## Sunday, December 02, 2007 ... //

### Michael Dine: String theory in the era of the LHC

Michael Dine (Santa Cruz) has a very nice article in the December issue of Physics Today:

String theory in the era of the Large Hadron Collider
He sketches some basic facts about the physics research that is expected to be relevant for the observations at the new collider. So you are offered some basic knowledge about the Standard Model and physics beyond the Standard Model, especially what has become stringy physics such as supersymmetry, grand unification, large extra dimensions, and warped extra dimensions. But he also talks about technicolor, CP violation, dark energy, and other things. You may read a pretty decent basic explanation of the concept of moduli and the character of the stringy landscape as well as the new tools to predict physical phenomena that it has led to.

One of his goals is to correct massive misinformation about a "gap" in particle physics that is being produced by the blogosphere and by the media that are close to the blogosphere. One basic thing that the "critics of science" haven't told their undemanding readers about high-energy physics is that among the theorists, there are two comparably large groups of people: pure theorists and phenomenologists. Phenomenologists who like to post on their favorite hep-ph archive are always interested in experiments that are doable in a foreseeable future, regardless whether their understanding is fully accurate, justified, and complete, while pure theorists who like to post on hep-th focus on ideas that are firmly rooted theoretically, regardless of their immediate relevance for doable experiments.

These are two theoretical approaches to high-energy physics that have been competing for quite some time but there is no inpenetrable gap in between them: it is rather a kind of continuum and many physicists are often switching from one mode of thinking to another. Michael Dine himself is a living example of this fact because he is one of the most solid bridges between hep-ph and hep-th.

The fuzzy border between pure theory and phenomenology is penetrable and the equilibrium between these two approaches is determined by the invisible hand of the market of ideas where scientists are both producers and consumers, not by media campaigns, intimidation, public votes, or undereducated but loud science-haters from the blogosphere. The opinion that one could social-engineer the ratio between different approaches to pretty much the same scientific topics "from above" is an artifact of an ultracommunist mode of thinking and doesn't belong to science.

And how does the equilibrium look like?

As Michael Dine makes very clear, the phenomenological approach usually ends up with random ideas and speculations that are not justified by any deeper fundamental reasons: many papers from the hep-ph archive are random constructions that someone just found interesting enough. This approach may lead to successes at many points of the development of physics but it is just a fact that in the last 20 years, the purely theoretical - one could say "Einsteinian" - approach has been much more successful because of the constant stream of solid and exciting conceptual results as well as new ideas for model building that have been coming out of string theory.

There is nothing universally better about one approach or another and when we are overwhelmed by new confusing data - and the LHC may lead to exactly this situation - the relative importance of phenomenology over pure theory may increase. But that's not where we stand at the end of 2007. Right now, it is extremely important for an idea about new physics to be reconciled with the solid cutting-edge picture of reality that is available, namely with string theory. In the absence of doable tests, this is pretty much the most important criterion that decides whether an otherwise conceivable idea is worth research or not.

And that's the memo.

#### snail feedback (7) :

Well, phenomenology seems to thrive best when there is a lot of data but not enough theoretical understanding. Theory thrives best if it has phenomenological models to explain. Note that you can't do theory without looking outside your window -- it's just that it less well focused in that case, compared to times when there is data to think about.

reader Travel Nepal, we support ! said...

great! me also a physics student from kathmandu!

hi Lubos, looking forward to reading Dine's article, thanks for the tip. I presume this is the same Dine as the author of the book 'Supersymmetry and String Theory', a superb book even I can understand.

Quick technical query: I note there is an entire chapter on SUSY breaking in Dine's book (including many references to the O' Raifeartaigh model although there is no formal citation).
Q: why do I so often read in the popular literature that "there is no known method of SUSY breaking?" Is it that the skeptics don't know the literature, or are the details outstanding? Cormac

Hi Prof R! I hope I remember well that you are the relative of O'R from SUSY breaking. ;-)

I guess that in your family, comments that there exists no known way to break SUSY must be as painful as for those who are creating very new and increasingly concrete and realistic models of SUSY breaking these days.

Complete descriptions of SUSY breaking and its mediation is really a very active field right now (and even Dine's book is already missing some insights about this topic that would probably be included if he were writing the book today).

It would be fair to say that we don't know any "canonical way" that would be as special as Weinberg's toilet (simple Higgs boson) is in the case of the electroweak symmetry breaking. But saying that we don't know any way to break SUSY is of course complete rubbish.

Thanks Lubos, just wondered.

Another thing that mystifies me is the issue of citation.
I regularly see references to the O'R model of SUSY breaking in textbooks and papers (quite often in the title of papers!). Yet the citation is often not given. Of course some scientific works are 'beyond citation' - but surely not a SUSY paper?

The result is that Lochlainn has a surprisingly low number of citations, making it difficult to convince people here his work was important.