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## Yet another workshop announcement….

I’m organizing a workshop in late September, together with Jun Nishimura and Toby Wiseman, taking place in London. We’re very close to the limit of participants that we can afford. The workshop will be on Numerical approaches to AdS/CFT, large N and (quantum) gravity. We’re going to put a lot of people who have not all met each other yet in a closed room, we’re going to `lock them in’ so to speak, and hope that fantastically new collaboratiosn and ideas will spring out of this.

Mostly, we will try to figure out what has been done in this area already and hope to get a road map of what can be done, what should be done and how much resources does it need in order to be done.

For more information, here is the website.

Below is the conference poster, which I cobbled up from some old photos of Big Ben, some photoshop magic and some creative license with masks trying to make it look cool. Of course, my co-organizers corrected all the mispelled names that I mistyped and it is likely that we saved a bundle on ‘artwork’ commisioning.  I really have no clue how much these things cost.

Conference Poster

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## Happy Birthday, Tom and Willy

The last few days I attended the conference in honor of Tom Banks and Willy Fischler on the occasion of their 60th Birthday. Here are the details of the conference.

Willy Fischler and Tom Banks at the conference dinner.

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## Belief and facts in theoretical physics

Today on the arxiv Oswaldo Zapata wrote an essay on issues about fact and belief systems in superstring theory. Naturally, Peter Woit decided that this was really important and wrote a whole article about it. Here I will collect a few recollections that serve as a rebuttal/complement to some of those discussions. Mostly, I feel implicated by some of this discussion since at least one of my works (together with Juan Maldacena and Horatiu Nastase) is mentioned as changing the history of an idea from belief to fact.

The whole issue is to quantify the following statement: the AdS/CFT correspondence is a true fact.

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## Small celebrations.

After complaining bitterly about my lack of free time, at least now I have finished writting the first paper of the year, so now I can show some of the work I’ve been doing. I’ve been feeling so overworked that at least I can celebrate the small accomplishments of the day. This is why, if I write a paper, I tell my family about it and have little celebrations. These are like drinking a nice glass of wine with dinner, or doing other silly little things to show my good mood.

It feels good to let go! There is still the apprehension of what will people say. But after writing so many papers, you kind of get used to it. Considering that from gestation of ideas, to calculations, to a paper it took more than 9 months, it’s not that different in time scale from delivering a baby. Seeing that it is only 4 pages, it doesn’t seem like it would take so much effort.

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## X-ray visions

Recently I went to the dentist and had a full set of routine X-rays taken. The technology has changed a lot since my childhood. Mostly because now my dentist hooks up his laptop to an electronic device that is put in my mouth and the X-rays are ready within fractions of seconds after exposure. This way I don’t have to wait as much for the X-ray films to be developed and in the end this is a cheaper way to get the information. I’m also assured that the new electronic readers require less exposure than film so that my total radiation exposure is reduced by quite a bit.   I also get to wear the lead apron to prevent some of the soft tissues in my chest cavity and lower body from being exposed to unnecessary radiation.

So what do X-rays actually measure? This is what I thought I would ask and answer today for my first post in a long time. Part of this question is about how the photons in the X-rays interact with matter and why is lead used to stop X-rays.

This is very different than the superhero X-ray vision. Surprisingly, for most superheroes it is still true that lead will stop them from seeing an object.

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## Exact Lattice Supersymmetry

Our first guest blogger is Simon Catterall from Syracuse university, who graciously agreed to write a post about the ongoing research attempting to formulate supersymmetric theories on the lattice. Enjoy!

#### Introduction

The problem of formulating supersymmetric theories on lattices has a long history going back to the earliest days of lattice gauge theory. However, after initial efforts failed to produce useful supersymmetric lattice actions the topic languished for many years. Indeed a folklore developed that supersymmetry and the lattice were mutually incompatible. However, recently, the problem has been re-examined using new tools and ideas such as topological twisting, orbifold projection and deconstruction and a class of lattice models have been constructed which maintain one or more supersymmetries exactly at non-zero lattice spacing.

While in low dimensions there are many continuum supersymmetric theories that can be discretized this way, in four dimensions there appears to a unique solution to the constraints — $N=4$ super Yang-Mills. The availability of a supersymmetric lattice construction for this theory is clearly very exciting from the point of view of exploring the connection between gauge theories and string/gravitational theories. In this posting I will outline some of the key ingredients that go into these constructions, the kinds of applications that have been considered so far and highlight the remaining difficulties.

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