The ever-increasing proton lifetime

In summary: So I was reading this article discussing how experiments have been able to observe proton decay:https://www.economist.com/news/science-and-technology/21734379-no-guts-no-glory-fundamental-physics-frustrating-physicistsIt states that after concluding that there has been any evidence of proton decay in certain experiment, the lower bound of the average lifetime of a proton must be increased. Is this simply a calculation that given a certain number of protons being observed for a certain amount of time, the statistical spread of lifetimes must be such that it would be *probable* (perhaps 50
  • #1
swampwiz
571
83
I was reading this article discussing how experiments have been able to observe proton decay:

https://www.economist.com/news/scie...ry-fundamental-physics-frustrating-physicists

It states that after concluding that there has been any evidence of proton decay in certain experiment, the lower bound of the average lifetime of a proton must be increased. Is this simply a calculation that given a certain number of protons being observed for a certain amount of time, the statistical spread of lifetimes must be such that it would be *probable* (perhaps 50%?) that a proton decay would have been observed if the average lifetime were a certain value (i.e., that becomes the minimum lifetime)?

It would seem to me that the answer all along is that protons don't decay, but I suppose that it is impossible to prove a negative. What gives physicists the notion that protons are supposed to decay in the first place?
 
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  • #2
Did you mean, "... how experiments have not been able to observe proton decay..." ??
 
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  • #3
By the way, for whatever it's worth, recently claims have appeared of GUT models without proton decay:
  • Andreas Mütter, Michael Ratz, Patrick K.S. Vaudrevange,
    "Grand Unification without Proton Decay"
    (arXiv:1606.02303)
  • Bartosz Fornal, Benjamin Grinstein,
    "SU(5) Unification without Proton Decay",
    Phys. Rev. Lett. 119, 241801 (2017)
    (arXiv:1706.08535)
 
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  • #4
Is this an A-level thread? i.e. do you have a graduate-level education in physics? I don't want to start writing and then find out it's all at the wrong level.
 
  • #5
Long live the proton!
 
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  • #6
Vanadium 50 said:
Is this an A-level thread? i.e. do you have a graduate-level education in physics? I don't want to start writing and then find out it's all at the wrong level.
I have the 2 semester sequence in calculus-based physics for technical students (degree in mechanical engineering and then graduate study in engineering mechanics), LOL. That said, I am on the path of discovery. If this thread should be at a lower level, I would have no problem in changing it.
 
  • #7
Nik_2213 said:
Did you mean, "... how experiments have not been able to observe proton decay..." ??
Yes, that is what I had meant.

I guess what I am having grokking is why should a proton be seen as something that decays? IIUIC, there has never been such an observation.
 
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  • #8
Well, according to the standard model, the proton does not decay. However, it is impossible to proof that experimentally, so the best we can do is say: "We have observed no proton decay in time T, so we know that the half life has to be at least τ to be consistent with this observation".

On the other hand, we know that the standard model has its flaws, and some theories beyond the standard model do have decaying protons, and a positive result on decaying protons would strengthen the validity of these theories.
 
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  • #9
swampwiz said:
hy should a proton be seen as something that decays?

Why shouldn't it?

A good theory would explain why and how fast the proton decays if it is unstable, or why it does not if it is stable.
 
  • #10
We live in a universe with matter and nearly no antimatter. Nearly all ideas where this asymmetry could come from imply that protons can decay, and some models predict a lifetime somewhere in the range of our experimental limits. The tests can either confirm proton decays or rule out some models.
 
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  • #11
mfb said:
Nearly all ideas where this asymmetry could come from imply that protons can decay, and some models predict a lifetime somewhere in the range of our experimental limits.

What would be a good source for discussion of observational proton decay limits in relation to models of baryogenesis via the chiral anomaly?
 
  • #12
Vanadium 50 said:
Is this an A-level thread? i.e. do you have a graduate-level education in physics? I don't want to start writing and then find out it's all at the wrong level.

With my knowledge background I have little occasion to visit this section of PF, but I had been intending for the last week to get around to bringing this article to the attention of members, hether here or in a more general section. .And, yes, hope that the priesthood could talk in simplified parables that convey something to us illiterate though worshipful peasants.

(I am one of those who has happily read quite a lot over time about this kind of physics. In a popular science journal an article on it will usually be the first thing I read. A lot of people are like that as a look at the popular science shelves in any bookshop will show - more books on this than on more concrete things of public concern like, say genetic engineering advances. We can't really understand the theories the books and articles talk about, I sometimes call them explanations without explaining or vice versa, but we have a pleasure in the patter and being bamboozled, and it's information about what's going on in this fundamental sphere. Okay it looks like there is some stuff I might try on this very site, must get around to that.)

At my level this article is well written and informative. I have long known of the hierarchy problem (gross disparity between the fundamental forces) but to the layman more telling than a number is just the comparison of a fridge magnet exerting more force electromagnetcally than the whole Earth gravitationally. I'd heard of most of the big science and big theories stuff, new to me and interesting were some small science endeavours. Trying to deform an electron in a field of 100GV/cm wow! that apparently exists in thorium monoxide, I imagine not a lot of people know that, whoever first did must have been really into some speciality? And I wonder why and whether it is that unique?

I wonder whether you physics people detect a slightly mischievous tone in the article and what your reactions are? It notes how the main theories have been around a long time. That they have a few successful predictions, seemingly about one each, but also predict lots of things that have not been found when looked for. That some of the theories can be tweaked endlessly. That “With every fudge applied, though, what were once elegant theories get less so”. That maybe they are trying to explain things that do not need to be explained? Quoting that “ideas became institutionalised. People stopped thinking of them as speculative.” (Also is it my lack of knowledge that makes me seem to see that there are breakthroughs in the theoretical field every now and then - but they are like breakthroughs in WW! - the follow-through of the initial promise of success seems always to get bogged down? Is only I who wondered whether it is a branch of the fashion industry? I have to say that the reports in PF by the sadly departed Marcus which we all enjoyed did a good job of making the subject bright, but at the same time quite far from dispelled this impression. I have also heard sometimes sceptical tones from physicists of more down-to-earth branches.)

The article concludes that Yes, it is all worthwhile, and should continue - but i's a sceptical undercurrent surfaces a bit with the funding question. It points out that the physics has for decades had a privileged relation with politics and funding. (I have had occasion to witness how physicists were just that much more effective, successful and better organized at chasing funding and at collaborating, thinking big and working like armies where other scientists were organised at the level of Boy Scout patrols.)

There is a companion article https://www.economist.com/news/lead...r-has-pushed-frontiers-knowledge-further-ever English they propose in which the economist proposes the next big facility after CERN should be in China. One can see that China's hunger for prestige technology hunger might bring full funding that others now would find it difficult to justify. I don't know whether this is a mischievous proposal of an influential Journal dabbling in things outside its field, Just good to know its own wheeze or whether reflects anything else e.g. does reflect something moving in the higher reaches of the profession.

I thought some issues came up for general discussion.
 
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  • #13
epenguin said:
And, yes, hope that the priesthood could talk in simplified parables that convey something to us illiterate though worshipful peasants.

Snark does not become you. And it sure doesn't make me want to participate and answer your questions.
 
  • #14
[URL='https://www.physicsforums.com/insights/author/urs-schreiber/']Urs Schreiber[/URL] said:
What would be a good source for discussion of observational proton decay limits in relation to models of baryogenesis via the chiral anomaly?
I'm not a theorist, I just see that from the side of what would be interesting experimentally.
epenguin said:
There is a companion article https://www.economist.com/news/lead...r-has-pushed-frontiers-knowledge-further-ever English they propose in which the economist proposes the next big facility after CERN should be in China.
China is interested in that, but it is unclear if they really want to spend so much money, and it is unclear where the expertise would come from. You need many experts, including many foreign experts, and China is not the most popular place in that aspect.
 
  • #15
mfb said:
I'm not a theorist, I just see that from the side of what would be interesting experimentally.

Sure. What would be a reference for your statement from your favorite point of view.
 
  • #16
Talks at the usual conferences (Moriond, EPS, ICHEP, ...). I remember the conclusion, but not the individual talks.
 
  • #17
mfb said:
I remember the conclusion, but not the individual talks.

I am just wondering,since its common to discuss proton decay for GUT models, but for some reason I never saw it discussed in the context of models for baryogenesis. I tried to look around with the evident keywords, but no luck so far. Good to hear from you that people at least say the words from time to time. :-)
 
  • #18
Baryogenesis is a strong argument the baryon number can be violated, and that number is the only thing that protects protons from a quick decay.
 
  • #19
mfb said:
Baryogenesis is a strong argument the baryon number can be violated, and that number is the only thing that protects protons from a quick decay.

Sure, I know, that's why it seems curious that one never sees discussion of proton decay issues in the context of baryogenesis. At least I never saw it discussed in that context. It seems you are saying that you heard people speak about it, but that there is nothing tangible in print that one could point to. (But I'll leave it at that now, unless you have more to say.)
 
  • #20
on the title: If the proton's lifetime keeps on increasing as fast as our limits, then we will never observe it...

Most of the limits set some confidence level (XX% CL) for the non-observation of proton decay.

What gives us the motivation to look for such decays: the fact that some GUTs predict these decays.
E.g. a GUT which could potentially have some kind of mechanism that breaks baryon symmetry (e.g. couplings to quarks+leptons) through the mediation of heavy bosons is such an analogy -like the SU(5)- (which is also used in baryogenesis if you somehow introduce some CP-violation https://arxiv.org/abs/hep-ph/9801306 )...
 
  • #21
[URL='https://www.physicsforums.com/insights/author/urs-schreiber/']Urs Schreiber[/URL] said:
Sure, I know, that's why it seems curious that one never sees discussion of proton decay issues in the context of baryogenesis. At least I never saw it discussed in that context. It seems you are saying that you heard people speak about it, but that there is nothing tangible in print that one could point to. (But I'll leave it at that now, unless you have more to say.)
A quick search for "proton decay baryogenesis" finds various results.
https://arxiv.org/abs/hep-ph/0005095
https://arxiv.org/abs/1207.5771
http://www.physics.mcgill.ca/~guymoore/research/baryogenesis.html
It even has its own section at Wikipedia: https://en.wikipedia.org/wiki/Proton_decay#Baryogenesis
 
  • #22
Vanadium 50 said:
Why shouldn't it?

Occam's Razor.
 
  • #23
swampwiz said:
Occam's Razor.

Is not a very good tool to judge experimental results. And experimentally we know that decays that are possible occur at some rate.
 
  • #24
mfb said:
A quick search

I understand the general idea that baryogenesis, by definition, involves baryon non-conservation. What I was hoping to see was some more concrete anlysis with maybe numerical exclusion bounds on what the implication of experimental bounds on proton decay is for models of baryogenesis, similar to the detailed discussion one sees for GUT models, where experimental results have led to some of these models being effectively ruled out.

But I gather that models of baryogenesis just aren't detailed enough in themselves to admit any of this? I gather there is just Sakharov's conditions justifying the general possibility of baryogenesis, without any quantitative ideas of the process. Is that right?

I suppose quantitative understanding of baryogenesis via chiral anomay ##\mathrm{div} J_{\mathrm{quark}} \propto tr(F \wedge F)## all depends on having some idea of ##tr(F \wedge F)## in the early universe, or maybe at least its local fluctuations or something? Maybe there is some indirect (probably very indirect?) experimental bounds on what that could have been?

Anyway, it's these concrete implications of experimental bounds on proton-decay to models of baryogenesis that I never saw discussed, also not in the references that you googled, or else I missed them. Probably they just don't exist. That's fine, I just wanted to know.
 
  • #25
swampwiz said:
Occam's Razor.
Why would Occam´s razor favour baryogenesis?
What is wrong with baryon number being initial parametre of universe? Why are models with primordial baryon number against mainstream and why does Occam´s razor favour models with zero primordial baryon number PLUS baryogenesis imbalance that somehow produces just the observed number of baryons, PLUS predicted proton lifetime that always seems to be not observed at the rate expected?
 
  • #26
snorkack said:
Why would Occam´s razor favour baryogenesis?
What is wrong with baryon number being initial parametre of universe? Why are models with primordial baryon number against mainstream and why does Occam´s razor favour models with zero primordial baryon number PLUS baryogenesis imbalance that somehow produces just the observed number of baryons, PLUS predicted proton lifetime that always seems to be not observed at the rate expected?

I'm with you on this. A positive finite baryon number of the universe as one of its initial conditions is no more problematic than a positive finite mass-energy of the universe at its inception and I have yet to see anyone argue for a Big Bang mass-energy in the universe that is either zero or infinite.

A positive baryon number of the universe as an initial condition is the only possibility that is consistent with the SM.

A vague desire for an initial condition of the universe to be different because it looks pretty if that is the case is not a very compelling reason to go head to head with overwhelming evidence that there are no observed cases of either baryon number violation in general by any means, or proton decay, or lepton number violation by any means, up to very, very stringent limits. It also goes up against the theoretical reality that the only possible baryon number violating process in the SM, the sphaeleron (forgive me if I've spelled it incorrectly), cannot account for baryon number asymmetry in the universe.

Also, keep in mind that the energy levels to which the SM has been experimentally tested are higher than those present in any natural phenomena in the universe for something like 13.5 billion years +/-. We haven't (and never will be able to) experimentally tested the SM at the energy scales of the Big Bang and a brief period of time immediately thereafter, but, any baryon number violating process has to be confined to a very short period of time. Any process that takes even hundreds of millions of years to produce the observed matter-antimatter asymmetry of the universe is too slow to be consistent with the experimental proof of the SM at energy scales we have tested. And, now that the Higgs boson mass has been determined, we know that the SM is theoretically consistent up to the GUT scale.
 
  • #27
ohwilleke said:
the energy levels to which the SM has been experimentally tested are higher than those present in any natural phenomena

Maybe it doesn't matter for your argument, but ultra-high energy cosmic ray particles way beyond LHC energies are rare, but routinely seen by the Pierre Auger observatory.
 
  • #28
ohwilleke said:
A positive baryon number of the universe as an initial condition is the only possibility that is consistent with the SM.

I am wondering if this is true. The chiral anomaly in the standard model says that baryon current conservation is violated by instantons, via ## \partial_\mu J^\mu_{B} \propto tr(F \wedge F)##. While it is true that this violation is not seen in perturbation theory, it is present non-perturbatively in the standard model.

Thus it seems that just as with GUTs, already in the plain SM the question is not "why would it violate baryon number conservation at a measurable rate" but "why would it not?".

I have been trying to discuss this with "mfb" above. For some reason much less seems to be known about this for the plain SM baryon number violation, than for hypothetical GUT extensions.
 
  • #29
[URL='https://www.physicsforums.com/insights/author/urs-schreiber/']Urs Schreiber[/URL] said:
Maybe it doesn't matter for your argument, but ultra-high energy cosmic ray particles way beyond LHC energies are rare, but routinely seen by the Pierre Auger observatory.

Fair point. But, it doesn't really affect the argument as these show no sign of SM violations.
 
  • #30
[URL='https://www.physicsforums.com/insights/author/urs-schreiber/']Urs Schreiber[/URL] said:
I am wondering if this is true. The chiral anomaly in the standard model says that baryon current conservation is violated by instantons, via ## \partial_\mu J^\mu_{B} \propto tr(F \wedge F)##. While it is true that this violation is not seen in perturbation theory, it is present non-perturbatively in the standard model.

I have seen several papers that calculated this and found the numbers to be insufficient. I'll try to find a cite to one or two of them.
 
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  • #31
ohwilleke said:
doesn't really affect the argument as these show no sign of SM violations.

Right. It's sometimes used to argue that the SM vacuum, should it be metastable, is stable at least to these much higher energies than accelerators can probe. Which may be comforting to know. :-)
 
  • #32
ohwilleke said:
I have seen several papers that calculated this and found the numbers to be insufficient. I'll try to find a cite to one or two of them.

I'd be really interested. Thanks.
 
  • #33
[URL='https://www.physicsforums.com/insights/author/urs-schreiber/']Urs Schreiber[/URL] said:
I'd be really interested. Thanks.

Here are some papers that establish the general proposition that: "A positive baryon number of the universe as an initial condition is the only possibility that is consistent with the SM.", although not in as many words, relying on prior scholarship for it as they explore BSM scenarios, some of which reference older papers containing the actual analysis and calculations in the Standard Model case.

Here's a quote from an October 17, 2016 preprint:

It is by now a standard statement, repeated at the beginning of (nearly) any talk on baryogenesis, that while the Standard Model (SM) includes nonzero effects for all three Sakharov’s ingredients – baryon number violation, CP violation and deviation from equilibrium – their products falls short of the observed baryonic asymmetry of the Universe nB/nγ ∼ 6 ∗ 10−10 (1) by many orders of magnitude.

As a result, the mainstream of baryogenesis studies focus mostly on “beyond the Standard Model” (BSM) scenarios, in which new sources of CP violation are introduced, e.g. in the extended Higgs or neutrino sector. Leptogenesis scenarios are based on superheavy neutrino decays, occurring at very high scales and satisfying both large CP and out-of-equilibrium requirements, with lepton asymmetry then transformed into baryon asymmetry at the electroweak scale.

However, as all BSM scenarios remain at this time purely hypothetical, without support from the LHC and other experiments so far, perhaps it is warranted to revisit the SM-based scenarios.

While most of this paper will be focused on the CP violation during baryon-number producing sphaleron transitions, let us here comment on the third necessary ingredient, a deviation from thermal equilibrium. Standard cosmology assumes that reheating and entropy production of the Universe take place at a scale much higher than the electroweak scale. In addition, the standard model with the Higgs mass at 125 GeV has an electroweak transition only of a smooth crossover type. If the assumption is correct, and there would be no new particles at the electroweak scale found, the transition would be very smooth, without significant out-of-equilibrium effects.

A July 11, 2011 pre-print which has since been published in Physics D opens with the same conclusion:

The question how the observed baryonic asymmetry of the Universe was produced is among the most difficult open questions of physics and cosmology. The observed effect is usually expressed as the ratio of the baryon density to that of the photons n B/n γ ∼ 10 −10 . Sakharov [1] had formulated three famous necessary conditions: the (i) baryon number and (ii) the CP violation, with (iii) obligatory deviations from the thermal equilibrium. Although all of them are present in the Standard Model (SM) and standard Big Bang cosmology, the baryon asymmetry which is produced by the known CKM matrix is completely insufficient to solve this puzzle.

A December 14, 2017 pre-print simply states at the outset:

Electroweak baryogenesis provides a minimal and compelling scenario for testing the idea that the matter / antimatter asymmetry of the Universe arose at the electroweak phase transition [1–6]. The Standard Model lacks the necessary ingredients for electroweak baryogenesis, and in general new physics is required if this scenario is to be successful. . . .

[1] V. A. Kuzmin, V. A. Rubakov, and M. E. Shaposhnikov, Phys. Lett. B155, 36 (1985).
[2] M. Shaposhnikov, JETP Lett. 44, 465 (1986).
[3] M. E. Shaposhnikov, Nucl. Phys. B299, 797 (1988).
[4] M. E. Shaposhnikov, Nucl. Phys. B287, 757 (1987).
[5] A. G. Cohen, D. B. Kaplan, and A. E. Nelson, Nucl.Phys. B349, 727 (1991).
[6] A. G. Cohen, D. B. Kaplan, and A. E. Nelson, Phys.Lett. B245, 561 (1990).

And here's a quote from a November 28, 2017 pre-print:

What these models have in common is that in order to generate light Majorana masses for the active neutrinos, L needs to be broken. This symmetry, along with baryon number B symmetry, is accidentally conserved in the SM at the perturbative level. Weak nonperturbative instanton and sphaleron effects through the chiral Adler-Bell-Jackiw anomaly do in fact violate baryon and lepton number but only in the combination (B+L). The ‘orthogonal’ combination (B −L) remains conserved and thus lepton number violation (LNV), or more generally (B−L) violation, along with the generation of Majorana neutrino masses requires the presence of New Physics beyond the SM (BSM).

In this context, a clear hint for physics beyond the SM is the observation of a baryon asymmetry of our Universe, quantified in terms of the baryon-to-photon number density η obs B = (6.20 ± 0.15) × 10−10 . (1) In order to generate a baryon asymmetry the three Sakharov conditions have to be fulfilled, namely (1) B violation, (2) C and CP violation and (3) out-of-equilibrium dynamics.

Different approaches exist which exhibit these conditions, one popular scenario is baryogenesis via leptogenesis (LG). In the standard “vanilla” scenario, a right handed heavy neutrino decays out of equilibrium via a lepton number violating decay and introduces a new source of CP violation. As long as this happens before the EW phase transition, the lepton asymmetry is translated into a baryon asymmetry.

While the violation of lepton number is a crucial ingredient e.g. in the leptogenesis scenario, in order to satisfy the third Sakharov condition, the LNV interactions must not be too efficient. Otherwise they remove the lepton number asymmetry and, due to the presence of sphaleron transitions in the SM, also the baryon number asymmetry before it is frozen in at the EW breaking scale.

The search for LNV processes, with neutrinoless double beta (0νββ) as the most prominent example, therefore provides a potential pathway to probe or rather falsify certain baryogenesis scenarios, if the lepton number washout in the early universe can be correlated with the LNV process rate. In this paper, we take a model-independent approach and study SM invariant operators of mass dimension 5, 7, 9 and 11 that violate lepton number by two units, ∆L = 2. We correlate their contribution to 0νββ, either at tree level or induced by radiative effects, with the lepton number washout 3 in the early universe. Assuming the observation of 0νββ decay, where we take the expected sensitivity of T 0νββ 1/2 ≈ 10^27 y of future 0νββ experiments, we determine the temperature range where the corresponding lepton number washout is effective. After the discovery of the sphaleron transitions, the constraint on LNV operators from the requirement to protect the observed baryon asymmetry was soon realized with the Weinberg operator as the most prominent example. More generic nonrenormalizable operators were discussed in while the argument can also be extended to baryon number violating ∆B = 2 operators inducing neutron-antineutron oscillations. More recently, we have shown that searches for resonant LNV processes at the LHC can be used to infer strong lepton number washout and in we have demonstrated the principle to correlate the washout rate with non-standard 0νββ contributions. . . .

Our results show that the scale Λ of many of the ∆L = 2 operators and the corresponding temperature range of strong washout are O(TeV) assuming an observation of 0νββ in future or planned experiments with a sensitivity of T1/2 ≈ 10^27 y. In this case, there is underlying new physics at work, potentially within the reach of the LHC and future colliders. Together with the B + L-violating sphalerons, the presence of LNV can erase a pre-existing baryon and lepton asymmetry generated at high temperatures. As a result, the observation of 0νββ decay will strongly constrain models of high-scale (& TeV) scenarios of baryogenesis and leptogenesis.

Some sources may be found in the citations to the introduction to this September 26 2017 pre-print (updated December 30, 2017) which begins:

The origin of BAU has long been a question of great interest in explaining why there is more baryon than anti-baryon in nature. Big bang nucleosynthesis (BBN) [1] and cosmic microwave background [2] measurements give the BAU as η ≡ nB/s ⋍ 10−10, where nB is the baryon number density and s is the entropy density. In order to address this issue, many different models and mechanisms have been proposed [3–7]. The mechanisms discussed in the literature satisfy the three Sakharov conditions [3], namely, (i) baryon number (B) violation, (ii) charge (C) and charge-parity (CP) violations, and (iii) a departure from the thermal equilibrium. For reviews of different types of models and mechanisms, see, for example, [8–10]. Recently, the variety of the method for the calculation of BAU has been also developed [11–13]. . . .

[1] J. P. Kneller and G. Steigman, New Journal of Physics 6, 117 (2004).
[2] P. A. R. Ade and Others, Astron. Astrophys. 594, A13 (2016).
[3] A. D. Sakharov, Pisma Zh. Eksp. Teor. Fiz. 5, 32 (1967).
[4] M. Yoshimura, Phys. Rev. Lett. 41, 281 (1978).
[5] M. Fukugita and T. Yanagida, Physics Letters B 174, 45 (1986).
[6] I. Affleck and M. Dine, Nucl. Phys B 249, 361 (1985).
[7] A. G. Cohen and D. B. Kaplan, Nuclear Physics B 308, 913 (1988).
[8] S. Davidson, E. Nardi, and Y. Nir, Physics Reports 466, 105 (2008).
[9] M. Trodden, Rev. Mod. Phys. 71, 1463 (1999).
[10] K. M. Zurek, Physics Reports 537, 91 (2013).
[11] A. Kobakhidze and A. Manning, Phys. Rev. D 91, 123529 (2015).
[12] D. Zhuridov, Phys. Rev. D 94, 035007 (2016).
[13] N. Blinov and A. Hook, Phys. Rev. D 95, 095014 (2017).
 
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  • #34
For what it is worth, near complete matter-antimatter asymmetry follows almost trivially in any case where particles are well mixed in a compact space in the Big Bang and immediately after and the initial baryon number and lepton numbers of the universe are not zero. And, almost every matter-antimatter balanced decay process from a Big Bang of the type observed in the SM is going to produce this kind of well mixed set of particles in a compact space.

Heuristically, matter particles can be taken without loss of generality to be the more numerous type and anti-matter particles can be taken to be the less numerous type. Matter and antimatter particles annihilate each other on a 1-1 basis leaving only matter particles and a tiny share of particles that were not fully mixed and continued to stay unmixed for billions of years. Ergo, in every scenario except the one in which B and L are exactly zero at the beginning of the Big Bang, you expect extreme BAU which is what we observe. The more homogeneous the expanding universe is, the longer the time available for this mutual annihilation until only matter or only antimatter is left to take place is, since you don't have large pockets that would be annihilation free.

A rigorous derivation of this result would be a considerably more laborious enterprise and would call for more formal assumptions but would follow the same basis logic. You could have a small but non-zero value of B or L or both and still end up without BAU, but the further you get from zero the less likely the system is to end up this way. But, if you simply track the SM back to the beginning without new physics, you get a minimum absolute value of B and L that very far indeed from zero by many orders of magnitude, so the marginal cases don't matter.

If you engage in the rather deplorable Baysean notion that the many worlds folks try to engaged in that there is a distribution of possible B and L values at the beginning of the universe from which the initial conditions of the universe are chosen on a probabilistic basis, there is only one infinitessimal point that is B=0 and L=0, while all other points lead to BAU, so BAU is almost infinitely likely relative to any other initial condition.
 
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  • #35
ohwilleke said:
there is only one infinitessimal point that is B=0 and L=0, while all other points lead to BAU, so BAU is almost infinitely likely relative to any other initial condition.
That is not how probability works.

If you roll a die, are numbers different from 1 "almost infinitely likely" relative to the single number 1?
 
<h2>1. What is the proton lifetime?</h2><p>The proton lifetime refers to the amount of time it takes for a proton to decay into other particles. It is currently estimated to be at least 10^34 years, which is an incredibly long time.</p><h2>2. Why is the proton lifetime important?</h2><p>The proton is one of the fundamental building blocks of matter, and understanding its lifetime can help us better understand the fundamental forces and laws of the universe. It can also have implications for theories such as the Grand Unified Theory.</p><h2>3. How is the proton lifetime measured?</h2><p>The proton lifetime is currently estimated through experiments that study the decay of other particles, such as neutrons and muons, which are known to decay into protons. By studying the rate of decay of these particles, scientists can indirectly estimate the proton lifetime.</p><h2>4. Has the proton lifetime always been the same?</h2><p>No, the estimated proton lifetime has changed over time as new experiments and technologies have become available. It was originally thought to be infinite, but as our understanding of particle physics has advanced, we have been able to refine our estimates.</p><h2>5. What are the potential implications if the proton lifetime is found to be finite?</h2><p>If the proton lifetime is found to be finite, it could have significant implications for our understanding of the universe and the laws of physics. It could also have practical applications in fields such as energy production and nuclear waste management.</p>

1. What is the proton lifetime?

The proton lifetime refers to the amount of time it takes for a proton to decay into other particles. It is currently estimated to be at least 10^34 years, which is an incredibly long time.

2. Why is the proton lifetime important?

The proton is one of the fundamental building blocks of matter, and understanding its lifetime can help us better understand the fundamental forces and laws of the universe. It can also have implications for theories such as the Grand Unified Theory.

3. How is the proton lifetime measured?

The proton lifetime is currently estimated through experiments that study the decay of other particles, such as neutrons and muons, which are known to decay into protons. By studying the rate of decay of these particles, scientists can indirectly estimate the proton lifetime.

4. Has the proton lifetime always been the same?

No, the estimated proton lifetime has changed over time as new experiments and technologies have become available. It was originally thought to be infinite, but as our understanding of particle physics has advanced, we have been able to refine our estimates.

5. What are the potential implications if the proton lifetime is found to be finite?

If the proton lifetime is found to be finite, it could have significant implications for our understanding of the universe and the laws of physics. It could also have practical applications in fields such as energy production and nuclear waste management.

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