# Boson

Bosons (after the Indian physicist Bose Satyendranath ), all particles which satisfy the Bose -Einstein statistics in the standard model of particle physics. After the spin - statistics theorem, they have an integer spin, so, etc. Figuratively speaking, those particles are bosons, which mediate the forces between the fermions, the matter particles.

The bosons are:

- Among the elementary particles: the gauge bosons as mediators of fundamental forces
- Among the composite particles: The composite composed of one cheese curd and an anti- mesons, all nuclei with an even number of nucleons (e.g., the core of the heavy hydrogen is deuterium), as well as quasi-particles such as phonons.

Bosons distance themselves from the fermions, which satisfy the Fermi -Dirac statistics and after the spin- statistics theorem have a half-integer spin. An elementary particle in three spatial dimensions is always either a boson or a fermion.

In very thin layers, ie two-dimensional systems, there are, bosons and fermions, the so-called anyons that meet its own quantum statistics.

## Classification according to the spin

Bosons are labeled differently, depending on the spin. Based on this designation is their transformation properties under Lorentz transformations actually orthochronous.

Tensors of higher levels ( ie bosons with spin > 2) are physically less relevant because they occur only as composite particles.

## Macroscopic quantum states

A special feature of bosons is that in exchange of two identical bosons, the quantum mechanical wave function does not change ( phase factor 1). In contrast, changes in an interchange of two identical fermions the sign of the wave function. The rationale for the invariance of the wave function at boson exchange takes place via the relatively complicated spin- statistics theorem.

One consequence is that similar bosons can in the same location (within the uncertainty relation ) at the same time. Several bosons then occupy the same quantum state, they form macroscopic quantum states. Examples are:

- Superconductivity ( Cooper pairs ),
- The laser (photons),
- The superfluidity of helium.

## Composite particles

Fermionic or bosonic behavior of composite particles can only come from a greater distance (compared to the system under consideration ) can be observed. On closer inspection (of the order in which the structure of the components is relevant) shows that a composite particle behaves according to the properties (spins ) of ingredients. For example, two helium-4 atom ( bosons ) does not occupy the same space, if the space looked similar to the internal structure of the helium atom, ( 10-10 ~ m) is, as the components of the helium-4 atom are fermions itself. This has a finite density of liquid helium, as well as an ordinary liquid.

## Supersymmetric bosons

In extended about supersymmetry model of elementary particles, there are other elementary bosons. On each fermion is calculated as a boson supersymmetric partner, called Sfermion, so that the spin is different in each case by ± 1/2. The superpartners of the fermions are commonly - named S by an additional prefix, it means, for example, the corresponding boson to the electron then Selektron.

Strictly speaking, a bosonic field is initially assigned as super affiliates in the interaction picture each fermionic field. In the mass, the observable image or predicted particles give each as linear combinations of these fields. The number and the relative proportion of contributing to the mixtures components on the side of the bosonic super partner does not comply with the conditions on the original fermionic page. In the simplest case (without or with only little mixing), however, a Fermion ( such as electron) or a specific boson Sfermion ( as Selektron ) are assigned.

In addition, the minimal supersymmetric standard model ( MSSM ) is already required in contrast to the standard model (SM ) Higgs boson several fields including their super affiliates.

So far, none of the postulated supersymmetric partner particles has been demonstrated experimentally. You must therefore have such a high degree that they do not occur under normal conditions. It is hoped that the new generation of particle accelerators can prove at least some of these bosons. There are indications that the lightest supersymmetric particle (LSP ) in the range of several hundred GeV / c ².