Carlo Heissenberg graduated with flying colors in 2019 from the Scuola Normale Superiore di Pisa, the Italian twin sister of the Ecole Normale de Paris. His initial research focused on the infrared properties of gravitational theories and higher spin theories from the perspective of asymptotic symmetries, a topic that later found phenomenological applications in the context of gravitational wave studies.

It was during his first postdoctoral period at Nordita-Uppsala (2019-2023) that Carlo started working on gravitational wave physics using ideas borrowed from particle physics, such as scattering amplitudes and eikonal exponentiation in particular. He quickly became a leader in the field, publishing several important papers with world-famous physicists such as Gabriele Veneziano. Carlo's group achieved, for instance, the first complete calculation of the gravitational deflection angle to the third post-Minkowskian order in the Newton coupling constant expansion, while simultaneously resolving the high-energy limit problem that was puzzling the community.

In the meantime, Carlo was granted a Marie-Curie fellowship and moved to his second postdoc at Queen Mary, while continuing to work on gravitational wave physics, focusing on new observables (waveforms, angular momentum loss, effect of spins…) that could be calculated efficiently using scattering amplitudes techniques.

Carlo accepted an offer from the IPhT and joined the lab as a permanent member the 4th of November 2024.

Link to the video

One purpose of the video is to explain how the proof the background independence (an important property of any quantum gravity theory) of string theory is a major success of string field theory. Harold describes which particular problems regarding background independence have been solved using string field theory and which additional progress can be expected in the future. He also discusses how he used machine learning techniques to solve geometrical problems required for constructing string field theory.

Moreover, he talks about his book on String field theory - A modern introduction (Springer, 2020) and how he arrived at writing it.

Congratulations to Harold !

Analysis of economic activities during a century of urban growth in Paris Evolution between 1829 and 1907 of the spatial distribution of cafes and restaurants in Paris. Researchers Marc Barthelemy (Institut de Physique Théorique and Centre d'Analyse et de Mathématique Sociales, EHESS), and Julie Gravier (Centre de Recherches Historiques and Centre d'Analyse et de Mathématique Sociales, EHESS) have just published in the prestigious journal Nature cities [1] their findings on the analysis of economic activities in a century of urban growth in the city of Paris.

Contemporary studies on the dynamics of economic activity in growing cities generally focus on periods of a few years or a few decades. Using a recently constructed geohistorical database containing around 1 million entries from historical directories, this study presents a detailed analysis of economic activities in Paris over almost a century (1829-1907).

The authors show that activities can be classified into three categories according to their dynamics and their scaling law in relation to population: (1) linear for everyday needs such as food and healthcare, (2) sublinear for public services such as education and administration, and (3) superlinear for specialized or temporary trends. The study also shows that these activities are highly sensitive to historical events, such as major public works or political conflicts, offering new insights into the evolution of activities in growing cities.

[1] Julie Gravier et Marc Barthelemy, A typology of activities over a century of urban growth, Nature Cities 1, pages 567–575 (2024)