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Strumia's dimensionless gravity

  1. Mar 29, 2014 #1

    marcus

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    Here, to get an idea what he's like, is video of his talk at the 2013 Moriond meeting
    http://webcast.in2p3.fr/videos-scalar_potential_and_stability

    Here, is something new, a paper that just came out relating to the BICEP2 finding.
    "Agravity" is short for "Adimensional gravity" (non-dimensional couplings make it renormalizable)

    http://arxiv.org/abs/1403.4226
    Agravity
    Alberto Salvio, Alessandro Strumia
    (Submitted on 17 Mar 2014)
    We explore the possibility that the fundamental theory of nature does not contain any scale. This implies a renormalizable quantum gravity theory where the graviton kinetic term has 4 derivatives, and can be reinterpreted as gravity minus an anti-graviton. We compute the super-Planckian RGE of adimensional gravity coupled to a generic matter sector. The Planck scale and a flat space can arise dynamically at quantum level provided that a quartic scalar coupling and its β function vanish at the Planck scale. This is how the Higgs boson behaves for Mh≈125 GeV at Mt≈171 GeV. Within agravity, inflation is a generic phenomenon: the slow-roll parameters are given by the β-functions of the theory, and are small if couplings are perturbative. The predictions ns≈0.967 and r≈0.13 arise if the inflaton is identified with the Higgs of gravity. Furthermore, quadratically divergent corrections to the Higgs mass vanish: a small weak scale is natural and can be generated by agravity quantum corrections.
    24 pages

    Here is the Inspire record and the author profile:
    http://inspirehep.net/record/1286134?ln=en
    http://inspirehep.net/author/profile/A.Strumia.1
    Born Dec. 1969, papers go back to 1993
    Some 140 published with average number of citations over 100 cites per paper.
    Mainly in Phenomenology, with emphasis on numerical calculation.
    In case of interest, here's an old CV http://www.df.unipi.it/~astrumia/CVitaliano2004.pdf
     
    Last edited: Mar 29, 2014
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  3. Mar 29, 2014 #2

    marcus

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    The general context is reminiscent of the Shaposhnikov Wetterich idea of no new physics between "here" and Planck scale. The physical quantity scales arise by some kind of symmetry breaking. At the highest energies the picture is "conformal" in the sense of no definite scale. I recall Hermann Nicolai was talking about that kind of picture in 2008, based on his work with Chris Meissner. I think Strumia cites Nicolai, as well as some Shapo-Wett papers. The key idea is that the SM is basically good all the way to Planck.

    You get that "no new physics" view in detail in the slides for the 2013 video. Also "no SUSY" which causes some discussion at the end of the video of the Moriond talk.

    Born in 1969, that means Strumia turns 45 this year. Have a look at his Inspire profile
    http://inspirehep.net/author/profile/A.Strumia.1

    Notice that Strumia and Salvio derive a tensor-scalar ratio r ≈ 0.13 that is a reasonable compromise between the recent BICEP2 and last years Planck value
    The predictions ns≈0.967 and r≈0.13 arise if the inflaton is identified with the Higgs of gravity.

    Does anyone want to explain what is meant by the phrase "the Higgs of gravity"?

    It would seem an analog or mirror of what we usually call the Higgs field. They write its (as yet undetermined) mass Ms.
     
    Last edited: Mar 30, 2014
  4. Mar 30, 2014 #3

    marcus

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    Here's their introduction paragraph:
    ==quote http://arxiv.org/abs/1403.4226 ==
    We propose a general principle that leads to a renormalizable and predictive theory of quantum gravity where all scales are generated dynamically, where a small weak scale coexists with the Planck scale, where inflation is a natural phenomenon. The price to pay is a ghost-like anti-graviton state.
    The general principle is: nature does not possess any scale. We start presenting how this principle is suggested by two recent experimental results, and next discuss its implementation and consequences.
    ==endquote==

    For the answer to the question in previous post about "Higgs of gravity" see section 4.2 on page 18.

    ==quote==
    We here consider the specific model presented in section 3.1, where the scalar S is identified with the Higgs doublet of a mirror sector which is an exact copy of the SM, with the only difference that S sits in the Planck-scale minimum of the SM effective potential.
    This model predicts that the β function coefficient in eq. (49) equals g4 ≈ 1.0 provided that we can neglect the gravitational couplings f0, f2 with respect to the known order-one SM couplings yt, g3, g2, g1. Thereby the observed scalar amplitude As = 2.2 10−9 [3] is reproduced for ξS ≈ 210. A large ξS is perturbative as long as it is smaller than 1/f0,2.
    We notice that ξS is not a free parameter, within the context of the SM mirror model: the vev of the Higgs mirror s is given by the RGE scale at which βλS vanishes (see fig. 3b), and in order to reproduce the correct Planck scale with ξS ≈ 210 one needs ⟨s⟩ = [STRIKE]M[/STRIKE] ̄Pl/ √ξS = 1.6 1017 GeV. The fact that this condition can be satisfied (within the uncertainties) is a test of the model.
    The inflaton mass Ms ≈ 1.4 1013 GeV is below the Planck scale because suppressed by the β-functions of the theory...



    In conclusion, we identified the inflaton with the field that dynamically generates the Planck scale. In the agravity context, such field must have a dimensionless logarithmic potential: this is why our predictions for r ≈ 8/N ≈ 0.13 differ from the tentative prediction r ≈ 12/N2 ≈ 0.003 of a generic ξ-inflation model with mass parameters in the potential [2].
    ==endquote==

    Here N is the number of e-folds taken to be 60. [STRIKE]M[/STRIKE]Pl is the reduced Planck mass where you divide by √(8π). In effect just setting 8πG=1 instead of G=1. I used the strike through instead of the overbar in transcribing their notation.

    It looks like whatever turns out to be the measured value of the tensor scalar ratio, they can within reason match it with 8/N just by adjusting the number N of e-folds.

    So FUNDAMENTAL PHYSICS HAS NO SCALE, and in particular it has no PLANCK SCALE. But the Planck scale is DYNAMICALLY GENERATED by a scalar field (the "Higgs of gravity") which also serves as INFLATON.
    And this scalar field is an analog of the familiar Higgs field that we know about, but far more massive.
     
    Last edited: Mar 30, 2014
  5. Mar 30, 2014 #4

    marcus

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    Lee Smolin has warned me off this paper. This avenue to QG was tried, it seems, as early as 1977 (when Alessandro Strumia, born in 1969, was 7 years old) and nothing good came of it.
    http://www.math.columbia.edu/~woit/wordpress/?p=6782#comment-208676

    I took a glance at the “agravity” paper, and it is just the old Kelly Stelle theory from 1977, which has been known since that time to be non-unitary in perturbation theory, in addition the Hamiltonan is not bounded from below. It is perturbatively renormalizable and in fact asymptotically free, which in this case is bad, because there is faint hope to save the theory by going beyond perturbation theory. Many people have tried unsuccessfully to save this theory, from Terry Tomboulis and Gary Horowitz back then to the contemporary asymptotic safety people and Phillip Mannheim more recently. If I read the paper correctly, the authors admit they have nothing to add to these issues. If this was the right answer, quantum gravity would have been solved long before string theory and LQG were even invented.​
     
  6. Mar 31, 2014 #5

    MTd2

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    Is this good for Penrose's Aeons?
     
  7. Mar 31, 2014 #6

    MTd2

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    Look at what they say:



    "We do not address the potential problem of a negative contribution to the cross-section for producing an odd number of anti-gravitons with mass M2 above their kinematical threshold. Claims in the literature are controversial [10]. Sometimes in physics we have the right equations before having their right interpretation. In such cases the strategy that pays is: proceed with faith [11], explore where the computations lead [12], if the direction is right the problems will disappear [13]."

    Where:

    [11] B. Mussolini, “Me ne frego”.
    [12] R. Feynman, “Shut up and compute”.
    [13] A. Einstein, “If we knew what we were doing it wouldn’t be research”.

    Where "Me ne frego" means "I don't give it a damn". Google image turns up quite odd stuff.

    Also, it's worth checking reference [10]. It seems that, unlike the Smoliln's claim, this subject is not set. The last reference is http://arxiv.org/pdf/1104.4543v1.pdf
     
    Last edited: Mar 31, 2014
  8. Mar 31, 2014 #7

    Chronos

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  9. Mar 31, 2014 #8

    marcus

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    It's not clear to me how it could be relevant, Chronos. In the paper you cite (Fairbairn et al) they study using the ordinary Higgs field as inflaton.

    Their motivation for this is that the Higgs field is "the only known fundamental scalar field".

    The associated mass is about 125 GeV.

    By contrast, Salvio and Strumia postulate a different fundamental scalar field, which they estimate to be almost a trillion times more massive, to serve as inflation.

    See post #3 above: "The inflaton mass Ms ≈ 1.4 1013 GeV "

    For lack of a better name they call this new field the "Higgs of gravity". It is not constrained to behave as the Higgs we are familiar with because it does not play the Higgs role, so it would presumably not encounter the problems discovered by Fairbairn et al---which face the ordinary Higgs, were it to play "inflaton", but not this new "Higgs of gravity" field.

    I had a look at the 't Hooft paper that is mentioned in Strumia Salvio reference [10] and to which MTd2 called attention. Strumia Salvio acknowledge serious objections to the approach they are exploring BUT they say those objections are "CONTROVERSIAL". And as evidence that the objections are not yet accepted as insurmountable, but remain controversial, they cite this 't Hooft paper, among others.
    http://arxiv.org/pdf/1104.4543v1.pdf
    http://inspirehep.net/record/897113?ln=en
    The 't Hooft paper has been cited 26 times including by Steve Giddings, Roberto Percacci, and Phillip Mannheim.
    To me it looks boldly speculative (as likewise the Strumia Salvio) and I don't feel competent to judge if it is crazy or not.
     
    Last edited: Mar 31, 2014
  10. Mar 31, 2014 #9

    marcus

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    Both Strumia and Salvio are Italian. I guess Salvio was born around 1980-1981---he entered U. Rome in 1998.
    http://inspirehep.net/author/profile/A.Salvio.1
    ==quote page 5==
    We do not address the potential problem of a negative contribution to the cross-section for producing an odd number of anti-gravitons with mass M2 above their kinematical threshold. Claims in the literature are controversial [10]. Sometimes in physics we have the right equations before having their right interpretation. In such cases the strategy that pays is: proceed with faith [11], explore where the computations lead [12], if the direction is right the problems will disappear [13].
    We here compute the one loop quantum corrections of agravity, to explore its quantum behaviour. Can the Planck scale be dynamically generated?…
    ==endquote==
    Indeed they may be WRONG. But the question will remain: can the Planck scale be dynamically generated? Is it by other than such (possibly foolish) boldness that this question will be explored?

    In Moz. Magic Flute, Zarastro says: Lasst sie der Prüfung Früchte sehen, doch sollen sie zu Grabe gehen, so lohnt der Tugend kühnen Lauf, nehmt sie in Euren Wohnsitz auf!

    http://arxiv.org/abs/1403.4226
     
    Last edited: Mar 31, 2014
  11. Mar 31, 2014 #10

    marcus

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    Chronos, MTd2, what seems to me (seems, I don't feel confident of it) the most telling criticism is that the particular solution Salvio Strumia are trying is perturbative and asymptotically free.
    It goes against the suggestive evidence that has accumulated in the past 10 years that gravity is
    assymptotically safe and thus non-perturbatively renormalizable. E.g. Smolin's comment:
    "..It is perturbatively renormalizable and in fact asymptotically free, which in this case is bad, because there is faint hope to save the theory by going beyond perturbation theory..."
     
  12. Mar 31, 2014 #11

    MTd2

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    It seems that they implicitly consider gravity perturbative renormalizable, AS and non perturbative renormalizable. Page 9, footnote 6:

    "6 - Other authors try to interpret ambiguous power-divergent corrections to gauge couplings from Einstein
    gravity as gravitational power-running RGE, with possible physical consequences such as an asymptotically free
    hypercharge [18]. We instead compute the usual unambiguous logarithmic running, in the context of theories
    where power divergences vanish."

    So, they do not discard that gravity may really have all these properties!
     
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