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  1. P

    How do protons decay?

    The basic process I describe for two protons can easily enough be modified to cover the other possibilities. Basically, you can replace any proton in that process with a neutron as long as one of the positrons changes into an anti-neutrino; and, you can also replace every particle with its...
  2. P

    How do protons decay?

    I assume you're asking about B-violating decays specifically, as there are many B-conserving nuclear decays that are well-known. Generically, sphalerons should be applicable to any process where B changes by 3 and B-L is conserved, provided that the process correctly conserves electric charge...
  3. P

    How do protons decay?

    So far as I know, sphalerons are the only source of B-violation in the Standard Model.
  4. P

    How do protons decay?

    Whoa, didn't think I'd see this thread resurrected... Anyway, I didn't say that the chiral anomaly violates B, I said that the V+L violation from sphalerons is like what happens with the chiral anomaly in that it's an effect that isn't explicit in the model but, rather, comes about due to some...
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    Photon absorption

    I'm going to have to disagree with Bill_K. This should, in fact, be possible; but, it should also be such a highly suppressed process that, in practice, we should never have significant enough statistics to have a reasonable chance of seeing it happen. The problem is that changing flavors...
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    Photon absorption

    It's actually pretty simple. In addition to conservation of energy and momentum, each particle must satisfy m^2 = E^2-|\vec{p}|^2. (Note that I'm using natural units where c=1. If you want to use conventional units, multiply every m by c2 and every p by c.) For the photon, which has m_\gamma...
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    Electron change?

    Or, we could just admit that Newton's original formulation was maybe not the best way to express the dynamical idea in the first place. Even in classical physics we can find places where F = ma doesn't work. But, \vec{F} = \frac{d\vec{p}}{dt} will; and, it will continue to work even in SR...
  8. P

    Electron change?

    So basically, the article is saying that relativistic mass is useful for hiding the places where relativistic dynamics are actually different from what would be expected classically. Again, though, most of those cases come right back to insisting that momentum is mv. And, the invoking of GR is...
  9. P

    Electron change?

    It doesn't. Energy increases without bound as speed approaches c. In the early days of relativity, some physicists found it convenient to define a quantity called "relativistic mass", which is really just energy divided by c2, because its use made the relativistic formula for momentum look...
  10. P

    Speed of light and dark matter

    Not at all. I'm just saying that the reporting of this result as evidence for dark matter is not a responsible representation of the data. I happen to think the AMS is an awesome experiment; and, I was actually quite excited when the shuttle mission was added in order to deliver it...
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    Speed of light and dark matter

    Despite the significant hype, the AMS results in no way point to dark matter any more than previous data about the same phenomenon had. The positron excess under discussion was actually first noted about 5 years ago by the PAMELA experiment; and, there was a flurry of papers at the time...
  12. P

    Speed of light and dark matter

    Your mistake seems to be in the presumption that all transverse waves must be mechanical. But, there's no reason for such a presumption. As DaleSpam points out, transverseness implies polarizability; and, I'll just add that the dynamics of the electromagnetic field require that, in the absence...
  13. P

    Speed of light and dark matter

    What makes you think that causality is fundamental in the first place? More to the point, though, all I've been trying to point out throughout this discussion is that causality is a separate issue from the validity of SR, as SR is simply about Poincare invariance. I personally suspect that...
  14. P

    Speed of light and dark matter

    Who said anything about violating Lorentz invariance? The simple statement I gave not only entails Lorentz invariance, it also requires translation and time translation invariance, giving the actual symmetry group of SR - Poincare invariance. Tachyons do not violate this. They only violate...
  15. P

    Neil Armstrong and unfaithful wives

    This appears to be the same as the blue forehead room puzzle; and, the answer has been discussed in some depth there. Suffice it to say .
  16. P

    Speed of light and dark matter

    This is simply not correct. At its most basic, all that special relativity states is that the spacetime interval between any two events is the same in all inertial frames of reference, where the spacetime interval is defined to be s = (c\Delta t)^2 - |\Delta \vec{x}|^2. That's it. This only...
  17. P

    Speed of light and dark matter

    The way you're thinking about this is a little inside out. The universal speed limit is a property of the geometry of spacetime. The fact that light travels at the speed limit really is telling us something about light, not something about the speed limit. What it's telling us is that light...
  18. P

    How do protons decay?

    It does conserve them perturbatively. But, in a similar way to how a chiral anomaly can break what looks like a good symmetry of a model once you consider quantum corrections, non-perturbative gauge configurations can violate certain global symmetries. The upshot here is that what looks like a...
  19. P

    How do protons decay?

    Strictly, they violate B+L while conserving B-L. Think of them as creating an effectively coupling of three quarks and one (anti)lepton.
  20. P

    How do protons decay?

    If we're going to get into free proton decay, it should probably be noted that the standard model actually has a channel for proton decay. It's just incredibly suppressed (even more than the GUT modes would be), as it involves the non-perturbative electroweak instanton configurations known as...
  21. P

    Can we destroy a proton?

    But, every free baryon eventually decays down to a proton. The only way to get rid of a proton is with an anti-proton (or other anti-baryon). Well, that is, unless you're at sufficiently high energy (and, probably, density) that non-perturbative weak processes are accessible, in which case...
  22. P

    Do ALL hadrons eventually decay into protons?

    Yes. They're pretty much inaccessible at ordinary scales. But, they're pretty strongly implicated to have some involvement in the matter/antimatter asymmetry. To wit, the availability of sphaleron transitions allows the entire asymmetry to be generated in either the baryon or lepton sector...
  23. P

    Do ALL hadrons eventually decay into protons?

    This is actually not correct. The Standard Model, by itself, has non-perturbative gauge configurations called "sphalerons" which violate both the conservation of baryon and lepton numbers, but leave the difference between the two conserved. In other words, these processes can convert three...
  24. P

    Higgs field and graviton

    If gravity were somehow a result of the Higgs, light would be totally unaffected by gravity, since the Higgs does not couple at all to photons. The trouble is one of the very first pieces of corroborating evidence for GR was the deflection of starlight by the sun as observed during a solar...
  25. P

    The Blue Forehead Room Problem

    You are misunderstanding. In the analysis, P2 never makes assumptions about P1. The entire discussion subject to assumptions being made by P1. To wit, P1 must consider what behavior he expects from the others in the room if he has a dot and what behavior he expects from them if he does not...
  26. P

    Why does popular science say that Energy is a form of Mass because of E = mc^2 when

    If they say that, then they have it exactly backwards. The correct statement is that mass is a type of energy; and that E = mc^2 states how much energy is associated with mass m. The statement needs to be made in this way specifically to be clear that energy due to motion is not in any way...
  27. P

    Feynman Diagram question

    Note, though, that the reverse is not true. There is at least one type of situation in which a Z cannot be replaced by photon - interactions involving neutrinos.
  28. P

    Higgs Boson and Dark Matter / Dark Energy

    field =/= particle. The Higgs particle has a mass of 125 GeV and decays away very quickly. The Higgs field is ubiquitous throughout space and it (or, stricly, its vacuum) is what is responsible for the masses of other fundamental particles. The field does not, itself, have mass; and, its...
  29. P

    2 questions about Neutrino oscillations

    At least 4 mixing parameters. If neutrinos turn out to be Majorana particles, there will be 2 extra CP violating phases in addition to those 4 parameters.
  30. P

    Is energy conservation necessary?

    Poincare invariance implies conservation of energy (also, momentum, angular momentum, and the quantities which serve as the generators of boosts from a group theoretic perspective but which don't, to my knowledge, have any generally accepted name). Remember that Noether's theorem relates...
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