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I 5 Higgs-like bosons -- natural supersymmetry required?

  1. Oct 4, 2016 #41


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    Too many questions for one reply close to bedtime. I'll take a stab at the easiest one. Don't have the focus to write sufficiently precisely about quantum corrections to the Higgs vev while half awake without a grave risk of flubbing it.

    I would be stunned/flabbergasted and highly skeptical.


    Even if SUSY particles or Extra Dimensions do exist, they almost certainly can't be "just around the corner" such that they could appear clearly at the LHC in the near future. Those phenomena would pretty much have to start giving rise to experimental hints of their existence orders of magnitude before they were observed directly because there are multiple observables in HEP that are sensitive to physics at much higher energy scales.

    While the direct exclusions on phenomena like these are in the low single digit TeV zone right now at the LHC, the indirect probes of higher energy scales pretty strongly disfavor this kind of phenomena much below 10 TeV. At best, you might can an inconclusive glimpse of it towards the end of Run 2.

    What you would expect instead is a mosaic of correlated deviations from SM predictions in multiple channels. For example, if SUSY exists, we should be able to experimentally observe material differences between the SM beta functions and the running of the SM coupling constants that are observed long before we can actually discover a new SUSY particle. Anomalous magnetic moments are also a pretty powerful indirect probe of high energy scale physics.

    Still, if that did happen, obviously I'd have to recalibrate my expectations just as physicists did decades ago when the muon suddenly appeared unheralded and unexpected, when SR and GR fundamentally altered our understandings of time, matter and energy, when the singularities predicted by GR turned out to be physically meaningful (even if they turn out not to be true classical singularities) instead of merely mathematical pathologies of the theory, when scientists discovered that quantum physics is inherently stochastic. It would dramatically change the entire field.

    Probably the best prospects out there right now for new physics are the multiple experimental hints of lepton flavor non-universality in interactions involving charged leptons. But, that particular example is tainted by the fact that other experiments in which any reasonable kind of lepton flavor non-universality that really exists should also manifest place extremely tight bounds on that possibility. It is extremely hard to come up with a sensible way to distinguish experiments that hint at non-universality from those that rule it out strictly in any plausible way.

    If the LHC or some other experiments do see BSM physics, it is more likely to be something that hasn't been analyzed to death by theorists because our currently event cuts, experimental designs, etc. are specifically calibrated to be as sensitive to those theories as possible and have, so far, come up with nothing. Some of the phenomena I think we might be more likely to stumble into more or less unexpectedly would include:

    1. A new boson that mediates neutrino oscillation.
    2. Definitive proof that space-time is not perfectly smooth and continuous and instead has quanta scale non-localities.
    3. A gravity modification arising from an effort to develop a quantum gravity theory that explains most or all dark matter phenomena and at least some dark energy/cosmological constant phenomena. Put another way, I expect the biggest deviations from GR in a quantum gravity theory to be in the weak fields and not in the strong fields.
    4. Extremely rare and short lived top quark hadrons.
    5. Inconclusive early indications of a composite nature for one or more "fundamental" particles of the SM that overcomes previous "no go" evidence with a novel loophole of some kind.
    6. A new unpredicted phase or state of matter analogous to Bose-Einstein condensate or quark-gluon plasma that emerges in some characteristic boundary conditions with surprising new properties.
  2. Oct 4, 2016 #42


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    Shorter answer: SUSY is a really crude and artificial way to tame quantum corrections. Its like a de eux machina resolution of a conflict in a play. I suspect that what really happens is more subtle than a crude one to one correspondence of SM particles and their superpartners. The insights that SUSY theories have provided to date (not a lot, but some) have more to do with the fact that they simplify the math in ways that still capture the essence of the actual high energy processes, than with their necessity or reality.
  3. Oct 4, 2016 #43
    Thanks a lot for your information above. We'd all be anxiously waiting for you in your sleep for the message about how exactly or approximately huge counterterms managed to cancel out to a value many, many orders of magnitude smaller to produce the Higgs mass.
  4. Oct 5, 2016 #44
    what's your fav approach to QG ? strings loops asymsafe graviton or spacetime approaches?
  5. Oct 5, 2016 #45
    how do you feel about string theory, which 100% depend on susy
  6. Oct 5, 2016 #46


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    String theory provides some interesting mathematical insights but is a poor way to model what we see in Nature. Like SUSY it is probably not an accurate description of the real world.
  7. Oct 5, 2016 #47
    which QG approach is most similar to your pet fav QCD = gravity? there is some overlap between spinfoam/lqg and lattice gauge theory used in QCD
  8. Oct 5, 2016 #48
    Let's take analogy of a skyscraper building constructions.
    If the steel and concrete and other materials just grow from the ground up.. then we can say it is Natural because steel and concrete came from the seed.
    But if steel and concrete are build by hands and by people. Then it is not natural or unnatural.
    I think ohwilleke treats physics as only understanding the finished product and some relations (like the finished skyscraper and relations between elevators)
    Then what occurred before like how the construction crew assembled the building is outside physics.
    If it is outside physics. Then what should it be called "Hyperphysics" or "Off limit Beyond Standard Model" or simply philosophy?
    But can we call the construction stages of the building as philosophy at all?
  9. Oct 7, 2016 #49
    I wish to note some details.

    The MSSM predicts two even-parity neutral Higgs particles, h and H0, one odd-parity Higgs particle, A, and two charged Higgs particles, H+ and H- (or two variants of one particle). The h and H0 have a 2*2 mass matrix, as one might expect.

    If one of the MSSM parameters is high enough, then the H0, A, and H+- have masses close to each other, masses much greater than the h mass.

    The MSSM has a "mu problem", from an interaction term (mu) * (Hu.Hd) (Hu and Hd are the two unbroken Higgs doublets in the MSSM). The problem with (mu) is lack of explanation of why it has an electroweak-scale mass rather than a GUT-scale mass. The NMSSM adds an additional Higgs particle, S, a Standard-Model gauge singlet. Electroweak symmetry breaking yields an additional even-parity neutral Higgs particle, an additional odd-party neutral Higgs particle, and an additional Higgsino. This means 3 even-party neutral Higgs particles, 2 odd-parity ones, and 5 neutralinos.

    That additional particle S replaces the (mu) in the above mass term, and SUSY breaking makes an effective (mu) value. So in the NMSSM, all the electroweak-scale masses are due to SUSY breaking.

    Turning to GUT's, SO(10) puts the Hu and the Hd in a single 10 (vector) multiplet H, and the elementary fermions into three generations of 16 (spinor) multiplets F. The S remains a gauge singlet in it.

    However, going to E6, the H, the F, and the S can be part of a single fundamental 27 multiplet. The triplet interaction (27).(27).(27) is a gauge singlet and also symmetric in the fields. Breaking down to SO(10) gives interactions S.H.H and H.F.F -- what the NMSSM needs.
  10. Oct 7, 2016 #50
    wouldn't all these additional higgs interact with one another and with SM particles that can be observed at LHC?
  11. Oct 9, 2016 #51
    Yes they would, if their masses are low enough for them to be produced by the LHC.

    They would likely be produced in much the same way that the SM Higgs is produced, and their production cross sections and decays are likely similar. That means that it may be hard to search for them, since they may not have decays that stand up above the background very much.

    But that's why the LHC will eventually get its High Luminosity upgrade, to search for particles and decay modes that are less distinguishable from the LHC's background than what it can currently see.
  12. Oct 9, 2016 #52
    wouldn't a higher energy upgrade to 28-33TEV be even more useful?
  13. Oct 11, 2016 #53
    True, but it would be difficult to keep the accelerated protons in the accelerator. The magnets' field strength would have to be over twice as great to steer them in place (Gyroradius - Wikipedia). The Large Hadron Collider has a radius of 4.3 km, and here's what magnetic field is necessary to get up to these energies:
    • 6.5 TeV - 5.0 T (LHC now)
    • 7 TeV - 5.4 T (LHC design)
    • 14 TeV - 10.7 T
    • 16.5 TeV - 12.7 T
    • 28 TeV - 21 T
    • 33 TeV - 25 T
    The actual maximum field of the LHC's steering magnets is 7.7 T.

    The synchrotron-radiation energy loss is proportional to (E4*v2)/(m4*r2) (E, v, m = particle energy, velocity, mass, r = radius of particle path). The previous occupant of the LHC's tunnels, the LEP, was an e-e+ collider. It was limited to 104.5 GeV per particle. If the LHC was limited by synchrotron-radiation losses, then it could go up to about 200 TeV.

    That's why proposals for more energy involve building larger accelerators.
  14. Oct 11, 2016 #54
    just replace the 5.4 T magnets with 25 T
  15. Oct 13, 2016 #55
    Has anyone ever built 25-tesla electromagnets? Is there any superconductor that won't be quenched by a magnetic field that strong?
  16. Oct 13, 2016 #56
    Well, https://en.wikipedia.org/wiki/Superconducting_magnet#History lists 26.8 T as world record. Of course, this does not mean you have this ready to use in an accelerator. Have a look at e.g. these slides https://indico.cern.ch/event/521926/attachments/1310549/1960888/160718_summer-students_II_final.pdf shown at a summer school this year. Anything above ~15 T seems be far in the future with time scales "beyond 2035". I am not in this field, and others might have different opinions on future developments, but I think it is clear that this is not as easy as "just replace the magnets"...
  17. Oct 13, 2016 #57


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    Is 5 the minimum?

    From degrees of freedom I would expect some susy theory with only three, consider a neutral higgsino weyl, and a charged one dirac. Only six spartners. Three dof are eaten to give mass to the Z and W and the other three are H0 H+ and H-

    Another look: a massive gauge supermultiplet is one spin 1 particle, two Weyl fermions, one scalar. We have three massive particles, so three scalars.
  18. Oct 31, 2016 #58
    do these additional higgs fields also generate mass in elementary particles? and since the LHC hasn't seen them, do they have to have masses higher than energies LHC can probe?
  19. Oct 31, 2016 #59

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    Yes. You need different Higgs fields to couple to u-type and d-type quarks. The problem isn't the quarks, strictly speaking: it's the squarks. In supersymmetric theories the scalars belong to chiral multiplets and their complex conjugates belong to multiplets of the opposite chirality; because multiplets of different chiralities cannot couple together in the Lagrangian, a single Higgs doublet is unable to give mass simultaneously to the u-type and d-type quarks. The same argument holds for leptons if the neutrino is Dirac.
  20. Oct 31, 2016 #60
    does this provide any predictions lhc can see with regards to the 1 higgs they see
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