Neutrino Asymmetry Passes Critical Threshold | Hacker News Reader

Neutrino Asymmetry Passes Critical Threshold

quantamagazine.org

59 pointsbainsfather20 comments

So... would this mean neutrinos are for sure not Majorana fermions? Because you'd think that a particle couldn't be its own anti-particle if it's anti-particle has different properties, but quantum mechanics has surprised me before.

https://en.wikipedia.org/wiki/Majorana_fermion

Well it’s tricky, see. Normal science might try to solve a paradox logically, but maybe this is the universe solving a paradox by multiplying both sides of the equation by a reciprocal paradox? The different properties of the anti-particle result in a remainder which is where all of the something rather than nothing comes from.

I guess my metaphor was a little too fast and loose and lost some key detail. I don’t want to misrepresent the science so here’s a link that explains the math better than I can.

https://en.wikipedia.org/wiki/Spinor

The known, light neutrinos would be Dirac, their massive counterparts Majorana:

https://en.wikipedia.org/wiki/Seesaw_mechanism

It's a bit of a subtle point but Majorana anti-neutrinos are still right handed chiral particle and a Majorana neutrino is still a left handed particle. So any particle-antiparticle effects from Delta-CP (or anything else) just becomes a left-right chirality effect. That behavior is built right into the term "Delta-CP", CP stands for charge-parity, meaning it's related to both a charge flip (particle to anti-particle) or a parity flip (left to right).

This isn't a full explanation but I'd have to go find some old text-books in order to provide a better one. Here's also a blog post that kinda sorta addresses the same point https://www.quantumdiaries.org/2011/06/19/helicity-chirality...

> ...further explaining why anything at all exists today, since matter and antimatter in equal portions would have mutually annihilated.

Shouldn't this read 'how' instead of why? I am far from an academic so please enlighten me. I presume 'why' to question reason and 'how' to explain means.

I agree. “Why” implies or presupposes such reason or reasons exists. “How” is more about context, explicability, understanding, justification, verification, and proofs. That’s just my reasoning anyway.

It’s a matter of the “why’s” of ontology versus the “how’s” of deontology.

That 12 story tank looks amazing.

Am I the only one who finds megastructures like this surreal? It’s not agoraphobia per se, but sometimes when I behold things like this tank or especially when I gaze upwards at a skyscraper, I get this sense that of not-rightness that it exists and that I’m so close to it to be looking at it from this angle. Vertigo maybe? It happens even in pictures so I’m sure it’s something about my mind thinking something is amiss somehow but I don’t know why. I actually am quite fascinated with megastructures like these but have a hard time appreciating them sometimes while grappling with the extrasensory overload that viewing them can induce.

I had something like that in NCY a few years ago. The upper parts of the new world trade centre building were always so far away they lacked parallax, so it was like looking at a skybox in a sprite-based FPS.

I don’t get the effect with pictures of big things, but in addition to not finding the lack of parallax confusing in that situation, I also know that is part of my mind getting the scale wrong.

Would this also imply that even today new mass could be created? Similar to how Hawking Radiation assumes virtual matter/antimatter pairs getting created all the time would it be plausible for neutrinos and their antimatter counterparts to pop into existence without fully annihilating each other?

A question to particle physicists: I've always thought that matter and anti-matter qualifications applied only to charged particles. Neutrinos have no charge, so how can it have an antiparticle? Does there exist an "anti-neutron" as well?

Not a physicist but I can answer this.

Antineutrinos have opposite lepton number compared to neutrinos. Lepton number is preserved by all particle reactions[1] so for example beta decay must produce an antineutrino (L=-1) in addition to an electron (L=1).

Antineutrons also exist. Neutrons are composed of three quarks, uud (u has charge 1/3 and d had charge -2/3), while antineutrons are composed of two up antiquarks (charge -1/3) and one down antiquark (charge 2/3). And as in the case of neutrinos, neutrons have baryonic number 1 like protons and antineutrons have baryonic number -1 like antiproton a. Hence, for example, a beta decay will always turn a neutron into a proton and an antineutron into an antiproton (though the latter is theoretical).

[1] More precisely there is a lepton number for each generation (electron/muon/tau) and all three are separately preserved.

This will blow your mind then:

A Majorana fermion (/maɪəˈrɑːnə ˈfɛərmiːɒn/[1]), also referred to as a Majorana particle, is a fermion that is its own antiparticle. They were hypothesized by Ettore Majorana in 1937. The term is sometimes used in opposition to a Dirac fermion, which describes fermions that are not their own antiparticles., from https://en.wikipedia.org/wiki/Majorana_fermion

Imagine that the relation between a particle and it's antiparticle is an abstract relation, and one of the easy to explain consequences is that they have the oposite charge. (Other consequence is that they have the same mass, but it's less interesting.)

There is an anti-neutron https://en.wikipedia.org/wiki/Antineutron I'm not sure of the details, but it should be easy to produce an antineutron beam, if you have the right equipment (perhaps like a particle acelerator worth a few million dollars :) ) Some random paper http://www.ph.unito.it/ccl/docenti/menichetti/CIVR/bressani.... take a look at section 2.

Neutrinos do have a charge, just not electric:

https://en.wikipedia.org/wiki/Weak_interaction#Weak_isospin_...

How does this square with the idea that antiparticles are particles traveling backwards in time?

That's not an idea, it's what some of the math in the standard model looks like.

The fact that we are here tells us there are fundamental differences between matter and anti matter, otherwise the big bang would have created exactly equal amounts that would have annihilated.

CP asymmetry is an observational fact, measured also bei LHC.

Is there anything in the science about locality? That is, is there anything that says there might be somewhere that has an abundance of anti-matter exactly offsetting our abundance of matter?

https://arxiv.org/abs/1204.4186

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