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).

A natural mechanism for "uplifting" the cosmological constant in string theory

*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 proposals available so far involve a mixture of mechanisms at different energy scales, whose interplay is not clear to result in energetically stable solutions. Furthermore, they remain technically challenging, as one needs to introduce a combination of the so called "fluxes" (higher-dimensional generalizations of the electromagnetic flux) tuned "ad hoc" to give unnaturally tiny contributions to the energy of the solution.

In a recent work [1], **Iosif Bena and Mariana Graña of the IPhT, together with their student Dimitrios Tulikas, their post-doc Gabriele Lo Monaco, as well as their collaborator E. Dudas (CPHT, Ecole Polytechnique)**, have found a much more straightforward "bare-bones” way of obtaining a solution with a positive cosmological constant, that does not require introducing such fine-tuned fluxes. Indeed, they have shown that one of the ingredients necessary in the game to uplift the cosmological constant from the negative value (that one gets easily) to a positive one, generates by itself fluxes resulting in a tiny energetic contribution. This construction is much more natural and avoids the fine-tuning problem of the original one, thus elegantly passing the "naturalness test".

E. De-laborderie, 2023-01-13 15:54:00

EPS PhD prize awarded to IPhT student

**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!

E. De-laborderie, 2022-11-04 10:33:00

Exact results for the "box ball system", a cellular automaton with solitons

__ 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. Although the balls move at each time step according to simple deterministic rules (see figure/animation), the BBS presents a rich physics due to the fact that we can identify some objects called "solitons" (a train of k consecutive balls) of all size and whose number are preserved over time.

Using the integrability of the model a recent study of **G. Misguich and V. Pasquier, researchers at the IPhT, together with A. Kuniba (Tokyo U.) [1] ** has shown how to determine several quantities related to currents and their fluctuations. These include the probability distribution of the number of balls passing through the origin during a time t, the long-time persistent current generated by a perturbation -- called Drude weight --, and some correlation functions associated with soliton currents.

[1] “Current correlations, Drude weights and large deviations in a box–ball system”, A. Kuniba, G. Misguich and V. Pasquier, J. Phys. A: Math. Theor., 55 244006 (2022). (https://doi.org/10.1088/1751-8121/ac6d8c) See also J. Phys. A: Math. Theor. 53 404001 (2020). (https://doi.org/10.1088/1751-8121/abadb9)

E. De-laborderie, 2022-10-11 10:10:00

Exact Macroscopic Fluctuations Far from Equilibrium

2022-08-25 15:09:00

Preparation of the exploitation of the Euclid mission

2022-07-11 16:06:00

Retreat of the IPhT in Autrans : aftermath

2022-06-22 09:05:00

Arrival of Ben Wieder on next september

2022-06-17 15:12:00

Arrival of Dalimil Mazáč at IPhT

2022-06-07 10:14:00

Maps day at IPhT on 24 June 2022

2022-06-03 10:33:00

Quantum bounds and fluctuation-dissipation relations

2022-05-12 11:47:00

26ème conférence Itzykson : "Black-Hole Microstructure IV"

2022-05-12 10:32:00

Colloquium Rencontres de l'IPhT in Autrans (Vercors) from 23 to 25 May.

2022-05-12 10:02:00

An extension of Tutte's formula 60 years later

2022-04-20 11:13:00

2022-04-05 11:28:00

Public talk of Stephane Lavignac on Tuesday March 15th

2022-03-11 09:17:00

A new book written by Marc Barthélémy about spatial networks

2022-02-22 11:05:00

Cédric Villani at IPhT on March 1st

2022-02-22 10:26:00

Summer School in Cargèse around exotic superconductivity

2022-02-07 15:39:00

Langevin Prize of the French Society of Physics for Mariana Graña

2022-02-04 10:46:00

2022-02-01 09:59:00

2022-02-01 09:21:00

Maxime Leroy joins the IPHT support team

2022-01-27 15:24:00

Un lien entre la masse du boson de Higgs et la constante cosmologique

2021-11-25 14:11:00

Conférence exceptionnelle de Cédric Villani le lundi 22 novembre à 19h30 (Institut Pascal)

2021-11-18 14:33:00

Problems in Quantum Field Theory : a book by François Gelis.

2021-10-11 16:12:00

Mathematical Harmony and the Quantum World

2021-10-07 15:24:00

The art of mathematical physics

2021-09-01 16:31:00

Correlation functions and wave functions in solvable models

2021-08-31 16:44:00

2021-05-01 11:45:00

Multipole Ratios : A New Window into Black Holes

2020-11-27 15:16:00

Orazio Scarlatella lauréat du prix de thèse Physique des Ondes et de la Matière (PhOM) 2020

2020-11-26 11:07:00

Modeling the city: an equation ends centuries-old controversies

2020-11-19 11:10:00

Quantum entanglement: A single photon takes two optical paths by "entangling" them!

2020-10-15 15:06:00

An strongly secured encryption

2020-09-17 17:01:00

David Kosower lauréat de l'ERC Advanced Grant "Ampl2Einstein"

2020-04-03 15:57:00

Un nouvel ouvrage co-écrit par Pierfrancesco Urbani, physicien à l’IPhT

2020-01-31 14:15:00

Un nouvel ouvrage co-écrit par Henri Orland, physicien à l'IPhT

2020-01-28 16:16:00

Fri, Jan. 27th, 10:00-12:30

Cours de physique théorique de Saclay - Michel Bauer

Mon, Feb. 06th, 11:00-12:00

Séminaire de physique mathématique - Sylvain Ribault

Thu, Feb. 09th, 14:00-15:00

Séminaire de physique des particules et de cosmologie - Deog Ki Hong