CNRS Physics Laboratory
CNRS Physics Laboratory
Delduc F.,CNRS Physics Laboratory |
Magro M.,CNRS Physics Laboratory |
Vicedo B.,University of Hertfordshire
Physical Review Letters | Year: 2014
An integrable deformation of the type IIB AdS5×S5 superstring action is presented. The deformed field equations, Lax connection, and κ-symmetry transformations are given. The original psu(2,2|4) symmetry is expected to become q deformed. © 2014 American Physical Society.
Serreau J.,University Paris Diderot |
Parentani R.,CNRS Physics Laboratory
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013
We study the O(N) scalar field theory with quartic self-coupling in de Sitter space. When the field is light in units of the expansion rate, perturbative methods break down at very low momenta due to large infrared logarithmic terms. Using the nonperturbative large-N limit, we compute the four-point vertex function in the deep infrared regime. The resummation of an infinite series of perturbative (bubble) diagrams leads to a modified power law which is analogous to the generation of an anomalous dimension in critical phenomena. We discuss in detail the role of high momentum (subhorizon) modes, including the issue of renormalization, and show that they influence the dynamics of infrared (superhorizon) modes only through a constant renormalization factor. This provides an explicit example of effective decoupling between high and low energy physics in an expanding space-time. © 2013 American Physical Society.
Roscilde T.,CNRS Physics Laboratory
Physical Review Letters | Year: 2014
Artificial gauge fields are a unique way of manipulating the motional state of cold atoms. Here we propose the use (practical or conceptual) of artificial gauge fields - obtained, e.g., experimentally via lattice shaking or conceptually via a Galilean transformation - to perform primary noise thermometry of cold atoms in optical lattices, not requiring any form of prior calibration. The proposed thermometric scheme relies on fundamental fluctuation-dissipation relations, connecting the global response to the variation of the applied gauge field and the fluctuation of quantities related to the momentum distribution (such as the average kinetic energy or the average current). We demonstrate gauge-field thermometry for several physical situations, including free fermions and interacting bosons. The proposed approach is extremely robust to quantum fluctuations - even in the vicinity of a quantum phase transition - when it relies on the thermal fluctuations of an emerging classical field, associated with the onset of Bose condensation or chiral order. © 2014 American Physical Society.
Divoux T.,CNRS Physics Laboratory |
Grenard V.,CNRS Physics Laboratory |
Manneville S.,CNRS Physics Laboratory
Physical Review Letters | Year: 2013
The nonlinear rheology of a soft glassy material is captured by its constitutive relation, shear stress versus shear rate, which is most generally obtained by sweeping up or down the shear rate over a finite temporal window. For a huge amount of complex fluids, the up and down sweeps do not superimpose and define a rheological hysteresis loop. By means of extensive rheometry coupled to time-resolved velocimetry, we unravel the local scenario involved in rheological hysteresis for various types of well-studied soft materials. We introduce two observables that quantify the hysteresis in macroscopic rheology and local velocimetry, respectively, as a function of the sweep rate δt-1. Strikingly, both observables present a robust maximum with δt, which defines a single material-dependent time scale that grows continuously from vanishingly small values in simple yield stress fluids to large values for strongly time-dependent materials. In line with recent theoretical arguments, these experimental results hint at a universal time scale-based framework for soft glassy materials, where inhomogeneous flows characterized by shear bands and/or pluglike flow play a central role. © 2013 American Physical Society.
Moine O.,CNRS Physics Laboratory
Quaternary International | Year: 2014
During the Weichselian glaciation, millennial timescale climatic changes are a major cause of environmental variability, which influence the composition of large mammal fauna and the geographical distribution of human prehistoric populations. Nevertheless, precise environmental contexts of archaeological artefacts may remain unknown due to an unclear stratigraphy and/or to the bad preservation of paleoenvironmental proxies. As pollen is badly preserved in glacial loess deposits, a compilation of age constrained high resolution molluscan records is used to initiate the establishment of a canvas of millennial timescale spatial and temporal environmental changes in the European Loess Belt during the Weichselian Upper Pleniglacial (ca. 37-20 ka) to look for relationships with spatial distribution of human settlements.In this study, new terrestrial mollusc assemblages have been added to the database previously established for north-western Europe. They strengthen the position of the limit between the two molluscan-based biogeographical domains initially highlighted for north-western Europe: a flat and poorly vegetated western domain extending around the Channel and in Belgium, and a hilly domain with more diversified vegetation to the east. The analysis of molluscan data shows the persistence of these two domains throughout alternations of loess deposition phases (interstadial-stadial transitions and stadial phases) with phases of development and degradation of tundra gley horizon (stadial-interstadial transitions and interstadial phases).The interpretation of malacofauna from both domains combined with associated pedological and sedimentological features, climate modelling and comparisons with present tundra environments reveals a significant effect of both seasonality and snow cover along a longitudinal gradient between both domains, but also between phases of loess deposition and phases of tundra gley development. During interstadial phases, the intense functioning of the active layer and the degradation of permafrost in north-western Europe led to more homogeneous environments, which were less favourable for the diversity of both vegetation and terrestrial mollusc fauna.Presently, uncertainties of numerical ages still preclude precise correlations of loess units and tundra gley horizons between different sites and with nonlocal prehistoric occupations. However, a first raw comparison of the molluscan data with spatial distributions of Aurignacian, Gravettian and Solutrean-Upper Magdalenian lithic cultures reveals that the northern limit of the first two ones fits well with the south-eastern border of the poorly vegetated western domain also characterised by well-developed ice-wedge networks during phases of permafrost installation. Later, an important southward shift of human populations in western Europe resulted from the extreme aridity of the Last Glacial Maximum. © 2014 Elsevier Ltd and INQUA.
Jost D.,CNRS Physics Laboratory
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2014
Cells often exhibit different and stable phenotypes from the same DNA sequence. Robustness and plasticity of such cellular states are controlled by diverse transcriptional and epigenetic mechanisms, among them the modification of biochemical marks on chromatin. Here, we develop a stochastic model that describes the dynamics of epigenetic marks along a given DNA region. Through mathematical analysis, we show the emergence of bistable and persistent epigenetic states from the cooperative recruitment of modifying enzymes. We also find that the dynamical system exhibits a critical point and displays, in the presence of asymmetries in recruitment, a bifurcation diagram with hysteresis. These results have deep implications for our understanding of epigenetic regulation. In particular, our study allows one to reconcile within the same formalism the robust maintenance of epigenetic identity observed in differentiated cells, the epigenetic plasticity of pluripotent cells during differentiation, and the effects of epigenetic misregulation in diseases. Moreover, it suggests a possible mechanism for developmental transitions where the system is shifted close to the critical point to benefit from high susceptibility to developmental cues. © 2014 American Physical Society.
Fayet P.,CNRS Physics Laboratory
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010
Invisible ψ and Υ decays into light neutralinos, within the minimal or next-to-minimal supersymmetric standard model, are smaller than for νν̄ production, even if light spin-0 particles are coupled to quarks and neutralinos. In a more general way, light dark matter particles are normally forbidden, unless they can annihilate sufficiently through a new interaction stronger than weak interactions (at lower energies), as induced by a light spin-1 U boson, or heavy-fermion exchanges in the case of scalar dark matter. We discuss the possible contributions of U-boson, heavy-fermion, or spin-0 exchanges to invisible ψ and Υ decays. U exchanges could lead, but not necessarily, to significant branching fractions for invisible decays into light dark matter. We show how one can get the correct relic density together with sufficiently small invisible branching fractions, and the resulting constraints on the U couplings to ordinary particles and dark matter, in particular |cχfbV|<5×10-3 from Υ decays, for 2mχ smaller than a few GeV. We also explain why there is no model-independent way to predict ψ and Υ branching fractions into light dark matter, from dark matter annihilation cross sections at freeze-out time. © 2010 The American Physical Society.
Jost D.,CNRS Physics Laboratory
Bioinformatics | Year: 2013
Summary: Local opening of the DNA double helix is required in many fundamental biological processes and is, in part, controlled by the degree of superhelicity imposed in vivo by the protein machinery. In particular, positions of superhelically destabilized regions correlate with regulatory sites along the genome. Based on a self-consistent linearization of a thermodynamic model of superhelical DNA introduced by Benham, we have developed a program that predicts the locations of these regions by efficiently computing base-pair and bubble opening probabilities in genomic DNA. The program allows visualization of results in standard genome browsers to compare DNA opening properties with other available datasets. © The Author 2013.
Monnier S.,CNRS Physics Laboratory
Communications in Mathematical Physics | Year: 2012
We investigate the metric dependence of the partition function of the self-dual p-form gauge field on an arbitrary Riemannian manifold. Using geometric quantization of the space of middle-dimensional forms, we derive a projectively flat connection on its space of polarizations. This connection governs metric dependence of the partition function of the self-dual field. We show that the dependence is essentially given by the Cheeger half-torsion of the underlying manifold. We compute the local gravitational anomaly and show how our derivation relates to the classical computation based on index theory. As an application, we show that the one-loop determinant of the (2, 0) multiplet on a Calabi-Yau threefold coincides with the square root of the one-loop determinant of the B-model. © 2012 Springer-Verlag.
Roscilde T.,CNRS Physics Laboratory
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2010
In this article, we theoretically discuss how quantum simulators based on trapped cold bosons in optical lattices can explore the grand-canonical phase diagram of homogeneous lattice boson models, via control of the trapping potential independent of all other experimental parameters (trap squeezing). Based on quantum Monte Carlo, we establish the general scaling relation linking the global chemical potential to the Hamiltonian parameters for the Bose-Hubbard model in a parabolic trap, describing cold bosons in optical lattices; we find that this scaling relation is well captured by a modified Thomas-Fermi scaling behavior-corrected for quantum fluctuations-in the case of sufficiently high density and/or sufficiently weak interactions, and by a mean-field Gutzwiller ansatz over a much larger parameter range. This scaling relation allows us to control experimentally the chemical potential, independent of all other Hamiltonian parameters, via trap squeezing; given that the global chemical potential coincides with the local chemical potential in the trap center, measurements of the central density as a function of the chemical potential give access to the information on the bulk compressibility of the Bose-Hubbard model. Supplemented with time-of-flight measurements of the coherence properties, the measurement of compressibility enables one to discern among the various possible phases realized by bosons in an optical lattice with or without external (periodic or random) potentials-for example, superfluid, Mott insulator, band insulator, and Bose glass. We theoretically demonstrate the trap-squeezing investigation of these phases in the case of bosons in a one-dimensional optical lattice and in a one-dimensional incommensurate superlattice. © 2010 The American Physical Society.