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.

Our method can also be used to calculate multipole ratios for supersymmetric black holes. There exist a large number of horizonless geometries that have the same charges as these supersymmetric black holes and only differ from them close to the horizon. We also develop an independent second method to calculate multipole ratios using these “microstate geometries,” and find striking similarities between the results of the two methods.

Contact: Iosif Bena

https://journals.aps.org/prl/abstract/10 ...

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.

One of the main results of his thesis is the development of the dynamical mean field theory (which allows to describe in a non-perturbative way the properties of certain strongly correlated materials) to open systems which dynamics are described by a Lindblad equation for the density matrix. It is a deep and very original work with a big impact in this rapidly expanding field, and where there are still relatively few powerful theoretical methods.

This prize will be awarded during the annual PhOM day which will be held online on Friday, December 4, 2020 from 2 p.m.

(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