Shaposhnikov Wetterich predicted 126 GeV Higgs in 2009

tom.stoer

it seems to be more interesting, more attractive, cool, ... to speculate about 11-dim. theories, SUSY with >100 free parameters, ... instead of doing physics, unfortunately

marcus

I know. Peter Woit's stance seems to require that he suppress discussion of any research line theorists might be pursuing instead of You-Know-Superwhat.

I think he takes exaggerated care not to be labeled as an advocate of any particular program--wanting to qualify (as I think he does) as an objective, disinterested critic.

It is annoying. His blog could be more of a part of the solution---and help the community see its way around the current impasse---rather than simply spotlighting the problem.

Haelfix

There are some serious theoretical problems with Shaposhnikov-Wetterich's proposal, although it does seem like an interesting partial solution to one (but not both) of the stability problems of the electroweak sector.

The biggest problem is that it doesn't even attempt to address the dozens of other problems that the standard model has, which would be fine, except that any additional resolutions to those problems will alter the running of the beta functions and alter many of the assumptions of the proposal, that is, unless the new physics were wrapped up in baroque constructions (hidden sectors, Higgs inflationary scenarios and the like) the exact details of which are problematic for cosmology and actually create highly nonminimal extensions of the standard model (the point that Nima is emphasizing where it seems like any new physics you can imagine is in some sort of trade off between naturalness and nonminimality).

Further, the prediction of the Higgs perse is actually not that impressive when you look at it from a certain point of view. It's very much related to the statement that a Higgs mass below 126 creates a scenario where the Higgs potential loses its absolute stability when run up to the Planck scale, so all it takes are assumptions that favor a data point right at the margin and presto you get your prediction.

A lot of this will become very clear in the next few years, as we get more precise precision electroweak observables that will squeeze the details on the Higgs potential and other relevant observables (top quark mass)

mitchell porter

Hi Haelfix, glad to see you comment on this. But how is that not worthy of attention? That's the mysterious thing. We have all this angst specifically about the value 125 or 126 GeV, about how to make that natural and about whether we should interpret it as finetuned. And, oh yeah, that value is also what you get if you make certain assumptions. Why is there relatively little interest in exploring variations of those assumptions, compared to the vigorous search for new natural models?

I understand the points you raise against the idea, in particular that it would be spoiled by most forms of BSM physics. I understand the possibility that it's just a coincidence. Still, I think the time is ripe for the scattered people who consider the SW type of explanation for the Higgs mass to be a serious contender for the truth, to get together. They could have a conference. Something like "The Higgs, Marginal Safety, and Minimalism in Physics Beyond the Standard Model".

The truth may well be a hybrid of "neo-minimalism" and "traditional baroque" - by the latter I mean the line of thought that encompasses GUTs, supersymmetry, and string phenomenology - but minimalism itself comes in different forms. There's minimalism that's "nothing but the SM up to the Planck scale" (the SW prediction is a great victory for this school of thought), and there's minimalism like "the simplest model that incorporates all the data". The "new minimal standard model" is an example of the latter, and this is a type of minimalism which by definition acknowledges the new data like neutrino masses and dark matter. Perhaps what needs to happen is embedding of the SW mechanism in something like the NMSM, and then investigation of how to hybridize that with "traditional baroque", so as to explain coupling unification, the structure of an SM generation, and all the other facts which really motivate GUTs and beyond.

Haelfix

I actually disagree with Nima about one thing. If I had to give up something, i'd give up minimalism.

It is often the case that what seems nonminimal from an effective field theory point of view, is actually ok from the perspective of the high energy theory. For instance, if we happened to discover a bunch of new Z' models floating around, I think a lot of people would be quite nonplussed on the face of it, but then it might really be elegant from say the stringy phenomenology perspective or perhaps some other type of high energy theory yet to be discovered.. Further from my perspective, the huge array of problems we face in physics is almost assuredly pointing towards a good deal of new as yet discovered physics. From my point of view, I can't imagine anything simple that could fit all the available data and contradictory threads.

On the other hand, I really don't know how to do physics with large amounts of finetuning. Anyone can do that, and all predictive power is ultimately lost.

mitchell porter

An example of minimalism that is also minimally consistent with standard ideas would be something which is just standard model up to a quantum gravity scale, where it then becomes string theory - either the superstring, in which case it's a type of supersplit supersymmetry, or a nonsupersymmetric string, perhaps like a Hellerman-Swanson cosmological solution. (For the opposite, "non-minimal", "neo-baroque" scenario, see the end of this comment.)

I'm mentioning this possibility mostly so we can see what's wrong with it. But first, what might one hope to be its features? A version of the Shaposhnikov-Wetterich mechanism might set the mass of the Higgs. It might specifically be the dilaton which first comes into play at the quantum gravity scale, causing a deviation from the pure SM beta functions, as in 't Hooft's notion of local conformal symmetry constraining the SM couplings. The Yukawas would come from the moduli or from corresponding attributes of a non-geometric phase.

What are the problems for this daydream manifesto? On the empirical side: evidence of gauge unification, neutrino masses, the dark sector and the CMB data need to be accounted for. On the theoretical side: there are probably technical problems in getting believable yukawas just from the moduli.

If we assume supersymmetry (but only at the string scale, so it doesn't interfere with the SW mechanism), then we will have gravitinos, perhaps those could be the dark matter? Given the susy-breaking scale, the mass is probably wrong, both for the early universe and for the present-day properties of dark matter. Perhaps susy can break in some unusual way, so that the usual relation between the gravitino mass and the susy scale doesn't apply.

This is a general issue in contemplating this class of possibilities: one wishes to use the conventional wisdom about how strings, susy-breaking, etc, work, in order to constrain and guide one's thinking; but one also wishes to be aware that theory itself may work differently than we have imagined. The only course of action seems to be to develop the scenario while simultaneously listing all the reasons why it shouldn't work.

Regarding gauge unification, there are definitely string models in which unification is deferred or blocked in some way. One can imagine pushing that up to the string scale, along with supersymmetry, again so as to give the SW mechanism a chance to work.

For neutrino masses and dark energy, I don't have any concrete "proposal", though I note that Hellerman-Swanson cosmology has quintessence, and perhaps neutrino masses could come from something like Tom Banks's cosmological supersymmetry breaking - virtual effects involving gravitinos at the cosmological horizon.

edit: The "neo-baroque" antithesis to this line of thought would involve looking for ways to meaningfully preserve something of the SW mechanism and calculation, while nonetheless having lots of new physics. For example, I'd like to know how far one can go towards making the SW mechanism consistent with the recent recovery of a Higgs mass in the right range within the G2-MSSM. My guess is, not far, but I couldn't say what the specific barriers to this theoretical consummation might be.

mitchell porter

Shaposhnikov-Wetterich watch: Shaposhnikov gave a talk at a symposium on the Higgs. It's a must read for all neo-minimalists: Shaposhnikov says that not only does he have an argument for the Higgs mass, but for the proposition that there is no new physics between Fermi scale and Planck scale (slide 27). Beyond-standard-model physics is to be explained with 3 right-handed neutrinos with keV-GeV scale masses (slide 41), and the Higgs can be the inflaton.

Matt Strassler, who also spoke at the symposium, noted the talk on his blog and promised to analyse it in a future post.

tom.stoer

wow

so there are two competing proposals for "SM with 126 GeV Higgs + neutrinos + no new physics"
- Shaposhnikov Wetterich
- Connes

Suppose the asymptotic safety scenario is correct:
a) there is nothing new to be expected out there
b) we don't have any idea where SM with its gauge group, 3 generations, Higgs, GR, 4-dim. spacetime, ... come from

mitchell porter

A new paper by F. Klinkhamer adds some context to the Shaposhnikov-Wetterich calculation, by listing their work alongside a few others (references 3-6), as just one example of a Higgs boson mass prediction deriving from ultra-high-energy boundary conditions.

marcus

Any concern about Hamber's paper? I haven't reviewed this but my impression is that Shaposhnikov is counting on gravity being asymptotically safe.

And what evidence (eg from Reuter, Percacci, and friends) we have for asymptotic safety depends on the cosmological constant running. But Hamber says:

http://arxiv.org/abs/1301.6259
Inconsistencies from a Running Cosmological Constant
Herbert W. Hamber, Reiko Toriumi
(Submitted on 26 Jan 2013)
We examine the general issue of whether a scale dependent cosmological constant can be consistent with general covariance, a problem that arises naturally in the treatment of quantum gravitation where coupling constants generally run as a consequence of renormalization group effects. The issue is approached from several points of view, which include the manifestly covariant functional integral formulation, covariant continuum perturbation theory about two dimensions, the lattice formulation of gravity, and the non-local effective action and effective field equation methods. In all cases we find that the cosmological constant cannot run with scale, unless general covariance is explicitly broken by the regularization procedure. Our results are expected to have some bearing on current quantum gravity calculations, but more generally should apply to phenomenological approaches to the cosmological vacuum energy problem.
34 pages.

mitchell porter

My interest here is somewhat broader than the original argument. I'm also keeping an eye out for generalizations and for similar ideas, in which the Higgs mass can be deduced from something that happens at the Planck scale. I don't know how universal Hamber & Toriumi's argument is, nor whether Lambda needs to run in every SW-like scheme. So connections are interesting but we need to distinguish cases.

MTd2

Don`t you mean diff? But, what`s the problem in not being diff? Most of the variation happens during inflation and inflation is an event essentially causually disconnected. Diff should be protected in general.

marcus

No, I actually meant what I said---in the 2009 paper we are discussing he is assuming that gravity is asymptotically safe. And the indications he points to, that this is reasonable to assume, all involve renormalization where BOTH of the two main coupling constants (G and Lambda, the c.c.) are allowed to run. All the numerical work I've seen that supports AS being plausible depends on letting Lambda run.

As a reminder, here is the 2009 paper we are talking about:
http://arxiv.org/abs/0912.0208
==quote==
Asymptotic safety of gravity and the Higgs boson mass
Mikhail Shaposhnikov, Christof Wetterich
(Submitted on 1 Dec 2009 (v1), last revised 12 Jan 2010 (this version, v2))
There are indications that gravity is asymptotically safe. The Standard Model (SM) plus gravity could be valid up to arbitrarily high energies...
==endquote==

I keep thinking that the way out of this could be for Hamber to turn out to be wrong, or for his result not to apply for some reason.

mitchell porter

I have just been reading "On the running of the gravitational constant", which atyy mentioned in another thread (and also see "The effective field theory treatment of quantum gravity", page 17 forwards) ... and it seems this is a far more direct challenge to asymptotic safety, and hence to the starting point of Shaposhnikov-Wetterich.

AS has both G and Lambda running, and so Hamber-Tomiuri's argument that Lambda doesn't run (and that it is in fact an emergent invariant scale) contradicts AS. But the running of Lambda doesn't matter for the prediction of the Higgs mass, whereas the running of G does.

marcus

I don't understand how it "doesn't matter", Mitchell. Shaposhnikov's scenario depends on the asymptotic safety of gravity---coupling constants converging to an UV limit. This has not been demonstrated to occur with a fixed value of Lambda.
This may not be the most direct challenge, but it surely must contribute to the difficulties this form of minimalism faces.

mitchell porter

Lambda doesn't appear in the formulas, G does. If Lambda was the only issue, you might hope to motivate the formulas in some other way. But problems with a running G are a direct challenge to the formulas.

Anber-Donoghue's criticism, by the way, is that the running of G is meant to encapsulate the momentum-dependence of many higher-order gravitational interaction terms, but that you can't do this in a way that is consistent across different scales and physical processes. There's no single "formula for the running of G", even within a single theory.

marcus

Lambda not running matters a LOT. So only G appears in some formula? So Lambda does not appear? The point is that as far as we know you do not get asymptotic safety of gravity without Lambda running.