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Posts posted by BenTheMan

  1. Absolutely. The New Scientist article says something like "Until recently, lattice QCD calculations concentrated on the virtual gluons, and ignored another important component of the vacuum: pairs of virtual quarks and antiquarks."...not that I trust whatever journalist who wrote this knows what they're talking about.


    But this doesn't seem to mesh with the "quenched" approximation.


    I probably looked too quickly at the article :)

  2. It is so annoying when papers are published in Science rather than a more respectable journal, because I can never read them! Does anyone know what lattice action they used? The staggered action?


    Yeah I don't know why they published in AAAS. I read the paper, and I didn't see anything about a proton mass, and I can't recall all of the lattice terminology---I do recall that they're using the quenched approximation, which seems a bit odd. In this approximation, you turn off the quark-anti-quark virtual pairs (I seem to recall), but the New Scientist article makes a big deal about the fact that this is what they were calculating.

  3. Fine-tuning theories walks the dangerous line between ad hoc hypothesis and making a theory fit the data. I'd say that if they had to fiddle around to get a Higgs mass they like, then they can't use the Higgs mass as evidence for their theory. However, if the same fine-tuned parameter then allows additional accurate predictions, then these would be evidence.


    Well, I don't know if "making the theory fit the data" is always a bad thing :) I'm sure if you could explain electroweak symmetry breaking without a higgs, in a similarly economical fashion (i.e. not "extended walking technicolor"), then you'd be invited many places to give many talks. The situation with the higgs mass is a bit intricate---the ONLY way we know how to break symmetries is to give scalar particles VEVs. Naturally, scalar particles are heavy, but we have a spontaneously broken symmetry at a low scale. So what can we do? Similarly, you could ask why the electron should have such a small mass and the top quark such a large one. Or why all three neutrinos have more or less the same mass, but none of the quarks and leptons do.


    PS Sverian---do you know a good review of the precision electroweak observables/data? I have this Phys Rept article by Heinemeyer, Hollik and Weiglein.

  4. Maybe there's not much discussion because people don't understand what "tuning" is. This has been my experience, at least---most non-physicists don't see a real problem with it because they don't understand the problem.


    The example I use is this:


    A + B - C = D


    Suppose I tell you that A, B, and C are all real numbers that are between 0 and 10. What do you expect D to be? Or, conversely, given all real numbers between 0 and 10, what would a random selection of A,B, and C produce for D?

  5. BTW I understand Hawking will vacate his Lucasian professorship at Cambridge come October 2009 or thereabouts. If his retirement from that position is actually in the works, have you heard anything about what he might be doing thereafter----a move to some other institution?


    There was a rumor that he was going to move to the Perimeter Institute.

  6. However, this is really an aesthetic problem. In reality each parameter must have one value, so why should one value be regarded as any less likely than any other. I am curious as to what non-physicists' views of fine-tuning would be - do you think it is a problem?


    I think, if you're willing to accept a fine tuned higgs mass, then you have a real problem model building. If you're willing to throw out "naturalness" as a criteria, then publishing hep-ph papers should be easy :)


    So how do you build models, if you only have to satisfy the LEP data and the WMAP bound?

  7. There do exist various competitors to GR, several of which make predictions nearly indistinguishable from SR/GR. To be viable, they of course have to be nearly indistinguishable from SR/GR because of the mountain of evidence that agrees with SR/GR. Gravity Probe B falsified some of these alternatives, but not as many as it should have.


    Agreed. One has the TeVeS (Tensor, Vector, Scalar) theories, Modified Newtonian Dynamics, etc etc. I wouldn't so much call these theories "competitors" as most people don't take these theories too seriously. Sure they're possible, but they don't have a lot of support in the community, as far as I can tell.

  8. As n tends to infinity this sequence gets infinitely boring.


    Does it always? IF you have simple harmonic motion, then yeah, all you get is a long series of sines and cosines. But what if you have some other function? Presumably you'd reach a point where you had something like


    [math]\frac{d^n v(t)}{dt^n} = const[/math].


    You're saying there's no physical significance in this?


    Edit: I thought tex tags worked here?

  9. Impossible; how can an experiment be conducted in more than one frame (i.e. between frames)? Special/General Relativity makes a prediction that is uncheckable.


    There are a uniquie (?) set of predictions which follow from SR/GR, NONE of which has ever been falsified. In essence, you are saying that GR is wrong because you don't like it. Very scientific.


    PS---I don't know that the predictions of GR are unique, and in fact, I know they aren't. You can build a sufficiently complicated theory of gravity a la Newton by adding epicycles or something, probably.

  10. But if you make V2 greater than C2 for a photon, it becomes 0/n>0. Zero divided by anything is zero, so that should mean that a photon should be able to travel much facter than C without requiring infinite energy.


    If my math is wrong, somebody convince me.


    Your math isn't wrong, however, your fizix leaves much to be desired.


    The first postulate of special relativity (which you've invoked by writing down your formulae) says that no object can travel faster than the speed of light.

  11. Can Fujikawas's method be applied to the V-V-A anomaly?


    This question has been turning over in my mind for a few days. I guess unparticle fermions would enter the path integral in the same manner, but I don't know---I've never seen someone write an un-path integral.

  12. You seem wise on this Ben




    I studied unparticles for a while. Basically, it's a kind of neat idea that doesn't really solve any problems or anything. You have to be famous like Georgi to propose these sorts of things.


    I don't have nearly as deep an understanding of these things as you would give me credit for. It has been a while since I've read any unparticle papers, so I will have to go back and spend some time going over notes.

  13. I would also point out that most of the literature on unparticles likely contains wrong assumptions. In particular, I think it was Terning and some others who showed that the scaling dimension of an operator in a theory with a conformal symmetry has to be greater than 3, I think. It might also have been in the paper by Galloway, Martin, and Stancato.


    Either way, I think that there is a lot of the literature that should be viewed with suspicion.

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