294 research outputs found
Signatures of Chiral Dynamics in Low Energy Compton Scattering off the Nucleon
We present a projector formalism which allows to define dynamical
polarizabilities of the nucleon from a multipole expansion of the nucleon
Compton amplitudes. We give predictions for the energy dependence of these
dynamical polarizabilities both from dispersion theory and from
leading-one-loop chiral effective field theory. Based on the good agreement
between the two theoretical frameworks, we conclude that the energy dependence
of the dynamical polarizabilities is dominated by chiral dynamics, except in
those multipole channels where the first nucleon resonance Delta(1232) can be
excited. Both the dispersion theory framework and a chiral effective field
theory with explicit Delta(1232) degrees of freedom lead to a very good
description of the available low energy proton Compton data. We discuss the
sensitivity of the proton Compton cross section to dynamical polarizabilities
of different multipole content and present a fit of the static electric and
magnetic dipole polarizabilities from low-energy Compton data up to omega=170
MeV, finding alpha_E=(11.04+-1.36)*10^(-4) fm^3, beta_M =(2.76-+1.36)*10^(-4)
fm^3.Comment: 43 pages, 13 figure
A model for A=3 antinuclei production in proton-nucleus collisions
A simple coalescence model based on the same diagrammatic approach of
antimatter production in hadronic collisions as used previously for
antideuterons is used here for the hadroproduction of mass 3 antinuclei. It is
shown that the model is able to reproduce the existing experimental data on
Tbar and 3hebar production without any additional parameter.Comment: 7 figures. submitted to Eur. Phys. J.
Ensemble evaluation of hydrological model hypotheses
It is demonstrated for the first time how model parameter, structural and data uncertainties can be accounted for explicitly and simultaneously within the Generalized Likelihood Uncertainty Estimation (GLUE) methodology. As an example application, 72 variants of a single soil moisture accounting store are tested as simplified hypotheses of runoff generation at six experimental grassland field-scale lysimeters through model rejection and a novel diagnostic scheme. The fields, designed as replicates, exhibit different hydrological behaviors which yield different model performances. For fields with low initial discharge levels at the beginning of events, the conceptual stores considered reach their limit of applicability. Conversely, one of the fields yielding more discharge than the others, but having larger data gaps, allows for greater flexibility in the choice of model structures. As a model learning exercise, the study points to a “leaking” of the fields not evident from previous field experiments. It is discussed how understanding observational uncertainties and incorporating these into model diagnostics can help appreciate the scale of model structural error
Exoplanetary Geophysics -- An Emerging Discipline
Thousands of extrasolar planets have been discovered, and it is clear that
the galactic planetary census draws on a diversity greatly exceeding that
exhibited by the solar system's planets. We review significant landmarks in the
chronology of extrasolar planet detection, and we give an overview of the
varied observational techniques that are brought to bear. We then discuss the
properties of the currently known distribution, using the mass-period diagram
as a guide to delineating hot Jupiters, eccentric giant planets, and a third,
highly populous, category that we term "ungiants", planets having masses less
than 30 Earth masses and orbital periods less than 100 days. We then move to a
discussion of the bulk compositions of the extrasolar planets. We discuss the
long-standing problem of radius anomalies among giant planets, as well as
issues posed by the unexpectedly large range in sizes observed for planets with
masses somewhat greater than Earth's. We discuss the use of transit
observations to probe the atmospheres of extrasolar planets; various
measurements taken during primary transit, secondary eclipse, and through the
full orbital period, can give clues to the atmospheric compositions,
structures, and meteorologies. The extrasolar planet catalog, along with the
details of our solar system and observations of star-forming regions and
protoplanetary disks, provide a backdrop for a discussion of planet formation
in which we review the elements of the favored pictures for how the terrestrial
and giant planets were assembled. We conclude by listing several research
questions that are relevant to the next ten years and beyond.Comment: Review chapter to appear in Treatise on Geophysics, 2nd Editio
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