B Could spin be a combination of magnetic monopoles?

[Wminus]

Hey all,

Is it correct to say that magnetic moment of particles with spin is because of the spin itself, and has nothing to do with any moving charge? The exception here would be the photon of course, but I'm not sure whether "photon spin" is the same kind of angular momentum as the spin of particles with mass or indeed if the photon actually has a magnetic dipole but it's behaving strangely because the photon moves at c.

If so, according to this https://en.wikipedia.org/wiki/Spin–charge_separation it's possible to somehow split an electron into its constituent "spinor" and "chargon". Since the spin particle is responsible for magnetism, wouldn't you have to conclude that it's a magnetic dipole itself made up of some kind of magnetically charged particles, i.e. perhaps the magnetic monopoles? My question is, would it be possible to further split the "spinor" particle and obtain pure magnetic monopoles?

 

[Wminus]

But then again according to this https://en.wikipedia.org/wiki/Magnetic_monopole#Searches_for_magnetic_monopoles the minimum possible mass of a magnetic monopole is 600GeV/c^2.. Which is far larger than the mass of electrons.

 

[stevendaryl]

But then again according to this https://en.wikipedia.org/wiki/Magnetic_monopole#Searches_for_magnetic_monopoles the minimum possible mass of a magnetic monopole is 600GeV/c^2.. Which is far larger than the mass of electrons.

I'm not sure it makes sense to think of an electron as a pair of monopoles, but the mass argument by itself doesn't disprove it. The mass of a composite system can be less than the mass of the components, when there is an attractive force between the components. That's why hydrogen fusion produces energy.

 

[Wminus]

I'm not sure it makes sense to think of an electron as a pair of monopoles, but the mass argument by itself doesn't disprove it. The mass of a composite system can be less than the mass of the components, when there is an attractive force between the components. That's why hydrogen fusion produces energy.

Why doesn't it make sense to think that the magnetic property of an electron is due to magnetic monopoles, while the other properties of the electron (e.g. charge) are due to other particles ("chargons")? Why is the electron considered a fundamental particle anyway?

As for the mass argument: You're correct that it doesn't disprove it, but it certainly does make it seem unlikely. At least for me, but I'm doing Engineering Physics and not particle physics so my intuition might be very off. And I don't think your example really applies, because one single monopole is around a million times heavier than an electron, while the mass that is converted into energy during the H-H fusion processes is less than 1% or so of the original mass. But then again, for all we know the models that are used by particle physicists to predict the monopoles are simply incorrect.

 

[vanhees71]

The electron is consider an elementary particle, because there's not the slightest hint that this might not be the case. To the contrary it's following this assumption with very high precision. E.g., the anomalous magnetic moment of the electron coincides with an accuracy of about 10 significant digits with the prediction by the Standard Model. So there is no hint that it is somehow composed of other particles, nor magnetic monopoles. There's no hint of the existence of magnetic monopoles either. In the current issue of Physics Today is a nice article about this:

http://dx.doi.org/10.1063/PT.3.3328

 

[Wminus]

The electron is consider an elementary particle, because there's not the slightest hint that this might not be the case. To the contrary it's following this assumption with very high precision. E.g., the anomalous magnetic moment of the electron coincides with an accuracy of about 10 significant digits with the prediction by the Standard Model. So there is no hint that it is somehow composed of other particles, nor magnetic monopoles. There's no hint of the existence of magnetic monopoles either. In the current issue of Physics Today is a nice article about this:

http://dx.doi.org/10.1063/PT.3.3328

How is that consistent with this https://en.wikipedia.org/wiki/Spin–charge_separation ? Here they say the electron is a bound state of "chargon", "orbiton" and "spinon" particles, but that they can deconfine under the right conditions. How is this consistent with the electron being an elementary particle?

As for the SM: From what I understand the magnetic moment of electrons, neutrons, protons etc. are explained by assuming these particles are literally spinning around some axis and hence generating a magnetic field due to motion of charge?

 

[jtbell]

How is that consistent with this https://en.wikipedia.org/wiki/Spin–charge_separation ? Here they say the electron is a bound state of "chargon", "orbiton" and "spinon" particles, but that they can deconfine under the right conditions. How is this consistent with the electron being an elementary particle?

Chargons, orbitons and spinons are not elementary particles. They are quasiparticles, tools for simplifying the analysis of complex systems like the bazillions of particles that make up a solid or liquid (condensed matter). You don't "see" them in particle-physics experiments at accelerators (e.g. CERN), but instead in condensed matter experiments.

See https://en.wikipedia.org/wiki/Quasiparticle (in particular, read the General Introduction section).

 

[vanhees71]

This Wikipedia article is about electron-like quasiparticles in condensed matter physics. It's not about the elementary electrons in the vacuum. In condensed-matter physics you find a lot of very "exotic" quasiparticles which are not found as elementary particles in the vacuum (yet?). E.g., in certain funny materials, known as "spin ice" you find quasiparticles that have the properties of magnetic monopoles or in graphen there are found Weyl fermions. In 2D structures you find fractional charges and anyons (see also the Nobelprize in physics of this year, part of which went to Haldane mentioned in the Wikipedia article; the other winners are Kosterlitz and Thouless). If you want to find new and exotic "particles" you have to turn to condensed-matter physics. In elementary-particle physics all the recent hopes to find something beyond the Standard Model this summer has turned out to have been just statistical fluctuations, and with more data all the signals are gone :-(.

Also note that spin doesn't mean there's a particle spinning around its axis. Elementary particles have no extension like a lump of matter. You must be content with the abstract description of them provided by relativistic quantum field theory. An (elementary) electron is described together with its antiparticle (positron) as a quantized Dirac-spinor field of a mass of about 511 keV and one negative elementary charge -e. As a Dirac-spinor field it has spin 1/2. This spin is a kind of "intrinsic angular momentum", but it must not be somehow thought of as a spinning little ball of finite extension. The best classical analogue is provided by the magnetic moment the electron carries and which is associated with the spin. So the electron is not only electrically charged and thus comes together with a Coulomb field (modulo quantum corrections to it) but also as an elementary magnetic dipole of about one Bohr magneton (gyro-factor 2 modulo quantum corrections, where the "anomalous magnetic moment", i.e., the deviation of the gyrofactor from 2 is predicted by QED with an accuracy of at least 10 significant digits compared to the measured value!).

 

[Nugatory]

This might be a good time to mention that the word "particle", when used in quantum mechanics and even more so in quantum field theories, means something very different than the normal English-language meaning of the word.

 

[Wminus]

Thanks for clearing this up for me friends! I see you have no chance at really understanding this without taking courses in QED, QFT, Many Body QM, Particle Physics etc.

Also note that spin doesn't mean there's a particle spinning around its axis. Elementary particles have no extension like a lump of matter. You must be content with the abstract description of them provided by relativistic quantum field theory. An (elementary) electron is described together with its antiparticle (positron) as a quantized Dirac-spinor field of a mass of about 511 keV and one negative elementary charge -e. As a Dirac-spinor field it has spin 1/2. This spin is a kind of "intrinsic angular momentum", but it must not be somehow thought of as a spinning little ball of finite extension. The best classical analogue is provided by the magnetic moment the electron carries and which is associated with the spin. So the electron is not only electrically charged and thus comes together with a Coulomb field (modulo quantum corrections to it) but also as an elementary magnetic dipole of about one Bohr magneton (gyro-factor 2 modulo quantum corrections, where the "anomalous magnetic moment", i.e., the deviation of the gyrofactor from 2 is predicted by QED with an accuracy of at least 10 significant digits compared to the measured value!).

How can you model a physical particle as some kind of field - is this reality or just some mathematical abstraction that happens to give the right results?

 

[jtbell]

is this reality or just some mathematical abstraction that happens to give the right results?

How would we tell the difference?

 

[Wminus]

How would we tell the difference?

good point