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If Dark Matter does not exist, would string/SUSY/GUT be falsified?

  1. May 16, 2010 #1
    I'm looking at this thread, https://www.physicsforums.com/showthread.php?t=403472
    Dark Matter, On the Ropes?

    If there is no dark matter, could the neutralino of MSSM, SUSY and string theory, or the axion of GUT's exist? IF there is no dark matter, doesn't this imply there are no neutralinos or other SUSY-partners, falsifying MSSM, SUSY and MSSM, and possibly higher dimensional kaluza-klein tower modes? If there is no dark matter, does this imply only SM particles exist (i.e only SM particles can be experimentally detected, particles that cannot be detected by any experiment could conceivably exist in the equally undetectable multiverse)?

    Dark matter would not prove MSSM since they could be say particles of a yet unknown theory, or perhaps microblack holes are stable, or geons, but no dark matter at all wouldn't that falsify string/MSSM/SUSY/GUT?
  2. jcsd
  3. May 16, 2010 #2


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    I believe one requires R-parity in order to get LSPs in the MSSM and other SUSY theories. R-parity is not a 'built in' symmetry of the theory. As for the KK tower, the resonant masses depend on the scale of the extra dimensions. This can be tuned so that the KK modes are not relevant cosmologically. Also, keep in mind that many popular models of KK dark matter are based on 'universal extra dimensions', a model that can not (as far as I know) be embedded in string theory.
    I know physicists that would need both a direct detection of DM and the production of an LSP at the LHC (that were the same particle) in order to be convinced that DM is a SUSY particle. But I would say no, that a lack of DM would not falsify anything.
  4. May 16, 2010 #3
    Wouldn't the lack of DM falsify R-parity, and if so, doesn't this make MSSM models disagree with experiment?

    So if DM does not exist (i.e no detection at LSP at LHC and no direct detection, inability to explain spiral halo galaxie formation) then for MSSM to be viable, there cannot be R-parity. If there is no R-parity, could the MSSM still be viable, with known experimental evidence?

    Isn't R-parity required so as to prevent SUSY-partners from interacting with SM particles in a way that disagrees with experiment ? Since baryon number and lepton number conservation has been tested, how could MSSM account for them without R-parity (i.e baryon number and lepton number conservation would be violated in MSSM without R-parity)


    R-parity is a concept in particle physics. In the supersymmetric extension of the Standard Model, baryon number and lepton number are no longer conserved by all of the renormalizable couplings in the theory. Since baryon number and lepton number conservation have been tested very precisely, these couplings need to be very small in order not to be in conflict with experimental data. R-parity is a Z2 symmetry acting on the Minimal Supersymmetric Standard Model (MSSM) fields that forbids these couplings and can be defined as:

    R = (-1)2j+3B+L.

    With spin j, baryon number B, and lepton number L. All Standard Model particles have R-parity of 1 while supersymmetric particles have R-parity -1.

    Possible origins of R-parity

    While on the face of it, R-parity is an ad hoc imposition upon the MSSM, it can arise as an automatic symmetry in SO(10) grand unified theories. This natural occurrence of R-parity is possible because in SO(10) the Standard Model fermions arise from the 16-dimensional spinor representation, while the Higgs arises from a 10 dimensional vector representation. In order to make an SO(10) invariant coupling, one must have an even number of spinor fields (i.e. there is a spinor parity). After GUT symmetry breaking, this spinor parity descends into R-parity so long as no spinor fields were used to break the GUT symmetry.
    Last edited: May 16, 2010
  5. May 17, 2010 #4


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    I suppose as well that SUSY can be broken at a higher scale than the inflation reheat temperature. In this case, no SUSY partners are generated after inflation.
  6. May 17, 2010 #5
    Nature could turn out this way, but then would SUSY explain EW-stabilization and Higgs against radiative correction? How would it be possible to experimentally verify SUSY in this scenario?
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