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Higgs particle, supersymmetry and dark matter.

  1. Sep 17, 2008 #1
    Could someone help explain how these are related?
    I kind of understand the Higgs particle/field. It is believed to be the reason why fundemental particles (fermions and bosons) have mass.

    So, then I read that one of the problems with the Higgs field is that if it is true things should be much more massive than they actually are.
    The paper I was reading stated that while the Higgs particle would be a nice find, and that many physicists believe to find it, it would be even more important to discover supersymmetry.
    Which kind of confused me. Ever where I read and on TV they keep talking about the Higgs particle. I don't recall hearing too much about Supersymmetry. I tried reading up on it but just got more confused.
    Something about how each particle will have a shadow particle that is more massive than the initial particle.

    If someone has a simple way to explain supersymmetry and how it relates to the Higgs particle I would greatly appreciate it.

    Also, does this mean that even anti-particles would have a superparticle as well?
    And are these superparticles believed to be what dark matter is composed of?
    How does the superparticle become more massive in the Higgs field, but the matter we interact with isn't as massive?

    Thanks.
     
  2. jcsd
  3. Sep 17, 2008 #2

    malawi_glenn

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    Supersymmetry predicts more than one Higgs boson. The reasons for why you introduce a SUSY theory are:

    i) Dark matter, we need heavy particles which does not interact "strongly" with electromagnetism
    ii) Unification of forces (weak,strong,EM)

    SUSY predicts many new particles, which are super-partners to the SM particles. And antiparticles such as positrons will have a superpartner aswell. The dark matter is then supposed to consist of the most long lived (stable) superparticles, with the neutralino as the strongest candidate of this. Since also the higgs boson will have superpartner(s), the higgsfield and interaction which give rise to mass also becomes more complicated.
     
  4. Sep 17, 2008 #3
    There are divergent contributions to the Higgs mass unless there is some special cancellation of the higher terms. (This is referred to as the hierarchy problem if you wish to read more.) One possible solution is supersymmetry, which would garauntee such cancelations.

    Yes.

    The lightest super particle has indeed been considered a candidate for dark matter.

    This depends on the details of how supersymmetry is spontaneously broken. Finding the higgs alone will probably not be enough to answer this question. We would need to find something that gives us more direct confirmation / access to information on super symmetry.
     
  5. Sep 17, 2008 #4
    Oops, looks like we posted at the same time.

    I was not aware of this. Is this where the discussion of the charged higgs comes from, or is that something else? (How would these higgs bosons differ from each other?)

    Edit: At least in the minimal supersymmetric model there is only one higgs boson, correct?
     
    Last edited: Sep 17, 2008
  6. Sep 17, 2008 #5
    No, this is incorrect.

    You may blame me with only providing references to you.

    Minimal Supersymmetric Standard Model
    Supersymmetry for Alp Hikers
     
  7. Sep 17, 2008 #6
    So, sparticles wouldn't make up all of the dark matter?
    Only the lightest sparticles (neutralino) are currently candidates for dark matter?


    So, sparticles in general interact more strongly with the Higgs field than particles that we are more familiar with. And this might account for the fact that particles aren't as massive as we would expect them to be. - - Is any of this on track?

    Thanks.
     
  8. Sep 17, 2008 #7
    Yes and no. Yes because indeed, only the lightest one would be stable (for sure). No because in principle, any electrically chargeless sparticle/particlino does the job in contributing to dark matter as long as it has not decayed. For all that matters, you could also have lots of neutrons around making up dark matter, provided those neutrons had a reason not to decay.
     
  9. Sep 17, 2008 #8
    Really?
    That's some cool stuff.
    So technically, if there were a way to keep a neutron stable, disallowing its decay... neutrons could then be a candidate to comprise some of the dark matter?
    As long as the particle doesn't interact with the electric and magnetic fields that permeate space it could fall under the scope of dark matter?

    Also,
    particles and sparticles both interact with the Higgs field (if it exists), sparticles interact more strongly (??). But only particles interact with electric and magnetic fields while sparticles don't. Do sparticles or dark matter interact with gravitational fields? And, is it likely that sparticles or dark matter have their own unique fields that they interact with that we are unable to?

    Thanks again.
     
  10. Sep 17, 2008 #9
    Wow, I was really misunderstanding part of that.
    Thanks for the very detailed response.

    I'm still not understanding parts of this, so I will clearly need to read more. But one more quick question: In order for the anomoly to be cancelled, does this mean the two higgsino's need to have the same mass? Is there something that garauntees this?


    Well, the main point was (I believe) merely that anything massive and weakly interacting enough would be a dark matter candidate (it doesn't need to be a supersymmetric partner particle).

    I heard a talk recently from a cold dark matter search. They have been able to rule out things interacting as strongly as neutrons. The searches are getting quite impressively sensitive.

    The charged ones will still interact with EM fields. Their electric charge property is no different than our 'ordinary' particles.

    Yes, all particles have energy and must therefore couple gravitationally.

    Hmm...
    As you can probably tell, this really isn't my field of physics. So I don't know, but that is a neat question.
     
  11. Sep 17, 2008 #10
    Jorge,
    You're saying dark matter and supersymmetric particles like they are two different things.
    Supersymmetric particles, if we do find out that they exist, are dark matter. Because sparticles are massive, weakly interacting, stable, and neutral. Exactly what dark matter is.
    Maybe you didn't intend on saying them seperately, but it does sound that way.
     
  12. Sep 17, 2008 #11
    First you need to accept the hypothesis that the lightest supersymmetric particle is absolutely stable. This is far from trivial and you don't even mention it. Second, even accepting this hypothesis, by no means does it necessarily imply that all dark matter is made up of superparticles. Why do you claim that superparticles are better a candidate than the QCD axion for instance ? Finally, dark matter is not all possible superparticles. So in short, yes, superparticles and dark matter are definitely two different things, and will remain so even if dark matter is proven to be made only of superparticles.
     
  13. Sep 17, 2008 #12

    Vanadium 50

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    No. In fact, one of the things we are absolutely sure of is that we don't live in a supersymmetric universe. In that universe, particles and sparticles would have exactly the same mass, and we would already have discovered all of the sparticles.

    So if there is supersymmetry, it's only an approximate symmetry. However, we don't need the radiative corrections to the Higgs mass to be zero - we just need them small enough so that the Higgs mass doesn't get too large. So an approximate symmetry is good enough. So long as superparticles have masses near the electroweak scale: 100's of GeV, this is not a problem.
     
  14. Sep 17, 2008 #13
    I think you misread my question. (Or I'm really misunderstanding your answer.)
    I didn't ask about (or expect) the particles and sparticles to have the same mass.

    humanino pointed out to me (and I'm still reading up on more of it), that even in the minimal supersymmetric model there are two higgs bosons. This is so that there are two higgsino's which allow cancelling of a gauge anomaly. So thisn't isn't talking about the hierarchy / higgs mass problem either.

    I asked if the two higgsino's need to have the same mass to cancel this gauge anomaly, and if anything garauntees this. Both of these energies should be beyond the symmetry breaking and thus there should be supersymmetry at this scale, no? Regardless, wouldn't they need to have the same energy in the pre-broken theory for the gauge anomaly to be cancelled?
     
  15. Sep 17, 2008 #14
    Hello humanino,

    I never said that all dark matter is made up of superparticles.
    I said that superparticles are dark matter. Me having to accept that the lightest supersymmetric particle is absolutely stable is the same as you having to accept that all dark matter is absolutely stable. Even if the those light sparticles are unstable, it doesn't mean that they couldn't fall under the purview of dark matter. Same as saying that we have no proof that all dark matter is stable. So, pointing to a sparticle and saying, "it might not be absolutely stable" doesn't show that it wouldn't be dark matter.
     
  16. Sep 17, 2008 #15
    Let me make it clear that I wanted to point out 2 things : neither all superparticles are dark matter, nor all dark matter is necessarily superparticles. So dark matter and superparticles are, indeed, two different things, at least as far as we know. Now as for
    This is not a given until we know what it is. It might very well be dynamical, unstable and re-generated permanently.
     
  17. Sep 17, 2008 #16
    Hello humanino,

    The reason why I stated that was that you seemed to be claiming that light sparticles may not be dark matter because they might not be stable.
    I said, that would need to be accepted with the claim that all dark matter is stable.
    But we don't know that. It's possible that some dark matter is unstable. Take a neutron. One, from a vantage different than ours, might state that all "light" matter (what we interact with) is stable. However, they can't interact with the matter and only have indirect support for the existence of the type of matter we are familiar with. We know that our matter is stable for the most part but there also exists types of matter that are not as stable.

    My statement wasn't supposed to be a declaration of the definite stability of dark matter. It was to show that even if light sparticles are unstable that doesn't mean they are exempt from being considered dark matter.
     
  18. Sep 18, 2008 #17
    Okay, I'm a bit more confused now.

    So is my understanding correct:
    We believe that dark matter exists because we can infer its existence via indirect means (like the Bullet Cluster). We know that it quite likely is stable, weakly interacting, neutrally charged, and very massive. We also have an issue with the mass of particles we do see and interact with. This can be account for with the Higgs particle/field. If this Higgs field exists it would help us understand why fermions have mass. But, we should expect fermions to be much more massive than they actually are. So with the theory of supersymmetry each fermion and boson will have their partner. A fermion will have a sparticle boson, and each boson will have a sparticle fermion.
    These sparticles MAY be dark matter. But even if discovered it won't show that all dark matter is made of sparticles.

    Is any of this on point?
     
  19. Sep 18, 2008 #18

    malawi_glenn

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    I would give you full point on an exam ;-)

    But there are light (MeV) dark matter models, which have particles interacting strongly etc, like this one: http://en.wikipedia.org/wiki/Light_Dark_Matter see "Scalar Dark Matter candidates" (I can link you to articles by C.Boehm if you want, this is a part of my diploma work)
     
  20. Sep 18, 2008 #19
    Thanks for the response and the link.
     
  21. Sep 18, 2008 #20
    So technically,
    if I grow a mustache there will be the sparticle partner of this mustache called a 'smustache' (or mustachio). And this smustache will be significantly more massive than my actual mustache? Will the massiveness of this smustache be expressed in the thickness of the mustache?
     
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