909 research outputs found
First experimental constraints on the disformally coupled Galileon model
The Galileon model is a modified gravity model that can explain the late-time
accelerated expansion of the Universe. In a previous work, we derived
experimental constraints on the Galileon model with no explicit coupling to
matter and showed that this model agrees with the most recent cosmological
data. In the context of braneworld constructions or massive gravity, the
Galileon model exhibits a disformal coupling to matter, which we study in this
paper. After comparing our constraints on the uncoupled model with recent
studies, we extend the analysis framework to the disformally coupled Galileon
model and derive the first experimental constraints on that coupling, using
precise measurements of cosmological distances and the growth rate of cosmic
structures. In the uncoupled case, with updated data, we still observe a low
tension between the constraints set by growth data and those from distances. In
the disformally coupled Galileon model, we obtain better agreement with data
and favour a non-zero disformal coupling to matter at the level.
This gives an interesting hint of the possible braneworld origin of Galileon
theory.Comment: 9 pages, 6 figures, updated versio
A Parallel General Purpose Multi-Objective Optimization Framework, with Application to Beam Dynamics
Particle accelerators are invaluable tools for research in the basic and
applied sciences, in fields such as materials science, chemistry, the
biosciences, particle physics, nuclear physics and medicine. The design,
commissioning, and operation of accelerator facilities is a non-trivial task,
due to the large number of control parameters and the complex interplay of
several conflicting design goals. We propose to tackle this problem by means of
multi-objective optimization algorithms which also facilitate a parallel
deployment. In order to compute solutions in a meaningful time frame a fast and
scalable software framework is required. In this paper, we present the
implementation of such a general-purpose framework for simulation-based
multi-objective optimization methods that allows the automatic investigation of
optimal sets of machine parameters. The implementation is based on a
master/slave paradigm, employing several masters that govern a set of slaves
executing simulations and performing optimization tasks. Using evolutionary
algorithms as the optimizer and OPAL as the forward solver, validation
experiments and results of multi-objective optimization problems in the domain
of beam dynamics are presented. The high charge beam line at the Argonne
Wakefield Accelerator Facility was used as the beam dynamics model. The 3D beam
size, transverse momentum, and energy spread were optimized
Survival of near-critical branching Brownian motion
Consider a system of particles performing branching Brownian motion with
negative drift and killed upon hitting zero.
Initially there is one particle at . Kesten showed that the process
survives with positive probability if and only if . Here we are
interested in the asymptotics as \eps\to 0 of the survival probability
. It is proved that if then for all , exists and is a
travelling wave solution of the Fisher-KPP equation. Furthermore, we obtain
sharp asymptotics of the survival probability when and .
The proofs rely on probabilistic methods developed by the authors in a previous
work. This completes earlier work by Harris, Harris and Kyprianou and confirms
predictions made by Derrida and Simon, which were obtained using nonrigorous
PDE methods
Why Don't We Have a Covariant Superstring Field Theory?
This talk deals with the old problem of formulatingn a covariant quantum
theory of superstrings, ``covariant'' here meaning having manifest Lorentz
symmetry and supersymmetry. The advantages and disadvantages of several
quantization methods are reviewed. Special emphasis is put on the approaches
using twistorial variables, and the algebraic structures of these. Some
unsolved problems are identified.Comment: 5 pages, Goteborg-ITP-94-24, plain te
Effet magnéto-optique et optique des couches minces à base de ferrite de cobalt
Cette Ă©tude a pour but la mesure des effets magnĂ©to-optiques (rotation Faraday) en fonction du champ magnĂ©tique appliquĂ© et en fonction de la longueur dâonde, ainsi que la mesure de la transmittance (effet optique) des couches minces Ă base de ferrite de cobalt. Les rĂ©sultats montrent une forte rotation Faraday spĂ©cifique avec des cycles d'hystĂ©rĂ©sis et des spectres de transmittance d'une bonne transparence dans la gamme TĂ©lĂ©com (â1550 nm).Mots-clĂ©s: ferrite de cobalt, sol-gel, couches minces, rotation Faraday, transmittance. Magneto-optical effect and optical thin films cobalt ferriteThis study was designed to measure the magneto-optical effect (Faraday rotation) according to the applied magnetic field and a function of the wavelength and the transmittance measurement (optical effect) thin film based on cobalt ferrite. The results show a high specific Faraday rotation with hysteresis cycles and transmittance spectra of a good transparency in the range Telecom (â1550 nm).Keywords: cobalt ferrite, sol-gel thin films, Faraday rotation, transmittance
Experimental constraints on the uncoupled Galileon model from SNLS3 data and other cosmological probes
International audienceAims. The Galileon model is a modified gravity theory that may provide an explanation for the accelerated expansion of the Universe. This model does not suffer from instabilities or ghost problems (normally associated with higher-order derivative theories), restores local General Relativity â thanks to the Vainshtein screening effect â and predicts late-time acceleration of the expansion.Methods. We derive a new definition of the Galileon parameters that allows us to avoid having to choose initial conditions for the Galileon field. We tested this model against precise measurements of the cosmological distances and the rate of growth of cosmic structures.Results. We observe a weak tension between the constraints set by growth data and those from distances. However, we find that the Galileon model remains consistent with current observations and is still competitive with the ÎCDM model, contrary to what was concluded in recent publications
Origin of Pure Spinor Superstring
The pure spinor formalism for the superstring, initiated by N. Berkovits, is
derived at the fully quantum level starting from a fundamental
reparametrization invariant and super-Poincare invariant worldsheet action. It
is a simple extension of the Green-Schwarz action with doubled spinor degrees
of freedom with a compensating local supersymmetry on top of the conventional
kappa-symmetry. Equivalence to the Green-Schwarz formalism is manifest from the
outset. The use of free fields in the pure spinor formalism is justified from
the first principle. The basic idea works also for the superparticle in 11
dimensions.Comment: 21 pages, no figure; v2: refs. adde
Induced Systemic Resistance (ISR) in Arabidopsis thaliana by Bacillus amyloliquefaciens and Trichoderma harzianum used as seed treatments
The Trichoderma fungal species and the bacteria Bacillus species were described as inducers of plant systemic resistance in relation to their antagonistic activity. The objective of this study was to evaluate the effect of selected strains of Bacillus amyloliquefaciens (I3) and Trichoderma harzianum (A) on inducing systemic resistance in Arabidopsis thaliana as a model for plant molecular genetics. The microorganisms were identified and were confirmed for their antagonistic potential in vitro and in vivo in previous studies. In order to explore this mechanism, two mutants of A. thaliana carrying a PR1 promoter (a conventional marker of salicylic acid (SA) pathway) and LOX2 promoter (a marker triggering jasmonic acid (JA) pathway activation) were analyzed after inoculating antagonists. Transgenic reporter line analysis demonstrated that B. amyloliquefaciens I3 and T. harzianum A induce A. thaliana defense pathways by activating SA and JA at a high level compared to lines treated with chemical elicitors of references (acibenzolar-S-methyl (Bion 50 WG (water-dispersible granule)), SA, and methyl jasmonate). The efficacy of B. amyloliquefaciens I3 and T. harzianum A in inducing the defense mechanism in A. thaliana was demonstrated in this study
- âŠ