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## Comments on “Exactly Marginal Deformations and Global Symmetries”

Last time I pointed to the paper by Green, Komargodski, Seiberg, Tachikawa and Wecht (GKSTW) I was asked to show what I would have done differently. Here is a sketch of some things that I would have put as a part of the main paper (this is not to be assumed to be comprehensive, or careful, nor will I add many references).

Part of the reason to do this is that I think some people out there might benefit from some aspects of this information. What follows is rather technical, so if you’re not well versed in basic SUSY, and on CFT’s,  I apologize in advance: you should not read this then. What I describe bellow is an extended version of the appendix to GKSTW paper. In a good tradition of computer games, this is a third-party add-on. Or you can think of it as a cheap mash-up. Up to you.

Notice: I’ve had some problems with formatting and colors. Temporary fixes have been put in place. Expect updates to text as I find mistakes.

## Must read papers of the week

The Gravity Research Foundation announced the results of the 2010 competition. Here are the results. At UCSB we discussed the prize-winning paper by Mark van Raamsdonk today. It was a very lively discussion and we thought it was a great paper to read. Mark’s paper provided some very tantalyzing evidence that entanglement seems to play a very important role in building up geometry.

On another note, a paper by Daniel Green, Zohar Komargodski, Nathan Seiberg,
Yuji Tachikawa, and Brian Wecht
appeared today. They solve a problem in four dimensional supersymmetric conformal field theories on counting how many marginal deformations there are. As a byproduct, they also solve the problem in 3-d field theories with N=2 Supersymmetry. The paper is beautiful and it is a huge improvement on the work by Leigh and Strassler on the subject many years ago. After reading it I was kicking myself because ‘I could have done it’ (I was interested in the problem and I knew many of the facts. I just didn’t put them together. But if I had thought hard about it I probably could have, although the paper would read rather differently). It’s not surprising that these authors at the Institute for Advanced Study found the solution and that it is written in the particular way that it is written since they have been studying very carefully the superfield formulation of supersymmetric theories in four dimensions. Lubos also commented on the paper.

## Finding pretty patterns in scientific graphs

Here is a graph I produced today as I was studying some problems I’m interested in. The important thing is not what the graph represents physically: it’s just a bunch of trajectories in a Hamiltonian system. What is interesting is that the patterns look pretty and seem to have meaning.

Trajectories in a dynamical system

## Wall street blips

I don’t know how many of the readers here pay attention to what’s happening in Wall Street. Yesterdays trade was quite spectacular, although from many points of view it is terrifying and it is a day that will probably live in infamy.  From the academic point of view I’m sure it will be studied to exhaustion.

All in a day's work.

## The quest for Quantum Ideal liquids

Clifford Johnson pointed to me his post on the quest for perfect quantum fluids. In a certain sense, we are used to thinking about fluids as low energy phenomena (relatively low temperature physics). Famous fluids are characterized by fun properties like superfluidity, or ferrofluids that can be a lot fund to play with in an exhibition. The most perfect fluids will be those with little to no viscosity $\eta$ (viscosity is sometimes related to friction, but this can be misleading).

The recent experiment of RHIC that has claimed detection of the quark-gluon plasma also produces some type of liquid with very low viscosity. To compare how this hot liquid compares with a cool liquid one also needs to measure the entropy density $s$. The quest of who is more perfect than whom depends on the ratio

$\frac \eta s$

Whoever gets the smallest value wins. These are difficult quantities to measure, but they can sometimes be estimated from other known data. From the point of view of theory, this figure of merit is the one that allows comparison of various theories with different numbers of microscopic degrees of freedom, and it is suggested by various gravity dualities (this way of  comparing fluids came from the work of Kovtun, Policastro, Son, Starinets around 2001-2003, in various papers that have made a big splash in physics).

There is an issue of Physics Today that is dedicated to the topic of perfect fluids from various points of view. The readers of this blog might want to wander there and look at the expository articles on the subject. Room will be left open for discussion and questions, although I don’t promise that I will be able to answer them.