Nonuniform neutron-rich matter and coherent neutrino scattering

C. J. Horowitz, M. A. Pérez-García, J. Carriere, D. K. Berry, J. Piekarewicz

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Abstract

Nonuniform neutron-rich matter present in both core-collapse supernovae and neutron-star crusts is described in terms of a semiclassical model that reproduces nuclear-matter properties and includes long-range Coulomb interactions. The neutron-neutron correlation function and the corresponding static structure factor are calculated from molecular dynamics simulations involving 40 000 to 100 000 nucleons. The static structure factor describes coherent neutrino scattering which is expected to dominate the neutrino opacity. At low momentum transfers the static structure factor is found to be small because of ion screening. In contrast, at intermediate momentum transfers the static structure factor displays a large peak due to coherent scattering from all the neutrons in a cluster. This peak moves to higher momentum transfers and decreases in amplitude as the density increases. A large static structure factor at zero momentum transfer, indicative of large density fluctuations during a first-order phase transition, may increase the neutrino opacity. However, no evidence of such an increase has been found. Therefore, it is unlikely that the system undergoes a simple first-order phase transition. Further, to compare our results to more conventional approaches, a cluster algorithm is introduced to determine the composition of the clusters in our simulations. Neutrino opacities are then calculated within a single heavy nucleus approximation as is done in most current supernova simulations. It is found that corrections to the single heavy nucleus approximation first appear at a density of the order of 1013 g/cm3 and increase rapidly with increasing density. Thus neutrino opacities are overestimated in the single heavy nucleus approximation relative to the complete molecular dynamics simulations.

Original languageEnglish
Article number065806
Pages (from-to)658061-6580615
Number of pages5922555
JournalPhysical Review C - Nuclear Physics
Volume70
Issue number6
DOIs
StatePublished - Dec 2004
Externally publishedYes

Bibliographical note

Funding Information:
We acknowledge useful discussions with Sanjay Reddy. M.A.P.G. acknowledges partial support from Indiana University and University of Oviedo. J.P. thanks David Banks and the staff at the FSU Visualization Laboratory for their help. We thank Brad Futch for preparing Figs. f3 f8 f12. This work was supported in part by DOE Grants DE-FG02-87ER40365 and DE-FG05-92ER40750, and by Shared University Research grants from IBM, Inc. to Indiana University.

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