Weak interactions that change lepton flavor

In summary, there are interactions in which lepton flavor can change, such as muon decay via a flavor-changing charged current. However, there are no flavor-changing neutral currents at tree level in the standard model. These interactions are highly suppressed, meaning they only represent small corrections to other processes. It is not possible for a changed weak current to conserve flavor, as a charged boson must couple to two fields of different charges. However, there can be charged current contributions to processes where overall flavor is conserved, even though flavor is not conserved at each vertex.
  • #1
Sebastian
17
1
Are there any [itex]W^\pm[/itex] or [itex]Z^0[/itex] interactions that change lepton flavor? For example, turn an electron into a muon or vice versa?

Thanks!
 
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  • #3
Thanks!

I wonder, what is the meaning of "highly suppressed" when describing flavor-changing neutral currents? Do such interactions exist and are just rare, or are they completely forbidden?

Also, is it possible for a changed weak current to conserve flavor?
 
  • #4
Do you know perturbation theory, Feynman diagrams and the meaning of vertices? For each vertex in a diagram you get a power of a small quantity, so a diagram with a large number of vertices comes always with a high power of a small quantity <1 and therefore represents a small quantity.

Highly suppressed means that you can draw diagrams for allowed processes of flavor changing neutral currents, but that these diagrams contain a typically more vertices and therefore represent only a small correction to other processes.
 
  • #5
I'm taking an introduction course in elementary particle physics (3rd year level). We did study Feynman diagrams, at least qualitatively. And I understood your explanation, thanks :)

Could you please answer my second question (is it possible for a changed weak current to conserve flavor)?
 
  • #6
It is not possible for a charged current to conserve flavor, because it must couple to two different fields to couple with two fields of different charges. A photon can couple to u-ubar or d-dbar, but a charged boson needs to couple to u-dbar or d-ubar.
 
  • #7
Vanadium 50 said:
It is not possible for a charged current to conserve flavor, because it must couple to two different fields to couple with two fields of different charges. A photon can couple to u-ubar or d-dbar, but a charged boson needs to couple to u-dbar or d-ubar.

There are charged current contributions to processes like [itex]e\nu_e \rightarrow e\nu_e[/itex] or [itex]ud \rightarrow ud[/itex] scattering where overall flavor is conserved, even though flavor is not conserved at each vertex. (If you object to the second case as relying on free quarks, it can be though of as a proxy for [itex]pn \rightarrow pn[/itex].)
 
  • #8
Yes, but that's not very helpful. Yes, technically you can have two interactions, each with flavor violation that cancels the other. But is that something likely to clarify the OP's understanding or add to the confusion?
 

FAQ: Weak interactions that change lepton flavor

1. What are weak interactions that change lepton flavor?

Weak interactions are one of the four fundamental forces in nature, responsible for changing the flavor of leptons (such as electrons, muons, and taus) by converting them into one another. This phenomenon is known as lepton flavor changing.

2. How do weak interactions change lepton flavor?

Weak interactions involve the exchange of particles called W and Z bosons, which can convert one type of lepton into another. For example, an electron can be converted into a muon by emitting a W boson, or a tau particle can become a muon by absorbing a W boson.

3. Why are weak interactions important in particle physics?

Weak interactions play a crucial role in understanding the behavior of subatomic particles and the structure of matter. They are also essential for explaining the abundance of certain particles in the universe, such as the ratio of protons to neutrons in atoms.

4. Can weak interactions violate conservation laws?

Yes, weak interactions can violate certain conservation laws, such as lepton flavor and lepton number conservation. This allows for processes like neutrino oscillations, where a neutrino can change into a different flavor state, violating the conservation of lepton flavor.

5. Are there any practical applications of weak interactions that change lepton flavor?

While not directly applicable to everyday life, studying weak interactions that change lepton flavor can lead to a better understanding of the fundamental laws of nature and contribute to the development of new technologies, such as particle accelerators and medical imaging techniques.

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