Neutrinos and theoretical necessity

[marce]

- One of the most fascinating particles for me , have always been neutrino's because of them balancing between mass and massless properties. So the question 'why was this needed' in the context of the weak force has led me to the question : as with attempts to explain 3 generations of particles ,could the neutrino be explained from a theoretical derivation(s) as a result 'or needed'. Has it been done , or are there attempts to do that ?

M.

 

[phinds]

balancing between mass and massless properties

Huh? Name one massless property of neutrinos.

why was this needed

How is that any different from the question "why are electrons needed?" or this one "why are quarks needed?"

 

[pines-demon]

@phinds has a point "why is [insert particle here] needed"? Is a why question. Do I have to add a link to Feynman here?

You can ask why some particles were introduced, for example the Higgs was introduced because we needed an additional field to add mass to some particles. The neutrino was introduced to conserve momentum in beta decay.

 

[pinball1970]

- One of the most fascinating particles for me , have always been neutrino's because of them balancing between mass and massless properties. So the question 'why was this needed' in the context of the weak force has led me to the question : as with attempts to explain 3 generations of particles ,could the neutrino be explained from a theoretical derivation(s) as a result 'or needed'. Has it been done , or are there attempts to do that ?

M.

a summary here https://en.wikipedia.org/wiki/Neutrino

If you scroll to History and Pauli's proposal and beta decay as per @pines-demon

 

[phyzguy]

- One of the most fascinating particles for me , have always been neutrino's.

Sorry to nitpick, but why the apostrophe?

 

[marce]

>...Huh? Name one massless property of neutrinos.
- I thought the lightest one was massless

>..."why are electrons needed?" or this one "why are quarks needed?"
Well the question arises from : why the weak interaction needed this so small correction and can it be modeled theoretically

M.

 

[berkeman]

Sorry to nitpick, but why the apostrophe?

Relax, it's a massless apostrophe.

 

[phinds]

>...Huh? Name one massless property of neutrinos.
- I thought the lightest one was massless

No

>..."why are electrons needed?" or this one "why are quarks needed?"
Well the question arises from : why the weak interaction needed this so small correction and can it be modeled theoretically

That would just move the question to "why is the weak force needed?"

 

[Orodruin]

Why is nobody tagging me here?

- I thought the lightest one was massless

No

Perhaps. It is not known.

What we know about neutrino masses is their mass squared differences. Even if they are all non-zero, it does not rule out that the lightest neutrino could be massless.

why the weak interaction needed this so small correction and can it be modeled theoretically

It is not a small correction to a lot of processes, such as many radioactive decays.

 

[phinds]

What we know about neutrino masses is their mass squared differences. Even if they are all non-zero, it does not rule out that the lightest neutrino could be massless

Thanks. I didn't realize that.

 

[Orodruin]

could the neutrino be explained from a theoretical derivation(s) as a result 'or needed'. Has it been done , or are there attempts to do that ?

Apart from the original introduction by Pauli (which was needed for momentum/energy conservation as mentioned, but at least as importantly for angular momentum conservation), there are also many arguments in hindsight. For example, without the neutrino the electron could not interact at all via charged currents. The field content of the Standard Model is also quite particular in that gauge anomalies all cancel out - making the theory self-consistent. This would not happen without the neutrino.

 

[marce]

No

That would just move the question to "why is the weak force needed?"

No my question was : why did the weak force need such a nearly none-existing particle ?

 

[Orodruin]

No my question was : why did the weak force need such a nearly none-existing particle ?

Neutrinos are the second most abundant (known) particle in the Universe. I would hardly classify that as ”near non-existence” …

 

[phinds]

No my question was : why did the weak force need such a nearly none-existing particle ?

I was trying to help you understand that you might as well ask why does ANYTHING exist?

 

[marce]

Thanks. I didn't realize that.

Indeed : ref https://golem.ph.utexas.edu/category/2022/12/neutrino_dark_matter.html
>...
>In Turok’s theory all the neutrinos have Majorana masses, described by a mass matrix. To make the heaviest right-handed neutrino stable, a bunch of matrix entries must vanish—and this makes the lightest left-handed neutrino massless!

M.

 

[Orodruin]

In Turok’s theory all the neutrinos have Majorana masses, described by a mass matrix. To make the heaviest right-handed neutrino stable, a bunch of matrix entries must vanish—and this makes the lightest left-handed neutrino massless!

This is not a theory confirmed by experiment. As I have already mentioned, whether the lightest neutrino is massless or not is still unknown.

 

[marce]

Neutrinos are the second most abundant (known) particle in the Universe. I would hardly classify that as ”near non-existence” …

Actually that confirms my question , but let's not dig into talk-at-the-bar (indeed)

 

[pines-demon]

I was trying to help you understand that you might as well ask why does ANYTHING exist?

ANYTHING was introduced by Parmenides to explain the existence of something in the absence of nothing.

 

[marce]

ANYTHING was introduced by Parmenides to explain something in the absence of nothing.

I would like to avoid going that path , and stay focused on a specific topic.

 

[pines-demon]

I would like to avoid going that path , and stay focused on a specific topic.

So what else do you want to know? It was a "why" question, can you narrow it into a non-"why" question?

 

[Orodruin]

Actually that confirms my question , but let's not dig into talk-at-the-bar (indeed)

Your question seems to have been answered. If not you need a better defined question.

 

[marce]

So what else do you want to know? It was a "why" question, can you narrow it into a non-"why" question?

Really !?

 

[Vanadium 50]

OK, so lets try this. Why are neutrinos needed? Because we see them coming out of reactors, accelerators, radioactive sources and supernovae.

 

[Vanadium 50]

Oops...and the sun and the upper atmosphere.

 

[pines-demon]

Really !?

Exactly like that, this is better than a why question.

 

[ohwilleke]

>...Huh? Name one massless property of neutrinos.
- I thought the lightest one was massless

At least two neutrinos are massive. There are probably three massive neutrinos, which there is lots of theoretical motivation for, but this hasn't been definitively confirmed. There is certainly no strong evidence that the lightest neutrino is massless. The mass of the lightest neutrino is probably on the order of 1 meV or less (i.e. 0.001 eV) which is a couple of orders of magnitude smaller than can be directly measured at this time. That estimate is based upon the differences between the neutrino masses which is determined from neutrino oscillation observations, and based upon cosmology based upper limits on the sum of the three neutrino masses.

The Standard Model assumed that all three neutrinos were massless until neutrino oscillation was discovered, and some pedantic folks would say that neutrino mass still isn't part of the Standard Model because the way that neutrino mass arises hasn't been determined, but it is a pretty fussy way to define the term Standard Model, and most people when they are talking about the Standard Model of Particle Physics include massive neutrinos and the PMNS matrix governing their oscillations.

>..."why are electrons needed?" or this one "why are quarks needed?"
Well the question arises from : why the weak interaction needed this so small correction and can it be modeled theoretically

In addition to (1) the conservation of mass-energy in W boson interactions, neutrinos were found to be necessary due to the way that (2) their existence produces the right branching fractions in the decay of W bosons and Z bosons, and (3) because without them, the conservation of lepton number which is observed in all experimental high energy physics tests requires them to work. They are also something that can be detected with instruments and in the case of high energy neutrinos aren't so small.

 

[Vanadium 50]

Except that the neutrino was discovered 27 years before the W was discovered and 8 years before it was even proposed.

 

[ohwilleke]

Except that the neutrino was discovered 27 years before the W was discovered and 8 years before it was even proposed.

Historically true. But we have more justifications and evidence now than we did then, as we've learned more, which reinforces the discoveries made at the time the neutrino was discovered, and ties the whole Standard Model framework together as a whole.

 

[Vanadium 50]

But we have more justifications and evidence now

I don't think we need any more "justification and evidence" than "we see them coming out of reactors etc." Certainly the Nobel committee didn't.

No need for any sort of retro-causality.

 

[arivero]

https://cerncourier.com/a/who-ordered-all-of-that/