Scientists are mystified why there is far more matter in the universe than antimatter, since equal amounts were presumably generated in the Big Bang.

But why would we expect that?

I gather there's some technical reason for particle genesis to be in opposite pairs; can it be explained in layman's terms?

Otherwise it just seems like boffins are creating a conundrum for no reason, when it's just that matter is as matter does 'cuz that's how she bangs.

Masque? Oh, nvm.

I think its pretty straightforward. There is no known mechanism that would create so much more matter than anti matter as we observe. There basically has to be some symmetry that is broken in terms of the math used in particle physics, but nobody is sure exactly how its done.

That seems to assume that a mechanism is known for creating a balance of matter--antimatter. What is it?

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

Well, technically the opposite of that. We don't see massive violations of CP symmetry, experimentally or theoretically. But apparently very very soon after the big bang there was some sort of massive CP violation that isn't yet well understood.

FIRST, PLEASE NOTE THAT I'M AN AMATEUR! so anybody with a real understanding of physics please feel free to correct anything here as it is being relayed by a layman. also note i bolded the key part for anybody who doesn't want to read the whole thing here.

i thought we recently found a pretty good basis regarding why there is more matter than anti-matter. i am not looking for links for this right now, but i'll come back with links, or others can throw some in here, but basically, neutrinos are the answer.

specifically, neutrino vs. anti-neutrino oscillations. for those who are unfamiliar with this stuff, there's a TON of cool things that have been recently discovered about neutrinos (well some very recently, some "recently" as in 1998).

first, they have mass. this was determined by the discovery that they oscillate among three different "flavors" (similar to the behavior of quarks; however, much moreso)*

second, they oscillate between flavors. this was an astonishing find (i think it was the japanese that found this? they have some huge detector over there where they house tens of thousands of gallons of H20 - literally, i.e. pure water - confined in a super sensor-loaded tank and they shoot neutrinos and anti-neutrinos at it to see what happens when they interact with matter and then detect the oscillations and decays). so a neutrino that started out as a muon neutrino may go through N oscillations before it decays. it can start as a muon, then become an electron, then a tau, then back to muon, then electron, and end up as a tau neutrino before it finally decays.

third, it is hypothesized that neutrinos and anti-neutrinos have supersymmetric heavy counterparts that would require a TON of energy to synthesize (and that could only have existed in the primordial universe). it is predicted that these supersymmetric heavy particles behave exactly as their lighter counterparts would (which is the case among all such cases of heavy matter)

fourth, and finally, we found out that there is a CP-violating asymmetry in the way that these oscillations (and thus the decays) occur with respect to neutrinos and anti-neutrinos (decays here means what happens at the end state of a neutrinos existence. so if it ends up as an electron or muon or tau etc. then it decays in some way vs. another).

in other words, we would expect there to be, say m end state neutrinos that ended up as muons, t neutrinos that ended up as taus, and e neutrinos that ended up as electrons (similarly, there would be t^ anti-neutrinos that ended up as tau anti-neutrinos, e^, and m^ etc. as well). i don't really remember if the fact that there are more of e and m neutrinos than t neutrinos violates CP, but i don't think it does IIRC (i.e. there's some mechanism that explains why we see more e/m than t neutrinos and why those flavors are favored)

anyways, in experiments, we found that e>e^. much moreso than we predicted via the calculations smart people made using the standard model equations. so we found an asymmetry in how neutrinos oscillate vs. how anti-neutrinos oscillate (and thus, there would be a difference in how heavy neutrinos and heavy anti-neutrinos decay as well).

so instead of N oscillations for neutrinos prior to decay and N for anti-neutrinos prior to decay, there's N^ oscillations for anti-neutrios where N>N^. so if the {e,t,m}^ set of anti-neutrinos takes longer to decay, it stands to reason that their supersymmetric heavy counterparts would also take longer to decay, thus creating a CP violating asymmetry in the primordial universe that could easily (given the magnitude of the difference we're seeing in neutrino vs. anti-neutrino end states) account for the matter-antimatter asymmetry that led to our existence.

in terms of "how sure we are" about this, currently the detection of this CP violation is at that 95% level. we need to get to that 5sigma level (vs. the approximately 2sigma level we're currently at) to be "absolutely sure" that the differences in neutrino oscillations are real. the issue is that neutrinos/neutrino oscillations and decays are SUPER SUPER SUPER hard to detect. even with that huuuuge tank in japan where they have tens of thousands of gallons of water and are shooting beams of neutrinos and anti-neutrinos through the tank, they only capture a few (i.e. like 50ish at most) interactions. so their sample size is realllllly small. but even for a small sample size, the difference was statistically significant at the 0.05 level.

note though that the significance level basically comes down to sample size. if the current 95% significance holds over a larger sample, then we're "basically there" in terms of detecting a real anomaly that could explain the reason why we're here vs. why we didn't just end up as empty space when matter and antimatter collided time and time again in the early universe.

*NOTE: the reason that this proves that neutrinos have mass is that they must start out in a quantum superposition of all three flavors, and this superposition requires mass. in other words, their oscillation indicates that they have tiny, nonzero masses since switching between flavors requires some degree of mass due to the energy involved in the oscillation.

Uphill,

I'm not getting why SUSY needs to be brought into this. My understanding (which might be outdated/wrong) is that all you need from the electroweak sector is CP violation peturbatavely (which as you explain has been observed) and a direct (nonpeturbative) violation of Baryon number, which hasn't but could be incorporated easily into the standard model? Maybe SUSY comes in because of some GUT mythology im forgetting about/never got in the first place. But I thought the mechanism I described only matters after electroweak symmetry breaking, so independent of anything at the SUSY scale?

Thanks for your post and apologies for the admittedly confused reply.

lol @ looking to me like i'm some kind of authority on this. seems like we're both just serious amateurs (serious as in high level amateurs, not serious as in seriously amatateurish) wrt this stuff.

my understanding was that we NEED SUSY here b/c the SUSY particles (heavy neutrinos and heavy anti-neutrinos) are the ones that have the potential to solve what has been termed here to be baryonic asymmetry (though aren't the mesons also affected by this asymmetry? i'm not sure about this so i'm legit asking lol. wouldn't it be hadronic - as in all particles made up of quarks including bosons - asymmetry vs. just baryonic asymmetry?). anyways, the SUSY particles are the ones that would be created in the early universe (the way heavier versions of the neutrino and anti-neutrino), thus we do need SUSY in order to explain the matter/antimatter asymmetry if this is the route that we're taking.

i do like how the term baryonic asymmetry sounds but my gut says it isn't 100% accurate, though i may be wrong here. i think "matter" also invokes the force particles that keep matter together, right? don't mesons also have SUSY partner particles as well? wouldn't they be needed to hold the baryonic SUSY partner particles together (is there a SUSY weak nuclear force whereby we'd need to invoke SUSY pions, for example)?

this is all super interesting stuff so i'm hoping we get a real physicist to help sort the terminology and logic out rather than have us kinda stumble around in the dark as we're doing .

to answer the OP though, we do have evidence of neutrino oscillations being responsible (indirectly as i kinda explained in my first post) for the matter/anti-matter asymmetry.

Yes and no I think.

No because Mesons aren't stable to begin with, so we don't observe alot more mesons than anti-mesons. Also some mesons are their own antiparticle to begin with.

Yes because some point after the big bang certain mesons were favored by the same mechanism that favored baryons over anti-baryons. But since we can't observe the mesonic asymmetry the problem isn't given the same status as the baryonic version.

My understanding is that you need new, heavy particles, but not necessarily any sparticles. The classic example is the Georgi-Glashow SU(5) GUT with new heavy X and Y bosons. I believe that together with weak force CP violation, it would have provided a mechanism for creating more baryons than antibaryons in the universe. Of course that theory was also falsified/ heavily constrained by lack of observed proton decay.

I might be misremembering/flat out wrong on my recollections of what I've been told about that from the real experts though.

i've been looking at this for a bit now and started out reallly confused to say the least. by the end of my reading for the day, though, i think we've got it all figured out from the 20,000ft perspective

ok, so, prior to this reading i just did, i thought that the susy particles for the neutrinos would be one of 3 neutralinos (obviously by the standard naming convention); however, it turns out that neutralinos are NOT the susy neutrino superpartners. instead, there's 4 neutralinos of different masses from very light (N~1) to very heavy (N~4).

i read through this PPT presentation (Very cool/helpful):

Cool PPT presentation

i suggest reading that and then checking out:

SUSY book chapter about neutrino masses

in this link, go to page 215 and you'll see a table where it shows the fields, the particles, the superpartners, and the gauge transformations (spin differentials going from i think particle to superparticle). you'll see here that neutrinos are just grouped under leptons, which is annoying!

so i did some more searching (googled "slepton" for lack of anything else) and FINALLY i found the superpartner particle for the neutrino--> the sneutrino lol. anyways, the "new heavy particles" that we'd need i think are indeed the sneutrinos and those would have to be pretty darn heavy (not sure where they'd have to fall on the mass scale, but i'm thinking somewhere on at least the GeV if not the TeV scale, which would be extreme in terms of mass relative to the neutrino itself). so those superheavy particles, the sneutrinos, would have the necessary oscillation and decay properties to explain why there were more reactions that produced matter, and thus, why we, and everything else, are/is here.

i really wanted to try to get a sense for the masses involved here so i found this paper:

New Constraints on General Slepton Flavor Mixing

and on page 4 in the first paragraph they note that a Dirac neutrino has a mass of 1 eV. so i thought maybe they'd have the estimated masses of the superpartner sneutrinos as well.

i thought i found SOMETHING like that on page 9 with that table there; however, i don't know what units those are in?

that turned out not to matter though b/c THANKFULLY on page 10 we get the answer:

so assuming a dirac neutrino isn't vastly different in terms of mass than the normal tau, electron, and muon neutrinos, we have that normal neutrinos have a supertiny mass (Which we expect ofc b/c it has to be barely nonzero) of 1 eV and the superpartner sleptons (sneutrinos) can be upwards of 500 GeV. now, the next question, is 500GeV sufficient for the oscillation/decay requirements such that we end up with more matter than anti-matter? if so, then this whole thing is solved

then it's just up to the experimental physicists to come up with more and more super genius ways to test for these particles.

Its not really that simple, simply fixing an sneutrino mass doesn't solve the problem. This seems like a good summary of the main issues

http://www.slac.stanford.edu/econf/C...apers/L018.PDF

You can see that some solutions don't require SUSY and when SUSY comes into the conversation its because its a natural way to have beyond the standard model CP violation, can help solve the flatness problem for the inflation potential etc. In short, it's like most applications of SUSY, never a smoking gun and often leads to more problems.

wow, this was an awesome paper. took me on and off all day to get through it. i had never even heard of some of the theorems, concepts, and formulations. this begs many questions though [ex post: and i ended up discussing a few of them and then getting off track and reading some other stuff that helped come to an interesting and favorable conclusion] such as:

1. where did you find/how did you come across this paper?

2. i'm very impressed w/ mark trodden. it takes a great deal of knowledge, ability, and talent to WRITE a paper like that (he obviously has both great command of the intense maths needed for physics calculations during the early universe - i.e. high energy particle physics, which is really not easy - along with a clear and succinct writing style, which makes the paper relatively easy to read and digest. he's organized it extremely well and presented material in a logical sequence.

in addition, this paper was basically a talk he gave and his acknowledgements indicate that it really was his work (sometimes, great papers come from a slew of physicists - the name soup you sometimes see on works like this - however, here, he thanked a few people and then SLAC for the simulation time, which indicates he likely did the work himself, or maybe him + 1 or 2 grad students to program in/perform the computations).

finally, before i hop off of troddens dick, unlike quite a few notable physicists, his footnotes are impeccable (they're numerous and include page numbers). for me, as somebody who wrote papers as an economist and who loves writing in general, that is one of the signs of a truly great academic researcher. he's willing to take the time and effort to organize and report over 140 footnotes. take it from me, or you know if you've ever written papers for publication (even if like mine, none were fully accepted lol), that is no mean feat.

i'm gunna look up what else this guy did because i get the feeling he's contributed a lot.

and actually i did a quick search and in a paper i found this about neutrino masses:

so it seems the sum of the neutrino masses is much more than 3 eVs (what i kinda assumed from my earlier posts in this thread) since their error is 19,000,000 to 12,000,000 lol. so, yea, that means that the actual sum of the 3 masses is quite a bit larger than....3.....

i'm still thinking "heavy neutrinos" would be in the giga or tera eV territory though; however, that's now not as large of a difference between the sum of their masses as it would be had the sum been like 3.

3. from the article:

the issue here though is that majorana neutrinos appear to have a limited mass:

from: https://physics.aps.org/synopsis-for...ett.117.082503

so if majorana neutrinos can't be heavier than that, then it doesn't seem possible that the heavy neutrino explanation for asymmetric baryogenesis holds water (and as an aside, i see now why you used baryogenesis as clearly that's the standard formulation in the literature. good to know).

that is, unless there is something to the "right handed" vs. "left handed"ness of particles and if one set weighs a great deal more than the other (i just checked and it seems that majorana neutrinos, by the simple definition, are just neutrinos that are their own antiparticle, so they could be left or righthanded)

in doing the above "down the rabbit hole" research/reading i came across this slideshow (slide 8 shows the above definition of majorana neutrinos in that ViBar(h) = Vi(h) if it's marjorana and ViBar(h) != Vi(h) for dirac neutrinos)

http://nucla.physics.ucla.edu/sites/...r_UCLA1211.pdf

first, note that the seesaw mechanism seems to be the reason we can have heavier neutrinos:

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

and on slide 15, we see the same thing: that light neutrinos have heavy partners. the slideshow then goes onto discuss leptogenesis and ACTUALLY GIVES WHAT SEEMS TO BE SOME KIND OF SOMETHING related to heavy neutrino masses (the higgs vev = 174GeV, which i think is saying that the LIGHT neutrino masses would be that heavy)

and yes, turns out that's the case and it's very confusing since the slideshow does indeed confirm that the LIGHT neutrino mass would be 174GeV and the HEAVY neutrino mass would be (incredibly) 10^(9-10)GeV, which puts it into a range well beyond tera, giga, and whatever other prefixes exist to describe large numbers lol. as the slideshow notes, that also clearly puts these particles way out of reach of the LHC, which sucks.

what's cool though is that the author of the slideshow indicates that a) it is possible to violate CP in neutrino oscillation without leptogenesis, and b) it is possible to have leptogenesis without neutrino oscillation CP violation; however, it is UNLIKELY that either of those are true i.e. it's more likely that both exist and thus we have an explanation for matter/antimatter asymmetry (the slideshow then goes on to provide an argument as such).

so the cool part that i'm now on board with and understand better is that neutrino oscillation CP violation and leptogenesis imply each other. that's GREAT b/c i am pretty comfortable with neutrino oscillation issues (as i discussed earlier) and how they almost surely violate CP, so if that holds true (which i think seems likely) that then also implies leptogenesis, which answers the OP pretty much in full

also note that this slideshow was from 2012 and we've found much more evidence for the "worldwide goal of finding CP violation via neutrino oscillation" since then.

SO TO SUMMARIZE: you appear to be correct in that my understanding of superpartners being the heavy neutrinos was clearly wrong. instead it's just the consequence of the seesaw mechanism whereby light neutrinos lead to heavy early universe neutrinos (though their actual masses is still confusing to me b/c those numbers seem crazy). and since boris (slideshow guy) showed that leptogenesis implies CP violation via neutrino oscillation, and since we see quite a bit of solid evidence for CP violation via neutrino oscillation, it seems that as i just wrote in the above sentence, we may have a decent case for the answer to your question of "what's the deal w/ matter/antimatter asymmetry?"

sorry for the LONG AND SUPER RAMBLY post, but that's just how i roll when examining this stuff and reading about it as i post lol

OP-> GREAT original post. i've learned a ton reading about all this stuff. and i found a guy to look up and whose stuff i look forward to getting in to. so nice job, sir!

and one last thought: it seems that to really prove this whole mess, we just need to find neutrinoless double beta decays. easier said than done, but at least it's a goal and it seems doable over the next few years. that's gotta result in a nobel prize for the team that can show how we came to be

FINALLLLLLLLLLLLY we have a good word on a) the upper limit on light neutrino masses, and b) the lower limit on heavy neutrino masses:

from: http://www.scholarpedia.org/article/Leptogenesis

i bolded the key part. m = light neutrino masses and M = heavy neutrino masses.

point is, it turns out that "heavy neutrino masses" really are that crazy big with GeVs * huge numbers like 10^8. and we see that light neutrinos are REALLLLLY light with the upper bound on their mass just 10% of what i thought it was before (0.1 vs. 1.0).

crazy stuff.

PS - ugh, just as i think we have a handle on understanding all this, that scholarpedia entry throws this wrench in as the very last sentence: "Finally, leptogenesis is possible without heavy Majorana neutrinos, as in Dirac leptogenesis, triplet scalar leptogenesis of triplet fermion leptogenesis (see the reviews (Davidson, 2008bu; Fong, 2013wr))." i thought the whole point was that heavy neutrinos were necessary and that they had to be their own anti-particle as well. i guess they're saying that leptogenesis is possible using only dirac particles vs. majorana ones. oh well, i guess i can swallow that.

New info from the LHCb:

https://www.sciencenews.org/article/...bserved?tgt=nr

Cool stuff. Nothing conclusive yet ofc but seeing baryon antimatter decay differently than baryons is certainly interesting and informative.