# Weak interactions that change lepton flavor

1. Jun 27, 2011

### Sebastian

Are there any $W^\pm$ or $Z^0$ interactions that change lepton flavor? For example, turn an electron into a muon or vice versa?

Thanks!

2. Jun 27, 2011

### tom.stoer

3. Jun 29, 2011

### Sebastian

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. Jun 29, 2011

### tom.stoer

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. Jun 29, 2011

### Sebastian

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. Jun 29, 2011

Staff Emeritus
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. Jun 30, 2011

### Parlyne

There are charged current contributions to processes like $e\nu_e \rightarrow e\nu_e$ or $ud \rightarrow ud$ 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 $pn \rightarrow pn$.)

8. Jun 30, 2011