26,547 research outputs found
Quantum Corrections in Massive Gravity
We compute the one-loop quantum corrections to the potential of ghost-free
massive gravity. We show how the mass of external matter fields contribute to
the running of the cosmological constant, but do not change the ghost-free
structure of the massive gravity potential at one-loop. When considering
gravitons running in the loops, we show how the structure of the potential gets
destabilized at the quantum level, but in a way which would never involve a
ghost with a mass smaller than the Planck scale. This is done by explicitly
computing the one-loop effective action and supplementing it with the
Vainshtein mechanism. We conclude that to one-loop order the special mass
structure of ghost-free massive gravity is technically natural.Comment: v2: References added, 29 pages, 7 figure
Obtaining adjusted prevalence ratios from logistic regression model in cross-sectional studies
In the last decades, it has been discussed the use of epidemiological
prevalence ratio (PR) rather than odds ratio as a measure of association to be
estimated in cross-sectional studies. The main difficulties in use of
statistical models for the calculation of PR are convergence problems,
availability of adequate tools and strong assumptions. The goal of this study
is to illustrate how to estimate PR and its confidence interval directly from
logistic regression estimates. We present three examples and compare the
adjusted estimates of PR with the estimates obtained by use of log-binomial,
robust Poisson regression and adjusted prevalence odds ratio (POR). The
marginal and conditional prevalence ratios estimated from logistic regression
showed the following advantages: no numerical instability; simple to implement
in a statistical software; and assumes the adequate probability distribution
for the outcome
Atmospheric monitoring and array calibration in CTA using the Cherenkov Transparency Coefficient
The Cherenkov Telescope Array (CTA) will be the next generation observatory
employing different types of Cherenkov telescopes for the detection of particle
showers initiated by very-high-energy gamma rays. A good knowledge of the
Earth's atmosphere, which acts as a calorimeter in the detection technique,
will be crucial for calibration in CTA. Variations of the atmosphere's
transparency to Cherenkov light and not correctly performed calibration of
individual telescopes in the array result in large systematic uncertainties on
the energy scale. The Cherenkov Transparency Coefficient (CTC), developed
within the H.E.S.S. experiment, quantifies the mean atmosphere transparency
ascertained from data taken by Cherenkov telescopes during scientific
observations. Provided that atmospheric conditions over the array are uniform,
transparency values obtained per telescope can be also used for the calibration
of individual telescope responses. The application of the CTC in CTA presents a
challenge due to the greater complexity of the observatory and the variety of
telescope cameras compared with currently operating experiments, such as
H.E.S.S. We present here the first results of a feasibility study for extension
of the CTC concept in CTA for purposes of the inter-calibration of the
telescopes in the array and monitoring of the atmosphere.Comment: All CTA contributions at arXiv:1709.0348
On Poisson quasi-Nijenhuis Lie algebroids
We propose a definition of Poisson quasi-Nijenhuis Lie algebroids as a
natural generalization of Poisson quasi-Nijenhuis manifolds and show that any
such Lie algebroid has an associated quasi-Lie bialgebroid. Therefore, also an
associated Courant algebroid is obtained. We introduce the notion of a morphism
of quasi-Lie bialgebroids and of the induced Courant algebroids morphism and
provide some examples of Courant algebroid morphisms. Finally, we use paired
operators to deform doubles of Lie and quasi-Lie bialgebroids and find an
application to generalized complex geometry.Comment: 12 page
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