Lars Brink (1943–2022)

Lars Brink passed away on October 29, 2022 at the age of 78. He was an Emeritus Professor at Chalmers University in Göteborg, Sweden, and a top class theoretical physicist. He had obtained many key results in string theory, supersymmetric field theory and supergravity theory which are often considered as prerequisites for a fundamental approach to the elusive quantum gravity.

And he also had an exceptional understanding and mastering of all other less conjectural domains in physics where he displayed the same depth and competence as in his exploration of the unknown. This is an essential element that enlightens the facts that during his many travels Lars was highly welcome in the many prestigious institutions he visited all over the world, and that in Sweden he became a member of the Royal Swedish Academy and served there for many years in the Nobel committee for Physics, and as its chairperson in 2013.

When I think about my friend Lars whose deep knowledge covers so many different domains of research, his exceptional career appears as a necessary concomitant. That is obvious from what was just evoked. But what may be less obvious is what often came first to my mind when I met him: the image of the humanity, the kindness that pervaded his behavior.

Let me first evoke an ancient encounter that may look insignificant but that I cherish to remember. We both attended a workshop in Vancouver (Canada) in the last week of July 1986 during the International Word Fair 1986. The playground exhibited an impressive four-loop rollercoaster which looked to me a bit terrorizing; but which reminded me that I promised my young daughter to go with her on a rollercoaster once back home. Here was the right place for me to give it a try but I admit I was scared. Come on, said Lars, we will do it both together; and although it was indeed somewhat scary, everything was of course fine.

This was essentially just fun but all our many encounters, connected with physics or not, revealed the profound sensitivity of Lars and the deep nature of our friendship. In 1991, I got married with Mira and the first time Lars met her at a physics conference where she had accompanied me, he talked to her and said: “We (?) are so happy to see François with you; we were deeply worried about him: he was not well; he seemed to have lost his joie de vivre. We knew that he cannot live alone and now we are so relieved to see him with you”. Clearly “we” meant friends of Lars and mine who were discussing “my case”$\dots$ and I felt a very nice feeling about this event: the simplicity with which friends may care about each other.

In December 2014, we found ourselves, Mira and I, Lars and his wife Åsa, in Chile at Valdivia, the kingdom of our physicist friend Claudio Bunster. On December 31, the four of us decided to spend New-Year’s eve together in Valdivia and the next day we decided to make a trip in the north of Chile. We drove up to the seaside and then to the verge of the magnificent colorful Atacama desert where Mira and I had spent eventful holidays a few years ago and this trip with Lars and Åsa was a very pleasant reminder.

I will close this evocation of my personal relation with Lars by expressing my pleasure in observing the collaboration and the friendship Lars developed with Pierre Ramond, Professor at the University of Florida at Gainesville. Their common interest and work in string theory and in its modern mathematical and physical developments nourished their friendship whenever they were both simultaneously present. This friendly atmosphere extended itself naturally to include Mira and me, and particularly manifested itself each time I was alone when I met Pierre: he unavoidably greeted me with the question “Where is your better half!”

In 2013, the Nobel Prize in Physics was awarded jointly to François Englert and Peter Higgs for the theoretical discovery of the Brout–Englert–Higgs (BEH) mechanism verified by the extraordinary experimental discovery at CERN of its predicted scalar BEH boson (often labeled Higgs boson) together with its predicted properties. Brout passed away in 2011 and was therefore deprived of the Nobel Prize he deserved as well as Englert and Higgs.

As might have been expected, the award ceremony speech was given by Lars Brink on December 10, 2013 in rather emotional terms; in particular he said: “$\dots$ We have found not only a multitude of new particles but also two forces that are only apparent in the Microcosm; the Strong Nuclear Force that binds the nuclei and the Weak Force responsible for radioactive decay. How can we describe such forces that only act over very small distances? The solution came almost fifty years ago in two papers, one by Englert and Brout¹ and the other by Higgs² — two short papers roughly a page long, that changed the world $\dots$”.

This statement was very concise but Lars explained in great detail the subject of the Nobel Prize (see attachment). This beautiful extensive analysis is a real piece of art. I will now briefly describe qualitatively its content. The full text is joined to this Memorial.

The universe appears constructed out of basic small constituents called elementary particles (e.g. the electron) interacting through fundamental interactions; these are called long range if their action can be felt arbitrarily far from their sources (as is the case for the electromagnetic interactions and for the gravitational interactions). If this is not the case, they are called short range interactions. All this was qualitatively known before the BEH mechanism was known but short range fundamental interactions were not understood.

The BEH mechanism became in the second half of the 20th century the cornerstone for the Standard Model of elementary particles. This included a classification of all presently known elementary particles and of the interactions that govern their behavior, including the weak and the strong short range interactions. These are all the interactions which are often assumed to govern all phenomena in which gravitational forces can be neglected. (These are indeed not fully understood because there is not yet a well-defined quantization of them.)

The BEH mechanism is based on the non-Abelian generalization of electromagnetism, Yang–Mills theory. This can be presented in the language most adapted to the subject, namely (the previously unpopular) quantum field theory. It was indeed, by using the properties of this approach, more precisely the results obtained by Englert et al.,³ that Englert and Brout made the educated guess at the 1967 Solvay conference in Brussels that the BEH theory was renormalizable.⁴

This was fully proven in the magnificent 1971 paper by ’t Hooft and Veltman⁵ (Nobel Prize 1999), that finally extended the precise scientific knowledge to nuclear and subnuclear scales on the path traced by Galilee, Newton, Maxwell and Einstein.