What Should I Study Next: SUSY, LQG, String Theory, or GUT?

[the_pulp]

I've been studying, just for pleasure, but studying in the end, a lot about QFT and its prerrequisites reaching some not so bad understanding of the Standard Model. I know that I still have to fill a lot of gaps, but nevertheless, I am looking for some new topic to start reading (while I fill the gaps mentioned).
I was giving a try to Supersymmetry (I've been looking at the youtube lectures of Susskind, which are incredibly clear and I am now trying to read the 3rd book of Weinberg which is much more difficult but also more precise) but now I am seeing in PF threads that LHC results are somewhat discouraging in terms of the potential of SUSY.
In this context what do you recommend me to study now: SUSY, LQG, String, GUT or what? Why? Which theory is more:
Likely to be true?
Useful?
Beautiful?
etc.

Thanks!

 

[marcus]

Sounds like you are considering diversifying. In case SUSY doesn't show up or in case the Superstring program looses some of its momentum you might be thinking it would be good to have studied some Loop basics.
That makes sense, the future of research is (by its nature) unknowable or at least very difficult to predict.

Trends in the job market, publication, and major conference are another matter. But I don't see how anyone can give you advice as to which line of research to follow as an amateur. What I would say would be merely my personal opinion. But if I understand your situation and motivation I think it would certainly be wise to get a TASTE of cosmology, and loop quantum cosmology too, to see if it grabs you.

The way I see it, for the next quarter century it's likely that fundamental physics will be all about the sky. The sky is the arena where the main theoretical innovations will be tested.

I'll get a link to a keyword search that might turn up some papers you'd like to sample to get a taste of what I will call "phenocosmo" (not knowing a handy conventional term for it.)
This is a slow link, takes 20 or 30 seconds sometimes. Currently gets 61 papers from 2009 and later:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+LOOP+SPACE+AND+%28QUANTUM+GRAVITY+OR+QUANTUM+COSMOLOGY%29+%29+AND+%28GRAVITATIONAL+RADIATION+OR+PRIMORDIAL+OR+inflation+or+POWER+SPECTRUM+OR+COSMIC+BACKGROUND+RADIATION%29+AND+DATE%3E2008&FORMAT=www&SEQUENCE=citecount%28d%29
Most of them have a definite phenomenological slant. Let me know if the link does not work for you. I just tried it and it was OK.

I have them ranked by number of citations so to get a first impression of this line of research there's no need to look down the whole list. scanning the first 15 or so titles, and maybe clicking on a few of the abstracts or pdf files should give a representative picture of what's going on in that area. Basically it is figuring out the observable consequences of bounce cosmology on inflation and the microwave background.
I also have some favorite 2012 papers that haven't been out long enough to be cited much, so are not showing up. You asked about beautiful and useful. In my view this line of development is that, and is starting to get quite active.

 

[arivero]

ask yourself, are you more interested on cosmology or in particles?

 

[marcus]

ask yourself, are you more interested on cosmology or in particles?

That is really good advice! Steven Weinberg had some remarks along those lines at the end of a video talk talk he gave about what could be expected from the LHC. He compared the feeling now in cosmology with what it was like in particle theory in the 1970s.


If someone is interested now in particles, I would suggest reading this paper that just came out. MTd2 spotted it and added it to our bibliography:

http://arxiv.org/abs/1208.1030
Resilience of the Spectral Standard Model

Ali H. Chamseddine, Alain Connes
(Submitted on 5 Aug 2012)
We show that the inconsistency between the spectral Standard Model and the experimental value of the Higgs mass is resolved by the presence of a real scalar field strongly coupled to the Higgs field. This scalar field was already present in the spectral model and we wrongly neglected it in our previous computations. It was shown recently by several authors, independently of the spectral approach, that such a strongly coupled scalar field stabilizes the Standard Model up to unification scale in spite of the low value of the Higgs mass. In this letter we show that the noncommutative neutral singlet modifies substantially the RG analysis, invalidates our previous prediction of Higgs mass in the range 160--180 Gev, and restores the consistency of the noncommutative geometric model with the low Higgs mass.

"Spectral geometry" is a better name than Connes' original choice of "Noncommutative geometry". Urs Schreiber already pointed that out some 6 years ago, in a pedagogical review of NCG he wrote. It is technically more specific.

If someone is interested in how to weld the Spectral SM onto LQG they can look up the papers of that Danish guy, Grimstrup.
http://pirsa.org/index.php?p=speaker&name=Jesper_Grimstrup

Spectral approach to rationalizing the particle SM is better than String approach in my estimation because more specifically risky, predictive, and informative. Do you have any view on that, Arivero?

 

[arivero]

Spectral approach to rationalizing the particle SM is better than String approach in my estimation because more specifically risky, predictive, and informative. Do you have any view on that, Arivero?

Both approaches are missing something.

I am not sure if someone else reads my threads on strings (they are in this BSM forum, not in the particle forum, and this forum reunites more people interested in cosmology than particles :tongue: ), but there recently I have implied how strings are wrong: they are looking at the flavour structure (all the Chan Paton consequences, E8xE8, SO(32) etc ) believing that it is the gauge structure. The point that in String Theory all the symmetries are gauged does not allow them to see this mistake.

On other hand, NCG only looks at the gauge structure (the extra dimensions). So it is being very hard to find yukawas, three generations, etc.

 

[the_pulp]

Hi, I didnt thought about going into cosmology. I prefer particle physics because I see it more fundamental, but perhaps there is nothing more useful to study in particle physics (ie something that in the next 5 or 10 years could be proven as sort of true) and perhaps in cosmology there is a lot of ignorance (Im talking about me) to be filled with proven knowledge and experimental evidences. If you think so perhaps that's the route I should follow.

 

[arivero]

Hi, I didnt thought about going into cosmology. I prefer particle physics because I see it more fundamental, but perhaps there is nothing more useful to study in particle physics (ie something that in the next 5 or 10 years could be proven as sort of true) and perhaps in cosmology there is a lot of ignorance (Im talking about me) to be filled with proven knowledge and experimental evidences. If you think so perhaps that's the route I should follow.

If you really prefer particle physics I think it is OK. My personal experience was that a lot of people comes to physics because of astrophysics but then go to particles because the astro offert in their campus is weaker. Some people even left and go to humanities! Other people comes because they like math but they do not feel as mathematicians, they just enjoy to solve problems. So at the end particles becomes a complicated mix.

 

[marcus]

Hi, I didnt thought about going into cosmology. I prefer particle physics because I see it more fundamental, but perhaps there is nothing more useful to study in particle physics (ie something that in the next 5 or 10 years could be proven as sort of true) and perhaps in cosmology there is a lot of ignorance (Im talking about me) to be filled with proven knowledge and experimental evidences. If you think so perhaps that's the route I should follow.

If that's your basic orientation, why try to change it. I simply let you know my different viewpoint. I think of geometry, too, as fundamental. Because matter occurs in it. And, significantly, geometry is not fixed or prearranged, it is in interplay with matter.
Cosmology (especially early universe cosmology) is where one sees geometry as dynamic.

There is now a rapid arrival of new instruments and new data, for cosmology. So the field is in a time of active change and growth. Major problems stand out.

I think this is where fundamental new physics will be developed and tested in the next couple of decades. (I guess one can think of cosmology as the project to understand the interaction between geometry and matter by studying its traces enlarged on the big screen of the CMB.)

I wouldn't offer advice beyond taking a few minutes to find out about the field so that you have a concrete idea of what your choice involves. I would suggest simply to look over the first 10 or 20 abstracts on this list:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+LOOP+SPACE+AND+%28QUANTUM+GRAVITY+OR+QUANTUM+COSMOLOGY%29+%29+AND+%28GRAVITATIONAL+RADIATION+OR+PRIMORDIAL+OR+inflation+or+POWER+SPECTRUM+OR+COSMIC+BACKGROUND+RADIATION%29+AND+DATE%3E2008&FORMAT=www&SEQUENCE=citecount%28d%29
If you do try to do this, and have any trouble with the link, please let me know. I might be able to help or else provide other search links to turn up recent pheno-cosmo papers.
Beyond having some awareness of the alternatives, I don't think anyone (who doesn't know you face to face in real life) can counsel you on what to study.

 

[tom.stoer]

I am not sure if someone else reads my threads on strings ...

I do

... but there recently I have implied how strings are wrong ...

I think I overlooked that

they are looking at the flavour structure ... believing that it is the gauge structure. The point that in String Theory all the symmetries are gauged does not allow them to see this mistake

I don't get this. It seems to be very intersting, but I don't get it. Can you please explain?

 

[arivero]

I do

And I thank you by that. Sometimes I am afraid that only mporter and myself are really thinking, and writing, about these "wrong turns" in string theory. Of course, there is also the silent public in the darkness of the 4th wall, and there is always future readers... or at least our future selves in 2022

I think I overlooked that

Well, I think that the main theme is that string theory could be correct at low energy. That the graviton could be a red herring, or be justifyed with some exponential mechanism, a la Randall or whatever, and most of the final content of the theory is already there in plain view.

The most evident thing is the electroweak mechanism. It has the following properties: the massless theory, the High Energy Standard Model, has the gauge group SU(3)xSU(2)xU(1). The completely broken theory, the Low Energy standard model, has the gauge group SU(3)xU(1). The minimum dimension needed to produce 4D space-time times Kaluza Klein SU(3)xSU(2)xSU(1) is D=11. The minimum dimension needed for 4D space-time times KK SU(3)xU(1) is D=9. So the electroweak breaking "interpolates" between D=9 and D=11. Do we know other object that happens to interpolate between such dimensions? Yes: the network of string theory dualities.

I don't get this. It seems to be very intersting, but I don't get it. Can you please explain?

I mean, it is very interesting that in string theory all the symmetries are local gauge symmetries, and that you can produce a lot of higher unification groups, but that does not mean that they are the symmetries that must to appear in the SM lagrangian as part of its gauge group. They could do not appear at all, being symmetries of dual theories etc... they could be just extra symmetries of the underlying manifolds (or whateverfolds); we are speaking D=4+7, and both dimensions are known to be very peculiar; from Octonions to Milnor Spheres a lot of phenomena happens there. Last, they can be symmetries of the "flavour" structure, this is of the Yukawas, CKM, number of generations, and all these extra parameters in the SM besides the gauge group. For instance, do you remember one of our threads here was about producting all the Susy SM scalars from SU(5) group? I could still expect these 5 to be related to SO(32), because a work in the pre-Dbrane-age was able to build SO(32) in the world-sheet by putting only five "quark labels" in the extreme of the string.

 

[mitchell porter]

Sometimes I am afraid that only mporter and myself are really thinking, and writing, about these "wrong turns" in string theory.

Since I was mentioned, let me state how I view some of Alejandro's ideas... The Koide waterfall is a definite discovery. The sbootstrap pattern is very interesting, but not as definite. But both of these are potentially consistent with "string orthodoxy". I'm not saying "ignore his other ideas", I'm just saying that the two best ideas could form the basis of a mainstream research program which accepts all the usual BSM hypotheses; you don't need to suppose that there were any "wrong turns" at all, in order to find waterfall and sbootstrap interesting.