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A What would falsify supersymmetry? LHC Nightmare scenario

  1. Aug 12, 2016 #1
    The LHC nightmare scenario

    after 15 years of operation and 3000 fb-1 total integrated luminosity at 14 TEV,
    it only finds Higgs and nothing else.

    with LHC not finding any SUSY partners and LUX/Panda not finding any WIMPS, obviously SUSY can be adjusted to accommodate these null results.

    One possible conclusion is that SUSY does not address the naturalness problem in the Higgs sector.

    This is called the Nightmare Scenario. LHC will only find results consistent with SM, no BSM. evidence of WIMPS has not been forthcoming.

    Is there any experimental or theoretical result that would falsify supersymmetry and any extension involving SUSY like MSSM and nMSSM that could be done in the near future ?

    Do we have to wait for the next collider with even higher energies, one being built in china with 50-70 GEV energies for SUSY, sometime in the 2040-2050 timeframe, or is there some experiment or theoretical result that can decide the issue sooner.

    currently we are in the Nightmare scenario where natural SUSY hasn't shown up at LHC and its WIMP candidate hasn't shown up in dark matter searches. Is there any single or multiple experiment such that it could falsify the entire framework of SUSY, or show that SUSY does show up, even if accelerators don't have enough energy to produce them?

    or what about the accumulation of null results, taken together, could that falsify SUSY? i.e null results of WIMPS in Xenon1t lux-zeppelin supercdms, null results in LHC, null results in rare process like b-meson decays, null results in both neutron and electron EDM measurements,null results on rare decays sensitive to BSM physics, etc?
     
    Last edited: Aug 13, 2016
  2. jcsd
  3. Aug 13, 2016 #2
    My understanding is that SUSY can not be completely falsified - parameters can always be tweaked so that it becomes unreachable by experiments.

    Whan can happen is that other new theories can appear and explain all currently unexplained phenomena (dark matter, dark energy, vacuum energy density, vacuum stability, UV and IR divergences, quantum gravity, inflation, neutrino masses (possibly also masses of other particles)) well enough that SUSY is simply "no longer needed".
     
  4. Aug 13, 2016 #3
    I think that you could build a very large collider and probe all the way to the Planck scale without finding any evidence of SUSY and the prediction would still be that we'll find it in the next place that we look.
     
  5. Aug 13, 2016 #4
    has there been any research into falsifying SUSY either by proposing experiments, or taking existing results and providing no-go theorems, or looking at the cumulative effects of multiple null results, plus existing problems with SUSY such as flavor changing neutral currents, SUSY-breaking etc?

    perhaps no-go theorems are the way forward?

    taking existing results from LHC nightmare scenario, construct no-go theorems that SUSY is ruled out.
    that or specific experiments that all classes of SUSY are expected to follow and compare with experiment.
     
  6. Sep 1, 2016 #5

    ohwilleke

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    There are several ways to falsify SUSY:

    1. Overconstrain the theory with bounds from below and beyond on sparticles.

    The LHC and future bigger colliders can narrow SUSY parameter space and set lower bounds on the masses of SUSY sparticles and extra Higgs bosons.

    But, to really falsify a major class of SUSY theories, you need to find some property of SUSY theories that sets a fairly generic upper bound on SUSY sparticle mass.

    The most promising approach I've seen to setting an upper bound is that it is apparently generically true for a large class of SUSY theories that rate of neutrinoless double beta decay are increased when its sparticles are heavier. So, if neutrinoless double beta decay is not observed with any frequency less than an experimentally established frequency, then this implies a generic upper bound on SUSY sparticle mass.

    Then, if the lower bound continues to rise and the upper bound continues to fall, eventually that class of SUSY theories can be ruled out. I explore this idea at greater length in a blog post from November of 2012: http://dispatchesfromturtleisland.blogspot.com/2012/11/neutrinoless-double-beta-decay.html

    The current experimentally measured mass of the Higgs boson also places some limits on SUSY parameter space from above in a fairly generic manner, although these bounds are not as strict.

    Also, keep in mind that all you have to do to falsify SUSY generally is to rule out one type of sparticle that is generically present in all major SUSY theories. For example, you can falsify most SUSY theories by ruling out all possible masses for a gluino, even if you can't rule out all possible masses of a stop squark.

    Another class of SUSY predicted particles that is attractive to try to rule out are the extra Higgs bosons predicted by this class of theories.

    2. You can falsify SUSY by discovering some new apparently fundamental particle that is not predicted to exist in any SUSY theory. SUSY theories generally predict new particles whose non-mass properties are for the most part exactly described. If you discover a particle that isn't predicted by a SUSY theory, for example, a lepton with a fractional electromagnetic charge, or a massless fermion, then this establishes that all SUSY theories that didn't have such particles have been falsified.

    3. There are various relatively low energy phenomena (e.g. single digit TeV scale) that can provide insights into much higher energy scales.

    For example, SUSY theories generically predict a different running of the coupling constants of the three Standard Model forces with momentum than the Standard Models does. So, a failure to detect non-SM running of coupling constants can provide insight equivalent to a failure to directly detect a SUSY sparticle at energy scales higher than can be reached in a direct search. This isn't enough by itself to falsify SUSY because one could argue that the coupling constant modification kicks in at a higher energy scale, but it does make it easier to close the gap between an upper bound from neutrinoless double beta decay or the Higgs boson mass in combination with other data, and the experimental lower bound.

    The magnetic moment and electron dipole moment of the muon and the neutron, for example, also provide an opportunity to probe higher energy scales than would be possible through direct means.
     
  7. Sep 1, 2016 #6
    #2 - if they find evidence for a 16.7 MeV protophobic gauge boson as described in the Feng paper, thats not predicted by any SUSY theory.

    how would that impact #2?
     
  8. Sep 1, 2016 #7

    ohwilleke

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    I think that would falsify SUSY, unless it could be determined to fit the properties of a SUSY particle and I can't think of any that would be a good fit.
     
  9. Sep 1, 2016 #8
    if accepted it is a new gauge interaction new force. it would falsify current MSSM and nMSSM and GUT's, based on 4 forces, but what i wonder is whether a new SUSY theory with this force, with its corresponding susy-fermion partner, can be made that is anomaly free and not in conflict with known bounds and new GUT based on 5 fundamental forces

    btw any chance u can look at this paper and offer your thoughts ty - imagine adding SUSY to the below model

    Particle Physics Models for the 17 MeV Anomaly in Beryllium Nuclear Decays
    Jonathan L. Feng, Bartosz Fornal, Iftah Galon, Susan Gardner, Jordan Smolinsky, Tim M. P. Tait, Philip Tanedo
    (Submitted on 11 Aug 2016)
    The 6.8σ anomaly in excited 8Be nuclear decays via internal pair creation is fit well by a new particle interpretation. In a previous analysis, we showed that a 17 MeV protophobic gauge boson provides a particle physics explanation of the anomaly consistent with all existing constraints. Here we begin with a review of the physics of internal pair creation in 8Be decays and the characteristics of the observed anomaly. To develop its particle interpretation, we provide an effective operator analysis for excited 8Be decays to particles with a variety of spins and parities and show that these considerations exclude simple models with scalar or pseudoscalar particles. We discuss the required couplings for a gauge boson to give the observed signal, highlighting the significant dependence on the precise mass of the boson and isospin mixing and breaking effects. We present anomaly-free extensions of the Standard Model that contain protophobic gauge bosons with the desired couplings to explain the 8Be anomaly. In the first model, the new force carrier is a U(1)B gauge boson that kinetically mixes with the photon; in the second model, it is a U(1)(B-L) gauge boson with a similar kinetic mixing. In both cases, the models predict relatively large charged lepton couplings ~ 0.001 that can resolve the discrepancy in the muon anomalous magnetic moment and are amenable to many experimental probes. The models also contain vectorlike leptons at the weak scale that may be accessible to near future LHC searches.
    Comments: 34 pages + references, 6 figures
    Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    Report number: UCI-TR-2016-12
    Cite as: arXiv:1608.03591 [hep-ph]
    (or arXiv:1608.03591v1 [hep-ph] for this version)
     
  10. Sep 2, 2016 #9

    ohwilleke

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    I think that the paper is barking up the wrong tree and grasping at straws, when something other than new physics is almost certainly the true cause.
     
  11. Sep 2, 2016 #10
    maybe, but they argue that given there is a DM sector, and all DM searches both at LHC and detectors have come up empty, any anomaly must be investigated and followed up on.

    the original point of the Hungarian experiment was to find Dark Photons.

    they do propose this could be related to DM.

    they do NOT suggest it is a SUSY partner of any known SM fermion so it must be a new gauge interaction.

    what if future experiments like mu3e and darklight confirm this boson?
     
  12. Sep 3, 2016 #11
    Could you elaborate to what extent this would falsify SUSY as a general principle? I would have thought that you could basically always construct a (broken) supersymmetric version of your current theory by adding the necessary super partners, at least as long as your current theory is just a straight forward modification of the SM like adding a new degree of freedom. So basically the SM would be replaced by (SM+new particle) and the MSSM would be replaced by MS(SM+new particle).
     
  13. Sep 3, 2016 #12
    adding the axion probably would not be much of a change, and there are already SUSY models that accept it, such as the axino. Feng is proposing a new gauge interaction to be added to the SM.
     
  14. Sep 4, 2016 #13
    Still, as far as I am aware Supersymmetrie is not posing any restrictions on the gauge structure of a theory, and broken SUSY is not restricting the particle content below some energy scale (would like to be told otherwise). So I don't see how a new particle would falsify SUSY (it could become "unnecessary" by solving all empirical problems of the SM though, as @nikkkom said in #2).
     
  15. Sep 4, 2016 #14
    Feng's paper points out that adding a new gauge interaction and new particle to the SM creates gauge anomalies that must be cancelled. Other researches also observe that a new gauge boson creates gauge anomalies to the SM. Their proposal is to add more particles to cancel those anomalies, so that this boson is part of a dark sector.

    Realistic model for a fifth force explaining anomaly in 8Be∗→8Bee+e− Decay
    Pei-Hong Gu, Xiao-Gang He
    (Submitted on 16 Jun 2016 (v1), last revised 12 Jul 2016 (this version, v5))
    A 6.8σ anomaly has been reported in the opening angle and invariant mass distributions of e+e− pairs produced in 8Be nuclear transitions. It has been shown that a protophobic fifth force mediated by a 17MeV gauge boson X with pure vector current interactions can explain the data through the decay of an excited state to the ground state, 8Be∗→8BeX, and then the followed saturating decay X→e+e−. In this work we propose a renormalizable model to realize this fifth force. Although axial-vector current interactions also exist in our model, their contributions cancel out in the iso-scalar interaction for 8Be∗→8BeX. Within the allowed parameter space, this model can alleviate the (g−2)μ anomaly problem and can be probed by the LHCb experiment. Several other implications are discussed.
    Comments: RevTex, 9 pages with no figures. New major changes are made to the older version
    Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Experiment (hep-ex)
    Cite as: arXiv:1606.05171 [hep-ph]

    i was thinking that adding a completely new gauge interaction and fundamental force, such as what Feng et al proposes with a 16.7 MeV boson, would make an already complicated MSSM theory even more complicated, since it allows for many more interactions that could result in disagreement with experiment. Feng's paper and other papers proposes additional particles to cancel gauge anomalies created by 16.7 MeV boson. They offer these additional particles as dark matter candidates, as part of a new dark sector. Doubling them via SUSY seems it could create more opportunities for gauge anomalies. I am well aware that MSSM adds 120 new parameters that have to be fine tuned so as to not disagree with experiment, such as flavor violation, CP violation, etc. Adding a new gauge interaction and new particles to cancel the anomalies would seem to require adding even more than 120 parameters of the new SUSY+new dark sector.

    The new interaction suggested by the anomalous 8Be transition sets a rigorous constraint on the mass range of dark matter
    Lian-Bao Jia, Xue-Qian Li
    (Submitted on 18 Aug 2016)
    The WIMPs are considered one of the most favorable dark matter (DM) candidates, but as the upper bound on the interaction between DM and standard model (SM) particles obtained by the upgraded facilities for direct detection of DM gets lower and lower. Researchers turn their attention to search for less massive DM candidates, i.e. light dark matter of MeV scale. The recently measured anomalous transition in 8Be suggests that there exists a vectorial boson which may mediate the interaction between DM and SM particles. Based on this scenario, we combine the relevant cosmological data to constrain the mass range of DM, and have found that there exists a model parameter space where the requirements are satisfied, a range of 10.4≲mϕ≲16.7 MeV for scalar DM, and 13.6≲mV≲16.7 MeV for vectorial DM is demanded. Then a possibility of directly detecting such light DM particles at the earth detector via the DM-electron scattering is briefly studied in this framework.
    Comments: 13 Pages, 7 figures
    Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
    Cite as: arXiv:1608.05443 [hep-ph]
     
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