652,337 research outputs found
Localization over complex-analytic groupoids and conformal renormalization
We present a higher index theorem for a certain class of etale
one-dimensional complex-analytic groupoids. The novelty is the use of the local
anomaly formula established in a previous paper, which represents the bivariant
Chern character of a quasihomomorphism as the chiral anomaly associated to a
renormalized non-commutative chiral field theory. In the present situation the
geometry is non-metric and the corresponding field theory can be renormalized
in a purely conformal way, by exploiting the complex-analytic structure of the
groupoid only. The index formula is automatically localized at the automorphism
subset of the groupoid and involves a cap-product with the sum of two different
cyclic cocycles over the groupoid algebra. The first cocycle is a trace
involving a generalization of the Lefschetz numbers to higher-order fixed
points. The second cocycle is a non-commutative Todd class, constructed from
the modular automorphism group of the algebra.Comment: 38 pages. v2: some inconsistencies with the use of pseudogroups have
been fixe
Convergence in law in the second Wiener/Wigner chaos
Let L be the class of limiting laws associated with sequences in the second
Wiener chaos. We exhibit a large subset L_0 of L satisfying that, for any
F_infinity in L_0, the convergence of only a finite number of cumulants
suffices to imply the convergence in law of any sequence in the second Wiener
chaos to F_infinity. This result is in the spirit of the seminal paper by
Nualart and Peccati, in which the authors discovered the surprising fact that
convergence in law for sequences of multiple Wiener-It\^o integrals to the
Gaussian is equivalent to convergence of just the fourth cumulant. Also, we
offer analogues of this result in the case of free Brownian motion and double
Wigner integrals, in the context of free probability.Comment: 14 pages. This version corrects an error which, unfortunately,
appears in the published version in EC
Random generation of finitely generated subgroups of a free group
We give an efficient algorithm to randomly generate finitely generated
subgroups of a given size, in a finite rank free group. Here, the size of a
subgroup is the number of vertices of its representation by a reduced graph
such as can be obtained by the method of Stallings foldings. Our algorithm
randomly generates a subgroup of a given size n, according to the uniform
distribution over size n subgroups. In the process, we give estimates of the
number of size n subgroups, of the average rank of size n subgroups, and of the
proportion of such subgroups that have finite index. Our algorithm has average
case complexity \O(n) in the RAM model and \O(n^2\log^2n) in the bitcost
model
Scattering rates and lifetime of exact and boson excitons
Although excitons are not exact bosons, they are commonly treated as such
provided that their composite nature is included in effective scatterings
dressed by exchange. We here \emph{prove} that, \emph{whatever these
scatterings are}, they cannot give both the scattering rates and
the exciton lifetime , correctly: A striking factor 1/2 exists between
and the sum of 's, which originates from the
composite nature of excitons, irretrievably lost when they are bosonized. This
result, which appears as very disturbing at first, casts major doubts on
bosonization for problems dealing with \emph{interacting} excitons
Size-assortative mating in simultaneous hermaphrodites: an experimental test and a meta-analysis
Assortative mating by size has been argued to be widespread in the animal kingdom. However, the strength of size-assortative mating is known to vary considerably between species and the underlying mechanisms promoting this inter-specific variation remain largely unexplored. Size-assortative mating has been proposed to be particularly strong in simultaneous hermaphrodites, i.e. organisms that produce male and female gametes at the same time. Here, we build on this hypothesis by arguing that size-assortative mating mediated by sexual selection is generally stronger in reciprocally mating hermaphrodites compared with unilaterally mating species and separate-sexed organisms. We report a series of empirical tests suggesting that size-assortative mating in the unilaterally copulating freshwater snail Physa acuta is caused by spatial clustering of similar-sized individuals and not by mate choice. In addition, we present a meta-analysis testing, for the first time, the hypothesis that sexual selection-mediated size-assortative mating is stronger in reciprocally copulating simultaneous hermaphrodites. Overall, we found significant size-assortative mating across 18 tested species and substantial inter-specific variation. Importantly, part of this variation can be explained by mating type, providing support for the hypothesis that size-assortative mating is stronger in reciprocally mating hermaphrodites compared with unilaterally mating species. We highlight potential pitfalls when testing for sexual selection-mediated size-assortative mating and discuss the need for more experimental and comparative approaches in order to resolve the observed variation in the strength of size-assortative mating among species.Fil: Graham, Stuart. Université de Montpellier. Centre d’Ecologie Fonctionnelle et Evolutive; Francia. Université Paul-Valéry Montpellier; Francia. Centre National de la Recherche Scientifique; FranciaFil: Chapuis, Elodie. Université de Montpellier. Centre d’Ecologie Fonctionnelle et Evolutive; Francia. Centre National de la Recherche Scientifique; Francia. Institut de Recherche pour le Développement,. Intéractions Plantes-Microrganismes-Environement; Francia. Université Paul-Valéry Montpellier; FranciaFil: Meconcelli, Stefania. Université de Montpellier. Centre d’Ecologie Fonctionnelle et Evolutive; Francia. Centre National de la Recherche Scientifique; Francia. Università di Torino; ItaliaFil: Bonel, Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia. Laboratorio de Zoología de Invertebrados I; Argentina. Université de Montpellier. Centre d’Ecologie Fonctionnelle et Evolutive; Francia. Université Paul-Valéry Montpellier; FranciaFil: Sartori, Kevin. Université de Montpellier. Centre d’Ecologie Fonctionnelle et Evolutive; Francia. Centre National de la Recherche Scientifique; Francia. Université Paul-Valéry Montpellier; FranciaFil: Christophe, Ananda. Université de Montpellier. Centre d’Ecologie Fonctionnelle et Evolutive; Francia. Centre National de la Recherche Scientifique; Francia. Université Paul-Valéry Montpellier; FranciaFil: Alda, Maria del Pilar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Estudios Parasitológicos y de Vectores. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Estudios Parasitológicos y de Vectores; ArgentinaFil: Patrice David. Université de Montpellier. Centre d’Ecologie Fonctionnelle et Evolutive; Francia. Centre National de la Recherche Scientifique; Francia. Université Paul-Valéry Montpellier; FranciaFil: Janicke, Tim. Université de Montpellier. Centre d’Ecologie Fonctionnelle et Evolutive; Francia. Centre National de la Recherche Scientifique; Francia. Université Paul-Valéry Montpellier; Franci
Processes with Long Memory: Regenerative Construction and Perfect Simulation
We present a perfect simulation algorithm for stationary processes indexed by
Z, with summable memory decay. Depending on the decay, we construct the process
on finite or semi-infinite intervals, explicitly from an i.i.d. uniform
sequence. Even though the process has infinite memory, its value at time 0
depends only on a finite, but random, number of these uniform variables. The
algorithm is based on a recent regenerative construction of these measures by
Ferrari, Maass, Mart{\'\i}nez and Ney. As applications, we discuss the perfect
simulation of binary autoregressions and Markov chains on the unit interval.Comment: 27 pages, one figure. Version accepted by Annals of Applied
Probability. Small changes with respect to version
Theory of spin precession monitored by laser pulse
We first predict the splitting of a spin degenerate impurity level when this
impurity is irradiated by a circularly polarized laser beam tuned in the
transparency region of a semiconductor. This splitting, which comes from
different exchange processes between the impurity electron and the virtual
pairs coupled to the pump beam, induces a spin precession around the laser beam
axis, which lasts as long as the pump pulse. It can thus be used for ultrafast
spin manipulation. This effect, which has similarities with the exciton optical
Stark effect we studied long ago, is here derived using the concepts we
developed very recently to treat many-body interactions between composite
excitons and which make the physics of this type of effects quite transparent.
They, in particular, allow to easily extend this work to other experimental
situations in which a spin rotates under laser irradiation.Comment: 12 pages + 1 figur
Conservation of geometric structures for non-homogeneous inviscid incompressible fluids
We obtain a result about propagation of geometric properties for solutions of
the non-homogeneous incompressible Euler system in any dimension . In
particular, we investigate conservation of striated and conormal regularity,
which is a natural way of generalizing the 2-D structure of vortex patches. The
results we get are only local in time, even in the dimension N=2; however, we
provide an explicit lower bound for the lifespan of the solution. In the case
of physical dimension N=2 or 3, we investigate also propagation of H\"older
regularity in the interior of a bounded domain
One more approach to the convergence of the empirical process to the Brownian bridge
A theorem of Donsker asserts that the empirical process converges in
distribution to the Brownian bridge. The aim of this paper is to provide a new
and simple proof of this fact
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