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Pretty simple question (I think), probably stemming from my lack of formal background in physics.

I've been reading questions like this one related to attraction with respect to spin (a term I'm not familiar with but have a basic understanding of thanks to this reading), and have become curious about something. Are anti-particles still spin-2? I would think that the reversal of their physical state would reverse pretty much all of their other properties as well, like giving them negative mass, yet they still appear to "seek out" normal matter through some form of attraction, or at the very least their net force doesn't repel normal matter. Is that because of gravity (in which case they must be spin-2 and not have negative mass)? Or is there another explanation for this? Or does my physics noob-ish-ness have me completely turned around and barking up the wrong tree entirely?

Edit: The linked question explains that mediators governed by an even-spin field will attract when their charges are similar, and repel when they are dissimilar, while mediators governed by an odd-spin field will do the opposite (as in electromagnetism).

Community
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thanby
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  • I would encourage you to give a summary of the linked question as yours is dependent on it – PhotonBoom Aug 08 '14 at 15:04
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    Also mass is not a property of matter. It is in fact emergent via the Higgs Mechanism, hence it does not become negative for anti-particles. – PhotonBoom Aug 08 '14 at 15:05

2 Answers2

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There are more spins than just 2. There are particles with spin zero (Higgs particle). Spin half (electrons, positrons, neutrions, quarks, muons, etc.), spin 1 (photons, gauge bosons of weak interaction), spin 3/2, spin 2 (hypothetical gravitons).

During attraction / repulsion there are 2 things that come into play:

1) The particles that get attracted / repelled

2) The field that mediates the attraction / repulsion

The question you referenced talks about the spin of the mediating field. If the mediating field is spin 0 or spin 2, it is alway attractive. If it is spin 1, it can be either attractive or repulsive, depending on the charge of the particles.

Now the particles and antiparticles that are attracted / repelled: they are not the mediating field. They are usually fermions, like electrons and positrons, so they have spin 1/2. Their spin does not decide whether the interaction is attractive or repulsive. This attractiveness / repulsiveness depends on the spin of the mediating field.

The whole subject is much more complex and my explanation is only a very simplified view. Just please note that antiparticles do not have negative mass. Their mass is positive. They are "anti-" for different reason then reversal of everything, so the name "anti-" is a bit misleading.

mpv
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  • Ah I was missing the fact that not all matter is mediated by spin 2. But the other question's answer led me to believe that spin 2 is only attractive if the charges are the same, and that the difference between it and spin 1 is that the charge comparison has opposite effects? – thanby Aug 08 '14 at 15:18
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    @thanby see e.g.. I don't know of a good reference or an intuitive explanation for this relationship, but it also applies to the spin-zero pion which is responsible for the attractive part of the nuclear potential. – rob Aug 12 '14 at 23:48
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The mathematical transformation from particle to antiparticle reverses the sign of the charge and the sign of the sign of the intrinsic parity. An antiparticle has the same (positive) mass and same spin as the corresponding particle.

In the theory of supersymmetry, the known particles have "superpartners" with different spin. Supersymmetry is a very attractive theory for a number of reasons. However, after several decades of searches, there is no experimental evidence for any particle's superpartner.

rob
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