Possibilty of flavor oscillation of an electron

[PeroK]

@Helena Wells

Here's something on what the Time-Energy uncertainty principle really says:

https://physicspages.com/pdf/Griffiths%20QM/Uncertainty%20principle%20-%20energy_time.pdf

 

[Helena Wells]

Since this comes from the official youtube channel of Fermilab which has the 2nd biggest particle accelerator in the world and dr.Don Lincoln is an experimental physicists there I don't think they would post something wrong.

 

[PeroK]

Since this comes from the official youtube channel of Fermilab which has the 2nd biggest particle accelerator in the world and dr.Don Lincoln is an experimental physicists there I don't think they would post something wrong.

It's not so much wrong, as a simplified version designed to try to explain a more complicated subject to a audience of non-physicists. In any case, such videos are not considered valid sources on PF for precisely this reason. They do not represent a valid academic presentation of the subject.

 

[George Jones]

Since this comes from the official youtube channel of Fermilab which has the 2nd biggest particle accelerator in the world and dr.Don Lincoln is an experimental physicists there I don't think they would post something wrong.

Read carefully the except below from the text "Intoduction to Elementary Particles" by David Griffiths, who is also the author of the quantum mechanics text referenced by @PeroK in post #36.

 

[PeroK]

And, to be fair to Dr Don Lincoln, when he invokes the borrowing of energy in the above video, he does accompany what he says with a slightly apologetic shrug! As if to say, "well, that's good enough for YouTube".

 

[Helena Wells]

Ok how do you explain that photons can be massive in QED for short timespans and while the time is passing they are more likely to become massless.

 

[weirdoguy]

And where are you getting this from?

 

[Helena Wells]

And where are you getting this from?

From the same video. 3:10-3:50 watch

 

[weirdoguy]

Well, as been said, this video is not a valid source on PF since it is a pop-sci video. I've never seen anything like that in any textbook on QED or QFT, so it would be nice if you could provide some other source of this claim (textbook or peer reviewed paper).

 

[Helena Wells]

Well, as been said, this video is not a valid source on PF since it is a pop-sci video. I've never seen anything like that in any textbook on QED or QFT, so it would be nice if you could provide some other source of this claim (textbook or peer reviewed paper).

Well ok you can google it right now 'Mass of photons in QED'.

 

[weirdoguy]

That's too broad and will bring up tons of pages not related to what you speciffically wrote. And what you wrote is not something that one would find in most textbooks, that is why I ask you if you have other sources of this claim. This video is not an acceptable source, and you've already been said why. If you want to learn something you should study textbooks, not fun videos on YouTube, even if they were recorded by someone from FemiLab. Even figures like Hawking wrote some very questionable things in their pop-sci books. That's why PF has this policy regarding sources. Argument from authority does not count.

 

[mfb]

@Helena Wells: Stop this. You are using popular science descriptions on youtube and suggestions for google searches as "source" to argue with physicists - including particle physicists relying on the exact conservation of energy in their daily job. This isn't going to work.

 

[vanhees71]

Since this comes from the official youtube channel of Fermilab which has the 2nd biggest particle accelerator in the world and dr.Don Lincoln is an experimental physicists there I don't think they would post something wrong.

"One should present physics as simple as possible, but not simpler." (free quote by Einstein). Sometimes there are legends built by popular-science writers that violate this rule, anc unfortunately the wrong legends are used again and again in the lack of a better idea. Taking "virtual particles" as real or reading Feynman diagrams as something different than an utmost efficient notation of formulas to calculate S-matrix elements is among them. I don't blame the scientists in there attempt to explain physics to the general public though. I've also no idea how to explain things without the only language we know, which is math. But still one should explain the science to the general public.

 

[Tendex]

Energy / momentum is not conserverd in QFT for small time intervals.

As previously pointed out by others QFT doesn't admit such "small time" breakings of energy-momentum conservation. I particularly find the pop-science to handle this quite silly and complicating the actual situation. While it is true that the actual reason the exact conservation is kept requires certain amount of mathematical sophistication I think it can be explained before entering more complicated perturbative situations in the free complex scalar field case given that anything concerning this conservation is sorted out in QFT even before interaction and the perturbative methods enter(and this indeed makes the math much more complicated).

So for the propagation of these quantized free fields that are going to serve later to build the classical limit(what particle physicists sometimes refer to as the tree level) in the full theory, there is what the author of a well knows QFT textbook calls a "beautiful Lorentz-invariant object", the Feynman propagator and this object involves a certain integral and this integral(written in one of the ways it can be represented) converges only in the limit in which a certain parameter #\epsilon#, that we can think of for this didactic purpose as the "small time intervals" you found in popular divulgative media, goes to zero.

So this keeps exact energy-momentum conservation already even if by itself it appears to be a "non-local" expression because it involves certain quantum tunneling properties, but in this limit this is exactly canceled out by oppositely charged fields in the relevant quantum commutation relations so the final result is fine. Of course all this gets more complicated with interaction and radiative corrections but the basic block are still the free fields and the radiative corrections at higher order are built from the tree level so this picture of exact conservation should hold.

 

[hilbert2]

There's this Arxiv document about the possibility of charged leptons converting to one another:

https://arxiv.org/pdf/0706.1216.pdf

There it's said that that the electron, muon and tau are the exact charged lepton mass eigenstates. But how do you justify this claim? Is there a possibility of even a little bit of mixing of those species in the mass eigenstates, or does something crazy result from the electroweak theory if you assume that?

 

[Vanadium 50]

And on page one of that paper it says: "Do e±, μ± and ± oscillate into each other? The answer to this question is the immediate ‘no’, the reason being that these charged leptons are mass eigenstates, i.e. states of definite mass. "

 

[Vanadium 50]

ut how do you justify this claim?

Because it's not a claim, it's a definition. There are 3 leptonic mass eigenstates. We call the lightest one "electron", the middle one "muon", and the heavy one "tau".

 

[mfb]

We could go the opposite way: Give the neutrino mass eigenstates flavor names and see the charged leptons as mixtures of these flavors. It would be really impractical, that's why we don't do it.