1,024 research outputs found
Convergence of U-statistics for interacting particle systems
The convergence of U-statistics has been intensively studied for estimators
based on families of i.i.d. random variables and variants of them. In most
cases, the independence assumption is crucial [Lee90, de99]. When dealing with
Feynman-Kac and other interacting particle systems of Monte Carlo type, one
faces a new type of problem. Namely, in a sample of N particles obtained
through the corresponding algorithms, the distributions of the particles are
correlated -although any finite number of them is asymptotically independent
with respect to the total number N of particles. In the present article,
exploiting the fine asymptotics of particle systems, we prove convergence
theorems for U-statistics in this framework
On the Stability and the Approximation of Branching Distribution Flows, with Applications to Nonlinear Multiple Target Filtering
We analyse the exponential stability properties of a class of measure-valued
equations arising in nonlinear multi-target filtering problems. We also prove
the uniform convergence properties w.r.t. the time parameter of a rather
general class of stochastic filtering algorithms, including sequential Monte
Carlo type models and mean eld particle interpretation models. We illustrate
these results in the context of the Bernoulli and the Probability Hypothesis
Density filter, yielding what seems to be the first results of this kind in
this subject
Production and decays of supersymmetric Higgs bosons in spontaneously broken R-parity
We study the mass spectra, production and decay properties of the lightest
supersymmetric CP-even and CP-odd Higgs bosons in models with spontaneously
broken R-parity (SBRP). We compare the resulting mass spectra with expectations
of the Minimal Supersymmetric Standard Model (MSSM), stressing that the model
obeys the upper bound on the lightest CP-even Higgs boson mass. We discuss how
the presence of the additional scalar singlet states affects the Higgs
production cross sections, both for the Bjorken process and the "associated
production". The main phenomenological novelty with respect to the MSSM comes
from the fact that the spontaneous breaking of lepton number leads to the
existence of the majoron, denoted J, which opens new decay channels for
supersymmetric Higgs bosons. We find that the invisible decays of CP-even
Higgses can be dominant, while those of the CP-odd bosons may also be sizeable.Comment: 21 pages, 8 figures; minor changes, final version for publicatio
On particle Gibbs Markov chain Monte Carlo models
This article analyses a new class of advanced particle Markov chain Monte
Carlo algorithms recently introduced by Andrieu, Doucet, and Holenstein (2010).
We present a natural interpretation of these methods in terms of well known
unbiasedness properties of Feynman-Kac particle measures, and a new duality
with many-body Feynman-Kac models. This perspective sheds a new light on the
foundations and the mathematical analysis of this class of methods. A key
consequence is the equivalence between the backward and ancestral particle
Markov chain Monte Carlo methods, and Gibbs sampling of a many-body Feynman-Kac
target distribution. Our approach also presents a new stochastic differential
calculus based on geometric combinatorial techniques to derive explicit
non-asymptotic Taylor type series of the semigroup of a class of particle
Markov chain Monte Carlo models around their invariant measures with respect to
the population size of the auxiliary particle sampler. These results provide
sharp quan- titative estimates of the convergence properties of conditional
particle Markov chain models with respect to the time horizon and the size of
the systems. We illustrate the implication of these results with sharp
estimates of the contraction coefficient and the Lyapunov exponent of
conditional particle samplers, and explicit and non-asymptotic Lp-mean error
decompositions of the law of the random states around the limiting invariant
measure. The abstract framework developed in the article also allows the design
of natural extensions to island (also called SMC2) type particle methodologies
Degenerate neutrinos from a supersymmetric A_4 model
We investigate the supersymmetric A_4 model recently proposed by Babu, Ma and
Valle. The model naturally gives quasi-degenerate neutrinos that are bi-largely
mixed, in agreement with observations. Furthermore, the mixings in the quark
sector are constrained to be small, making it a complete model of the flavor
structure. Moreover, it has the interesting property that CP-violation in the
leptonic sector is maximal (unless vanishing). The model exhibit a close
relation between the slepton and lepton sectors and we derive the slepton
spectra that are compatible with neutrino data and the present bounds on
flavor-violating charged lepton decays. The prediction for the branching ratio
of the decay tau -> mu gamma has a lower limit of 10^{-9}. In addition, the
overall neutrino mass scale is constrained to be larger than 0.3 eV. Thus, the
model will be tested in the very near future.Comment: 11 pages, 6 figures. Talk given at the International Workshop on
Astroparticle and High Energy Physics (AHEP), Valencia, Spain, 14-18 Oct.
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Biotechnological approaches to develop nitrogen-fixing cereals: A review
Funding: This work has been funded by the Junta de Andalucia through the research group AGR123.Agricultural yields are often limited by nitrogen (N) availability, especially in countries of the developing world, whereas in industrialized
nations the application of chemical N fertilizers has reached unsustainable levels that have resulted in severe environmental
consequences. Finding alternatives to inorganic fertilizers is critical for sustainable and secure food production. Although gaseous nitrogen
(N2) is abundant in the atmosphere, it cannot be assimilated by most living organisms. Only a selected group of microorganisms termed
diazotrophs, have evolved the ability to reduce N2 to generate NH3 in a process known as biological nitrogen fixation (BNF) catalysed by
nitrogenase, an oxygen-sensitive enzyme complex. This ability presents an opportunity to improve the nutrition of crop plants, through the
introduction into cereal crops of either the N fixing bacteria or the nitrogenase enzyme responsible for N fixation. This review explores three
potential approaches to obtain N-fixing cereals: (a) engineering the nitrogenase enzyme to function in plant cells; (b) engineering the legume
symbiosis into cereals; and (c) engineering cereals with the capability to associate with N-fixing bacteria.Junta de Andaluci
Minimal supergravity radiative effects on the tri-bimaximal neutrino mixing pattern
We study the stability of the Harrison-Perkins-Scott (HPS) mixing pattern,
assumed to hold at some high energy scale, against supersymmetric radiative
corrections. We work in the framework of a reference minimal supergravity model
(mSUGRA) where supersymmetry breaking is universal and flavor-blind at
unification. The radiative corrections considered include both RGE running as
well as threshold effects. We find that in this case the solar mixing angle can
only increase with respect to the HPS reference value, while the atmospheric
and reactor mixing angles remain essentially stable. Deviations from the solar
angle HPS prediction towards lower values would signal novel contributions from
physics beyond the simplest mSUGRA model.Comment: 13 pages, 3 figures; added reference; final version for publicatio
Predicting Neutrinoless Double Beta Decay
We give predictions for the neutrinoless double beta decay rate in a simple
variant of the A_4 family symmetry model. We show that there is a lower bound
for the neutrinoless double beta decay amplitude even in the case of normal
hierarchical neutrino masses, corresponding to an effective mass parameter
|m_{ee}| >= 0.17 \sqrt{\Delta m^2_{ATM}}. This result holds both for the CP
conserving and CP violating cases. In the latter case we show explicitly that
the lower bound on |m_{ee}| is sensitive to the value of the Majorana phase. We
conclude therefore that in our scheme, neutrinoless double beta decay may be
accessible to the next generation of high sensitivity experiments.Comment: 4 pages, 5 figures, 1 tabl
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