1,356 research outputs found
A Froggatt-Nielsen flavor model for neutrino physics
Superheavy neutrinos can, via the seesaw model, provide a mechanism for
lepton number violation. If they are combined with flavor violation as
characterized by the Froggatt-Nielsen mechanism, then the phenomenology for the
neutrinos in oscillation experiments, neutrinoless double beta decay, and other
experiments can be described by a relatively few number of parameters. We
describe the low-energy neutrino mass matrix and show that the results are
consistent with currently available data.Comment: 7 pages, no figure
Sufficient Covariate, Propensity Variable and Doubly Robust Estimation
Statistical causal inference from observational studies often requires
adjustment for a possibly multi-dimensional variable, where dimension reduction
is crucial. The propensity score, first introduced by Rosenbaum and Rubin, is a
popular approach to such reduction. We address causal inference within Dawid's
decision-theoretic framework, where it is essential to pay attention to
sufficient covariates and their properties. We examine the role of a propensity
variable in a normal linear model. We investigate both population-based and
sample-based linear regressions, with adjustments for a multivariate covariate
and for a propensity variable. In addition, we study the augmented inverse
probability weighted estimator, involving a combination of a response model and
a propensity model. In a linear regression with homoscedasticity, a propensity
variable is proved to provide the same estimated causal effect as multivariate
adjustment. An estimated propensity variable may, but need not, yield better
precision than the true propensity variable. The augmented inverse probability
weighted estimator is doubly robust and can improve precision if the propensity
model is correctly specified
On the Equivalence of Three-Particle Scattering Formalisms
In recent years, different on-shell scattering
formalisms have been proposed to be applied to both lattice QCD and infinite
volume scattering processes. We prove that the formulation in the infinite
volume presented by Hansen and Sharpe in Phys.~Rev.~D92, 114509 (2015) and
subsequently Brice\~no, Hansen, and Sharpe in Phys.~Rev.~D95, 074510 (2017) can
be recovered from the -matrix representation, derived on the basis of
-matrix unitarity, presented by Mai {\em et al.} in Eur.~Phys.~J.~A53, 177
(2017) and Jackura {\em et al.} in Eur.~Phys.~J.~C79, 56 (2019). Therefore,
both formalisms in the infinite volume are equivalent and the physical content
is identical. Additionally, the Faddeev equations are recovered in the
non-relativistic limit of both representations.Comment: 13 pages, 5 figure
Information Aggregation in Exponential Family Markets
We consider the design of prediction market mechanisms known as automated
market makers. We show that we can design these mechanisms via the mold of
\emph{exponential family distributions}, a popular and well-studied probability
distribution template used in statistics. We give a full development of this
relationship and explore a range of benefits. We draw connections between the
information aggregation of market prices and the belief aggregation of learning
agents that rely on exponential family distributions. We develop a very natural
analysis of the market behavior as well as the price equilibrium under the
assumption that the traders exhibit risk aversion according to exponential
utility. We also consider similar aspects under alternative models, such as
when traders are budget constrained
Significance in gamma-ray astronomy - the Li & Ma problem in Bayesian statistics
The significance of having detected an astrophysical gamma ray source is
usually calculated by means of a formula derived by Li & Ma in 1983. We solve
the same problem in terms of Bayesian statistics, which provides a logically
more satisfactory framework. We do not use any subjective elements in the
present version of Bayesian statistics. We show that for large count numbers
and a weak source the Li & Ma formula agrees with the Bayesian result. For
other cases the two results differ, both due to the mathematically different
treatment and the fact that only Bayesian inference can take into account prior
knowldege.Comment: 12 pages, 3 figures, accepted for publication in A&
Computational algebraic methods in efficient estimation
A strong link between information geometry and algebraic statistics is made
by investigating statistical manifolds which are algebraic varieties. In
particular it it shown how first and second order efficient estimators can be
constructed, such as bias corrected Maximum Likelihood and more general
estimators, and for which the estimating equations are purely algebraic. In
addition it is shown how Gr\"obner basis technology, which is at the heart of
algebraic statistics, can be used to reduce the degrees of the terms in the
estimating equations. This points the way to the feasible use, to find the
estimators, of special methods for solving polynomial equations, such as
homotopy continuation methods. Simple examples are given showing both equations
and computations. *** The proof of Theorem 2 was corrected by the latest
version. Some minor errors were also corrected.Comment: 21 pages, 5 figure
Effects of Epistasis and Pleiotropy on Fitness Landscapes
The factors that influence genetic architecture shape the structure of the
fitness landscape, and therefore play a large role in the evolutionary
dynamics. Here the NK model is used to investigate how epistasis and pleiotropy
-- key components of genetic architecture -- affect the structure of the
fitness landscape, and how they affect the ability of evolving populations to
adapt despite the difficulty of crossing valleys present in rugged landscapes.
Populations are seen to make use of epistatic interactions and pleiotropy to
attain higher fitness, and are not inhibited by the fact that valleys have to
be crossed to reach peaks of higher fitness.Comment: 10 pages, 6 figures. To appear in "Origin of Life and Evolutionary
Mechanisms" (P. Pontarotti, ed.). Evolutionary Biology: 16th Meeting 2012,
Springer-Verla
Métodos de avaliação da segurança de pontes existentes
O presente trabalho pretende descrever, de uma forma acessível, os
métodos de análise de fiabilidade e a metodologia de verificação da
segurança por etapas, que podem ser úteis na avaliação da segurança de
pontes existentes. A metodologia apresentada sugere o recurso a uma
análise mais avançada sempre que a ponte não cumpra os requisitos
estabelecidos no nível de avaliação anterior, culminando no método de
avaliação que combina a análise não-linear com a análise probabilística.The present work aims to describe, in an accessible way, the methods of
reliability analysis and the step-level assessment methodology, which
might be useful in the safety evaluation of existent bridges. The
presented methodology suggest to use a more advanced analysis when
the bridge doesn’t fulfill the requirements established in the previous
safety evaluation level, culminating in the method of evaluation that
combines the non-linear and probabilistic analysis.Comissão Europeia - VI Programa Quadro "Sustainable Bridges” FP6-PLT-0165
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