String non-theory failing its "tests"---we need a replacement


by marcus
Tags: failing, nontheory, replacement, string, testswe
marcus
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Dec17-10, 02:25 PM
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http://www.math.columbia.edu/~woit/wordpress/?p=3338
String Theory Fails Another Test, the “Supertest”
==sample excerpt==
Wednesday’s CMS result finding no black holes in early LHC data has led to internet headlines such as String Theory Fails First Major Experimental Test (for what this really means, see here). At a talk today at CERN, yet another impressive new CMS result was announced, this one causing even more trouble for string theory (if you believe in purported LHC tests of string theory, that is…).

Back in 1997, Physics Today published an article by Gordon Kane with the title String Theory is Testable, Even Supertestable. It included as Figure 2 a detailed spectrum which was supposed to show the sort of thing that string theory predicts.

...At CERN today, the CMS talk in the end-of-year LHC jamboree has a slide labeled “First SUSY Result at the LHC!”, showing dramatically larger exclusion ranges for possible squark and gluino masses. Over much of the relevant range, gluino masses are now excluded all the way up to 650 GeV. It looks like string theory has failed the “supertest”.

If you believe that string theory “predicts” low-energy supersymmetry, this is a serious failure. ...
==endquote==

It's clear that string theory is fine as a mathematical theory. Interesting and with many potential uses. I have never criticized string theory as such---though sometimes skeptical of claims by the theorists.

On the other hand as physics theories of unification go it has not produced predictions (or even a clear formulation of M-theory). Advertised "predictions"---more hopes than tests---like large extra dimensions, collider black holes, low-energy supersymmetry---do not seem to be working out.

What could we turn to as an alternative physical theory of unification? Something to think speculatively about, instead of this growing disillusionment.

Would Connes spectral geometry fill the bill? It does not require supersymmetry. It does not raise the tantalizing prospect of collider black holes. It makes some concrete physical predictions. It appears to be a serious unification bid.

Maybe the Connes NCG realization of the Standard Model could fill the mental gap, as a speculative unification prospect.
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arivero
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Dec17-10, 03:20 PM
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Connes model is better, because it is near of Kaluza Klein that string theory. String theoretists abandoned Kaluza Klein in 1984, lured by the oportunities of E8xE8, SO(32), etc...

But Connes should have supersymmetry somewhere, if it is living in dimension 10.
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Dec17-10, 04:29 PM
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But this is not string theory being ruled out, but the simples supersymmetric models. If anything, this would discourage any attempt to come up with any susy theories.

yoda jedi
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Dec17-10, 04:46 PM
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String non-theory failing its "tests"---we need a replacement


and

http://people.roma2.infn.it/~glast/A...nature.GRB.pdf

........even our most conservative limits greatly reduce the parameter space for n=1
models.................Our other limits, and especially our least conservative limit............. make such theories highly implausible *


*string theory, same thing for loop theory.



-----------------------

...................A value this close to the Planck length means that quantum gravity models in which there's a linear relationship between photon energy and speed are "highly implausible." That leaves other quantum gravity options open, including those in which the the relationship is non-linear. Hopefully, theoreticians will be able to devise real-world tests for some of these.............


the ultimate theory have to be nonlinear.
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Dec17-10, 05:02 PM
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Quote Quote by yoda jedi View Post
and

http://people.roma2.infn.it/~glast/A...nature.GRB.pdf

........even our most conservative limits greatly reduce the parameter space for n=1
models.................Our other limits, and especially our least conservative limit............. make such theories highly implausible *


*string theory, same thing for loop theory.
I don't follow you here. String theory is perfectly lorentz covariant, so this paper does not apply to it. For loopy theories, it is a very different matter. The conclusion of this paper is that c(E) = c + a E^2 + ...but it doesn't exclude the possibility a = 0 etc (actually that is the most likely one).

Careful
marcus
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Dec17-10, 06:26 PM
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Quote Quote by yoda jedi View Post
and

http://people.roma2.infn.it/~glast/A...nature.GRB.pdf

........even our most conservative limits greatly reduce the parameter space for n=1
models.................Our other limits, and especially our least conservative limit............. make such theories highly implausible *


*string theory, same thing for loop theory...
What "loop theory" do you mean? Apparently not the current standard LQG since:

http://arxiv.org/abs/1012.1739
Lorentz covariance of loop quantum gravity
Carlo Rovelli, Simone Speziale
6 pages, 1 figure
(Submitted on 8 Dec 2010)
"The kinematics of loop gravity can be given a manifestly Lorentz-covariant formulation: the conventional SU(2)-spin-network Hilbert space can be mapped to a space K of SL(2,C) functions, where Lorentz covariance is manifest. K can be described in terms of a certain subset of the 'projected' spin networks studied by Livine, Alexandrov and Dupuis. It is formed by SL(2,C) functions completely determined by their restriction on SU(2). These are square-integrable in the SU(2) scalar product, but not in the SL(2,C) one. Thus, SU(2)-spin-network states can be represented by Lorentz-covariant SL(2,C) functions, as two-component photons can be described in the Lorentz-covariant Gupta-Bleuler formalism. As shown by Wolfgang Wieland in a related paper, this manifestly Lorentz-covariant formulation can also be directly obtained from canonical quantization. We show that the spinfoam dynamics of loop quantum gravity is locally SL(2,C)-invariant in the bulk, and yields states that are preciseley in K on the boundary. This clarifies how the SL(2,C) spinfoam formalism yields an SU(2) theory on the boundary. These structures define a tidy Lorentz-covariant formalism for loop gravity."

Note this is a recent paper, December 2010. A lot of people have out-of-date information about LQG.

It was never clear that LQG violates Lorentz invariance---people tried unsuccessfully for several years to prove that it did. What is new about this paper is that it proves that it does not. By giving a manifestly covariant formulation.
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Dec17-10, 08:00 PM
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I think to remember that one of the last improvements of Connes theory was to incorporate SU(2)xSU(2) as forefather of SU(2)xU(1). This is interesting because it goes as far as possible in the number of helicity states without susy.

Let me review, again, the count of helicity states:

- The old SM without massive neutrinos had 117 helicity states (90 from fermions, 27 from bosons).

- With massive neutrinos, the SM has 123 helicity states. Lets keep the massive neutrinos in the following:
- Asking gauge interactions to be massless, the SM has 120 helicity states.
- With a minimal Higgs, it has 124.
- With SU(2)xSU(2), but no higgs, it has 126.
- The SM With supersymmetry but no higgs, 126 helicity states plus partners.
- And the MSSM has 128 plus partners.

... and we could like to be able to put the graviton (2 helicity states) in the account.

Now, what about string theory? E8 has 248 states (yep, 120+128), and charged string theory in D=10 needs, besides the supergravity multiplet, 496 states, so the famous E8xE8 or SO(32) groups. Which seem to come from a "charged D=11 supergravity" called M-theory. If we forget about these charges, we still have the D=11 supergravity multiplet, with 128 helicity states (plus partners). And we know that the compactification of D=11 Sugra in the torus T7 or the sphere S7 produces another theory in the D=4 again with 128 helicity states (plus partners) but too many supersymmetries. S7 has as symmetry group SO(8), but it is remarkable that S7 is a fiber bundle with basis S4 and fiber S3, that S4 quotiented by complex conjugation is CP2, and that a fiber bundle with basis CP2 and fiber S3 has as symmetry group SU(3)xSU(2)xSU(2). So S7 is only a "discrete quotient" away from the Standard Model, but the only person in the mainstream aware of it seems to be Atiyah.

(Edit: are there relevant groups with irreps in 120, 123, 124, 126, 128, or even 130? Some role could be expected from SU(8), which has a 120, or from SO(16), whose 120 and 128 allow to decompose E8. Sometimes SU(8) has been considered as a hidden symmetry of the scalars produced in a compactification from D=11 to D=4. For 123, 124 or 130, I dont see any in the most usual tables; on the contrary, the other numbers are very typical)
MTd2
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Dec17-10, 08:26 PM
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Quote Quote by arivero View Post
- The SM With supersymmetry but no higgs, 126 helicity states plus partners.
- And the MSSM has 128 plus partners.
What is the SM with supersymmetry? If MSSM has 128 helicity states, why is it called minimal supersymmetric, if there is another smaller?
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Dec17-10, 08:47 PM
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Quote Quote by arivero View Post
Now, what about string theory? E8 has 248 states (yep, 120+128), and charged string theory in D=10 needs, besides the supergravity multiplet, 496 states, so the famous E8xE8 or SO(32) groups. Which seem to come from a "charged D=11 supergravity" called M-theory. If we forget about these charges, we still have the D=11 supergravity multiplet, with 128 helicity states (plus partners). And we know that the compactification of D=11 Sugra in the torus T7 or the sphere S7 produces another theory in the D=4 again with 128 helicity states (plus partners) but too many supersymmetries. S7 has as symmetry group SO(8), but it is remarkable that S7 is a fiber bundle with basis S4 and fiber S3, that S4 quotiented by complex conjugation is CP2, and that a fiber bundle with basis CP2 and fiber S3 has as symmetry group SU(3)xSU(2)xSU(2). So S7 is only a "discrete quotient" away from the Standard Model, but the only person in the mainstream aware of it seems to be Atiyah.
What of instead of 11D Sugra, it were 11D pure gravity? Can you make it have 128 helicities for the graviton?
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Dec17-10, 08:57 PM
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Quote Quote by MTd2 View Post
What is the SM with supersymmetry? If MSSM has 128 helicity states, why is it called minimal supersymmetric, if there is another smaller?
Without the higgs mechanism. You can can not add susy to a massive vector particle by itself. You must add a new scalar for each massive vector, doing four helicity states, which you can partner then to a pair of weyl fermions -making a Dirac fermion, in principle-.

The Minimal higgs mechanism for a SSM has a higgs with 8 states, three of them go to the zero of each vector, another three go to the scalars, and two of them are -I guess- the h and H bosons.
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Dec17-10, 09:01 PM
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Quote Quote by MTd2 View Post
What of instead of 11D Sugra, it were 11D pure gravity? Can you make it have 128 helicities for the graviton?
No for the graviton. The 11D gravitino has 128 helicities, of spin 3/2 of course. The 11D graviton has 44, and then sugra forces the adition of a tensor field holding other 84 helicities.
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Dec17-10, 09:05 PM
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Just a crazy question then. So, a pure fermionic gravity would have all the needed helicities for SU(2)xSU(2), without Higgs, plus gravitons?
marcus
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Dec17-10, 09:13 PM
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Don't want to interrupt the flow of discussion but I'd like to remind about MTd2's recent thread
called Connes GUT
http://physicsforums.com/showthread.php?t=455898

It got 17 posts so far and some informative Q&A contributions by Arivero and Tom.Stoer

The first post has among other things the following list of Connes particle theory predictions based on NCG, taken from a recent paper with Ali Chamseddine.

==quote Ali and Alain==
...We re-derive the leading order terms in the spectral action. The geometrical action yields unification of all fundamental interactions including gravity at very high energies. We make the following predictions:

(i) The number of fermions per family is 16.

(ii) The symmetry group is U(1)xSU(2)xSU(3).

(iii) There are quarks and leptons in the correct representations.

(iv) There is a doublet Higgs that breaks the electroweak symmetry to U(1).

(v) Top quark mass of 170-175 Gev.

(v) There is a right-handed neutrino with a see-saw mechanism. Moreover, the zeroth order spectral action obtained with a cut-off function is consistent with experimental data up to few percent.

We discuss a number of open issues. We prepare the ground for computing higher order corrections since the predicted mass of the Higgs field is quite sensitive to the higher order corrections. We speculate on the nature of the noncommutative space at Planckian energies and the possible role of the fundamental group for the problem of generations.
==endquote==
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Dec17-10, 09:51 PM
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Quote Quote by MTd2 View Post
Just a crazy question then. So, a pure fermionic gravity would have all the needed helicities for SU(2)xSU(2), without Higgs, plus gravitons?
Er, no, because a "pure fermionic" should mean only the gravitino. And then only the fermions of the SM; you need the bosons too. Sorry that in the above discussion I have not separated between fermions and bosons. It is right to say that a SSM theory has 126+126 fermions plus bosons, while Connes use of SU(3)xSU(2)xSU(2) only has 96+31. Well, damm'it, I did the wrong count before , of course SU(3) has 16, SU(2) is 6 and SU(2)_EW is 9 (because of the masses), so the total is 31 and the grand total is 96+31=127. Put the graviton, and you are in 129. Conclussions: if you want SU(2)xSU(2), it is better to have it broken down to SU(2)xU(1). And, for 120 or 128 bosons or 120 or 128 fermions, susy is the recipe to follow.

My whole point is that I am pretty sure that Connes' theory has susy hidden somewhere.
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Dec17-10, 09:59 PM
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What`s the problem with the bosons? You can make them appear like phonons.
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Dec17-10, 10:08 PM
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Quote Quote by MTd2 View Post
What`s the problem with the bosons? You can make them appear like phonons.
I have not idea how. Can you describe the mechanism (not references, please, just the basic facts and math)
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Dec18-10, 08:48 AM
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No references. I just had this idea while typing the post #12. With so many almost coincident numbers, it seems YOU are asking me to conclude that. And with so many emergent gravity things around, YOU just gave me the media for things to emerge, that is gravitino pure gravity in 11D.

There is nothing of the sort anywhere. I cannot give you any link or math right now, because it was past 1am when I typed that. I briefely looked for something and couldn't find anything.

Do you have any idea?
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Dec18-10, 09:23 AM
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Quote Quote by marcus View Post
What could we turn to as an alternative physical theory of unification? Something to think speculatively about, instead of this growing disillusionment.
As always, my crazy vote is for further development of a combination of the following ideas

- inference perspective: ET Jaynes, Ariel Caticha, Kevin Knuth
- the idea of evolving law: Lee smolin, Roberto Unger

There unification of interactions ~ unification of inference models, as constrained by the complexityscaling -> 0.

But it seems that this must go hand in hand with a reconstruction of the physical counting procedure, and not just be described in terms of existing mathematics.

/Fredrik


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