A couple of recent scientific results obtained by members of LPT

— "**Gravitational Origin of Dark Matter**" *by Eugeny Babichev, Luca Marzola, Martti Raidal, Angnis Schmidt-May, Federico Urban, Hardi Veermäe and Mikael von Strauss* :

Observational evidence for the existence of Dark Matter is limited to its gravitational effects. The extensive program for dedicated searches has yielded null results so far, challenging the most popular models. Here we propose that this is the case because the very existence of cold Dark Matter is a manifestation of gravity itself. The consistent bimetric theory of gravity, the only known ghost-free extension of General Relativity involving a massless and a massive spin-2 field, automatically contains a perfect Dark Matter candidate. We demonstrate that the massive spin-2 particle can be heavy, stable on cosmological scales, and that it interacts with matter only through a gravitational type of coupling. Remarkably, these features persist in the same region of parameter space where bimetric theory satisfies the current gravity tests. We show that the observed Dark Matter abundance can be generated via freeze-in and suggest possible particle physics and gravitational signatures of our bimetric Dark Matter model.

https://arxiv.org/abs/1605.02627

— "**The melting of the classical two-dimensional Wigner crystal**" *by Martial Mazars* :

We report an extensive Monte-Carlo study of the melting of the classical two dimensional
Wigner crystal for a system of point particles interacting via the $1/r$-Coulomb potential. A hexatic phase is found in systems large enough. With the multiple histograms method and the finite size scaling theory, we show that the fluid/hexatic phase transition is weakly first order. No set of critical exponents, consistent with a Kosterlitz-Thouless transition and the finite size scaling analysis for this transition, have been found.

Published in EPL, 110 (2015) 26003

— "**The polymorphic behavior of Wigner bilayers**" *by Moritz Antlanger, Gerhard Kahl, Martial Mazars, Ladislav Samaj and Emmanuel Trizac* :

Self-assembly into target structures is an efficient material design strategy. Combining
analytical calculations and computational techniques of evolutionary and Monte Carlo types, we report about a remarkable structural variability of Wigner bilayer ground states, when charges are confined between parallel charged plates. Changing the inter-layer separation, or the plate charge asymmetry, a cascade of ordered patterns emerges. At variance with the symmetric case phenomenology, the competition between commensurability features and charge neutralization leads to long range at-
traction, appearance of macroscopic charges, exotic phases, and non conventional phase transitions with distinct critical indices, offering the possibility of a subtle, but precise and convenient control over patterns.

Published in PRL, 117 (2016) 118002

http://journals.aps.org/prl/abstrac...

— "**Efficiency fluctuations of small machines with unknown losses**" *by Hadrien Vroylandt, Anthony Bonfils, and Gatien Verley* :

In the recent years, our understanding of nonequilibrium statistical physics has improved in many ways. In this paper, I discuss similarities between equilibrium and nonequilibrium statistical physics. The main focus is on the definition of new thermodynamic observables that allows to introduce a so called nonequilibrium thermodynamic potential.

http://pperso.th.u-psud.fr/page_per...