B Understanding the Conversion of Energy Forms in Particle Interactions

[TheCanadian]

Different forces (e.g. electromagnetism, colour) are mediated via different force-carrying particles (e.g. photon, gluon). When converting from one form of energy to another, what force-carrying particles are involved in converting acceleration (or more generally a change in kinetic energy) of charged particles into electromagnetic radiation as observed in bremsstrahlung emission?

 

[PeterDonis]

When converting from one form of energy to another, what force-carrying particles are involved in converting acceleration (or more generally a change in kinetic energy) of charged particles into electromagnetic radiation as observed in bremsstrahlung emission?

None. Charged particles interact directly with photons (EM radiation).

 

[TheCanadian]

None. Charged particles interact directly with photons (EM radiation).

Ahh yes, here's a different example although perhaps more in line with my original question:

When discussing matter-antimatter pairs, the energy released by the annihilation event is proportional to the mass. But what permits this between antimatter-matter pairs? Why is this not ordinarily observed for any two massive particles (e.g. an electron and another electron)? Is there a force carrier associated with annihilation events and a field where this energy is stored before the annihilation/releasing a photon (or other possible products depending on the total mass/energy)?

 

[Nugatory]

Why is this not ordinarily observed for any two massive particles (e.g. an electron and another electron)?

That interaction would violate several conservation laws, including charge and lepton number.

A particle/antiparticle interaction is pretty much the only annihilation that is guaranteed not to violate any conservation laws.

 

[TheCanadian]

That interaction would violate several conservation laws, including charge and lepton number.

A particle/antiparticle interaction is pretty much the only annihilation that is guaranteed not to violate any conservation laws.

Fair enough, and that's very cool. I suppose the concept is still a bit unformed in my head. Maybe more examples will help:

If one could hypothetically construct a particle that has all of the same properties as a positron (e.g. charge, lepton number) except for mass, would it still be able to annihilate with an electron? Is gravity/gravitons predicted to influence annihilation in current theoretical frameworks?

 

[PeterDonis]

If one could hypothetically construct a particle that has all of the same properties as a positron (e.g. charge, lepton number) except for mass, would it still be able to annihilate with an electron?

This is not a hypothetical; it's actually realizable, and the answer is no. There are three "families" of leptons in the Standard Model: the electron family, the muon family, and the tau family. (Each family contains a charged lepton and its antiparticle, and an uncharged lepton and its antiparticle; in the electron family these are the electron/positron and the electron neutrino/antineutrino.) Each lepton can only annihilate with its own antiparticle, the one in the same family and with opposite charge. The neutrinos (electron, muon, and tau, each with its own antiparticle) are particularly interesting in this regard, since they have no conserved charges other than lepton number.

The underlying reason for all this is that, in quantum field theory, particles and antiparticles are not just two separate things that happen to be opposites in all conserved charges. They are states of the same underlying quantum field. (The technical term is that they are CPT conjugates of each other.) The process we have been describing as "annihilation", from the viewpoint of QFT, is just a difference in the state of the quantum field between one region of spacetime and another.

 

[TheCanadian]

This is not a hypothetical; it's actually realizable, and the answer is no. There are three "families" of leptons in the Standard Model: the electron family, the muon family, and the tau family. (Each family contains a charged lepton and its antiparticle, and an uncharged lepton and its antiparticle; in the electron family these are the electron/positron and the electron neutrino/antineutrino.) Each lepton can only annihilate with its own antiparticle, the one in the same family and with opposite charge. The neutrinos (electron, muon, and tau, each with its own antiparticle) are particularly interesting in this regard, since they have no conserved charges other than lepton number.

The underlying reason for all this is that, in quantum field theory, particles and antiparticles are not just two separate things that happen to be opposites in all conserved charges. They are states of the same underlying quantum field. (The technical term is that they are CPT conjugates of each other.) The process we have been describing as "annihilation", from the viewpoint of QFT, is just a difference in the state of the quantum field between one region of spacetime and another.

Well that's fascinating. It seems like fairly standard QFT, but do you have any particular resources/texts you would suggest for this topic (and perhaps QFT more generally)?

 

[bhobba]

Well that's fascinating. It seems like fairly standard QFT, but do you have any particular resources/texts you would suggest for this topic (and perhaps QFT more generally)?

First what's your level of standard QM?

Thanks
Bill

 

[TheCanadian]

First what's your level of stnadard QM?

Thanks
Bill

I've taken standard QMI and QMII and a graduate QM course for selected topics (e.g. entanglement, identical particles, classical to quantized EM fields, perturbation techniques), but haven't yet studied group theory, Feynman diagrams, or delved into QCD.

 

[bhobba]

That's good enough - here are the two books I would recommend to start with:
https://www.amazon.com/dp/0984513957/?tag=pfamazon01-20
https://www.amazon.com/dp/019969933X/?tag=pfamazon01-20

Then - Schwartz:
https://www.amazon.com/dp/1107034736/?tag=pfamazon01-20

Then THE book on QFT that IMHO is simply the best - Weinberg:
https://www.amazon.com/dp/0521670535/?tag=pfamazon01-20

QFT is one of those areas you should build up to and not tackle the best ie Weinberg - straight away. Take your time - its not a race.

Thanks
Bill