles with integer spin) and fermions ( particles with half-integer spin). This produces particles that transform under a SUSY transformation into each other, super affiliates are called.
Because of their potential to answer open questions in particle physics and astrophysics, supersymmetric theories in particular in theoretical physics are very popular. Most Grand Unified Theories and superstring theories are supersymmetric. The minimum possible, compatible with previous findings Extension of the Standard Model of particle physics (SM ), the Minimal Supersymmetric Standard Model ( MSSM ) is the experimentally most studied candidate for physics beyond the Standard Model ( BSM physics ).
However, despite promising theoretical arguments to date, no experimental evidence can be provided that supersymmetry actually exists in nature - in particular, no superpartners of known particles were still observed. This means that this symmetry, if it exists, is broken. On the other hand, the refractive mechanism of this symmetry and the energy is from the symmetry applies, unknown.
- 3.1 MSSM: Minimal Super Symmetric Standard Model
- 3.2 Unified Theories
- 3.3 supergravity
- 4.1 See also
- 4.2 Literature
- 4.3 External links
Formulation story: Wess - Zumino model and MSSM
The supersymmetry ( in the four-dimensional space-time ) was introduced in 1971 by Yuri A. golfand and his students Evgeni Likhtman ( in Moscow ) and regardless of 1972 by DV Volkov and VP Akulov ( in Kharkiv / Kharkov, Ukraine), as well as through string theories (initially only on the two-dimensional string world sheet ) by Jean -Loup Gervais, Bunji Sakita, André Neveu, John Schwarz and Pierre Ramond. Previous work by Hironari Miyazawa from the 1960s through a Baryon - meson symmetry were then ignored.
As a model of elementary particle physics, the theory was only in 1974 that more attention by the independent work of Julius Wess and Bruno Zumino. This is known today under the name of Wess - Zumino model model describes two scalar bosons that interact with themselves and with a chiral fermion. Although unrealistic, the Wess - Zumino model is a favorite because of its simplicity example where the most important characteristics show supersymmetric field theories.
The first compatible with the previous experimental observations supersymmetric model, the Minimal Supersymmetric Standard Model ( MSSM ), was proposed in 1981 by Howard Georgi and Savas Dimopoulos. According to their predictions, the masses of hitherto unobserved superpartners are in the range of 100 GeV / c ² to 1 TeV / c ², which is for the 2009 went into operation in the Large Hadron Collider ( LHC) accessible. These masses are consistent with the finding that up to now no superpartners have been observed, and suggest that the LHC super affiliates already known elementary particles can be detected.
General characteristics
Supersymmetry algebra
The supersymmetry transformations that convert fermions and bosons into one another, extend the space-time symmetry, the Poincaré group.
Sidney Coleman and Jeffrey showed Mandula 1967, as it seemed, general conditions, that - except for the generators of the Poincaré group - all generators of physically relevant symmetries under Poincaré transformations must be invariant, ie, that every major symmetry of a physical model of a must be the product group of the Poincaré group with a group that has nothing to do with the space-time ( Coleman - Mandula theorem).
But after Wess and Zumino in 1974 had shown that there can be fermionic generating of symmetries that change as particles with spin 1/2 with twists and which had not been considered by Coleman and Mandula, classified 1975 Rudolf Haag, Jan Lopuszanski and Martin Sohnius the possible bosonic and fermionic generators with Symmetriealgebren ( Haag- Lopuszanski - Sohnius theorem) ..
The simplest supersymmetric extension of the Poincaré group is realized in the Wess - Zumino model and extended it to two Weyl spinors. The relevant commutator and Antikommutatorrelationen are
It denotes the Pauli matrices and the four-momentum.
Loop corrections
The existence of additional elementary provides additional contributions to the loop corrections for observable physical parameters. Do Super Affiliates other than the exact same spin quantum numbers, the loop corrections are identical in magnitude, but differ ( due to the different spins) in sign: the corrections add up to zero.
In broken, especially spontaneously broken, SUSY models, the corrections do not necessarily add up to zero, but often provide relatively small effects.
The ( partial) compensation of the loop corrections by super affiliate has two interesting effects:
- Supersymmetry provides a way to solve the naturalness problem (English Naturalness problem- or fine-tuning problem). This problem is that lead with the energy scale quadratically divergent loop diagrams to interfere large correction contributions to the renormalized mass of the Higgs boson. Each square divergent correction term now could be an equivalent term of the respective Super Partners exist with opposite sign, the problematic corrections would add up to zero.
- In spontaneously or not broken SUSY theories the expectation value of the energy density in the field-free space, in contrast to the standard model at last. Thus, it seems easier gravitation, for their field, the energy density is the source to include in a quantum- theoretical model (see below supergravity ).
Dark Matter
In order not to come into conflict with experimental results, one must assume that decay processes of superpartners in Standardmodellteilchen ( without another super affiliates as the decay product) strongly suppressed or impossible (R - parity conservation ). Thus, the lightest supersymmetric partner particle (LSP ) is practically stable. Since, according to current cosmological models in the early stages of the universe particles of any mass could be generated, is an electrically neutral LSP - such as the lightest neutralino - a candidate for the explanation of dark matter dar.
Selected aspects
MSSM: Minimal Super Symmetric Standard Model
The MSSM is the smallest particle in terms of the opportunity to build a realistic supersymmetric Teilchenphysikmodell. The MSSM extends the standard model with an additional Higgs doublet and order SUSY partner particles for all particles of the model. In this case there is no explicit mechanism is specified, the reason why the new particles have different masses than their standard model partners. Instead, all super symmetry-breaking terms that are renormalizable, gauge invariant and R- parity preserving, explicitly incorporated with initially unknown coupling constants in the model.
Unified Theories
The existence of new particles from a mass of 100 to 1000 GeV affects the running, ie, the energy dependence of the parameters ( " coupling constants " ) that characterize the strength of the three occurring in the standard model interactions, so that they are one at extremely high energies of GeV approach the same value. In the standard model they meet only almost at a point, while supersymmetric theories provide a much more accurate " rallying point ". This is sometimes interpreted as an indication of unified theories in which the three interactions of the Standard Model are just different effects of a single parent interaction, analogous to the electric and the magnetic interaction.
Supergravity
The extended by the SUSY generators spacetime symmetries are first as well as in the standard model global symmetries. If you declare SUSY but as a local symmetry, so this forces two new particles: the graviton with spin 2, which is expected to be the interaction particles of gravity, and the gravitino with Spin 3 / second Therefore, local SUSY theories are also called supergravity ( SUGRA ).
This has over local spacetime symmetry within the Standard Model, which is not renormalizable, two potential benefits that particular supersymmetric in the initial phase approaches fueled hopes that SUSY provides a possible mechanism for a theory of quantum gravity:
- The different spin of graviton and gravitino could cause not compensate renormalizable terms and the theory is renormalizable in total.
- The vacuum energy density of space, according to the theory of relativity a source term for gravity, SUGRA is finite, in the case of unbroken supersymmetry even exactly zero. In contrast, in the standard model the expectation value of the energy density is infinite already in vacuo to Loop corrections.
To date, however, it is - with the potential exception of superstring approaches that go beyond simple supersymmetry - not succeeded in formulating a consistent theory of supergravity. SUGRA, however, could be an effective theory below the Planck scale: it is a possible mechanism for the spontaneous breaking of supersymmetry.
In some models, the detection of gravitinos at accelerator experiments such as the LHC is conceivable.