Question about particle interactions and the forces between them

[simplemind]

I have read that if the exchangeparticle of an interaction has even spin then the force between them is
attractive if the charge is equal (gravitation) and repulsive if the charge is not equal.
Is this wright?

 

[PeterDonis]

I have read

Where? Please give a specific reference.

 

[simplemind]

It is german:

http://erlangen.physicsmasterclasses.org/sm_ww/sm_ww_02.html

It says even spin (for example graviton spin= 2) exchangeparticles only acts attractive other says
even spin exchangeparticles acts attractive if charge is equal and repulsive if charge is not equal.

So i am unsafe because there a lot of different inromations in the web.

 

[PeterDonis]

i am unsafe because there a lot of different inromations in the web

You've only given one reference. What other ones have you seen that contradict it?

 

[simplemind]

The opposite is discussed here.

https://scienceblogs.de/hier-wohnen...fur-alle-anziehung-abstossung-und-der-spin/6/

also in german language.

Hence i am not sure if exchangeparticles with even spin always acts attractive or only if the charge is the same?

 

[PeterDonis]

i am not sure if exchangeparticles with even spin always acts attractive or only if the charge is the same?

The first reference gives no details or arguments at all, so it's not very helpful.

The second reference does give some details and arguments (on previous pages to the one you linked to), but only for the spin-0 and spin-1 cases. Basically, those arguments boil down to this (for the simplest case where the two interacting objects start out at rest): the interaction energy is the product of the two charges (which appear as two $J$ factors in the formula) and a "propagator" $D$, whose sign depends on the spin; for spin-0 it is negative, for spin-1 it is positive. The overall sign of the interaction energy determines whether the interaction is attractive or repulsive: negative interaction energy means attractive, positive interaction energy means repulsive. So if we consider like charges (meaning, the sign of the product of two of them is positive), then the spin-0 interaction is attractive and the spin-1 interaction is repulsive.

Can you see what the above implies for the case of unlike charges for spin-0 and spin-1?

 

[vanhees71]

The only paper I know about this is

https://journals.aps.org/prd/abstract/10.1103/PhysRevD.33.2475

 

[simplemind]

The first reference gives no details or arguments at all, so it's not very helpful.

The second reference does give some details and arguments (on previous pages to the one you linked to), but only for the spin-0 and spin-1 cases. Basically, those arguments boil down to this (for the simplest case where the two interacting objects start out at rest): the interaction energy is the product of the two charges (which appear as two $J$ factors in the formula) and a "propagator" $D$, whose sign depends on the spin; for spin-0 it is negative, for spin-1 it is positive. The overall sign of the interaction energy determines whether the interaction is attractive or repulsive: negative interaction energy means attractive, positive interaction energy means repulsive. So if we consider like charges (meaning, the sign of the product of two of them is positive), then the spin-0 interaction is attractive and the spin-1 interaction is repulsive.

Can you see what the above implies for the case of unlike charges for spin-0 and spin-1?

It is for unlike charges vice versa which means spin 0 repulsive and spin 1 attractiv.
Then the last open question:Is this true for all even and odd spins?
Is the propagator negative for all even spins and positiv for all odd spins?

 

[PeterDonis]

It is for unlike charges vice versa which means spin 0 repulsive and spin 1 attractiv.

Yes.

Is this true for all even and odd spins?
Is the propagator negative for all even spins and positiv for all odd spins?

The only other spin for which I have seen a calculation of the propagator is spin-2, for which the propagator is negative (as in the case of gravity), so its behavior is the same as spin-0.

IIRC there are other issues with quantum field theory at spins higher than spin-2, so the question might not be meaningful for those spins.

 

[vanhees71]

QFT has already problems with spin-2 (gravity). In the paper I quoted above it's shown that in classical field theory fields with even spin are lead always to attraction between the "charges" (sources) of these fields and those with odd spin can be attractive and repulsive for charges of opposite and the same sign respectively (as in electromagnetism, where the electromagnetic field is a spin-1 field).

 

[PeterDonis]

In the paper I quoted above it's shown that in classical field theory fields with even spin are lead always to attraction

The abstract of that paper (I can't read the full paper since it's behind a paywall) seems to indicate that only the case of like sources, i.e., charges with the same sign, is examined. The relative sign of the charges, just by inspection, must affect the sign of the interaction energy for all spins.

In even-spin cases, such as spin-2 gravity, it is often assumed that there is no such thing as "unlike charges"--that all "charges" (masses in the case of gravity) are positive, so only the like charge case is relevant. Under that assumption, the statement that "gravity is always attractive" would be correct. But I don't think it is if the possibility of unlike charges is included.

 

[vanhees71]

That's true! Only like-signed charges are considered. So it's shown that for even (odd) spin of the field like-signed charges are attractive (repulsive).

 

[simplemind]

The abstract of that paper (I can't read the full paper since it's behind a paywall) seems to indicate that only the case of like sources, i.e., charges with the same sign, is examined. The relative sign of the charges, just by inspection, must affect the sign of the interaction energy for all spins.

In even-spin cases, such as spin-2 gravity, it is often assumed that there is no such thing as "unlike charges"--that all "charges" (masses in the case of gravity) are positive, so only the like charge case is relevant. Under that assumption, the statement that "gravity is always attractive" would be correct. But I don't think it is if the possibility of unlike charges is included.

It seems that it is not a common known result?

 

[PeterDonis]

It seems that it is not a common known result?

All of the results I have described are well known.

I think you are reading too much into the first reference you gave. I don't think that reference is claiming that interactions mediated by even spin exchange particles are always attractive. I think that reference is just referring to the case of even spin exchange particles and two sources with positive charge (or mass in the case of gravity), which, as I said in post #11, is often the only case considered for even spin exchange particles.

 

[simplemind]

Thanks to all but the basic question is unfortunately not answered.

even spin of exchangeparticle (f.e. graviton) : attracitve when charges of particles are like
repulsive when charges of particles is unlike.

odd spin of exchangeparticle(f.e. photon) : attracitve when charges of particles are unlike
repulsive when charges of particles are like.I think i have to look somewhere else.

 

[PeterDonis]

the basic question is unfortunately not answered

Yes, it is. You give the answer yourself:

even spin of exchangeparticle (f.e. graviton) : attracitve when charges of particles are like
repulsive when charges of particles is unlike.

Yes, that's what has already been said.

odd spin of exchangeparticle(f.e. photon) : attracitve when charges of particles are unlike
repulsive when charges of particles are like.

Yes, that's what has already been said.

I think i have to look somewhere else.

I have no idea why you would think this. The above entirely answers your question.