Wednesday, January 8, 2014

Random Physics Thoughts

This post contains some unsourced random musings on physics, some of which are trivial observations, others of which may illustrate my ignorance or constitute category errors, and none of which necessarily even deserve the status of conjectures, as that implies some confidence that a proposition is true, rather than merely throwing an idea "out there" to put it on paper for future consideration.

* In the Standard Model, baryon number (B) is conserved and lepton number (L) is separately conserved, and there is also on obscure kind of interaction which can't be illustrated in a Feynman diagram, in which only B-L is conserved.

* But, the number of fundamental bosons present in the universe is not conserved.  It is interesting that there is not conservation of fundamental boson number even though there is indirectly something akin to composite boson number via baryon number conservation.  Would mesons, which are baryons made of fermions, be a good place to look for possible violations of baryon number by analogy to non-conservation of fundamental bosons number?

* There is also not a fixed number of fermions (because baryon number assigned positive numbers to particles and negative numbers to antiparticles, and lepton number similarly assigns positive numbers to particles and negative numbers to antiparticles).

* Is there any process in which we can determine that we have assigned the correct charges to what we view as particles and antiparticles respectively? In other words, how do we know, that up type quarks with positive electric charge, down type quarks with negative electric charge, and charged leptons with negative electric charge are matter, while up type quarks with negative electric charge, down type quarks with positive electric charge, and charged leptons with positive electric charge are antimatter?

Obviously, the decision to call one of these groups matter and the other antimatter is purely arbitrary, although the stylistic choice to call the kind of charged fermion that makes up 99.9999999999%ish percent of all charged fermions in the universe matter, and the kind of charged fermion that makes up one part in 10^-10ish of all charged fermions antimatter is the obvious and eminently sensible way to make that arbitrary decision.

But, is there any reason, for example, that up type with positive electric charge quarks could be matter, while down type quarks with negative electric charge could be antimatter?

Suppose that a down quark emits a W- boson and becomes an up quark, and the W- boson then decays to an electron and an electron anti-neutrino in simple beta decay.  If an up type quark with positive electric charge were matter, but a down type quark with negative electric charge were antimatter, then ordinary beta decay via the weak force would violate conservation of baryon number.  So, the matter-antimatter designations of quarks in the Standard Model have to be as they are to be consistent with each other.

What about the other side of the beta decay process, however?  Suppose that negatively charged leptons were antimatter and that positively charged leptons were matter.  In simple beta decay, you could get an anti-electron and an electron neutrino, which would still conserve lepton number, if the matter-antimatter assignments were reserved.  Indeed, separate lepton number conservation implies that matter-antimatter assignments for leptons, in general, are separable from matter-antimatter assignments in the baryon sector.

If the ordinary charged leptons were considered to be antimatter, and the ordinary quarks were considered to be matter, then there would be no matter-antimatter asymmetry in the universe in the charged particle sector.  The baryon number of the universe is equal, to a high degree of precision that could easily be perfect due to conservation of charge in baryogenesis and leptogenesis, to the number of charged leptons in the universe.  In that case, all of the matter-antimatter asymmetry in the universe would arise in the electrically neutral neutrino sector.

* The W+ boson and W- boson are antiparticles of each other.  Is there any principled way to state that one is matter while the other is antimatter, or is that a distinction that does not apply to fundamental bosons at all?

Both W+ bosons and W- bosons can be emitted by ordinary matter quarks.  A W+ boson will frequently decay into a charged lepton with positive electric charge which is ordinarily called antimatter, and a corresponding neutrino (as opposed to a corresponding antineutrino) in order to preserve lepton number.  A W- boson will frequently decay into a charged lepton with negative electric charge which is ordinarily called matter, and a corresponding antineutrino.

Since W and Z boson decays produce equal numbers of matter particles and antimatter particles, and since W and Z bosons can be emitted by both matter particles and antimatter particles, it is probably most appropriate to say that they are neither matter nor antimatter (something also true of photons).  There is an irrational part of me that is tempted to think of the charged lepton that is more important than the neutrino produced in a W boson decay, and hence to link of the W- boson as matter and the W+ boson as antimatter.  But, upon reflection, that view simply must be wrong.

* If there truly only one Z boson particle, or are there Z bosons and anti-Z bosons which we simply lack the capacity to distinguish from each other.  The photon analogy, and the fact that the W+ mass plus W- mass plus Z mass equals Higgs boson mass divided by two formula suggests that there are no anti-Z bosons, because otherwise the formula would be W+ mass plus W- mass plus two times the Z mass.  The absence of right handed neutrinos also suggests that there are no anti-Z bosons.

* How can a neutrino be its own anti-particle, and hence have Majorana mass, if its very existence was based upon its need to conserve lepton number in beta decays by balancing out the lepton number of the charged lepton created in those decays?  This is one of the reasons, rightly or wrongly, that I favor the view that neutrinos have Dirac mass, but not Majorana mass.

* The matter or antimatter status of a quark or charged lepton can be determined simply from its electric charge.  In neutrinos, of course, the only way to distinguish neutrinos from anti-neutrinos observationaly is their parity.  If it has left parity, it is matter.  If it has right parity, it is antimatter.

In order for a theory in which there are right handed neutrinos that are direct counterparts of the Standard Model neutrinos with identical masses in the same generations, a particles matter-antimatter status would have to be a completely hidden variable (testable only by seeing if it interacted with W or Z bosons, I suppose), rather than a property determinable by observation of some other property of the particle.

If, as I have supposed, massive fundamental particles acquire their mass through their weak force interactions, however, since all particle types which have no weak force interactions have no rest mass and all particle types which have weak force interactions have rest mass, then sterile neutrinos, if they are really sterile, ought to be massless.

* Do W bosons, Z bosons and/or gluon have the properties of helicity and polarization that photons do?

* How do quarks know how to produce gluons with the right color charges?  Alternately, what happens, for example, to a blue-antired gluon emitted by a blue quark, if there is no red quark around to receive it?

* Is color charge conserved?  I think that it is.  How would we test for that experimentally?

* Gluons carry color charges including anti-color charges.  Am I right that gluons always carry a color charge and an anti-color charge providing it a net balance of matter affiliated charge and antimatter affiliated charge?  If so, gluons are matter-antimatter neutral but in a rather more dynamic way than other bosons.  Maybe not matter-antimatter neutral so much as simultaneously matter and antimatter objects.

* One often thinks, lazily, of color charge as a thing, a particle of its own, that quarks carry around singly and that gluons carry around in pairs.  But, this is wrong, because if it was right, there would be nine kinds of gluons instead of eight.  This in turn makes one wonder if maybe color charge could be a topological feature in three dimensions of a quark or gluon.

* Would it be possible for one to make a W+ boson couple to an up type quark, or to make a W- boson couple to a down type quark?  Does anything but electromagnetic repulsion prevent this from happening?  Could very strong electromagnetic repulsion at very short ranges always prevent this from happening?

* Some days I'm still not entirely clear on why electrons don't spiral down into protons, although I guess conservation of momentum has something to do with it.

* Does gluon source rest mass in a composite particle behave any differently than Higgs boson source rest mass in a composite particle?  Apparently not, but why?

* Supposedly, a hypothetical proton made up of massless quarks would have a mass of 870 MeV or so, extrapolating from the QCD equations.  But, what if that's wrong.  What if gluons actually amplify the rest mass of individual quarks, but can't create rest mass in the absence of a particle that has Higgs boson source rest mass?  If gluons merely amplify the rest mass of individual quarks, then glueballs would have no rest mass.  But, if gluons really do create rest mass in composite objects via their binding energy without Higgs boson interactions, then glueballs would have mass, as predicted.  At some point, does a failure to observe massive glueballs imply that the accepted theory regarding how mass is generated in QCD is wrong?

* All fundamental bosons have some mass-energy, even those with no rest mass like photons and gluons. Each fundamental fermions of the same type (twelve possibilities) and the three kinds of massive fundamental bosons has an exact rest mass associated with it that always stays the exactly the same for all particles of that type (subject to running masses with energy scale).  Given matter-energy conservation, therefore, the only possible source of energy that a fermion can call upon to emit bosons like photons and gluons is kinetic energy or potential energy from its position in fields.  What if an electron is perfectly at rest with no kinetic energy?  How can it emit photons?  How can it have electric charge if it doesn't emit photons, however?  Does it follow that an electron or other charged particle is incapable of being perfectly at rest with no kinetic energy?  Do hot magnets have different amounts of electro-magnetic charge than cold ones as a result?

* I strongly suspect that the possible 1 eV-ish sterile neutrino predicted from reactor anomalies is eventually determined not to exist.


Tienzen said...

You have hit two very important issues for the advancement on going beyond the Standard Model.
1. The arbitrariness of naming the matter over the anti-matter.
2. Why the fermion numbers are conserved while the boson numbers are not.

By resolving these two issues, most of the unresolved issues in physics will be resolved.

For the issue one: in the G-string physics, the M-string can produce 8 G-strings, but they alone cannot produce the ‘known’ matter particles, such as proton and neutron. An anti-M-string is needed for producing 8 anti-G-strings. And, proton is composited of parts from both the M-string and anti-M-string. That is, the anti-matter is not the mirror-like symmetry partner of matter but is complimentary partner of matter. See “BaryonGenesis, the master-key of all mysteries ( )” for details.

For the issue two: the whole thing is about how to divide the ‘pie’. For the American constitution, that pie is divided into three parts. Then, the numbers of courts is defined by the constitution (the system) while the numbers of plaintiff has no restriction. For the universe, its pie is divided into two parts, the ocean (dark energy) and the land-‘mass’-continent. This land-‘mass’-continent is further divided into 48 ‘dominions’ (48 fermion particles) with ‘equal’ share while the manifested fermion particles are only the name tag (or pimple) for the dominion. That is, only fermions have the right to share the land-‘mass’-continent while the ‘bosons’ are the servants (similar to the plaintiffs in the court system) which are already counted in their masters’ dominions. With this way of pie-sharing, not only the issue of boson numbers is resolved but the dark mass mystery is also no more. See “Dark matter, mystery no more, part 2! ( )”.

andrew said...

Sorry, but the whole physics as con law analogy just doesn't do it for me. Save analogies for instances that are vaguely analogous in some more essential way. I have no idea what you are talking about and after reading that, I am disinclined to learn more.

Anonymous said...

On a serious note:
I have loads of similar questions. Here's my best attempt at answering only some of your questions.

(1) The force carriers (photons, W+, W-, Z, and the 8 gluons) are virtual particles. If they have an energy of deltaE, then they can last for a time less than h/deltaE, where h is Planck's constant. As virtual particles, there's no way one could conserve force-carrier-boson-number.

(2) The force carriers don't have anti-particles. There's no anti-particle to the photon, and the 8 gluons don't have anti-particles. W+ is not the antiparticle of W-. In the complex plane, think of Z as (1,0), W+ as (-0.5,0.87), and W- as (-0.5,-0.87), i.e. unit vectors with 0deg, 120deg, and 240deg.

(3) The best way I can think about explaining the force carriers is the following: the force carriers are the wrinkles that radiate out in space-time when you twist the fabric of space-time at a discrete point (i.e. where there's a fermion.) You can visualize the effect of an electrically charged particle by making a twist in the center of a napkin or a tablecloth. The wrinkles that radiate out are like the photons. It's harder to visualize the W/Z particles because the wrinkle in space-time is not symmetric in each directions and you need more than 2 dimensions to visualize.

(4) You raise an excellent point that a sterile neutrino should be almost massless. The rule of thumb is that the more means of force interaction, the heavier the particle. Quarks are heavier than electrons, which are heavier than left-handed neutrinos. Quarks can interact with all of the 4 forces, electrons with 3, and left-handed neutrinos with 2. Right handed neutrinos can only act with 1 force. Following this line of thinking, a particle like a sterile neutrino should be less massive than neutrinos, and that means extremely light.

(5) This would imply that the 'dark matter' candidate with ~2-8 keV would have to be a mu or tau neutrino of the left handed kind...or some particle that is not predicted by the SM. Not a (likely) nearly massless sterile neutrino.

(6) The matter / anti-matter distinction is tough, as you mentioned. But it's possible that the universe is predominantly anti-matter neutrinos. If dark matter is left-handed mu or tau anti-neutrinos, then most of the (non-dark-energy) universe is anti-matter neutrinos followed by matter quarks and electrons. The distinction is likely arbitrary; however, I'm not 100% sure because physicists used to think that there's no way to tell left from right in the universe until the ~1950s/60s.

Keep asking these questions because I don't see enough people doing this these days.