Abstract. The type II supernova is considered as a candidate site for the production of heavy elements. Since the supernova produces an intense neutrino flux, neutrino scattering processes will impact element formation. We examine active-sterile neutrino conversion in this environment and find that it may help to produce the requisite neutron-to-seed ratio for synthesis of the r-process elements.The r-process of nucleosynthesis accounts for the most neutron rich of the heavy elements. The most likely environment for this type of synthesis is the late time (t > 10 s post-core bounce) supernova environment. Many studies have explored this 'neutrino driven wind' as a candidate environment and found it to be potentially viable [1,2]. However, to date, no model correctly reproduces the observed abundance pattern.In the neutrino driven wind, material in the form of free nucleons is 'lifted' off of the surface of the neutron star by energy deposited by neutrino interactions. Analytic and semianalytic parameterizations of the thermodynamic and hydrodynamic conditions in the wind can be obtained [3,4]. Models of this type may be used to explore the range of conditions within the context of the wind which will produce the solar system distribution of r-process elements. The key determinant of whether a given scenario will produce the r-process is the neutron to seed nucleus ratio at the onset of the neutron capture phase. This ratio must be quite high (R > 100) in order to produce the very neutron-rich r-process elements. The factors which determine the neutron-to-seed ratio are the entropy of the material, the hydrodynamic outflow timescale and the electron fraction, Y e = 1/(1 + n/p) where n/p is the neutron-to-proton ratio. A study of many possible model parameters shows that one must decrease the electron fraction, and/or increase the entropy and/or decrease the hydrodynamic outflow timescale, relative to the conditions found in typical wind models, in order to produce the neutron-to-seed ratio necessary for the r-process [5,6].Including the effects of neutrino interactions in general tends to make the requisite conditions for r-process element production more extreme [7,8]. In particular, neutrino capture on free nucleons during alpha particle formation increases the elec-
The astrophysical site or sites responsible for the r-process of nucleosynthesis still remains an enigma. Since the rare earth region is formed in the latter stages of the r-process it provides a unique probe of the astrophysical conditions during which the r-process takes place. We use features of a successful rare earth region in the context of a high entropy r-process (S 100k B ) and discuss the types of astrophysical conditions that produce abundance patterns that best match meteoritic and observational data. Despite uncertainties in nuclear physics input, this method effectively constrains astrophysical conditions.
The flavor evolution of neutrinos in core collapse supernovae and neutron star mergers is a critically important unsolved problem in astrophysics. Following the electron flavor evolution of the neutrino system is essential for calculating the thermodynamics of compact objects as well as the chemical elements they produce. Accurately accounting for flavor transformation in these environments is challenging for a number of reasons, including the large number of neutrinos involved, the small spatial scale of the oscillation, and the nonlinearity of the system. We take a step in addressing these issues by presenting a method which describes the neutrino fields in terms of angular moments. Our moment method successfully describes the fast flavor neutrino transformation phenomenon which is expected to occur in regions close to the central object. We apply our moment method to neutron star merger conditions and show that we are able to capture the three phases of growth, saturation, and decoherence by comparing with particle-in-cell calculations. We also determine the size of the growing fluctuations in the neutrino field.
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