University of Paris-Sud is a French university distributed among several campuses in the southern suburb of Paris . The main campus is located in Orsay . This university is a member of the UniverSud Paris.Paris-Sud is one of the largest and most renowned French universities, particularly in science and mathematics. Paris-Sud is ranked 2nd in France, 7th in Europe and 39th worldwide by the 2013 Academic Ranking of World Universities . Furthermore, in this latest edition of ARWU ranking, the university is ranked 15th globally in the field of Natural science and Mathematics; in the five general subject rankings, the university is ranked 7th in mathematics and 19th in physics. Wikipedia.
Goerbig M.O.,University Paris - Sud
Reviews of Modern Physics | Year: 2011
The basic aspects of electrons in graphene (two-dimensional graphite) exposed to a strong perpendicular magnetic field are reviewed. One of its most salient features is the relativistic quantum Hall effect, the observation of which has been the experimental breakthrough in identifying pseudorelativistic massless charge carriers as the low-energy excitations in graphene. The effect may be understood in terms of Landau quantization for massless Dirac fermions, which is also the theoretical basis for the understanding of more involved phenomena due to electronic interactions. The role of electron-electron interactions both in the weak-coupling limit, where the electron-hole excitations are determined by collective modes, and in the strong-coupling regime of partially filled relativistic Landau levels are presented. In the latter limit, exotic ferromagnetic phases and incompressible quantum liquids are expected to be at the origin of recently observed (fractional) quantum Hall states. Furthermore, the electron-phonon coupling in a strong magnetic field is discussed. Although the present review has a dominant theoretical character, a close connection with available experimental observation is intended. © 2011 American Physical Society.
Moreau G.,University Paris - Sud
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013
First, we study the fit of the Higgs boson rates, based on all the latest collider data, in the effective framework for any extra fermion(s) (EF). The best-fit results are presented in a generic formalism allowing us to apply those for the test of any EF scenario under the assumption that the corrections to the Higgs couplings are coming exclusively from EF effects. The variations of the fit with each one of the five fundamental parameters are described, and the obtained fits can be better than in the Standard Model (SM). We show how the determination of the EF loop contributions to the Higgs couplings with photons and gluons is relying on the knowledge of the top and bottom Yukawa couplings (affected by EF mixings); for determining the latter coupling, the relevance of the investigation of the Higgs production in association with bottom quarks is emphasized. In the instructive approximation of a single EF, we find that the constraints from the fit already turn out to be quite predictive in both cases of an EF mixed or not with SM fermions, and especially when combined with the extra-quark (-lepton) mass bounds from direct EF searches at the LHC (LEP) collider. In the case of an unmixed extra quark (in the same color representation as SM quarks), nontrivial fit constraints are pointed out on the Yukawa couplings for masses up to ∼200 TeV. In particular, we define the extra dysfermiophilia, which is predicted at 68.27% C.L. for any single extra quark (independently of its electric charge). Another result is that, among any components of SM multiplet extensions, the extra quark with a -7/3 electric charge is the one preferred by the present Higgs fit. © 2013 American Physical Society.
Lenz M.,University Paris - Sud
Physical Review X | Year: 2014
Movement within eukaryotic cells largely originates from localized forces exerted by myosin motors on scaffolds of actin filaments. Although individual motors locally exert both contractile and extensile forces, large actomyosin structures at the cellular scale are overwhelmingly contractile, suggesting that the scaffold serves to favor contraction over extension. While this mechanism is well understood in highly organized striated muscle, its origin in disordered networks such as the cell cortex is unknown. Here, we develop a mathematical model of the actin scaffold's local two- or three-dimensional mechanics and identify four competing contraction mechanisms. We predict that one mechanism dominates, whereby local deformations of the actin break the balance between contraction and extension. In this mechanism, contractile forces result mostly from motors plucking the filaments transversely rather than buckling them longitudinally. These findings shed light on recent in vitro experiments and provide a new geometrical understanding of contractility in the myriad of disordered actomyosin systems found in vivo.
Langevin D.,University Paris - Sud
Annual Review of Fluid Mechanics | Year: 2014
When surfactants adsorb at liquid surfaces, they not only decrease the surface tension, they also confer rheological properties to the surfaces. The most common rheological parameters are the surface compression elasticity and viscosity and the surface shear viscosity. These parameters usually depend on the timescale of the deformation, owing to surface relaxations, and on its amplitude, owing to nonlinear responses. In addition, surfactants can exchange between the bulk and surface, in a way that depends on the amount of bulk surfactant locally available. This complexity explains why the topic has progressed slowly over the years. This review describes the current knowledge, focusing on recent advances, and gives examples of phenomena in which surface rheology plays an important role. Copyright © 2014 by Annual Reviews. All rights reserved.
Petrov D.S.,University Paris - Sud
Physical Review Letters | Year: 2014
We propose a method of controlling two- and three-body interactions in an ultracold Bose gas in any dimension. The method requires us to have two coupled internal single-particle states split in energy such that the upper state is occupied virtually but amply during collisions. By varying system parameters, one can switch off the two-body interaction while maintaining a strong three-body one. The mechanism can be implemented for dipolar bosons in the bilayer configuration with tunneling or in an atomic system by using radio-frequency fields to couple two hyperfine states. One can then aim to observe a purely three-body interacting gas, dilute self-trapped droplets, the paired superfluid phase, Pfaffian state, and other exotic phenomena. © 2014 American Physical Society.