Proton: stable or unstable?

[ElliePhysicsStudent]

Hi

I've been reading websites about particle physics recently, and in some places they say the proton is stable and others they say it is unstable, with a half life of 10 to the power of 32 years. I know it is the most stable baryon.
The only possible decay I've read about is a proton decaying into a positron and a photon, which does not conserve baryon number, in which case, how can it have a half life at all? Are there any other possible decays?
Also, would a proton with a half life of 10 to the power of 32 years be classified as unstable or stable, as my physics teacher argued that this was so long that it would be pretty stable (and also that this was longer than the universe, which I thought physicists hadnt calculated the length of definitively yet).
This could be a stupid question so sorry if it is.
Thankyou
Ellie

[selfAdjoint]

Originally posted by ElliePhysicsStudent
Hi

I've been reading websites about particle physics recently, and in some places they say the proton is stable and others they say it is unstable, with a half life of 10 to the power of 32 years. I know it is the most stable baryon.
The only possible decay I've read about is a proton decaying into a positron and a photon, which does not conserve baryon number, in which case, how can it have a half life at all? Are there any other possible decays?
Also, would a proton with a half life of 10 to the power of 32 years be classified as unstable or stable, as my physics teacher argued that this was so long that it would be pretty stable (and also that this was longer than the universe, which I thought physicists hadnt calculated the length of definitively yet).
This could be a stupid question so sorry if it is.
Thankyou
Ellie

They did an experiment where they observed 10^33 protons for a year, and none of them decayed. Nobody has ever reported seeing a proton decay. Some theories require proton decay after a very long time, but those theories haven't yet made enough correct predictions to become highly plausible.

[xeguy]

The proton is considered stable on time scales much greater than the age of the universe. Experiments like the one mentioned above establish that proton decay (if it happens) is extremely rare. The experiment referred to was carried out at the Super-Kamiokande water detector in Japan (also used for neutrino research). The lower bound for the proton half-life was something like 10^35 years. When you consider that the agreed upon age of the universe is in the 10-15 billion year range, that corresponds to on the order of 10^9 years. That's why the proton is considered a stable particle, though some Grand Unified Theories predict the decay on very long time scales.

[LURCH]

Originally posted by xeguy
... though some Grand Unified Theories predict the decay on very long time scales.

Doesn't the second law of thermodynamics also require it? A proton has mass and therefroe energy. It constitutes a localised density of energy sarounded by an environment of lesser enrgy density. This is a condition that cannot remain intact forever, according to entropy. The energy contained in a small space must radiate otu into its relatively cold saroundings untill the two achieve equal energy states, mustn't it?

[eagleone]

Originally posted by LURCH
Doesn't the second law of thermodynamics also require it? A proton has mass and therefroe energy. It constitutes a localised density of energy sarounded by an environment of lesser enrgy density. This is a condition that cannot remain intact forever, according to entropy. The energy contained in a small space must radiate otu into its relatively cold saroundings untill the two achieve equal energy states, mustn't it? Well, I don’t know how much I would meddle thermodynamics in that topic, after all it’s statistical model, and it doesn’t consider quantum properties of mass/energy. But theoretically yes.

[suyver]

Originally posted by LURCH
Doesn't the second law of thermodynamics also require it? A proton has mass and therefroe energy. It constitutes a localised density of energy sarounded by an environment of lesser enrgy density. This is a condition that cannot remain intact forever, according to entropy. The energy contained in a small space must radiate otu into its relatively cold saroundings untill the two achieve equal energy states, mustn't it?

Following the same argument, one could also proclaim the electron to be unstabile. Does that follow from any of the unified theories so far?

[chroot]

Terry and Antonio,

I split your last posts off into a new thread of the same title in the Theory Development subforum. That is where alternative or personal theories should be posted.

- Warren

[Mr. Robin Parsons]

Originally posted by chroot
Terry and Antonio,

I split your last posts off into a new thread of the same title in the Theory Development subforum. That is where alternative or personal theories should be posted.

- Warren Who is "Terry and Antonio"?

[beacon]

Originally posted by suyver
Following the same argument, one could also proclaim the electron to be unstabile. Does that follow from any of the unified theories so far?

There is no any unified theories predicting the decaying of electrons, I think. LURCH's viewpoint is very interesting. Can anyone explain this?

[Nereid]

Originally posted by Mr. Robin Parsons
Who is "Terry and Antonio"? Terry Giblin and Antonio Lao. Their posts - one of each - can be found in Theory Development, in a thread called "Proton: stable or unstable"

[Haelfix]

Assuming conservation of baryon number is a good quantum number in the universe and quarks are subject to confinement, the proton in this ground state can't decay or give off energy. It would be 'stable'.

Statistical mechanics applies of course, but ask yourself, what else can it decay too? Theres no other mode. Its stuck in that configuration essentially forever.

[Mr. Robin Parsons]

Originally posted by Nereid
Terry Giblin and Antonio Lao. Their posts - one of each - can be found in Theory Development, in a thread called "Proton: stable or unstable" Thanks! found it sorta strange as I didn't see there names attached to, or in, any posts in here (this thread).....

[suyver]

Originally posted by beacon
There is no any unified theories predicting the decaying of electrons, I think. LURCH's viewpoint is very interesting. Can anyone explain this?

I also have never heard of it. I'd be most interested in hearing more from LURCH's argument.

[chroot]

MRP:

I have split off your questions and comments about electrons and generators to a new thread, entitled "Generators and Electrons" in the Theory Development subforum.

- Warren

[selfAdjoint]

Jackiw, in his Yang-Mills retrospective says

‘tHooft concluded that baryon number is not conserved in the standard
model. By evaluating the Euclidean functional integral in a Gaussian approximation around
the instanton solution of Belavin et al., he calculated the baryon lifetime. Fortunately it is
exponentially small, but diamonds in principle are not forever

[kurious]

The particle which causes proton decay may be antimatter that decayed in the early universe along with all the other antimatter that's missing.

[Antonio Lao]

Proton decay is a prediction of the grand unified theories. These are theories that attempt to unify the electroweak force and the strong force of particles and fields in quantum field theories. These theories assert that since quarks are heavier than leptons, quarks should ultimately decay into leptons. The theories have nothing to say about the involvement of antimatter.

The mystery of the asymmetry of matter-antimatter remains to be resolved. At the present time, no such a theory of resolution exist.

[kurious]

The mystery of the asymmetry of matter-antimatter remains to be resolved. At the present time, no such a theory of resolution exist.

What if matter and antimatter have slightly different masses which in the conditions of the big bang meant that antimatter was split into tiny fragments which fill all of space whereas matter survived.

[suyver]

What if matter and antimatter have slightly different masses

I think that would violate the CPT-theorem.... That would be bad news.

[Antonio Lao]

In order not to violate the CPT Theorem, the antimatter must be found dominantly in a universe by themselves and this anti-universe is connected to ours at various time-zero points which we call the vacuum. The phenomena of vacuum fluctuation is a direct proof that this is what is actually happening.

[kurious]

Does this mean that antimatter could be all around us?

[Antonio Lao]

We are surrounded by air but antimatter are in the vacuum and it is stabilized by the existence of virtual photons. If we by accident touch any of the antimatter, we will be turned into pure energy. Then there is also the question of dimension. We are basically four dimensional beings. The vacuum is zero dimensional. To "reach" the vacuum, we must contract our dimension from 4 to 3, from 3 to 2, from 2 to 1, from 1 to 0. Each of these steps is controlled by a force. EM force (4 to 3), Weak force (3 to 2), strong force (2 to 1), gravity (1 to 0).

[chroot]

kurious,

Yes, antimatter particles spring into existence everywhere, all the time, and promptly annihilate with the matter particles that sprung into existence at the same time. When particles are created, they are always created in pairs -- one normal matter, one anti-matter. There's a good chance that your body has encountered at least one anti-matter particle sometime in your lifetime, created by interactions between the atmosphere and a cosmic ray.

Antonio,

You were making good sense up until your "contract our dimensions" business.

- Warren

[Mr. Robin Parsons]

kurious,

Yes, antimatter particles spring into existence everywhere, all the time, and promptly annihilate with the matter particles that sprung into existence at the same time. When particles are created, they are always created in pairs -- one normal matter, one anti-matter. There's a good chance that your body has encountered at least one anti-matter particle sometime in your lifetime, created by interactions between the atmosphere and a cosmic ray.

Antonio,

You were making good sense up until your "contract our dimensions" business.

- Warren
So were you, till the 1stemboldened, not quite....

[chroot]

How did I fail to make sense?

- Warren

[kurious]

The vacuum must have a temperature equal to the temperature of the matter in its neighbourhood or else I reckon all rest mass would decay.
I reckon you're right and the vacuum has entropy too.I estimate that to reach a temperature of 10 to the power of 32 K - the temperature at the time of the big bang- the universe must have had a radius of 10 ^ 16 metres.
Far larger than is currently thought.

[Mr. Robin Parsons]

If it was "all the time" wouldn't it be eminently detectable and wouldn't the universe be doing nothing but...?

EDIT could just be me not 'seeing it' properly, as well, so don't take it as a criticism please, more like a quest for better info...

[Antonio Lao]

chroot,

I am still working on my sense. I start from being crazy then thru self-psychoanalysis, I hope to arrive at being normal when at a ripe old age.

[chroot]

MRP:

It *is* all the time, and it *is* eminently detectable.

- Warren

[Mr. Robin Parsons]

The prepoderance of antimatter anihilations has been detected, and proven, as all the time, everywhere?

Hummm, you would wonder what/why I would question?

[garytse86]

you can say that a proton is not stable chemically, thats why you get h30+ ions, the proton is not going to sit in solution doing nothing

[chroot]

gary:

Compounds of hydrogen have nothing to do with the stability of the proton itself.

- Warren

[Mr. Robin Parsons]

But I would be curious to know if, in separating protons from their respective electrons, by ionizational energies, (then a magnet to evacuate the protons), if placed back into an ionizing chamber, then turning the ionizing energy off, will the electrons that were once there, re-appear, from the energy that the ionization process imparted?

[chroot]

If you separate electrons from protons, you have a box of electrons and a box of protons. You can't destroy electrons, nor can you create them.

- Warren

[garytse86]

yes but in an acid, you don't get H+ ions but H30+ ions instead

[Terry Giblin]

If you separate electrons from protons, you have a box of electrons and a box of protons. You can't destroy electrons, nor can you create them.

- Warren

Warren,

Assuming you now have a box of electrons, and the walls of the box, act as a square-square potential well - quantum barrier which we can control, to release only one single electron at a 'time'.

Now we build two concentric circular walls around the box, the inner wall has two slits in it and the outter wall is painted white.

How did the electrons tunnel throught the wall?

Where do all the electrons disappear too?

Where did all the photons appear from and how?

I can only see a intereference wave pattern, but no electrons?

"You can't destroy electrons" - or matter or energy only change its form.

Regards

Terry Giblin

[ahrkron]

yes but in an acid, you don't get H+ ions but H30+ ions instead

How is that relevant?

In a chemical reaction, by definition the number of protons do not change. Actually, even the number of protons in each nucleus is not altered.

[garytse86]

How is that relevant?

In a chemical reaction, by definition the number of protons do not change. Actually, even the number of protons in each nucleus is not altered.

yes but the proton is not chemically stable otherwise it would not form an ion with H2O.

[chroot]

We're not talking about "chemical stability," gary, for the last time.

- Warren

[chroot]

I have split off MRP's discussion of whether or not chemistry includes nuclear effects to the Theory Development subforum.

- Warren

[IooqXpooI]

Isn't a proton just a combination of quarks?

It is stable, yet turns into a Neutron by means of Weak Force quickly...(in the atom)

[Nereid]

Isn't a proton just a combination of quarks?Yes.It is stable, yet turns into a Neutron by means of Weak Force quickly...(in the atom)I think you mean 'in a nucleus', and only in certain cases, e.g. where it can capture an orbital electron, and where the resulting nucleus has lower energy than the starting one, ...

[Mr. Robin Parsons]

And in radio-active decay, it reverts back to a proton, from a neutron by decay emitance of either, an electron, or a positron. (and a neutrino too, I suspect, I recall)

[chroot]

Beta decay:

n \rightarrow p + e^- + \overline{\nu}_e

- Warren

[Haelfix]

Note the inverse process is not a 'decay', its a reaction... One with very small cross section too I might add.

So the point stands, the proton has nothing to decay into... In nuclear and particle physics, any situation like that is defined to be 'stable'. Note this is not the same meaning as a chemist would use, where typically you aren't dealing with extreme vacuums.

You have to go beyond the SDM* to find a mechanism for its decay. (*aside from one technicality which has vanishingly small contribution)

[Antonio Lao]

What I don't understand is why the sum of the mass of the quarks composing the proton is larger than the mass of the proton.

Experimentally it can be said that the formation of proton liberates mass in term of energy because it takes about the same energy to form the jets which have proven the existence of quarks. But individual quark cannot be isolated. How much more energy does it takes to isolate the quark?

[Mr. Robin Parsons]

Have protons been created experimentally? or are you simply refering to the math's prediction(s)?

[Antonio Lao]

Experimental verification of quarks by the formation of jets proving the compositeness of nucleons and mesons of all hadrons.

[chroot]

What I don't understand is why the sum of the mass of the quarks composing the proton is larger than the mass of the proton.
You have it backward. The proton has more mass than the sum of its constituent quarks, because the binding energy between them counts as additional mass via E=mc2.
How much more energy does it takes to isolate the quark?
You can't isolate quarks, because the energy required to pull two apart is more than the energy required to create two more. In other words, you can pull a pair apart to a point and then *pop* you'll wind up with two pairs.

- Warren

[Mr. Robin Parsons]

Uhmmm, this was the question I had asked: "Have protons been created experimentally?" Lord knows what question you answered......

[Antonio Lao]

The natural decay of the "free" neutron does produce a proton as shown by trivial experiments requiring a lot less energy than all other modern accelerators.

[chroot]

I'd like to make sure that you understand, Robin, that these protons are not being created out of nothingness; that would violate many conservation rules. Instead, when you smash bits of matter together in particle accelerators, the kinetic energy of the particles can be manifested in the creation of various kinds of particles, some very exotic -- that's the fun part. In no situation does an experiment end up with more mass and energy than it started with, however.

- Warren

[Antonio Lao]

Robin Parsons,

As a novice in any experimental process, I know I don't how to create a proton. And I don't recall any experiment done by the experts. But in the early age of the universe, I think, it was naturally done by the first nucleosynthesis?.

[ZapperZ]

Just to make sure that there are NO misconceptions about our ability to create protons experimentally, we can do this the quick and dirty way (zap a hydrogen atom with enough energy and voila! We have a proton), or systematically to generate a high "quality", low emittance, high brightness proton beam as done routinely at Fermilab and many other accelerator/collider facilities.

http://www.fnal.gov/pub/inquiring/physics/accelerators/chainaccel.html

Zz.

[Antonio Lao]

I am thinking more in the line of creating proton from the component quarks than that of dissociation of hydrogen atoms.

[ZapperZ]

I am thinking more in the line of creating proton from the component quarks than that of dissociation of hydrogen atoms.

Yes, I was aware of that. I was merely addressing to the broader issue of "can we create protons experimentally", in case there are peole jumping in in the middle and see a discussion that might give them the impression that we do not know decisively that we have created protons.

As for your line of thinking, either beta decay (change of flavor by quarks) might answer your question, or you will have to wait till we make and verify the first gamma-gamma collider.

Zz.

[Antonio Lao]

Sorry for my being narrow and one trackly minded.

[taxman]

If the theroies are correct mass and energy are essentially the same thing just in a different form. It is not impossible for a decay of protons. Everything changes so over time it is not unlikely that the energy of the proton would decay into its principle parts. I just dont think that we know or understant all of the parts yet.

[chroot]

taxman,

According to the standard model, it is absolutely impossible for protons to decay. The argument "everything changes over time" is not a strong one at all.

- Warren

[Nereid]

If the theroies are correct mass and energy are essentially the same thing just in a different form. It is not impossible for a decay of protons. Everything changes so over time it is not unlikely that the energy of the proton would decay into its principle parts. I just dont think that we know or understant all of the parts yet.Welcome to Physics Forums, taxman!

As chroot said, the proton is a stable particle in the Standard Model, so it will not decay (by itself; there are certainly situations under which it will 'decay' e.g. in certain proton-rich nuclides). Of course, one of the tests of the Standard Model is to look for decays of the proton. AFAIK, several research projects to find proton decays, by a wide variety of channels, have been undertaken. No confirmed proton decays have been observed, so we can conclude that the proton's 'half-life' is at least 1038 years (though it may be somewhat less, in some hypothesised decay modes).

To put this into context, a proton half-life of 1038 years would mean an expectation of just *one* decay in ~12,000 moles of ordinary hydrogen, in a period of time equal to the life of the universe to date!

[Tom Mattson]

taxman,

According to the standard model, it is absolutely impossible for protons to decay. The argument "everything changes over time" is not a strong one at all.


To that I would add only that "everything changes over time" does not imply "everything decays". The proton does constantly change--internally. There are gluons running around, virtual quark-antiquark pairs constantly popping into and out of existence, etc. Also, if struck with a sufficiently energetic particle, the proton will be exicted into a resonance, and then deexcite back down.

The inside of a proton is a hive of activity. It just so happens that it goes through all that change without changing its asymptotic identity (that is, it don't decay :tongue: ).

[arivero]

As for the question of artifitial production of protons.... Machines as the LEP get hadrons, ie mesons and barions, from the product of electron positron colisions. This should include protons, shouldnt it?

[bkfizz02]

The original question was about the stability of the proton. I agree that the proton does not decay, but I do not believe that we can "prove" this. One could imagine a scenario the the original post presented - proton --> positron + photon. Certainly this is allowed by energy considerations. But it is not allowed by conservation of lepton number. In fact, for every proton decay that you can imagine that does not violate conservation of energy (a physics axiom), a conservation law is broken.
I think that this fact is what makes the original question really important. If we could observe a proton decay, we would be observing the breaking of a conservation law. Since we believe in many conservation laws, the direct experimental contradiction of them would be crucial for retooling our thinking.

Another example of a process which "cannot" happen is neutrinoless beta decay. People look for this process, which would violate lepton number conservation. If they found it, the proton decay question would almost certainly need to be revisited.

[Terry Giblin]

More to the point..........

Unless the laws of statistics have changed since I left school.

Has anyone simply calculated the probability that we have not seen a proton decay already, by now - whats the definition of a "half-life"?

Regards

Terry Giblin

[marlon]

The only way a proton would disintegrate is if it were to have a tremendously high speeds. Asymptotic freedom then states that the strong force becomes smaller so the fluxtube between the constituent quarks will "decay" into gluons and the quarks would move away from each other.

At least this is the picture of the dual abelian higgs model using the concept of dual superconductivity and the S-duality of coupling constants + charge quantization from Dirac.

Ahhh, and you also need magnetic monopoles, responsible for this quantization.

regards
marlon

[humanino]

I really don't get it Marlon. The proton is more likely to decay at higher speed !? Usually, at higher speed, decay is just lowered by lorentz contraction of time. Or : the fastest decay should occur in the rest frame !

I could concieve that there is a dynamical process occuring during the acceleration process.





for every proton decay that you can imagine that does not violate conservation of energy (a physics axiom), a conservation law is broken.

Barionic number conserved through other conservation laws !?
Oh, by the way : is barionic number conservation not much better experimentaly tested than the other conservation laws (with regards to proton's lifetime. I have been checking PDG online, and I am not quite sure.) ?

[vanesch]

The original question was about the stability of the proton. I agree that the proton does not decay, but I do not believe that we can "prove" this. One could imagine a scenario the the original post presented - proton --> positron + photon. .

The idea of proton decay comes from GUT (Grand Unifying theories). In the standard model, we have the gauge group SU(3)xSU(2)xU(1), where SU(3) describes a (non-broken) gauge symmetry group between the colors of the quarks (and the relevant bosons are the gluons of the strong interaction), while SU(2)xU(1) describes the (broken) symmetry of the electroweak charges (essentially chirality, hypercharge and electrical charge) and the relevant bosons are W+, W-, Z0 and the photon.

As such, there is no interaction possible which turns a quark into a lepton and from this follows baryon conservation. In the standard model, the 3 lepton families, and the 3 quark families, have a priori not much to do with each other, but the very fact that there are 3 of each cries out for a deeper structure.
Indeed, if you make a large tuple of all the fermion fields in one family (the 2 quarks - righthand, the two quarks - lefthand, the electron and neutrino - lefthand, and the electron, righthand) this big tuple transforms under a composite representation of SU(3)xSU(2)xU(1) which is really put in there by hand. On the other hand, it fits into only 2 different representations of SU(5), which contains SU(3)xSU(2)xU(1), namely the so-called 5* and the 10 representation. But SU(5) is not equal to SU(3)xSU(2)xU(1), it contains in fac t 24 gauge bosons, so there are EXTRA INTERACTIONS, and some of these link quarks and leptons, which comes down to say that a quark could, through this interaction, change into a lepton. Of course one assumes that this symmetry is broken, and that the relevant bosons have a big mass (the "GUT" scale), which decreases this interaction rate. If one estimates this scale (that's where the 3 coupling constants of the standard model should unify) one arrives at something of 10^15 GeV. Using this value, the proton decay rate should be of the order of a life time of 10^31 years, which has been falsified by experiment. So that's where all the hassle came from.
But people have not given up: other groups than SU(5) are possible ; this was simply the "smallest" group that could contain the standard model. People have been working on SO(10), for example.

cheers,
Patrick.

[Nereid]

IIRC, the experimentally observed limit on the proton's half-life is ~1035 years, at least for several (one?) of the more 'likely' decay modes.

[Terry Giblin]

the proton decay rate should be of the order of a life time of 10^31 years, which has been falsified by experiment.



Lets assume the half-life on an electron, as estimated is 10^31 years, based on our current on going testing for detection of the first ever observed proton decay.

Is it not time to start considering alternative ideas and models

Regards

Terry Giblin

[Nereid]

Lets assume the half-life on an electron, as estimated is 10^31 years, based on our current on going testing for detection of the first ever observed proton decay.Why not simply do an experiment to measure the half-life of the electron? How do experimental results showing that the half-life of the proton is ~>1035 years lead to an estimate of half-life of the electron?Is it not time to start considering alternative ideas and modelsOf course! It's been obvious for some time that the Standard Model is in need of replacement/extension/etc! I doubt that there are any researchers active in particle physics who feel that the Standard Model is the end. :rolleyes:

[vanesch]

Of course one assumes that this symmetry is broken, and that the relevant bosons have a big mass (the "GUT" scale), which decreases this interaction rate. If one estimates this scale (that's where the 3 coupling constants of the standard model should unify) one arrives at something of 10^15 GeV. Using this value, the proton decay rate should be of the order of a life time of 10^31 years, which has been falsified by experiment. So that's where all the hassle came from.


I should add a few things. The GUT scale is in fact already build into the standard model (together with the experimental values of the coupling constants), as we know, at "low" energies what are the coupling constants, and we can calculate how they evolve (running of the coupling constants in renormalization) when we go to higher energies (a few low-order Feynman graphs are sufficient). The nice thing is that they all cross (the electroweak couplings rise, and the strong coupling falls) at about 10^15 GeV. They ALMOST cross, but not really. If they are the results of a broken symmetry, then at the scale of the symmetry, they should become equal to the one and only coupling constant of the grand unifying interaction. And now, the precision on experimental parameters is such that we know that they do not cross exactly at the same point.
Comes in supersymmetry. It is possible to twiddle a bit here, and then one can make the running constants cross exactly. I'm not an expert on this, but apparently, supersymmetry can also "inhibit" proton decay, so that its life time becomes longer than naively estimated. So proponents of supersymmetry say that SUSY can save GUT and that the long proton decay life time is an indirect indication. Others say that this is a bit too artificial twiddling to get out what people wanted to get out.

cheers,
Patrick.

[jtolliver]

The mystery of the asymmetry of matter-antimatter remains to be resolved. At the present time, no such a theory of resolution exist.
We dont know that there is an asymmetry between matter and antimatter, except in this portion of the universe. Most astronomical data is from photons emitted by far away sources. Antiparticles interactions with other antiparticles are the same as particles interactions with other particles. If some region of the universe consists of antimatter, astronomical measurements would not be able to determine that, since there is no matter interacting with it for us to compare it with.

[Nereid]

We dont know that there is an asymmetry between matter and antimatter, except in this portion of the universe. Most astronomical data is from photons emitted by far away sources. Antiparticles interactions with other antiparticles are the same as particles interactions with other particles. If some region of the universe consists of antimatter, astronomical measurements would not be able to determine that, since there is no matter interacting with it for us to compare it with.a) there'd be all kinds of fireworks from a zone of contact ... even the inter-galactic medium isn't empty, and cosmic rays pervade everything (no such fireworks observed); b) while not impossible for there to be regions of matter and regions of anti-matter in both of which there are stars, galaxies etc ... which don't ever get to an opposite region, there will be stars, planets, even galaxies that travel far from their parent cluster (no such megafireworks observed); c) cosmological models with this slight imbalance between matter and anti-matter fit observations well (I'm not sure models in which the matter and anti-matter are equal would fit at all).

[marlon]

I really don't get it Marlon. The proton is more likely to decay at higher speed !? Usually, at higher speed, decay is just lowered by lorentz contraction of time. Or : the fastest decay should occur in the rest frame !

I could concieve that there is a dynamical process occuring during the acceleration process.




Barionic number conserved through other conservation laws !?
Oh, by the way : is barionic number conservation not much better experimentaly tested than the other conservation laws (with regards to proton's lifetime. I have been checking PDG online, and I am not quite sure.) ?

This is the priciple of asymptotic freedom coming from renormalization. It states that the strong force gets weaker when the energyscale gets higher. The strong force gets stronger when the energyscale gets lower. This is why quarks are never allone in the QCD-vacuum. Wellcome to the world of Quarkconfinement

marlon

[humanino]

I don't see how asymptotic freedom could affect the stability of the proton.

Asymptotic freedom tells you that quarks look like free particles at high energy scales. Which scale ? In the context I am working in, Deep Inelastic Scattering (DIS), one typically has an lepton beam incident on an hydrogen target. The lepton exchange a virtual boson with (one of the quarks inside) the target. The energy scale at which one probes the hadronic structure is typically given by the invariant mass of the virtual particle. For instance, the mass of the photon exchanged. Upon selecting highly virtual exchanged bosons, one observes free quarks.

I am not working on experiments involving hadronic beams. However, I am still convinced that the decay of any particle is the fastest in the rest frame.

[Haelfix]

Again to nitpick, its possible that the proton can decay, even in the minimal standard model. Its just vanishingly small in principle, and again its only a theoretical argument and never been observed.

It has to do with baryon and Lepton # nonconservation from the electroweak sector first discovered by T'Hooft when he was studying topological effects on guage theories. Its also really hard to quantify, particularly when you add in GUT interactions (that also imply a proton decay) as you end up with monopole contributions that makes things a nice mess.

Despite many attempts to find a proton decay signature, it has still remained elusive. Perhaps the best indirect evidence that this is true lies in the theory and models of Baryogenesis and the emerging field of Leptogenesis.

But if the world was pure QCD, you would never find a single quark anywhere. The force would grow to infinity the further you pull them apart, and our naive guess would be satisfied.

[zefram_c]

Again to nitpick, its possible that the proton can decay, even in the minimal standard model... It has to do with baryon and Lepton # nonconservation from the electroweak sector first discovered by T'Hooft when he was studying topological effects on guage theories. Its also really hard to quantify, particularly when you add in GUT interactions (that also imply a proton decay) as you end up with monopole contributions that makes things a nice mess. This is new to me; would you care to elaborate? My understanding of the standard electroweak model is that quarks couple only to other quarks and leptons to leptons. How would this break down?

[Haelfix]

I couldn't find T' Hoofts remarkable paper on SLAC (its in physical review somewhere) upon cursory browsing..

But I did manage to find a few papers that talk a little about these effects.

Briefly:

http://arxiv.org/PS_cache/hep-ph/pdf/9608/9608456.pdf

For more emphasis on astrophysics:

http://arxiv.org/PS_cache/hep-ph/pdf/9603/9603208.pdf