Presentation of IPhT : The Institute of Theoretical Physics (IPhT) is an Institute of the Direction of Fundamental Research (DRF) of the Commissariat for Atomic Energy and Alternative Energies (CEA).
Next Carlo Heissenberg's arrival at IPhT!  


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 will join the lab as a permanent member in Fall 2024.


E. De-laborderie, 2024-03-15 10:17:00


Measuring the speed of sound at 2.5 trillion degrees  

Figure: momentum per particle versus number of particles seen in a collision between two nuclei of lead atoms at the LHC. Both quantities are normalized by their values in the 5% most central collisions. The increase predicted by IPhT physicists (Gardim at al.) in ultracentral collisions (to the right) is verified by the CMS collaboration at CERN (red symbols). The speed of sound squared, cs2, is the relative slope of the right part of the curve. Credits CERN/CMS. CC-BY-4.0

Collisions between nuclei of lead atoms are carried out at the Large Hadron Collider (LHC) at CERN to study the quark-gluon plasma, a state of matter where neutrons and protons are dissociated into their elementary constituents, quarks and gluons. Its temperature at the LHC has been measured to be (2.540+-0.090) trillion Kelvin [1], [3]. Another important thermodynamic property is the compressibility, which is related to the speed of sound through standard thermodynamic identities.

Back in 2019, Fernando Gardim (a physicist from Brazil who was on sabbatical leave at IPhT), Giuliano Giacalone (PhD student at IPhT) and Jean-Yves Ollitrault (IPhT) proposed to extract the speed of sound from LHC data by analyzing "ultracentral" collisions, defined as collisions at zero impact parameter [2]. The number of particles in ultracentral collisions can vary by 10-15%, corresponding to a variation of density, which can be used to probe the compressibility. They predicted that the momentum per particle, which is proportional to the temperature, should increase as a function of the multiplicity, and that the relative change would provide a direct measure of the speed of sound.

This prediction [2] has motivated a dedicated analysis by the CMS collaboration at the LHC [3]. CMS has recently observed the predicted increase of the momentum per particle and extracted a precise measure of the speed of sound, (49.1 +- 1.6)% of the speed of light, in perfect agreement with first-principles calculations from the theory of strong interactions, QCD.


[1] "Thermodynamics of hot strong-interaction matter from ultrarelativistic nuclear collisions", Fernando G. Gardim, Giuliano Giacalone, Matthew Luzum, and Jean-Yves Ollitrault. Nature Physics Letters 16 (2020) 615-619,

Voir aussi :

[2] "Measuring the speed of sound of the quark-gluon plasma in ultracentral nucleus-nucleus collisions", Fernando G. Gardim, Giuliano Giacalone, Jean-Yves Ollitrault Physics Letters B 809 (2020) 135749

[3] "Extracting the speed of sound in the strongly interacting matter created in ultrarelativistic lead-lead collisions at the LHC", CMS Collaboration, Submitted to Reports on Progress in Physics.

R. Guida, 2024-03-05 16:17:00


Two IPhT researchers feature in the latest issue of "Sciences et Avenir- La recherche".  

Two IPhT researchers feature in the latest issue of "Sciences et Avenir- La recherche" (925, March 2024).

Kirone Mallick was interviewed as part of the article "Maison Poincaré - Les mathématiques en partage" marking the opening of the new Maison Poincaré at the Institut Henri Poincaré. Clémentine Laurens interviewed Kirone, a mathematician, and a biologist. Among other topics, Kirone explains the relationship between physics and mathematics.

Francis Bernardeau, Deputy Director of the Euclid consortium, was interviewed as an expert cosmologist for a special report on Dark Energy (by Fabrice Nicot and Sylvie Rouat) in the same journal issue. In his intervention, Francis gives the general public an overview of the various theoretical models that describe the nature of dark energy, which accounts for around 68% of the energy in the known universe.

R. Guida, 2024-02-29 19:06:00


Henry Navelet (1938-2023)

2023-07-18 20:42:00

SLE multifractal news

2022-04-05 11:28:00

Arrival of Pierre Fleury

2022-02-01 09:21:00

An strongly secured encryption

2020-09-17 17:01:00

Tue, Apr. 23rd, 11:00-12:00
Séminaire général de l'IPhT - Sophie Szopa
Tue, Apr. 23rd, 14:00-15:00
Séminaire de physique des particules et de cosmologie - Lucas Pinol
Tue, Apr. 30th, 11:00-12:00
Séminaire général de l'IPhT - Gary Horowitz
Tue, Apr. 30th, 14:00-15:00
Séminaire de physique des particules et de cosmologie - Stefan Stelzl
Thu, May. 02nd, 15:00-16:00
Séminaire de physique statistique - Pierfrancesco Urbani
François David
Presentation of IPhT
Catherine Pépin
What is so facinating about supraconductivity?
David Kosower
Precision Calculations in the Search for Unification


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