## Wednesday, 27 November 2019

### Preprints and other tools of open research: contribution to the Open Access roundtable at GFP 2019

In the context of the conference GFP 2019 on polymer chemistry, I am taking part in a roundtable on Open Access. Chemists are coming quite late to the Open Access debate. The preprint archive Chemrxiv is young, not widely used, and not independent from publishers. The traditional subscription-based publishing system, and the standard bibliometric indicators, dominate communication and evaluation. And when chemists are dragged into the debate by discipline-agnostic initiatives such as Plan S, their positions tend to be conservative.

Inevitably, chemists are being affected by Open Access and other evolutions of the research system, whether or not these evolutions seem beneficial to them. It would be useful for chemists to know more about preprints and other tools of scientific communication, beyond the traditional journals: not only to comply with Open Access mandates, but also to make their own choices among the existing innovations and best practices.

## Tuesday, 1 October 2019

### Learning scientific writing from great writers

For scientists, writing well (or well enough) is a critical skill, as written texts are essential for communicating research. Of course, not every scientist should be able to write well, as some may rely on collaborators. In a lecture on "Writing physics", David Mermin emphasizes the importance of language and writing through a famous example:
It is also said that even Landau's profound technical papers were actually written by Lifshitz. Many physicists look down on Lifshitz: Landau did the physics, Lifshitz wrote it up. I don't believe that for a minute. If Evgenii Lifshitz really wrote the amazing papers of Landau, he was doing physics of the highest order. Landau was not so much a coauthor, as a natural phenomenon — an important component of the remarkable coherence of the physical world that Lifshitz wrote about so powerfully in the papers of Landau.

## Friday, 31 May 2019

### Uniqueness of the $2d$ critical Ising model

This post is motivated by a request from JHEP to review a recent article by Anton de la Fuente. I am grateful to the author for stimulating correspondence.

#### The conformal bootstrap: analytic vs numerical

The critical Ising model is described by a unitary conformal field theory. In two dimensions, that theory is part of a family called minimal models, which can be exactly solved in the analytic bootstrap framework of Belavin, Polyakov and Zamolodchikov. Minimal models are parametrized by two coprime integers 2 ≤ p < q, they are unitary when q = p + 1, and the Ising model is the case (p, q)=(3, 4).

These 2d bootstrap results date back to the 1980s. More recently, the bootstrap method has been successfully used in higher dimensional CFTs, such as the 3d Ising model. While the basic ideas are the same, there are important technical differences between 2d and higher d.

## Monday, 27 May 2019

### Academics and Wikipedia: the WikiJournal experiment

Since November 2017, I have been an editor of the WikiJournal of Science, a Wikipedia-integrated, broad scope, libre open access journal. For me this is one way of encouraging academics to write in Wikipedia, by making it possible to publish Wikipedia articles in a recognized academic journal. The WikiJournals as they now exist may not yet be ideal for that, but they are already providing valuable insights into the difference between Wikipedia standards and academic standards, academics' attitudes towards Wikipedia, etc.

I am discussing these insights in a Wikipedia essay, for which this blog post is an announcement. This leads me to suggest that WikiJournals be radically reformed - or that any organization with similar aims should follow a different approach. The essay can be discussed at its Talk page.

## Thursday, 9 May 2019

### One software to rule them all? Open source alternatives to Mathematica

This post is based on a joint talk with Riccardo Guida given at IPhT Saclay on May 7th.

Wolfram’s Mathematica has been the dominant computer algebra system for decades (at least in theoretical physics), and in an advertisement it even compared itself to Sauron’s One Ring.

Mathematica’s dominance however does not come from black magic, but rather from its quality and power compared to other available computer algebra systems. But dominant positions are often abused, and Wolfram’s commercial practices can verge on the abusive, though much less systematically than say Elsevier’s. In this blog post we will denounce the problems with Mathematica, and discuss four open source alternatives: SymPy, SageMath, Maxima, and FriCAS. In the case of SymPy, we will also provide a demonstration notebook.

## Wednesday, 6 February 2019

### Solving two-dimensional conformal field theories

This is the text of my habilitation defense, which took place on December 21st 2018. The members of the jury were Denis Bernard, Matthias Gaberdiel, Jesper Jacobsen, Vyacheslav Rychkov, Véronique Terras, Gérard Watts and Jean-Bernard Zuber.

In this habilitation defense, I gave a subjective overview of some recent progress in solving two-dimensional conformal field theories. I discussed what solving means and which techniques can be used. I insisted that there is much to discover about Virasoro-based CFTs, i.e. CFTs that have no symmetries beyond conformal symmetry. I claimed that we should start with CFTs that exist for generic central charges, because they are simpler than CFTs at rational central charges, and can nevertheless include them as special cases or limits. Finally, I argued that in addition to writing research articles, we should use various other media, in particular Wikipedia.

## Introduction

Two-dimensional CFTs are defined by the presence of a Virasoro symmetry algebra. This symmetry is sometimes enough for solving CFTs, and even classifying the CFTs that obey some extra conditions. For example, we can classify CFTs whose spaces of states decompose into finitely many irreducible representations of the Virasoro algebra: they are called minimal models. In some cases, Virasoro symmetry is not enough, but the CFT can nevertheless be solved thanks to additional symmetries. In particular, we can have symmetry algebras that contain the Virasoro algebra.
Let me discuss a few CFTs that I find particularly interesting. I will classify them according to their symmetry algebras, and characterize these algebras by the spins of the corresponding chiral fields. In this notation, the Virasoro algebra is $(2)$, as its generators are the modes of the energy-momentum tensor, which has spin $2$. The sum of the spins of the generators gives you a rough idea of the complexity of an algebra.

## Wednesday, 30 January 2019

### The Im-flip condition in the two-dimensional Potts model

I have been using this blog for publishing the reviewer reports that I write for journals, since the journals typically do not publish the reports. However, the new journal SciPost Physics does publish the reports for accepted articles. I have recently reviewed an article by Gorbenko, Rychkov and Zan for SciPost Physics, and written about the experience: it would seem that I need not blog about that article, since my report is already online.

However, not everything that I have to say on the article made it into the report. I will now write on two calculations that I did: the first one is a test of one of the article’s main predictions in more general cases, the second one is a direct derivation and generalization of a technical result that they obtain in a roundabout way.

## Sunday, 13 January 2019

### Plan S implementation: in danger of mission creep?

The principles behind plan S have already sparked lots of debate, including an open letter denouncing the plan, based on objections that I found not very convincing. Now that the plan’s promoters have published their draft implementation guidance (and are inviting comments on it), the discussion can become more specific. Given the boldness of the principles, their implementation cannot be painless, and is bound to raise criticisms if not resistance. It is therefore both crucial and difficult to get the implementation right, and to inflict the minimum amount of pain that is necessary for achieving the goals.

This means that the implementation should be tightly focussed on open access and cost reduction, to the exclusion of other possible goals that a reform of the publishing system might have. I will discuss whether the draft implementation guidance is indeed focussed enough. But first, let me be more specific about what a minimal implementation might look like.