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I Evaluation of SMASH - most minimal extension of SM

  1. Oct 27, 2016 #1
    does this paper

    Standard Model-Axion-Seesaw-Higgs Portal Inflation. Five problems of particle physics and cosmology solved in one stroke
    Guillermo Ballesteros, Javier Redondo, Andreas Ringwald, Carlos Tamarit
    (Submitted on 5 Oct 2016)
    We present a minimal extension of the Standard Model (SM) providing a consistent picture of particle physics from the electroweak scale to the Planck scale and of cosmology from inflation until today. Three right-handed neutrinos Ni, a new color triplet Q and a complex SM-singlet scalar σ, whose vacuum expectation value vσ∼1011 GeV breaks lepton number and a Peccei-Quinn symmetry simultaneously, are added to the SM. At low energies, the model reduces to the SM, augmented by seesaw generated neutrino masses and mixing, plus the axion. The latter solves the strong CP problem and accounts for the cold dark matter in the Universe. The inflaton is comprised by a mixture of σ and the SM Higgs and reheating of the Universe after inflation proceeds via the Higgs portal. Baryogenesis occurs via thermal leptogenesis. Thus, five fundamental problems of particle physics and cosmology are solved at one stroke in this unified Standard Model - Axion - Seesaw - Higgs portal inflation (SMASH) model. It can be probed decisively by upcoming cosmic microwave background and axion dark matter experiments.
    Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
    Cite as: arXiv:1610.01639 [hep-ph]

    succeed in solving the issues, by adding the fewest number of fields and particles to the SM to solve these problems?

    add in some form of non-SUSY 4D QG in the form of AS safe gravity or LQG and all major issues of physics solved.
     
  2. jcsd
  3. Nov 2, 2016 #2
    I didn't fully understand about that heavy quark Q. It is a right-handed quark (meaning SU(2) singlet)? Okay, but then they say it has weak hypercharge -1/3. This means that it has electric charge of -1/6? They also say that it can mix with down-quarks. But right-handed down quarks have weak hypercharge of -2/3, not -1/3. Something does not add up here. It's almost like the paper mixes up electric charge with weak hypercharge.
     
  4. Nov 2, 2016 #3
    The relation between electric- and hypercharge is not unique (see e.g. the comment in the wikipedia entry http://hthttps://en.wikipedia.org/wiki/Weak_hypercharge [Broken], though I would disagree that it is only a minority that uses this convention...). However, I would guess their convention is also that $Y = Q - I_W^3$. That way, electric charge is equal to hyper charge for SU(2) singlets.
     
    Last edited by a moderator: May 8, 2017
  5. Nov 5, 2016 #4
    I like the general approach. An inflaton field probably isn't needed since the effective action for gravity under the asymptotic safety scenario has extra terms that lead naturally to an inflationary phase*.

    * https://arxiv.org/abs/0911.3165
     
  6. Nov 5, 2016 #5
    what would be the most minimal extension of the SM that solves the 5 listed problems?
     
  7. Nov 5, 2016 #6

    mfb

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    We do not have such an extension so we don't know the minimal one. We have approaches that might turn out to work in the future, but I would be surprised if any of them work without further modifications. This includes SMASH.
     
  8. Nov 5, 2016 #7
    SMASH got a lot of publicity in the press, as the first approach that solves , five fundamental problems of particle physics and cosmology are solved at one stroke - are there other approaches that also solve these same five problems and does so minimally ?
     
  9. Nov 5, 2016 #8

    mfb

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    So did various other approaches.
    See above: it might solve them. We don't know, more research is needed.

    You can also tune supersymmetry to nearly everything. The advantage of SMASH is the smaller number of free parameters.
     
  10. Nov 5, 2016 #9
    does mssm and supersymmetry by itself solve the strong cp problem? i understand you can add an axion and its superpartner the axino, but that SMASH just adds axion without supersymmetry. and does supersymmetry/mssm by itself also offer inflaton and account for neutrino masses?
     
  11. Nov 7, 2016 #10

    ohwilleke

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    In my view, SMASH clumps together some of the ugliest and baroque approaches to issues with the Standard Model and is almost certainly incorrect.

    1. I don't think that the strong CP problem or that axions are necessary to solve anything.
    2. I don't think that axions are an attractive dark matter candidate.
    3. I think that the seesaw mechanism to generate neutrino masses is misguided.
    4. I don't think that right handed neutrinos are necessary or that they exist.
    5. I don't think that baryon number violation or lepton number violation have any plausible chance of being broken by a TeV scale complex scalar.
    6. Most simple models of inflation were ruled out empirically by the Planck data and it is not at all obvious that a mixture of σ and the SM Higgs would do any better.
    7. There is no compelling need for a new color triplet.

    I suspect that dark matter phenomena are really a quantum gravity effect, that neutrinos have Dirac rather than Majorana mass, that any baryon number violation or lepton number violation is limited to energies close to the GUT scale, that the lack of CP violation by the strong force is a natural consequence of the gluon having a zero rest mass, and that the graviton and the Standard Model particles are probably a complete set, at least up to close to the GUT scale.
     
  12. Nov 8, 2016 #11
    Could you elaborate how that would work in a viable setup (or point to some references where this is discussed)?
     
  13. Nov 8, 2016 #12
    so do you favor MOND or some variation of MOND over dark matter?
    what is your preferred inflationary model?
     
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