string theorists, will the LHC see SUSY and if not, will this be a huge blow?

jal

Will the LHC see SUSY?
No!
They will see
http://aliceinfo.cern.ch/static/HIF/Talks/Gelis0606.pdf
Color Glass Condensate and forward physics at the LHC
Franc¸ois Gelis
CEA / DSM / SPhT
-------
This is just another way of saying a Quark-Gluon Plasma ball (QGP)
jal

arivero

Except that toponium does not exit.

arivero

Well, Maldacena is more evolution than revolution. Or both; it was a revolution when it happened, and it keeps returning to the top all the years, specially after the (very slight) fading of large dimensions.

All these stats from spires top cites are useful to understand how the topic evolves. For instance in the last four years you can see Maldacena attacting more work than Randall-Sundrum, Antoniadis paper losing some interest, and a pair of papers, of Gubser and Witten, regaining positions each year. Also, you can see that the total number of citations to the top five theoretical papers does not decrease, marking constant work.

If you look in the full range of arxived statistics, you can see that the top cites of the field are really stable since the Maldacenian age. They lost some attention when other topic reclaims work hours: flux compactifications, m-theory, matrix models, randall-sundrum... but then when the focus on this topic dissappears, they escalate positions again.

Coin

I would like to ask a slightly different version of the OP question:

1. If the LHC does not find SUSY-- do people continue to expect SUSY is true? Of course we all know SUSY could still be true even without evidence of such from the LHC, but I'm asking here more from a social standpoint-- would people continue to take SUSY seriously if the LHC does not support it?

2. Let us say that for one reason or another the LHC results lead people to rule out SUSY as realistic. How does String Theory research continue on past this point? Will changes to the String Theory program be necessary for it to survive in a post-SUSY era?

Micha

Honest discussion. Interesting to read. But I think, a little overly pessimistic.

Even if the LHC finds a SM Higgs only, there is still a job to do for theoretical physicists:
a unification of GR and QFT.

In the past progress in physics has come from successful unifications of existing
physical theories, which themselves were backed up by empirical data.
Since a lot of emperical knowledge is encoded in the two theories GR and QFT and since we all believe that nature can not manifestly be built from two incompatible frameworks, there should be one consistent theory which we can find, which has these two theories as a limit. Looking for this theory, that is the point here, is not a search in the wild, but a search backed up by empirical data, which is encoded in the mathematical structure of the two theories.

Some (not me) might argue, that string theory is this unified theory. Well, if this is true, then the task is, bring string theory under control to make predictions.

To be honest, I stole this view from Rovelli (in my own words, so I screwed it up
probably).

It is very nice to listen:
http://www.fuw.edu.pl/~kostecki/school.html

Haelfix

If SuSY is not found at the LHC, it will still be utilized by theorists in wide contexts. Pretty much like every good idea from particle physics, that may or may not be part of the real world (Peccei Quin symmetry, seesaw mechanism, etc)

It just won't be seen as something necessarily physical and more a toy model that has improved analytic properties.

BenTheMan

With what data? Beter values of Lambda? A higgs mass to three decimal places?

The point is that people make very strong arguments based on naturalness---in fact, this is one of the main reasons that people hate string theory. String theorists are willing to accept some UN-naturalness if the end result is natural (i.e. fine tuning the cosmological constant is ok if you can derive the Standard Model). Also, string theorists are willing to TUNE parameters that their theory should explain---this is called moduli fixing. (I know because I'm writing a paper on it now, and hopefully finishing the damned thing soon.) This is one thing that the non-string QG community HATE---they want no tunings. In my mind, this is the best argument AGAINST string theory, that it seems to require tons of tuning to get the SM out.

So, if we only find a single higgs and nothing else, you MUST accept that the weak scale is fine tuned. Period. SUSY stabilizes the hierarchy, as do half a dozen other theories---so we THINK we can explain things. If you are willing to accept that the weak scale is fine tuned, though, then there is no reason to apply naturalness arguments any more. And this will definitely be the case if we only find a single higgs.

So finding just the higgs will be bad for everybody---experimentalists, theorists, model builders, lab managers, the guy who mops the floors at CERN---everybody. There will be no more data---the higgs mass will be measured accurately over 20 years of LHC and (hopefully) vLHC, and that will be that. We won't be able to distinguish models except on the basis that they describe the measurements that we have made, and if one is willing to accept tunings, then you can ALWAYS introduce parameters in your Lagrangian to make things work.

So unifying GR and QFT turns into kind of a moot point untill some government decides to take a VERY risky gamble on a new particle accelerator. And with looming oil shortages, and energy and food prices soaring, no government would risk the billions of dollars needed to build a new collider.

So it's not just string theorists who should be hoping to find something interesting other than just a bunch of top quarks and a few higgses at LHC. The coffee shops in Geneva should be saying their prayers, too!

BenTheMan

I think it's an interesting point that nobody builds models that don't have low energy SUSY. Well, let me say that very few people build models that don't have low energy SUSY---I've never read a paper that describes a non-supersymmetric compactification, but that doesn't mean they don't exist.

But in principle, it is possible to do. I think a generic stack of D branes in some Type IIA background breaks all of the SUSYs (correct me Haelfix or anybody if I'm wrong). Also, you can take a torus and mode out by some discrete symmetries untill you kill all of the SUSYs (i.e. project out all of the gravitinos), then compactify a heterotic string on it.

I think if we don't see SUSY very soon, then string model building will die for about a month, and then there will be a HUGE flux of string models without low energy SUSY. And I'll be close behind, I hope :) The point is, not seeing SUSY won't necessarily harm string theory---it just means that its broken at a higher scale.

Coin

Hm, okay. So would you say then that string models without SUSY are just not in the cards, period?

Micha

You are probably right, as far as experimental high energy physics is concerned. Also I am not saying, I particularly would like this outcome.

I was talking about theoretical physics.

As an example:
What data did Einstein need to develop GR?
Zero. He unified Newtons gravity with SR.

What data did he have to develop SR?
Zero. (Arguable, ok)
He in fact noticed that the transformation properties of classical mechanics
and Maxwells theory were inconsistent.

What data did Newton use to develop classical mechanics?
Zero. He unified Keppler's theory of the planitary motion with Galilei's theory
of falling bodies.

George Jones

From Becker, Becker, and Schwarz:

"The third general feature of string theory is that its consistency requires supersymmetry, which is a symmetry that relates bosons to fermions. There exist nonsupersymmetric bosonic string theories (discussed in Chapters 2 and 3), but lacking fermions, they are completely unrealistic. The mathematical consistency of string theories with fermions depends crucially on local supersymmetry. Supersymmetry is a generic feature of all potentially realistic string theories. The fact that this symmetry has not yet been discovered is am indication that the characteristic energy scale of supersymmetry breaking and the masses of supersymmetry partners of known particles are above the experimentally determined lower bounds."

BenTheMan

Ahh...but who would have believed GR if it weren't for the experimental predictions. Almost immediately, Eddington tested GR's predictions that light follows geodesics, and the perhelion of mercury was derived.

Writing something down isn't the problem. Getting everybody to believe it's correct is always the issue.

This string scale supersymmetry, which we could never test at an accelerator. If SUSY is broken at a very high scale, then there is no way we'd know about it.

Haelfix

Theres nothing preventing SuSy from being broken at higher scales, other than naturalness and minimalism. It so happens (maybe a historical accident) that its a good model for stabilizing the electroweak scale (the original motivation).

If naturalness goes out the window, people will need to figure out better constraints from somewhere else (probably astrophysics/cosmology), unfortunately it is unlikely we will see something as strong and scale independant in our lifetime absent some unforseen theoretical breakthrough.

So like I said, high energy physics in the LHC disaster scenario will become the poorly funded domain of theorists. The ILC will be built b/c there is still some residual political will (a remant imo of the cold war) to do such a thing, but its unlikely another will be built after that unless there really is a compelling breakthrough.

nrqed

I am surprised by this. What countries do you feel stil have this will? After the cancellation of the SSC (which was planned to be even more powerful than the LHC and therefore seemed like a good bet for some form of new physics or at least dicovery of the Higgs) it seemed to me that the US will not be a major source of funding for any future large accelerator. I am not sure that even a consortium of countries will have the will and means to invest billions and billions of dollars. But that's just an impression I have and I may be completely off target.

BenTheMan

Seriously? You're talking about the same Democrats that just CUT funding for high energy physics?

I think that the best that we can hope for is something like SUSY at the LHC. Honestly---there will then be a strong case to make for the ILC, which is a precision experiment, not an energy experiment. If this can be couched in a way that US politicians (thick skulled as they can be) can actually COMMIT to funding, then we MAY get an ILC in 30 years.

Either that, or we'll put more ant farms in space.

jal

How about something else.
http://arxiv.org/abs/0707.2923v1
The Odderon at RHIC and LHC
Authors: Basarab Nicolescu
(Submitted on 19 Jul 2007)
Abstract: The Odderon remains an elusive object, 33 years after its invention. The Odderon is now a fundamental object in QCD and CGC and it has to be found experimentally if QCD and CGC (Color Glass Condensate) are right. In the present talk, we show how to find it at RHIC and LHC. The most spectacular signature of the Odderon is the predicted difference between the differential cross-sections for proton-proton and antiproton-proton at high s and moderate t. This experiment can be done by using the STAR detector at RHIC and by combining these future data with the already present UA4/2 data. The Odderon could also be found by ATLAS experiment at LHC by performing a high-precision measurement of the real part of the hadron elastic scattering amplitude at small t.
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QGP (quark-gluon plasma ) Is still a phase that needs experimentation if we ever want to be able to tap into this kind of energy.

BenTheMan

I don't know what kind of ``energy'' there is to tap into.