Detection of magnetic monopoles

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Discussion Overview

The discussion centers on the theoretical and experimental aspects of magnetic monopoles, including their interactions with neutrons, detection methods, and the limits of their existence. Participants explore concepts from quantum chromodynamics (QCD) and propose various experimental setups to detect monopoles.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants question how neutrons would interact with magnetic monopoles, with one suggesting that the interaction would be analogous to that of an electric dipole with a point charge.
  • There is a proposal that magnetic monopoles are used in QCD to explain the fluxtube between quarks, though this is noted as a theoretical construct without experimental backing.
  • One participant seeks clarification on the difference between "gluon-magnetic" monopoles and genuine electromagnetic monopoles, indicating a lack of consensus on definitions.
  • Another participant discusses the possibility of detecting magnetic monopoles using a cylindrical superconductor, describing how an induced current could signal the passage of a monopole.
  • Concerns are raised about the experimental limits on the existence of monopoles, including inquiries about searches for monopoles in composite bodies like planets.
  • Some participants express uncertainty regarding the calculations and interpretations related to neutron interactions and scattering involving magnetic monopoles.

Areas of Agreement / Disagreement

Participants express differing views on the nature of magnetic monopoles and their interactions, with no clear consensus reached on definitions or experimental results. The discussion remains unresolved regarding the specifics of neutron interactions and the detection methods proposed.

Contextual Notes

Participants mention various theoretical frameworks and experimental limits, but there are unresolved assumptions about the definitions of monopoles and the conditions under which interactions are considered.

tavi_boada
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How would neutrons interact with magnetic monopoles?
 
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tavi_boada said:
How would neutrons interact with magnetic monopoles?

They would not...

To my knowledge, magnetic monopoles are used in QCD where they are responsible for constructing the fluxtube among two quarks. However this is a theoretical picture and it is NOT backed up by experiments. The presence of the monopoles, that is

marlon
 
What is the experimental/observational limit on the existence of monopoles (inc composite bodies, such as a planet)?
 
I don't understand your answer nerid. I took an exam yesterday. This question came up. I've searched the web and have found nothing. My fellow students all gave different answers. My calculations yielded that the scattering would be inversely proportional too the square of the sine of half the polar angle. The question also said we could consider the neutrons to be polarized in the direction of the incident beam. Any ideas?
 
Here's a CDF+D0 combined report for the Tevatron:

http://arxiv.org/pdf/hep-ex/0306045

For different magnetic charges, it puts limits of at least 265GeV on masses, and at most 0.6 pb. I know that CDF is in the process of preparing an update on their cross section limit, but I don't know how much better than this it will be (if at all).
 
tavi_boada said:
I don't understand your answer nerid. I took an exam yesterday. This question came up. I've searched the web and have found nothing. My fellow students all gave different answers. My calculations yielded that the scattering would be inversely proportional too the square of the sine of half the polar angle. The question also said we could consider the neutrons to be polarized in the direction of the incident beam. Any ideas?
Sorry for the confusion ... what I meant by 'composite bodies' was 'other than a (sad and lonely) particle'. To use an analogy; back when there was interest in isolated quarks, macroscopic objects (such as tiny Nb spheres, blobs of ink in an ink-jet) were examined to see if any had a fractional charge. So the second part of my question is something like 'has anyone looked for monopoles in macroscopic blobs of matter? if so, what limits did those experiments/search set (e.g. fewer than 1 monopole in 10^25 atoms of Ni, or 10^32 molecules of NaCl)?
 
marlon said:
To my knowledge, magnetic monopoles are used in QCD where they are responsible for constructing the fluxtube among two quarks.

Are these "gluon-magnetic" monopoles - with that I mean the gluon-field equivalence of an electromagnetic monopole, or are you talking about genuine electromagnetic monopoles ?
(in another way, are you talking about the A^n_mu fields of QCD, or about the A_mu field of QED)

cheers,
Patrick.
 
vanesch said:
Are these "gluon-magnetic" monopoles - with that I mean the gluon-field equivalence of an electromagnetic monopole, or are you talking about genuine electromagnetic monopoles ?
(in another way, are you talking about the A^n_mu fields of QCD, or about the A_mu field of QED)

cheers,
Patrick.

Euuh, to be honest i must admit that i don't really know the difference between the two kinfs of monopoles here. Could you please elaborate?

The monopoles which i am referring to are the dual variant of electric charges like quarks. When two quarks interact via the colour-electric field one can perform the EM-duality transformation. This means the we replace the E field by the B field and the other way around. So basically two of these monopoles (two dual quarks if you will) interact via the "colour"-magnetic field which is the dual of the colour-electric field. So i am talking about the FIRST kind of monopole that you mentioned. The monopole that arise as the dual of the geniune electric charged-particle (like the electron, so no colour-charge but electric-charge) is not used...at least not to my knowledge and certainly NOT in QCD or when describing quark-confinement...

This is how i see the difference between the two kinds of monpoles that you brought up? You agree or not ??

regards
marlon
 
marlon said:
So basically two of these monopoles (two dual quarks if you will) interact via the "colour"-magnetic field which is the dual of the colour-electric field. So i am talking about the FIRST kind of monopole that you mentioned. The monopole that arise as the dual of the geniune electric charged-particle (like the electron, so no colour-charge but electric-charge) is not used...at least not to my knowledge and certainly NOT in QCD or when describing quark-confinement...

This answers indeed my (naive) question, thanks !

Patrick.
 
  • #10
One way to detect a magnetic monopole is to construct a cilindrical superconductor. Within this superconductor we have magnetic field lines and the B-field is zero at the boundaries of the conductor. Due to the Meissner effect, electrical field lines will be pushed out of the superconductor. Now suppose that we place a circular wire (it can conduct electrical current and it is superconductive in nature so this current will not diminish due to resistivity-effects inside this wire) inside the cilinder (a wire of smaller radius ofcourse so that it is totally inside the superconductor) If a magnetic monople were to pass through the circular surface of the wire, an electrical current will be induced inside the wire. Why ? Well, because the magnetic monopole changes the magnetic flux through the circular surface of the wire. This change must be eliminated because of the Meissner-effect and this "elimination" happens via the induced current inside the wire. So basically the electrical current is induced in order to keep the magnetic flux constant inside the superconductor. This electrical signal can be captured and thus we have an alarm that shows us the passage of a magnetic monopole. It is important to realize that this current will only remain when a MONOPOLE has passed through the surface of the wire. In the case of dipole or multipole there will also be induced supercurrents (you know, the above mentioned the electrical currents in the wire that is superconductive in nature) as the mutlipole passes through the surface but once they have passed the net-change will be ZERO. So there is only a current during the passage of the multipole through the surface but this current will evolve towards zero once the multipole moves away from the wire. Only in the case of a monopole, there will remain an electrical current in the wire


regards
marlon
 
  • #11
That sounds interesting, Is such an experiment performed?
 
  • #12
tavi_boada said:
How would neutrons interact with magnetic monopoles?
The neutron has a magnetic moment.
The interaction of a neutron with a magnetic monopole would be the same as that of an electric dipole with a point charge.
 

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