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Peter Steinberg | USLHC | USA

View Blog | Read Bio

Branes Has A Flavor?

Naturally, many people are interested in the LHC physics program because of its promise to give a glimpse into whole new realms of physics: SUSY, extra dimensions, etc. A much smaller group is excited about the prospects of testing string theory in a completely different regime, via the proposed (and theoretically well-explored) duality between gauge theories and gravity. Leonard Susskind (everyone calls him Lenny, but I haven’t earned my stripes yet) has even been so bold as to call the physics which drives collisions at RHIC quantum gravity that is “blown up and slowed down by a factor of 10^20“. Lisa Randall was quoted in Seed last February saying that after her excitement about the LHC coming online in 2007 (ah, memories), exciting thing #2 was RHIC physics:

Also of interest is the recent application of string theory to the physics being done at the Relativistic Heavy Ion Collider (RHIC), where string theory permits some calculations that would otherwise be intractable. The idea at RHIC is to better understand the strong force that binds together the elements of a nucleon, and 2007 may see the theoretical advances of string theory inform the experimental results from RHIC.

From that perspective, it’s always boggled my mind why everyone hasn’t just dropped everything to understand both RHIC physics and string theory from this perspective. If the analogy really holds, then everyone wins: 1) heavy ion physics finally has a theoretical framework which is in principle better applicable than perturbative QCD (pQCD), which is only thought to work for asymptotically large momentum transfers between quarks and gluons (e.g. jets), and 2) string theory (although not necessarily a full “theory of everything” version) finally gets an experimental playground to propose and test observables. Even better, anything discussed at RHIC will have an immediate chance to be tested at 30x the energy at the LHC. People usually have to wait a generation for this kind of thing!

But reality is what it is and two factors work against this (what I thought would be inevitable) revolution. One, RHIC physics is still in its relative infancy and there is still lots of interesting debate about the meaning of various observables (although we all seem to agree that the “perfect fluid” we observe is deeply connected to the quark gluon plasma), and two, no-one is sure how to make a precise correspondence between the QCD we know, love, and use in real life, and the gravity dual that many thing should exist.

To catch up on things, members of both camps met up on Friday in one of the big lecture halls at Pupin Hall at Columbia University for what was called “AdS Strings Intersect with Nuclear Beams at Columbia“. It was unsurprisingly well attended by about 50 physicists, most from the NY-area institutions (Columbia, BNL, Stony Brook, Princeton, Yale) but a few from farther afield (e.g. MIT). The topics ranged widely, from overviews of the RHIC and LHC experimental programs (by Bill Zajc and John Harris), a discussion of QCD energy loss from a string theory perspective (by Steve Gubser, working from the blackboard and handwritten notes), applications of string theory to energy loss phenomenology (Will Horowitz, Hong Liu, and Derek Teaney) and an interesting discussion of bulk viscosity in QCD, which controls the transition to scale invariance (conformal symmetry) by Dima Kharzeev of BNL. A marathon afternoon to be sure, and not without its share of excitement and frustration, but everyone I chatted with agreed that the cross-currents between the nuclear physics at RHIC and the LHC and the string theory communities can only be a good thing, pushing both sides in directions they never expected.

Afterwards, about 20 of us ventured via NYC subway to a Turkish place in midtown for a post-workshop dinner. Good fun to let people finally hang out and discuss the open issues of the day (which had multiplied since that morning…you know what they say about the more you know…). We all certainly appreciated the Columbia Physics Department’s hospitality and Will Horowitz’ tireless work to pull the day together.

And, yes, the photos are up on my Flickr page. And as a bonus, I tried to write down a few of the good lines from the day:

  1. On the choice of r vs z for the 5th dimension (which are, duh, inversely proportional to each other making the “real” world sit near zero in one variable, and infinity in the other), Hong Liu suggested “always ask”
  2. “Wherever there’s tickling, there’s dragging” – Derek
  3. And while it’s not a “line” per se, the idea of branes carrying a “flavor” (i.e. using them to implement SU(N) symmetries) put me in mind of Return of the Living Dead and Halloween.

OK, so not that funny out of context, but it was that kind of afternoon.

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