Caption: The string theory solution is a product of a four-dimensional universe times a small  six-dimensional space. The cosmological constant (Λ) is the minimum value of the potential energy, here plotted as a function of the volume of the six-dimensional manifold. The cosmological constant before the “uplifting” (red curve) is negative, while after it (blue curve) is positive and tiny, as that of our universe. Experiments reveal that our universe has an accelerating expansion, which, in the context of general relativity, requires the positivity of Einstein's cosmological constant.  A positive cosmological constant poses several problems in the context of quantum gravitational theories.   String theory, one of the most developed theories of quantum gravity, has been struggling to find solutions of the equations of motion that include a four-dimensional space with positive cosmological constant.

The Nuclear Physics Division of the European Physical Society has awarded Giuliano Giacalone, a former student of IPhT, its PhD prize. This prize is awarded every third year, and the ceremony took place during the EuNPC 2022 conference in Santiago de Compostela, Spain, in October 2022. https://indico.cern.ch/event/1104299/page/26561-npd-2021-phd-prize-winners Giuliano, now a postdoc at the University of Heidelberg, completed his PhD thesis "Observing the shape of nuclei at high-energy colliders" in November 2020 under the supervision of Jean-Yves Ollitrault. His thesis has previously been honoured with an award of the French Physical Society. https://www.sfpnet.fr/accessits-prix-jeunes-chercheurs-euses-2020-de-la-sfp Congratulations!

Figure caption: The rules governing the dynamics of the balls in the "box ball system" can be illustrated with the help of a carrier that loads and unloads the balls by running through the system from left to right at each time step.   Understanding how macroscopic laws and large-scale properties emerge from the microscopic interactions between the constituents of a system is a major problem in statistical physics. One can for instance consider the appearance of hydrodynamic behaviors or the way currents react to external forces. It is generally very challenging to connect the microscopic rules to these large-scale properties, and there are relatively few systems for which exact results can be obtained. The “Box-ball system” (BBS), a particular cellular automaton, is such an example. The BBS consists of “balls” occupying “boxes” arranged on a line, with at most one ball per box.

Many natural systems remain far from thermodynamic equilibrium by exchanging matter, energy or information with their surroundings. As these transfers, or fluxes, break timereversal invariance, such processes are beyond the realm of traditional thermodynamics and their statistical fluctuations do not follow the principles of equilibrium statistical mechanics. Though a fully general theory of non-equilibrium systems still remains to be constructed, a physical principle describing the macroscopic behaviour of diffusive systems far from equilibrium has been proposed by G. Jona-Lasinio and his collaborators in 2001: this is the Macroscopic Fluctuation Theory (MFT). In the MFT framework, macroscopic fluctuations far from equilibrium are determined by two coupled non-linear hydrodynamic equations. However, for a long time, the MFT equations have remained intractable. In a recent work that has appeared in Physical Review Letters, K. Mallick (IPhT), H. Moriya and T.

The IPhT is strongly involved in the preparation of the scientific exploitation of the Euclid mission. This participation is done at two levels. Francis Bernardeau is in charge of the coordination of the Science Performance Verification, an exercise that aims to ensure that the core objectives of the mission - constraints on the parameters of the dark energy equation of state - will be achieved given what is known about the general parameters of the mission. But more generally, the IPhT researchers are involved in the preparation of the tools necessary for the analysis of cosmological data. In particular, it is a question of developing and validating the tools allowing to predict the expected observables for a large variety of cosmological models. Thus, Filippo Vernizzi coordinates the efforts within the Euclid consortium to develop simulations and theoretical tools to study the non-linear development of modified gravity models.

The retreat of the Institute of Theoretical Physics was held in Autrans (Vercors) from May 23 to 25. The approximately one hundred participants enjoyed the benefits of the altitude and the gorgeous environment surrounding the Escandille congress center, which hosted the event. This intense and joyful retreat provided an opportunity to strengthen the cohesion between members of our laboratory and to discuss among ourselves issues of science and the life of the Institute. The IPhT is characterized by a broad spectrum of research topics. In order to highlight the skills and to pedagogically transmit the knowledge to other non-expert colleagues, 7 scientific presentations of IPhT researchers were organized, complemented by 2 presentations held by external speakers, Professors Luc Blanchet (Institut d'Astrophysique de Paris, long-term visitor at IPhT) and Emil Martinec (University of Chicago).

We are pleased to announce that Ben Wieder will arrive at the IPhT at the end of September 2022 on the position of permanent junior researcher. Benjamin Wieder completed his PhD at the University of Pennsylvania with Charlie Kane in 2016.He was then a postdoc in Andrei Bernevig's group at Princeton University. He is currently a postdoc at MIT, working with T. Senthil among others. He is a theoretical physicist of condensed matter and more specifically of electronic properties in materials with topologically non-trivial band structure. He has worked on the combined aspects of geometry and topology in materials with complex nodal surfaces. He then studied the relationships between energy band connectivity of solids, structural chirality, topology and magnetism. He collaborated with Zahid Hasan's group at Princeton to identify candidate materials with these new properties.

We are pleased to announce that Dalimil Mazáč will join the IPhT as a CEA Permanent Researcher as of August 1, 2023. Dalimil prepared his thesis at the Perimeter Institute under the supervision of Davide Gaiotto, he then did a first postdoc at the SCGP at Stony Brook before joining the IAS at Princeton where he will stay until he will join our Institute. During his thesis, Dalimil wrote a paper on Analytic Bounds and Emergence of AdS2 Physics from the Conformal Bootstrap which raised a lot of interest, as he introduced the notion of analytic functional crucial to obtain rigorous bounds in the conformal bootstrap framework. Even more remarkably, his approach is in fact equivalent to Viazovska's solution of the optimal sphere stacking problem in dimension 8, as Dalimil discovered in later developments.

In the past 10 years, the French community working on maps on surfaces has come together several times per year during the so-called "maps days". The next edition of these maps days will take place at IPhT on Friday 24 June 2022. The scientific program is as follows: see also the webpage   Program: 10h15-11h15 : Nicolas Curien (Université Paris-Saclay), Parking on the infinite binary tree  11h30-12h30 : Fedor Levkovich-Maslyuk (Université Paris-Saclay / CEA), Critical phenomena for dually weighted graphs and spanning forests via matrix models 14h-15h : Zéphyr Salvy (Université Gustave Eiffel), Random planar maps decomposed into blocks: a phase study 15h15-16h15 : David Keating (University of Wisconsin-Madison), k-tilings of the Aztec diamond The talks will take place in person in the Bloch amphitheater.

The chaotic behaviour of classical non-linear systems is an ubiquitous effect which refers to the unpredictability of their complex dynamics, a phenomenon known as the butterfly effect.  In mathematical terms this concept is characterized by the so-called Lyapunov exponent, a quantity which expresses the rate at which trajectories which start from close-by initial conditions (position and velocity), diverge with time. In quantum mechanics it is difficult to find good diagnostics of chaos and this question has been intensively debated since the beginnings of quantum mechanics. Recently, groundbreaking results from high energy physics [1] showed that quantum mechanics imposes a strict bound on the Lyapunov exponent. This novel effect has motivated enormous interest over different fields, leaving, however, several outstanding open questions.

La description microscopique des trous noirs est un défi depuis plus de quarante ans. Il existe aujourd'hui un certain nombre d'approches prometteuses pour résoudre ce problème et l'objectif principal de cette conférence et de ce workshop est de réunir des experts dans ces domaines afin d'identifier les synergies, de s'engager dans une critique constructive et de résoudre les conflits apparents. Une attention particulière sera accordée à la dynamique de la microstructure des trous noirs : comment la matière entrante est brouillée et comment l'information est récupérée. La conférence se tiendra seulement en ligne le lundi 6 juin (jour férié en France) puis en personne à l'IPhT, CEA-Saclay du mardi 7 au vendredi 10 juin. Chaque jour de la conférence sera également retransmis. Inscription sur le site web.

The next colloquium Rencontres de l'IPhT conference will be held in Autrans (Vercors) from 23 to 25 May. It will consist of conferences and lectures concerning both the major fields of research in theoretical physics and supporting activities. The main themes of physics will be: - Mathematical physics: group A - Cosmology, particles and nuclei: group B - Statistical physics - condensed matter: group C Main goals: - To share knowledge on scientific topics and strengthening cohesion within the Institute. - To bring together all of the Institute's collaborators in order to discuss common subjects and activities and to strengthen interactions between members of the different teams, including support. - To unite the teams around a common project. See you soon in Autrans!  

Given a set of deformable polygons with prescribed numbers of sides, in how many inequivalent ways can one glue them edge to edge so as to build a sphere? This mathematical question, which pertains to map combinatorics in random geometry, was partially answered by the mathematician William Tutte in a famous 1962 article "A census of slicings" where he solves the problem in the particular case where all the polygons, except at most two of them, have an even number of sides. In a recent article, Jérémie Bouttier and Emmanuel Guitter (IPhT), in collaboration with the mathematician Grégory Miermont (ENS de Lyon), succeeded, 60 years later, in extending Tutte's formula to the most general case, namely for polygons whose numbers of sides have arbitrary parities. Even though more complex, their general explicit formula is still very elegant and conceals numerous symmetries. It is with no doubt the starting point for new combinatorial discoveries.

Bertrand Duplantier (IPhT) and his collaborators have just obtained an exact expression for the generalized multifractal spectrum, which characterizes the highly singular behavior of the universal fractal curve, here arcuate in a semi-infinite logarithmic spiral, and associated with Schramm-Loewner Evolution (SLE), a   paradigmatic planar stochastic process. The method of passage through Liouville quantum gravity is successfully applied there. The attached file contains a simplified presentation of this mathematical physics result. Developped results

Stéphane Lavignac (IPhT) will be giving a public talk (in French) about « Les neutrinos Les neutrinos, ces particules  mystérieuses qui interrogent les physiciens on Tuesday, March 15th at 7 pm in the framework of the Conférences Université Citoyenne at the Patronage laïque Jules Vallès in Paris. https://www.patronagelaique.eu/event-details/les-neutrinos-ces-particules-mysterieuses-qui-interrogent-les-physiciens-1 You also can find this conference on Youtube: Conferences

  This book Spatial Networks - a complete introduction : From Graph Theory and Statistical Physics to Real-World Applications provides a complete introduction into spatial networks. It offers the mathematical tools needed to characterize these structures and how they evolve in time and presents the most important models of spatial networks. All the theoretical discussions are illustrated on real-world examples.

 The value of the Higgs boson mass and of the neutron electric dipole moment (EDM) have been mysterious for decades. They remain among the deepest open questions in particle physics. Until now they have been treated separately, as they are related to very different symmetries and physical processes. Raffaele Tito D'Agnolo (IPhT Saclay) and Daniele Teresi (CERN) recently proposed a joint solution to the two problems, based on the observation that a single operator in our current theory of Nature has a special sensitivity to both parameters. In their model a Multiverse is populated at early times, as shown in the Figure. It is composed of universes with different values of the fundamental parameters of Nature. A fraction of a second after the birth of these universes, the vast majority of them "crunches" becoming much smaller than an atom.

We will have the pleasure to welcome Cédric Villani at IPhT on Tuesday, March 1st morning. Mathematician, Cédric Villani is a university professor, laureate of the 2010 Fields medal and former director of Institut Henri Poincaré. He is also deputy (MP) for Essonne's 5th constituency in the National Assembly of France.   Here is the program of the meeting :  09:00-09:10 introduction, by Catherine Pépin et François David  09:10-10:00 scientific talk by Cédric Villani 10:00-10:30 break 10:30-11:30 talks by IPhT members : Kirone Mallick, Philippe Brax, Jérémie Bouttier 11:30-12:00 question session, chaired by Bertrand Duplantier  Conference site  The meeting will take place in amphi Bloch and will be streamed online via BBB and on www.youtube.com/c/IPhTTV.

We announce the ExoSup Summer School on unconventional superconductivity,co-organized by Catherine Pépin from IPhT..It will take place at the Institut d'Etudes Scientifiques de Cargèse from June 13 to 25, 2022.

Good news for the IPhT, Mariana Grana has just received the Langevin Prize of the French Society of Physics! Congratulations to Mariana for this well deserved success! Prize citation:

We warmly welcome Luc Blanchet, who will be a regular visitor of the IPhT  during the next six month. 

We are pleased to welcome Pierre Fleury, who joins the astrophysics and cosmology group of the IPhT as of February 1st. Pierre Fleury is a specialist of general relativity and gravitational lensing. After a PhD at the Institut d'Astrophysique de Paris in 2015, he successively held postdoctoral positions at the University of Cape Town in South Africa, the Department of Theoretical Physics at the University of Geneva and the Institute of Theoretical Physics at the Universidad Autónoma de Madrid. His research program covers both very formal aspects, such as the study of backreactions in alternative theories of relativity or the study of the concept of emergent gravity, and phenomenological aspects such as the exploration of gravitational lensing effects in a wide variety of contexts. He now joins the IPhT as a permanent CNRS researcher of section 02.  We welcome him !

We are pleased to welcome Maxime Leroy to the IPHT's support team, who took up his post on January 19th as part of an 18-month fixed-term contract. Maxime is a graphic video editor and a graduate of the EMC (Ecole supérieure des métiers de l'image, du son et de la création 2D-3D). Trained by Philippe Girault and Laurent Sengmanivanh, he will be responsible for the use of our new equipment in the Itzykson room and soon in the Bloch amphitheatre. His technical skills will be invaluable for the recording and retransmission of conferences, courses and seminars organized by researchers and will thus contribute to a better influence of the Institute. He will also be your contact for announcements and room reservations on the IPhT website. Welcome to Maxime !

Pendant des décennies nous avons progressé dans l'étude des lois fondamentales de la nature à travers les collisionneurs des particules. Le Grand Collisionneur de Hadrons (LHC) a eu un impact énorme sur notre connaissance de la physique des particules. Une des conséquences les plus importantes de ce programme expérimental est que la valeur de la masse du boson de Higgs et son origine restent mystérieux.

l’Institut Pascal à l’Université Paris-Saclay organise pendant six semaines avec le concours de plusieurs physiciens dont Philippe Brax de l’IPhT (du 18 octobre au 26 novembre 2021) des exposés  pour le grand public, donnés par des physiciens de renom. Dans ce cadre, Cédric Villani donnera une conférence exceptionnelle le  lundi 22 novembre à 19h30 (Institut Pascal) sur le thème La flèche du temps, du billard moléculaire à la danse des astres. l’accueil du public se fait à partir de 19h. Vous pourrez avoir davantage d’informations via ces liens : https://indico.ijclab.in2p3.fr/event/7119/ Renseignements pratiques et localisation de la conférence Affiche en PDF  

  Francois Gelis's book, Problems in Quantum Field Theory, largely inspired by his QFT lectures in the Master program High Energy Physics at Ecole Polytechnique, has just been published by Cambridge University Press. This new book is a follow-up on his earlier textbook, "Quantum Field Theory", published by CUP in 2019. Editor's page  

A conference honouring the 60 years anniversary of our former colleague Denis Bernard will take place at the ENS Paris : 45 rue d’Ulm, Salle Dussane - October 14-16, 2021.

Our friend and colleague Hubert Saleur has recently turned 60. A conference celebrating his anniversary and focusing on his numerous contributions to condensed matter physics, low-dimensional quantum field theory, and mathematical physics will take place at the IPhT on September 20-23, 2021.  Participation and talks will be in hybrid mode. On-site participants will have to wear masks inside the Institute building and will have to show a valid immunisation certificate or a valid negative test for SARS-CoV-2 (of less than 72 hours) upon registration on Monday morning. Since the maximum capacity of the Amphi Claude Bloch is restricted to 50 persons, registration is necessary. More details can be found on the webpage of the conference :  http://www.phys.ens.fr/~jacobsen/AMP21.html Organisers: Jesper Jacobsen (ENS Paris), Didina Serban (IPhT Saclay), Nicholas Warner (USC Los Angeles)

The meeting will be held at the Institut de Physique Théorique (IPhT-CEA) in Saclay from Sept 13 to 15 and at the Ecole Normale Supérieure (ENS) in Paris on Sept 16. It will bring together experts in the field of integrable systems and address important open questions in the calculation of correlation functions and wave functions in integrable models, with applications to N=4 Super-Yang-Mills theory, Heisenberg spin chains and 2d relativistic QFTs. Participation will be in person only. Participants will have to wear masks inside the Institute building and will have to show a valid immunisation certificate or a valid negative test for SARS-CoV-2 (of less than 72 hours) upon registration on Monday morning. The maximum capacity of the Amphi Claude Bloch being restricted to 50 persons, registration is necessary and it can be done via the corresponding link on the webpage of the conference: https://indico.in2p3.

Thermalization and out of equilibrium dynamics of many body strongly interacting quantum systems have been the subject of a recent burst of research activities. In particular the dynamics of operator and information spreading (scrambling) as well as its chaotic behavior have been recently investigated starting from models originated in the context of strongly correlated many body systems and have found application to black holes physics. This has been triggered by the appearance of a new class of exactly soluble large N quantum field theories, such as the celebrated Sachdev-Ye-Kitaev model. The aim of this workshop is to review the recent advances in the field and to stimulate further research in this direction which lies at the interface between statistical and condensed matter physics and high-energy/mathematical physics. Due to the current situation, the conference will take place online.

CC BY 3.0 (as fig. 1 from  Event Horizon TelescopeCollaboration, K. Akiyama et al., First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring, Astrophys.J. Lett.875(2019), no. 1, L5,1906.11242 ) More than a century after their theoretical discovery, black holes still hold many mysteries. We have developed new methods to calculate an infinite number of hitherto unknown parameters of any arbitrary black hole, some of which we believe could be observed in current and future experiments. Half of these multipoles are finite, and the other half vanish.  Any ratio of two vanishing moments thus seems to be ill-defined. By embedding black holes in string theory, we develop a novel method to define and calculate such multipole moment ratios unambiguously for any black hole. In this way, we find an infinite number of previously unknown multipole ratios for any Kerr black hole.

  Orazio Scarlatella, former doctoral student at IPhT, is the winner of the 2020 PhD prize "Physics of Waves and Matter" of the Physics Graduate School of the University of Paris-Saclay, in the speciality "Theoretical Physics, Numerics and Modelling". Orazio Scarlatella's thesis work focuses on the dynamics of dissipative quantum many-body systems. These problems are of great richness and complexity because they combine the effects of interactions, quantum fluctuations, and out-of-equilibrium physics. The work of O. Sacarlatella consisted of several new conceptual and methodological developments in this field at the interface between correlated materials and quantum optics, with applications to systems such as arrays of superconducting cavities or ultra cold atoms trapped in optical arrays.

(c) Leo Patrizi Marc Barthelemy and Vincent Verbavatz proposed a new equation to understand the distribution of urban populations in a country and their results are published in the journal Nature (online November 18, 2020) This equation, constructed from data for several countries, accounts for the first time for the temporal variations of urban populations and their organization. This stochastic equation of a new type (with two multiplicative noises, one gaussian and the other of the Levy type) highlights the importance of “interurban migratory shocks”, rare but significant population movements, and makes it possible to understand the hierarchical structure of cities and statistical regularities such as Zipf's law.    More information and the interview with Marc Barthélémy

An IPhT researcher, Nicolas Sangouard, and his partners from the universities of Geneva and Basel have succeeded for the first time in "intriguing" the outputs of two optical fibers sharing a single photon at a distance of 2 km. By this performance, they show how a form of quantum entanglement that is simple to produce can be distributed and detected over long distances. An important step towards the construction of a secure quantum the internet! Quantum entanglement or entanglement refers to a very surprising phenomenon in which two systems form a linked state, with the state of each individual system remaining undefined. Regardless of the distance between them, these systems have correlated physical properties. Without stopping being amazed, physicists have learned to use entanglement and to imagine technological applications that have no classical equivalent.

How do we protect the privacy of a communication if we cannot trust the devices used to communicate? Researchers from IPhT, the University of Basel and ETH Zurich have provided innovative answers to this question, which is at the heart of research in quantum cryptography. Hackers in possession of quantum computers pose a serious threat to some of today's crypto-systems. An interesting solution uses encryption methods based on keys produced by quantum principles. However, current quantum encryption protocols assume that the devices used to communicate are known and trustworthy. Otherwise, a door is opened for eavesdropping. A team of physicists around Nicolas Sangouard from IPhT and the University of Basel, as well as Professor Renato Renner from ETH Zurich, have developed the theoretical bases of a communication protocol that offers ultimate protection of the privacy and can be implemented experimentally.

David Kosower vient d’obtenir l’ERC Advanced Grant Ampl2Einstein. Ce projet sera consacré au développement de nouveaux calculs perturbatifs pour l’étude de l´émission d´ondes gravitationnelles lors de la fusion de trous noirs ou d'étoiles à neutrons. Ces calculs de précision sont une étape cruciale afin de pouvoir extraire des observations des informations sur la structure de ces astres. L' ambition du projet “Ampl2Einstein” est de repousser les limites de la théorie quantique des champs et de développer le lien entre théories de Yang-Mills et théories de gravitation.

Le nouvel ouvrage Theory of simple glasses, co-écrit par Giorgio Parisi, Pierfrancesco Urbani , physicien à l’IPhT, et Francesco Zamponi, vient de paraître chez Cambridge University Press. Félicitations Pierfrancesco !

Le nouvel ouvrage  Molecular Kinetics in Condensed Phases: Theory, Simulation, and Analysis, écrit par Ron Elber, Dmitrii E. Makarov, et Henri Orland, physicien à l'IPhT, vient de paraître chez Wiley. Félicitations Henri !