6 research outputs found
Two-Moment Neutrino Flavor Transformation with applications to the Fast Flavor Instability in Neutron Star Mergers
Multi-Messenger Astrophysics (MMA) has produced a wealth of data with much
more to come in the future. This enormous data set will reveal new insights
into the physics of Core Collapse SuperNovae (CCSN), Binary Neutron Star
Mergers (BNSM), and many other objects where it is actually possible, if not
probable, that new physics is in operation. To tease out different
possibilities, we will need to analyze signals from photons, neutrinos,
gravitational waves, and chemical elements. This task is made all the more
difficult when it is necessary to evolve the neutrino component of the
radiation field and associated quantum-mechanical property of flavor in order
to model the astrophysical system of interest -- a numerical challenge that has
not been addressed to this day. In this work, we take a step in this direction
by adopting the technique of angular-integrated moments with a truncated tower
of dynamical equations and a closure, convolving a flavor-transformation with
spatial transport to evolve the neutrino radiation quantum field. We show that
moments capture the dynamical features of Fast Flavor Instabilities (FFI) and
provide comparable results to a more precise particle-in-cell method. We
propose areas for improvement in the future.Comment: 27 pages, 4 tables, 11 figure
Neutrino flavor mixing with moments
The successful transition from core-collapse supernova simulations using
classical neutrino transport to simulations using quantum neutrino transport
will require the development of methods for calculating neutrino flavor
transformations that mitigate the computational expense. One potential approach
is the use of angular moments of the neutrino field, which has the added appeal
that there already exist simulation codes which make use of moments for
classical neutrino transport. Evolution equations for quantum moments based on
the quantum kinetic equations can be straightforwardly generalized from the
evolution of classical moments based on the Boltzmann equation. We present an
efficient implementation of neutrino transformation using quantum angular
moments in the free streaming, spherically symmetric bulb model. We compare the
results against analytic solutions and the results from more exact multi-angle
neutrino flavor evolution calculations. We find that our moment-based methods
employing scalar closures predict, with good accuracy, the onset of collective
flavor transformations seen in the multi-angle results. However in some
situations they overestimate the coherence of neutrinos traveling along
different trajectories. More sophisticated quantum closures may improve the
agreement between the inexpensive moment-based methods and the multi-angle
approach.Comment: Accepted in Physical Review
Electoral uncertainty, fiscal policy and macroeconomic fluctuations
In this paper we study the link between elections, fiscal policy and aggregate fluctuations. The setup is a stylized dynamic stochastic general equilibrium model incorporating both technology and political re-election shocks. The latter are incorporated via a two-party model with elections. The main theoretical prediction is that forward-looking incumbents, with uncertain prospects of re-election, find it optimal to follow relatively shortsighted fiscal policies, and that this hurts capital accumulation. Our econometric estimation, using U.S. data, finds a statistically significant link between electoral uncertainty and policy instruments and in turn macroeconomic outcomes