## Friday, 21 October 2016

### Finite operator product expansions in two-dimensional CFT

While the conformal bootstrap method has recently enjoyed the wide popularity that it deserves, its applications have been mostly restricted to unitary conformal field theories. (By definition, in a unitary theory, there is a positive definite scalar product on the space of states, such that the dilatation operator is self-adjoint.) Unitarity brings the technical advantage that three-point structure constants are real, so squared structure constants are positive, leading to bounds on allowed conformal dimensions. However, dealing with non-unitary theories using similar methods is surely possible, at the expense of having the signs of squared structure constants as extra discrete variables. And unitarity is sometimes assumed even in cases where it brings no discernible technical benefit, such as in studies of torus partition functions, where multiplicities are positive integers whether the theory is unitary or not.

So it is refreshing that, in their recent article, Esterlis, Fitzpatrick and Ramirez apply the conformal bootstrap method to non-unitary theories.

## Tuesday, 27 September 2016

### Abonnements aux revues scientifiques: les chiffres du CEA

En page 10 de son rapport d’activité 2015, le Service de Valorisation de l’Information du CEA publie les coûts des abonnements aux revues électroniques pour les années 2014, 2015 et 2016, avec pour 2015 l’évaluation du coût par article téléchargé. Je voudrais ici diffuser et commenter ces chiffres.

## Sunday, 24 July 2016

### SciPost: the right tool for commenting arXiv articles?

ArXiv has not changed much since it started in 1991, and it is only starting to consider the obvious next steps: allowing comments on articles, followed by full-fledged open peer review. Scientists have not all been waiting idly for the sloth to make its move, and a few have tried to build systems for doing that. Here I will discuss a recent attempt, called SciPost.

#### A strong editorial college

The most distinctive feature of SciPost is its editorial college, made of well-known theoretical physicists. These people do not just lend their names to the project. Given how SciPost functions, they have a lot of work:

## Saturday, 28 May 2016

### Was it such a good idea to put this review article in the public domain?

Two years ago, when posting a review article on Arxiv, I did the experiment of putting it in the public domain. The idea was to allow anyone to distribute and even to modify it, in the hope of increasing the circulation and usefulness of the article, as I explained in this blog post.
Putting the text in the public domain also has potential drawbacks:
• losing revenue,
• losing control.
The potential loss of revenue is not a problem for me, as I am already employed and paid to do research by the French research agency CNRS. In fact I am not sure whether scientists should earn money from their professional writings or patents. Anyway, in the case of such a specialized text, the potential revenue would be small.
The potential loss of control is a priori more worrisome. Could my reputation be damaged if someone did something bad with my text? In order to find out, I had to wait until people actually did something with my text.

My review article is now available for sale on Amazon, in the Kindle format, at the price of about $9. I had nothing to do with that edition, I guess it was done by an Amazon robot. ## Monday, 18 April 2016 ### Building a website for physics courses with Drupal I have been involved in building a new website for the theoretical physics courses at IPhT, using the content management framework Drupal. This post is the story of this experience, written for researchers who are considering embarking in similar projects. Riccardo Guida and I have been organizing the IPhT courses for years (many years in Riccardo's case), and one year ago we finally decided to escape the IPhT website and set up a dedicated website for the courses. The problem with the IPhT website was that it did not know what a course was. A course was a collection of various objects: a number of "seminars", a "publication" where lecture notes could be stored, a few lines in a list of courses on a static webpage, etc. These objects did not talk to one another, and the same information had to be copy-pasted several times. ## Tuesday, 12 April 2016 ### The light asymptotic limit of$W\$ algebra conformal blocks

$W$ algebras are natural extensions of the Virasoro algebra, the symmetry algebra of local conformal field theories in two dimensions. Conformal field theories with $W$ algebra symmetry include $W$ minimal models and conformal Toda theories, which are generalizations of Virasoro minimal models and Liouville theory respectively. In particular, $sl_N$ conformal Toda theory is based on the $W_N$ algebra, which has $N-1$ generators with spins $2,3,\dots, N$, and reduces to the Virasoro algebra in the case $N=2$.

#### The problem of solving conformal Toda theory

Solving $sl_{N\geq 3}$ conformal Toda theory is an outstanding problem. One may think that this is due to the complexity of the $W_N$ algebra, with its quadratic commutators. I would argue that this is rather due to the complexity of the fusion ring of $W_{N}$ representations, with its infinite fusion multiplicities. Due to these fusion multiplicities, solving $sl_N$ conformal Toda theory does not boil down to computing three-point function of primary fields: rather, one should also compute three-point functions of infinitely many descendent fields.

## Saturday, 2 April 2016

### Perverse bibliometrics: the case of patents

Bibliometrics, the counting of publications and citations, is being used for evaluating researchers, research institutions, and academic journals. But simple bibliometric indicators can be gamed, and complex indicators lack transparency. No known indicator avoids these two problems, while some indicators (such as the journal impact factor) manage to have both. As a result, the misuse of bibliometrics has been widely denounced.

In spite of these problems with bibliometrics, someone had the idea to do bibliometrics with patents, in order to rank research institutions. The result is Reuters' list of the world's most innovative research institutions, which is topped by the Alternative Energies and Atomic Energy Commission (CEA). The methodology for establishing the list is not known in detail, but we do know that it is involves 10 different criterions, and is mainly based on the numbers of patents and citations thereof.