17,986 research outputs found
The Challenge of Machine Learning in Space Weather Nowcasting and Forecasting
The numerous recent breakthroughs in machine learning (ML) make imperative to
carefully ponder how the scientific community can benefit from a technology
that, although not necessarily new, is today living its golden age. This Grand
Challenge review paper is focused on the present and future role of machine
learning in space weather. The purpose is twofold. On one hand, we will discuss
previous works that use ML for space weather forecasting, focusing in
particular on the few areas that have seen most activity: the forecasting of
geomagnetic indices, of relativistic electrons at geosynchronous orbits, of
solar flares occurrence, of coronal mass ejection propagation time, and of
solar wind speed. On the other hand, this paper serves as a gentle introduction
to the field of machine learning tailored to the space weather community and as
a pointer to a number of open challenges that we believe the community should
undertake in the next decade. The recurring themes throughout the review are
the need to shift our forecasting paradigm to a probabilistic approach focused
on the reliable assessment of uncertainties, and the combination of
physics-based and machine learning approaches, known as gray-box.Comment: under revie
Quasi-classical Gravity effect on neutrino oscillations in a gravitational field of an heavy astrophysical object
In the framework of quantum field theory, a graviton interacts locally with a
quantum state having definite mass, i.e. the gravitational mass eigenstate,
while a weak boson interacts with a state having definite flavor, i.e. the
flavor eigenstate. An interaction of a neutrino with an energetic graviton may
trigger the collapse of the neutrino to a definite mass eigenstate with
probability expressed in terms of PMNS mixing matrix elements. Thus, gravitons
would induce quantum decoherence of a coherent neutrino flavor state similarly
to how weak bosons induce quantum decoherence of a neutrino in a definite mass
state. We demonstrate that such an essentially quantum gravity effect may have
strong consequences for neutrino oscillation phenomena in astrophysics due to
relatively large scattering cross sections of relativistic neutrinos undergoing
large-angle radiation of energetic gravitons in gravitational field of a
classical massive source (i.e. the quasi-classical case of gravitational
Bethe-Heitler scattering). This graviton-induced {\it decoherence} is compared
to {\it decoherence} due to propagation in the presence of the Earth matter
effect. Based on this study, we propose a new technique for the indirect
detection of energetic gravitons by measuring the flavor composition of
astrophysical neutrinos.Comment: 25 pages, 4 figures, minor revision with clarifications, main
conclusions are unchange
Quantum Color Transparency and Nuclear Filtering
Color transparency is the proposal that under certain circumstances the
strong interactions can be reduced in magnitude. We give a comprehensive review
of the physics, which hinges on the interface of perturbative QCD with
non--perturbative strong interactions. Color transparency is complementary to
{\it nuclear filtering}, which is the conversion of quark wave functions in
hadrons to small transverse space dimensions by interaction with a nuclear
medium. We review current approaches, including pictures based on modeling the
time evolution of hadronic wave--packets as well as the use of light cone
matrix elements. Spin plays an intrinsic role in testing and understanding the
physics and is discussed at length. We emphasize the use of data analysis
procedures which have minimal model dependence. We also review existing
experimental data and the experimental program planned at various facilities.
The subject has strong scientific complementarity and potential to make
progress in exploring hadron physics at current and future facilities.Comment: 131 pages, review article in LaTeX to appear in Physics Reports, no
postscipt figures, approximately 30 figures available from Ralston on reques
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