Light fermions and ~125 GeV Higgs from asymptotic safety

mitchell porter

From http://arxiv.org/abs/1112.2415, "Planck scale Boundary Conditions and the Higgs Mass", I learn of http://arxiv.org/abs/0912.0208, "Asymptotic safety of gravity and the Higgs boson mass", which predicts a Higgs mass of 127 GeV as a consequence of the vanishing of the Higgs self-interaction and its beta function at the Planck scale.

I have also found my way to http://arxiv.org/abs/1104.5366, "Light fermions in quantum gravity", which seems to be proposing that gravity itself can play the role of a technicolor force: "We specifically address the question as to whether metric fluctuations can induce chiral symmetry breaking and bound state formation."

I never had much interest in asymptotic safety, but I know it was discussed here. Can anyone offer a sensible evaluation of the claims in these papers?

Demystifier

Whatever the final Higgs mass will turn out to be (perhaps we will know today), there are already a few theories which predict it:
http://lanl.arxiv.org/abs/0708.3344

marcus

But among those listed as predicting around 125 GeV, the one Mitch mentioned stands out. Here is their conclusions paragraph

==quote Shaposhnikov and Wetterich==
In conclusion, we discussed the possibility that the SM, supplemented by the asymptotically safe gravity plays the role of a fundamental, rather than effective field theory. We found that this may be the case if the gravity contributions to the running of the Yukawa and Higgs coupling have appropriate signs. The mass of the Higgs scalar is predicted m_H = m_min ≃ 126 GeV with a few GeV uncertainty if all the couplings of the Standard Model, with the exception of the Higgs self-interaction λ , are asymptotically free, while λ is strongly attracted to an approximate fixed point λ = 0 (in the limit of vanishing Yukawa and gauge couplings) by the flow in the high energy regime. This can be achieved by a positive gravity induced anomalous dimension for the running of λ . A similar prediction remains valid for extensions of the SM as grand unified theories, provided the split between the unification and Planck-scales remains moderate and all relevant couplings are perturbatively small in the transition region. Detecting the Higgs scalar with mass around 126 GeV at the LHC could give a strong hint for the absence of new physics influencing the running of the SM couplings between the Fermi and Planck/unification scales.
==endquote==
http://arxiv.org/pdf/0912.0208
Asymptotic safety of gravity and the Higgs boson mass
Mikhail Shaposhnikov
(Institut de Théorie des Phénomènes Physiques, École Polytechnique Fédérale de Lausanne)
Christof Wetterich
(Institut für Theoretische Physik, Universität Heidelberg)
12 January 2010

MTd2

This is also impressive, from 1993. Correct values for Top (before its discovery) and Higgs.

http://lanl.arxiv.org/abs/hep-ph/9312316

Top and Higgs Masses in Dynamical Symmetry Breaking

David E. Kahana, Sidney H. Kahana
(Submitted on 21 Dec 1993)
A model for composite electroweak bosons is re-examined to establish approximate ranges for the initial predictions of the top and Higgs masses. Higher order corrections to this $4$-fermion theory at a high mass scale where the theory is matched to the Standard Model have little effect, as do wide variations in this scale. However, including all one loop evolution and defining the masses self-consistently, at their respective poles, moves the top mass upward by some $10$ GeV to near $175$ GeV and the Higgs mass down by a similar amount to near $125$ GeV.

marcus

But what collateral predictions do they get, besides the two masses? If you know please save the rest of us a little trouble.
Shaposhnikov and Wetterich have, in addition to their Higgs mass prediction, something falsifiable to say about the running of SM coupling constants and a combined theory of SM+asymsafe gravity remaining valid. The appearance of new physics at an intermediate energy scale would rule their idea out.

Do the Kahana have something comparably interesting and falsifiable on the table?

MTd2

I don't know. I have yet to read that paper. I found it listed in that paper which lists several prediction of the Higgs' mass.

Vina31

"Light fermions in quantum gravity" is about the question if asymptotically safe quantum gravity can induce chiral symmetry breaking, so that would be a technicolour mechanism where the technibosons are in fact gravitons. There's a problem with that, namely that the induced fermion masses would be of the order of the Planck scale, so we would never get any light fermions (as we observe in our universe).
Thus the paper addresses the question if such a symmetry breaking mechanism can be avoided (otherwise asymptotic safety would be ruled out by observations.)
The main result is, that this mechanism is avoided (which is good news for the asymptotic safety scenario, and a non-trivial result.)

There's also a proceedings paper on the same topic (http://arxiv.org/abs/1109.3784), which I think is a bit easier to read (not so technical and shorter).

Demystifier

Now we can see whose predictions were correct.

atyy

Cosmic Variance says there are hints of a non-SM Higgs. Do any of these models predict that?

BTW, there's a recent paper by Anber and Donoghue arguing that there is no useful and universal definition of a running gravitational constant below the Planck scale.

phyzguy

I found what I think are two falsifiable predictions based on this nu-MSM model. The claim is that right-handed sterile neutrinos are the dark matter, and this paper makes predictions of their masses and gives some ideas on how to detect both the lightest sterile neutrino (predicted to be in the keV range) and the heavier sterile neutrinos (predicted to be in the GeV range). This paper also makes a prediction of the tilt of the fluctuation spectrum, which should soon be verified by the Planck satellite.

These ideas seem reasonable to me, but I'm an astrophysicist and not a particle physicist and may not understand. I'd appreciate comments.

Edit: Sorry, Marcus, I realize I misread your comment and you were asking about falsifiable predictions of the Kahana model. In any case, I'd be interested in comments on the predictions of the nu-MSM model.