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.

Wednesday, 16 March 2016

Free bosons and Virasoro null vectors

In a recent article, Manabe and Sulkowski have proposed a method for deriving Virasoro null vectors, starting with certain deformed matrix integrals. In this blog post I will look for a conformal field theory interpretation of this method.

Quick reminders on Virasoro null vectors.

A null vector of the Virasoro algebra is labelled by two integers $r,s\geq 1$, whose product is the level of the null vector. This null vector occurs in the Verma module with a specific conformal dimension $\Delta_{r,s}$, and it can be written as
$|\chi_{r,s}\rangle = L_{r,s} |\Delta_{r,s}\rangle$ where $|\Delta_{r,s}\rangle$ is the primary state of our Verma module, and $L_{r,s}$ is a level $rs$ creation operator.

Wednesday, 30 December 2015

République numérique et Open access: les leçons d'une expérience

Après avoir consulté le public au sujet du projet de loi pour une République numérique, le gouvernement français a donné ses réponses aux suggestions qui ont été faites, et le conseil des ministres a adopté un projet de loi modifié en conséquence. Ayant participé à la consultation au sujet de l'article 9 du projet initial, intitulé "Libre accès aux publications scientifiques de la recherche publique", je voudrais ici évaluer dans quelle mesure l'exercice a été utile, et quelles leçons en tirer pour d'éventuelles consultations futures au sujet d'autres projets de loi.

Monday, 14 December 2015

Peut-on former les chercheurs à encadrer des thèses?

Travailler en équipe, communiquer, recruter et encadrer stagiaires, doctorants et postdocs: quelques facettes du métier de chercheur pour lesquelles ils n'ont souvent pas de méthodes de travail bien définies, faute d'y avoir été formés. Mais existe-t-il des méthodes à la fois assez souples pour marcher dans des domaines de recherche variés, et assez simples pour faire l'objet d'une brève formation? C'est ce que je me demandais en m'inscrivant à une formation proposée par le CNRS, intitulée "Accompagner et encadrer un doctorant", que j'ai suivie les 19 et 20 novembre en compagnie de neuf autres chercheurs.

La formation était faite par Simon Thierry, de la société Adoc Mètis, une société formée de trois jeunes anciens chercheurs et d'un doctorant. Ces personnes se sont donné pour mission de développer et de diffuser des méthodes de gestion de resources humaines pour l'enseignement supérieur et la recherche, méthodes inspirées de ce qui se fait dans les entreprises, mais aussi informées par une réflexion et une recherche spécifiques. Le résultat est, à première vue, assez convaincant, et je vais résumer certaines des idées et méthodes proposées.

Tuesday, 8 December 2015

Relations between conformal field theories with affine and $W$-algebra symmetries

This is a commentary of the recent article by Creutzig, Hikida and Ronne, which I was asked to review for the Journal of High-Energy Physics. I am grateful to the authors for helpful correspondence.

It has been known for a long time that $W$-algebras can be obtained from affine Lie algebras by Drinfeld-Sokolov reduction. The reduction eliminates a number of generators of the affine Lie algebra, leaving a $W$-algebra with fewer generators (but more complicated relations). The reductions of algebras are most useful when they can be promoted into relations between correlation functions of conformal field theories. For example, the reduction from the $\widehat{\mathfrak{sl}}_2$ affine Lie algebra, to the Virasoro algebra, can be promoted into a relation between correlation functions of the $H_3^+$ model and Liouville theory, two CFTs whose symmetry algebras are $\widehat{\mathfrak{sl}}_2$ and Virasoro respectively.

Generalizing the $H_3^+$-Liouville relation to models with larger symmetry algebras could be helpful for understanding, or even solving, such models. In order to find such generalizations, there are two approaches: