4,502 research outputs found
Optimal predictive model selection
Often the goal of model selection is to choose a model for future prediction,
and it is natural to measure the accuracy of a future prediction by squared
error loss. Under the Bayesian approach, it is commonly perceived that the
optimal predictive model is the model with highest posterior probability, but
this is not necessarily the case. In this paper we show that, for selection
among normal linear models, the optimal predictive model is often the median
probability model, which is defined as the model consisting of those variables
which have overall posterior probability greater than or equal to 1/2 of being
in a model. The median probability model often differs from the highest
probability model
The Median Probability Model and Correlated Variables
The median probability model (MPM) Barbieri and Berger (2004) is defined as
the model consisting of those variables whose marginal posterior probability of
inclusion is at least 0.5. The MPM rule yields the best single model for
prediction in orthogonal and nested correlated designs. This result was
originally conceived under a specific class of priors, such as the point mass
mixtures of non-informative and g-type priors. The MPM rule, however, has
become so very popular that it is now being deployed for a wider variety of
priors and under correlated designs, where the properties of MPM are not yet
completely understood. The main thrust of this work is to shed light on
properties of MPM in these contexts by (a) characterizing situations when MPM
is still safe under correlated designs, (b) providing significant
generalizations of MPM to a broader class of priors (such as continuous
spike-and-slab priors). We also provide new supporting evidence for the
suitability of g-priors, as opposed to independent product priors, using new
predictive matching arguments. Furthermore, we emphasize the importance of
prior model probabilities and highlight the merits of non-uniform prior
probability assignments using the notion of model aggregates
Radiative corrections to the background of decay
Radiative muon decay in the kinematics similar to the neutrinoless decay
is considered. Radiative corrections due to 1-loop virtual
photons and emission of additional soft or hard photons are taken into account.
Analytical expressions and numerical estimations are presented.Comment: 11 pages, LaTeX, misprints in Eqs.(9,12,14) fixe
U(2) and Maximal Mixing of nu_{mu}
A U(2) flavor symmetry can successfully describe the charged fermion masses
and mixings, and supress SUSY FCNC processes, making it a viable candidate for
a theory of flavor. We show that a direct application of this U(2) flavor
symmetry automatically predicts a mixing of 45 degrees for nu_mu to nu_s, where
nu_s is a light, right-handed state. The introduction of an additional flavor
symmetry acting on the right-handed neutrinos makes the model
phenomenologically viable, explaining the solar neutrino deficit as well as the
atmospheric neutrino anomaly, while giving a potential hot dark matter
candidate and retaining the theory's predictivity in the quark sector.Comment: 20 pages, 1 figur
Gamma-ray burst jet propagation, development of angular structure, and the luminosity function
The fate and observable properties of gamma-ray burst jets depend crucially
on their interaction with the progenitor material that surrounds the central
engine. We present a semi-analytical model of such interaction, which builds
upon several previous analytical and numerical works, aimed at predicting the
angular distribution of jet and cocoon energy and Lorentz factor after
breakout, given the properties of the ambient material and of the jet at
launch. Using this model, we construct synthetic populations of structured
jets, assuming either a collapsar (for long gamma-ray bursts -- LGRBs) or a
binary neutron star merger (for short gamma-ray bursts -- SGRBs) as progenitor.
We assume all progenitors to be identical, and we allow little variability in
the jet properties at launch: our populations therefore feature a
quasi-universal structure. These populations are able to reproduce the main
features of the observed LGRB and SGRB luminosity functions, although several
uncertainties and caveats remain to be addressed.Comment: 15 pages, 12 figures. Revised version, submitted to A&A (several new
figures and expanded discussion. Conclusions unchanged). Comments and
suggestions are welcome
Electric Dipole moments of charged leptons and lepton flavor violating interactions in the general two Higgs Doublet model
We calculate the electric dipole moment of electron using the experimental
result of muon electric dipole moment and upper limit of the BR(\mu -->
e\gamma) in the framework of the general two Higgs doublet model. Our
prediction is 10^{-32} e-cm, which lies in the experimental current limits.
Further, we obtain constraints for the Yukawa couplings \bar{\xi}^{D}_{N,\tau
e} and \bar{\xi}^{D}_{N,\tau\mu}. Finally we present an expression which
connects the BR(\tau\to \mu\gamma) and the electric dipole moment of
\tau-lepton and study the relation between these physical quantities.Comment: 8 pages, 4 Figures (required epsf sty
Carbon based double layer capacitors with aprotic electrolyte solutions: the possible role of intercalation/insertion processes
The extraordinary stability and cycle life performance of today's electrochemical double-layer capacitors (EDLCs) are generally ascribed to the fact that charge storage in activated carbon (AC) is based on pure double-layer charging. In contrast, Faradaic charge-transfer reactions like those occurring in batteries are often connected with dimensional changes, which can affect the cycle life of these storage devices. Here we report the charge-induced height change of an AC electrode in an aprotic electrolyte solution, 1mol/l (C2H5)4NBF4 (TEABF4) in acetonitrile. The results are compared with those obtained for a graphite electrode in the same electrolyte. For both electrodes, we observe an expansion/contraction of several percent for a potential window of ±2V vs. the immersion potential (ip). For the EDLC electrode, significant expansion starts at about 1V remote from the ip and hence is well within the normal EDLC operation range. For the graphite electrode, the height changes are unambiguously caused by intercalation/deintercalation of both anions and cations. The close analogies between the graphite and the EDLC electrode suggest that ion intercalation or insertion processes might play a major role for charge storage, self discharge, cyclability, and the voltage limitation of EDLC
Flavour physics from an approximate U(2)^3 symmetry
The quark sector of the Standard Model exhibits an approximate U(2)^3 flavour
symmetry. This symmetry, broken in specific directions dictated by minimality,
can explain the success of the Cabibbo-Kobayashi-Maskawa picture of flavour
mixing and CP violation, confirmed by the data so far, while allowing for
observable deviations from it, as expected in most models of ElectroWeak
Symmetry Breaking. Building on previous work in the specific context of
supersymmetry, we analyze the expected effects and we quantify the current
bounds in a general Effective Field Theory framework. As a further relevant
example we then show how the U(2)^3 symmetry and its breaking can be
implemented in a generic composite Higgs model and we make a first analysis of
its peculiar consequences. We also discuss how some partial extension of U(2)^3
to the lepton sector can arise, both in general and in composite Higgs models.
An optimistic though conceivable interpretation of the considerations developed
in this paper gives reasons to think that new physics searches in the flavour
sector may be about to explore an interesting realm of phenomena.Comment: 29 pages, 5 figure
Two-Loop Large- Electroweak Corrections to for Arbitrary Higgs Boson Mass
We consider for the first time the leading large top mass corrections,
arising at higher order in electroweak interactions, to the rare decays
and the related modes and . Higher order effects of similar type have previously been calculated
in the large- limit for key observables of precision electroweak physics
at Z-factories. Here we obtain the corresponding corrections of order at the amplitude level for short-distance dominated rare meson
decays. This allows us to quantify the importance of higher order electroweak
effects for these processes, which can be reliably computed and have very small
uncertainties from strong interactions. Simultaneously it becomes possible to
remove, to some extent, ambiguities in the definition of electroweak parameters
describing the strength of FCNC interactions. The corrections we discuss are at
the level of a few percent.Comment: 11 pages, LaTeX, 1 eps-figur
- …