Photon-Photon Repulsion-Attraction

[what_are_electrons]

Can a single photon repulse or attract another single photon under some certain conditions?

 

[vanesch]

Can a single photon repulse or attract another single photon under some certain conditions?

Yes, through higher-order interactions in QED: namely by coupling to a virtual e+-e- pair.

cheers,
Patrick.

 

[what_are_electrons]

Yes, through higher-order interactions in QED: namely by coupling to a virtual e+-e- pair.

cheers,
Patrick.

If I think electrostatics, then there is an attractive interaction. Yes?

 

[vanesch]

If I think electrostatics, then there is an attractive interaction. Yes?

There is an attraction between charged particles, but not between photons (if you exclude those subtle higher-order effects).

cheers,
Patrick.

 

[dextercioby]

I wouldn't call light scattering on light an "attraction or repulsion".It's simply scattering.In fact,at quantum level,even though we still deal with ELECTRICALLY charged particles,we don't have that attraction/repulsion pictured so nicely by Coulomb's law.
For the record,the simplest QED process of photons scattering on photons is 4-th order...Not really easy to calculate,even after u renormalize.

Daniel.

 

[what_are_electrons]

I wouldn't call light scattering on light an "attraction or repulsion".It's simply scattering.In fact,at quantum level,even though we still deal with ELECTRICALLY charged particles,we don't have that attraction/repulsion pictured so nicely by Coulomb's law.
For the record,the simplest QED process of photons scattering on photons is 4-th order...Not really easy to calculate,even after u renormalize.

Daniel.

Please describe what is meant by "scattering" in this case.

 

[dextercioby]

All elementary processes in QFT are scatterings.In this case 2 photons interact (scatter one on the other) via a field of positrons and electrons.A more "classical" analogy would be the Coulomb scattering of charged particles (described in most QM books).The scattering,or the interaction,is accomplished via a classical electrostatic field...

Daniel.

 

[Edgardo]

Hey,

can light be scattered by a neutron? :shy:

 

[dextercioby]

Hey,

can light be scattered by a neutron? :shy:

Interesting question.Obviously photons would interact/scatter with the quarks inside,but it's not the case.Now,theory doesn not prevent us from building Feynman diagrams in which in the same vertex to have a photon & neutron propagator (the propagator would probably be similar to the one of a massive neutrino,because spin 1/2,mass+ zero electric charge) ,but i cannot really imagine a standard scattering process in the lowest order (BTW,whose theory...?? ) similar to Compton effect,namely one incoming photon & one incoming neutron interacting through an (inimaginable to me) virtual field and in the final state the same photon and the same neutron...

Maybe someone else would give a more elaborate and convincing answer...

Daniel.

 

[Janitor]

...(the propagator would probably be similar to the one of a massive neutrino,because spin 1/2,mass+ zero electric charge)...

One difference between the massive neutrino and the neutron is the nonvanishing magnetic dipole moment of the neutron, deriving from the fact that the neutron is composed of charged quarks. Still, to lowest order, there may be no photon-neutron interaction.

 

[vanesch]

One difference between the massive neutrino and the neutron is the nonvanishing magnetic dipole moment of the neutron, deriving from the fact that the neutron is composed of charged quarks. Still, to lowest order, there may be no photon-neutron interaction.

Well, there is an interaction between neutrons and a classical B-field, so I would think that to first order, there IS an interaction !
Also, deep inelastic scattering of say, electrons on neutrons is (unless at very high Q values where the Z0 contribution becomes important) dominated by the photon exchange.

cheers,
patrick.

 

[what_are_electrons]

To clarify my interest, please let me know if "photon-photon scattering" for a photon (with spin = 1) is a physical phenomenon that has a billiard ball appearance, or if, scattering is a transient interaction between the two photons, or if, scattering is a quantum field interaction between two photons? Thanks in advance!

 

[dextercioby]

To clarify my interest, please let me know if "photon-photon scattering" for a photon (with spin = 1) is a physical phenomenon that has a billiard ball appearance, or if, scattering is a transient interaction between the two photons, or if, scattering is a quantum field interaction between two photons? Thanks in advance!

No,at classical level billiard balls get into contact (moreover they are deformed),while for particles (elementary or not),the scattering is realized through quantum fields.There's no "touching"...For the last question,the answer is:yes,the photon-photon scattering is a quantum field (of lepton-antilepton pairs) interaction...

Daniel.