# Unification of String theory and the Standard Model

1. Sep 11, 2007

### kurt.physics

I was looking at a page in wikipedia about well-known theoretical physicists, i stumbled across the physicists Dimitri Nanopoulos and John Ellis. It mentioned that they both worked together to unify string theory and the standard model and quote

Does anyone know if they were successful in doing so, and what are the ramifications of it.

Thanks

2. Sep 11, 2007

### marcus

Several posters may want to respond to this. I don't think the job of relating SM to string is completed, people are still working on deriving SM phenomenology from stringy assumptions. I don't know if Ellis and Nanopoulos have accomplished anything out of the ordinary in that department. I do know that many string researchers have worked on it and are still doing so.

Just as a side remark, what comes to mind in connection with Ellis and Nanopoulos is a recent paper they wrote with a team of astronomers ("the MAGIC collaboration"). this created a big controversy. Ellis and Nanopoulos, and another string theorizer named Nick Mavromatos, said that some version of string might predict Lorentz violation so that different energy photons could travel at slightly different speed. this was something the MAGIC astronomers thought they had observed. It infuriated a lot of other people including stringfolks and made Mavromatos, Nanopoulos, Ellis and the others at least temporarily famous. Definitely a big deal. Scientific American coverage. Lubos Motl (a prominent citizen of Pilsen in the Czech Republic) threw a fit. If you are at all interested in the people you might want to have a look at the storm-causing paper.

http://arxiv.org/abs/0708.2889
Probing Quantum Gravity using Photons from a Mkn 501 Flare Observed by MAGIC
J. Albert, et al., for the MAGIC Collaboration, John Ellis, N.E. Mavromatos, D.V. Nanopoulos, A.S. Sakharov, E.K.G. Sarkisyan
5 pages, 3 figures, submitted to Phys. Rev. Lett
(Submitted on 21 Aug 2007)

Last edited: Sep 11, 2007
3. Sep 11, 2007

### BenTheMan

Hi Kurt---

The probem of finding the SM within string theory is still an open one. But lots of people get close. I don't know how detailed of an answer you want, so here goes :)

Typically there are a few signposts that one looks for in building models.
1.) Get the gauge group right---SU(3)xSU(2)xU(1).
2.) Get the spectrum right. Three families of quarks and leptons, etc.
3.) Get the hypercharge right. Generally this isn't so hard if you follow one of the traditional embeddings of the standard model in SO(10) or SU(5).
4.) Look at the Yukawa sector. We know which standard model interaction terms should be present, and we know the coefficients which sit in front of those terms. The first cut is to look for a heavy top. (Faraggi estimated the top quark mass from heterotic strings to within somethin like 10%, from looking at heterotic string models.)

Most of the successful phenomenology that has been done in particle physics from string theory starts with the (weakly coupled) heterotic string. Probably the best studied model is by Nanopoulos, Cleaver, and Faraggi. There are a few German groups who do pretty well, too---Buchmueller, Nilles, and students, along with Stuart Raby and Akin Wingerter (his postdoc) at OSU. All of these constructions get the standard model (MSSM) with a heavy top and realistic higgs sector, along with no extra stuff that string models typically come with. By stuff'', I mean extraneous matter in the low energy theory that we should have seen by now in particle accelerators.

Some outstanding problems are with gauge coupling unification and getting good low energy phenomenology at the level of yukawa couplings out. The problem is that it is a long and tedious process to get the lo energy spectrum of a model out (well, for me at least!). And once you find a model with the content of the MSSM, it is a tedious process to work out the yukawa couplings, which is REALLY the step that most people are at.

There have been some other attempts, but I am not very familiar with those. The D-brane constructions (from Type IIA), by people like Shiu, cvetic, and Blumenhagen, can't get a spectrum without chiral exotics in the low energy spectrum, I think. This means that these models are not physical.

4. Sep 11, 2007

### marcus

Hi Ben! Nice to see you here! I see it is your 11 th post so I want to welcome you to PF. I know that getting SM numbers out of stringy models is your special research area so you really know whereof you speak in that department. I appreciate your well-informed voice when you speak about this and would guess that others do as well.

Last edited: Sep 11, 2007
5. Sep 11, 2007

### BenTheMan

Hi marcus. You don't go by martin on the other forum, do you?

Either way, consider my voice somewhat informed:) But I do know how tricky it is to get the SM out of strings. I have 5000 lines of code that attest to that.

6. Sep 11, 2007

### marcus

I'll never tell

this is what I like, you have real hands-on experience and you are often forthright about it.
Sometime I hope some PF posters engage you in conversation about how you actually set up a string model that gives SM numbers. I seem to recall hearing about the work of Volker Braun and Burt Ovrut back maybe in 2004...and I think you mentioned Braun's name. But I dont have either the time or the braincells to get into it, so it would have to be some other PF poster who starts the discussion. I would kind of listen from the side only.

Last edited: Sep 11, 2007
7. Sep 11, 2007

### marcus

Turns out it wasn't 2004 it was 2005. this seeming impressive paper:

http://arxiv.org/abs/hep-th/0512177
The Exact MSSM Spectrum from String Theory
Volker Braun, Yang-Hui He, Burt A. Ovrut, Tony Pantev
15 pages
(Submitted on 15 Dec 2005 (v1), last revised 7 Feb 2006 (this version, v3))

"We show the existence of realistic vacua in string theory whose observable sector has exactly the matter content of the MSSM. This is achieved by compactifying the E_8 x E_8 heterotic superstring on a smooth Calabi-Yau threefold with an SU(4) gauge instanton and a Z_3 x Z_3 Wilson line. Specifically, the observable sector is N=1 supersymmetric with gauge group SU(3)_C x SU(2)_L x U(1)_Y x U(1)_{B-L}, three families of quarks and leptons, each family with a right-handed neutrino, and one Higgs-Higgs conjugate pair. Importantly, there are no extra vector-like pairs and no exotic matter in the zero mode spectrum. There are, in addition, 6 geometric moduli and 13 gauge instanton moduli in the observable sector. The holomorphic SU(4) vector bundle of the observable sector is slope-stable."

But I still have the feeling I heard of Volker Braun back in 2004. Maybe it was just informal news and they hadn't published yet. I suppose there are dozens of papers that trace ancestry back to this one.

Last edited: Sep 12, 2007
8. Sep 12, 2007

### Haelfix

The line I've always been told by String theorists (not phenomenologists) is that once you get 'close enough', you should in principle have the freedom to deform the geometry of the theory such that the correct Yukawa couplings (+CKM matrix etc) fall right out.

Yet (afaik) we have still to see this exact MSSM worked out in full detail. But yea traditionally many promising models end up with too many Fcncs and low energy residual exotics. (there tends to be a lot of U(1) factors floating around also).

So while I think its a very promising line of research, I don't think its fair to say we're quite there yet.

9. Sep 12, 2007

### arivero

There is also a lot of work being published from Madrid: Uranga, Ibañez, etc. Intersecting branes.

10. Sep 12, 2007

### BenTheMan

Haelfix---

This is kind of a hand waving argument. What you generally get is a superpotential that you have to work out. The Cleaver, Faraggi, Nanopoulous model was calculated to like 17th order or something ridiculous like that. In principle, one can suppose that at such an order, by giving the appropriate scalar fields vevs, you can get any numbers you like. But it has yet to be done for even one example---probably because the combanitorics tell you that the problem is impossible to solve!

arivero---the types of models these guys work on typically end up with chiral exotics. Chiral exotics are bad because there is no reason to give them large masses. In the older heterotic approaches, one can get exptics which are vector-like...these guys can form vector-like pairs, which are sinlets under everything, and can safely be given mass at a large scale.

11. Sep 12, 2007

### arivero

Hmm I see, hep-th/0107143 speaks of "a chiral (but anomaly-free) set of exotic multiplets," But hep-th/0105155 tells "no extra fermions nor U(1)'s"

12. Sep 12, 2007

### arivero

My own take, very off mainstream, is that perhaps some bit of new physics into the QCD string can do all the work, instead of the GUT scale string, or perhaps dual to it. The observation is that for every quark (and lepton) charge there is the same number of degrees of freedom than QCD strings and these strings (diquarks and mesons) are bosons, so what you need is a mechanism to couple scalar QCD strings to the Higgs with the same intensity than the standard model fermions do their yukawa coupling. Find such a mechanism, and you have got to control the hierarchy problem.

This observation was not done in the primitive superstring literature because in the 1970 there was not a notion of a top so massive that it does not participate of QCD strings, so to terminate the strings with only five flavour labels was not an option. Also, it is intriguing to notice that five Chen-Paton labels quantize to SO(32). I would like to understand more of the role of SO(32) in open strings, both in oriented and unoriented.

Last edited: Sep 12, 2007
13. Sep 13, 2007

### Haelfix

Hi Ben, yea thats generally what I understood from it. I should note that people like Gordon Kane seem to disagree with this sort of argument, as they feel that varying parameters for any given model yields a quite specific signature space, so you can't get 'anything you want'.

Anyway, super tough problem, hopefully the LHC gives us something about Lsoft terms.

14. Sep 13, 2007

### BenTheMan

I think that this is technicolor, and it's AdS dual.

15. Sep 13, 2007

### arivero

Hmm yes it is. AdS/TechniQCD :D

Actually I have been looking some books on TC and ETC this afternoon. Of course the hierarchy problem here dissapears when the higgs itself dissapears. On the other hand, one seems to need some extra stuff: technifermions and so on. :-( And it seems that TC by itself does the symm breaking, but needs ETC to give mass to the quarks and leptons.

Last edited: Sep 13, 2007
16. Sep 13, 2007

### CERDES

And in the "end........"

Ultimately, there is an answer or there exist answers. Can we ascertain them at our developmental level to date? I believe we can understand whatever there is to be found but can we determine it without it being handed to us? I remain hopeful.

Best
Frustrated Physicist in Behavioral Sciences

17. Sep 14, 2007

### BenTheMan

At the risk of (possibly) offending some of my firends who work on technicolor models, I don't even think they have a viable model which gives the correct masses to quarks and leptons. And there are other problems with fitting the electroweak data, I think.

18. Sep 16, 2007

### arivero

I have mixed feelings about TC. It seems that some NJS approach to sym breaking could work, but I am not happy about having subcomponents (I started the idea of being susy to composite instead of being composite because of being afraid to preon composites even for the gauge bosons) and I am not sure about straighforwardly scaling SU(3). I like topcolor because it appreciates the singular role of the top quark, but about its viability I am not sure neither.

In could be nice to get some of your friends to write an apology of TC, either here or in some other blog.

There is a peculiar scaling phenomena relating the lifetimes of neutral bosons, it only fails for bottomonium, and amazingly the Z0 follows the rule: the lifetime scales as the cube of the mass, and all of them can be aligned with the one of the pion. ie
$${\Gamma_\pi \over M_\pi^3} \approx {\Gamma_Z \over M_Z^3}$$
It could indicate that some of the TC ideas can be valid for the Z0, but the pion is standard SU(3), and on the other hand Z0 decays are perfectly understood from electroweak GWS, so a missing duality between GWS and some QCD or string like formulation should be playing a surprising role.

19. Sep 18, 2007

### CERDES

Would deforming the symmetry also apply to the deformation of tha mathematics present at the big bang? If proximity creates deformity then is it not possible to alter the math model present right before the Planck moment...........
Cerdes

20. Sep 18, 2007

### BenTheMan

The apology for technicolor is this: we've seen it once already, and we have never seen a Lorentz scalar:)

As far as the lifetime estimate, isn't this just simple kinematics? I may be slow, but it seems like a bit of numerology.

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