# What is the definition of an exchange particle?

After reading through articles, i concluded that a suitable definition is that when 2 particles interact bosons are exchanged between the 2 particles creating a force?

What would a good definition be for exchange particle?

An exchange particle is a virtual particle that mediates the interaction between two other particles. It is virtual because it need not be on the mass shell and hence is not directly observable.

In the standard model of elementary particle physics all particle in the table can be exchange particles:

They are called "exchanged particles" because of the invention of Feynman diagrams to picture elementary particles interacting or decaying, using the quantum field theoretical formalism.

Before that we had the Fermi interaction where

The theory posits four fermions directly interacting with one another (at one vertex of the associated Feynman diagram). This interaction explains beta decay of a neutron by direct coupling of a neutron with an electron, a neutrino (later determined to be an antineutrino) and a proton.

Fermi first introduced this coupling in his description of beta decay in 1933. The Fermi interaction was the precursor to the theory for the weak interaction where the interaction between the proton–neutron and electron–antineutrino is mediated by a virtual W− boson.

The standard model progressed to having vertices with only three lines leaving, and, as an example, this shows a number of possible diagrams where the exchanged particles are not only bosons.

The exchanged "particle" keeps the particle named in the table of elementary particles, because it , the lines between the vertices are position holders for the energy and momentum and quantum number exchanges between incoming and outgoing, and are under the integral which the diagram represents.They are off mass shell, because the four vector mass, varies under the integration. The mass of the exchanged particle is in the denominator, in the propagator of the integration.

The gauge bosons are usually involved in the lowest order diagrams of exchanges , ( it is a parturbation series that is summed with the feynman diagrams), but no, it is not only bosons that are exchanged. The other conserved quantum numbers are important too.

Yes, the exchange carries momentum over a time interval, dp/dt, so it is a force that is being exchanged.

Nice question because the answer would be a little bit different from what you perhaps expect.

Suppose you "throw" an electron on another electron. As for any scientific question we are obliged to look at it from different sides.

1. The electrons during their approach exchange photons, call them virtual or not. This exchange works only in the case the photons get emitted and absorbed without loses to the surrounding. This statement is true as long as nobody observe any hysteresis in the behavior of the approach and the following rejection. IF any emission to the surrounding takes place during the approach THAN during the rejection some photons must occure "just in time" OR any hysteresis has to be observed. This are not the case. The introduction of virtual photons is a good model for a process we could not describe more in detail.
2. During the approach of an electron towards a proton an emission of real photons takes place. The energy difference between the two particles gets realized by photon emission. This phenomenon corresponds with the opposite process of the photoelectric effect where photons excite electrons or with the excision of electrons in an atom.

A definition of an exchange particle

when 2 particles interact bosons are exchanged between the 2 particles creating a force

implies that the exchange has to be asymmetrically. Photons obey a momentum which is equal but of different sign for the emission from and the absorption to a particle.

For the electron-electrons-interaction no force is definable in such an exchange. In the case of the electron-proton-interaction real photons get emitted (or absorbed) and an attracting (or repulsive) force occurs. Here we can talk about exchange photons.

How to explain the different phenomena? In the case of fields with equal sign one can use the experience "Where a body is, there can be no second" and apply it to equal signed fields. For unequal signed electric fields it is different. They partially eliminate each other by the exchange and emission of photons.

Conclusion: For equal signed electric fields virtual photons are a model but not needed to explain the repulsion between them. For unequal signed electric fields the photon is the result of the approach and the condition for the repulsion between electron and proton.

## protected by Qmechanic♦Jun 4 '17 at 16:50

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