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The University of Tennessee

University of Tennessee | Department of Physics and Astronomy | Theoretical Astrophysic Group

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Spherically Symmetric Models

Agile-BOLTZTRAN is our platform for high-quality, detailed one-dimensional simulations of stellar core-collapse and supernovae. Agile is a spherically symmetric, adaptive-mesh hydrodynamics code with a complete treatment of general relativity. Agile is coupled to BOLTZTRAN, a spherically symmetric, multi-flavor, multi-group, discrete ordinates Boltzmann neutrino transport code with detailed neutrino-matter interactions. Agile-BOLTZTRAN remains a valuable tool for problems where it's strengths (full general relativity and Boltzmann neutrino transport) outway it's primary weakness (the assumption of spherical symmetry). We make significant use of Agile-BOLTZTRAN as a verification standard for mCHIMERA and improvements to BOLTZTRAN also benefit the eventual bCHIMERA development.

Impact of the Nuclear Equation of State on Core Collapse Supernovae (Baird, Lentz, Hix, Messer, Mezzacappa)

As part of his M.S. degree, UTK graduate student M. Baird, has completed a study using Agile-BOLTZTRAN to explore the impact of different parameterizations of the nuclear Equation of State (EOS). Spherical symmetry is an adequate approximation when studying the bounce and early shock propagation, but Newtonian gravity is not, making Agile-BOLTZTRAN, as a fully general relativistic code, ideally suited to this exploration of different EOSs. This study compared the industry standard EOS of Lattimer & Swesty (1991) with the Relativistic Mean Field EOS of Shen et al. (1998) and the EOS of Wilson (see, e.g., Wilson & Mayle 1993), which includes a contribution from pions. Comparison of models using these EoSs demonstrated significant differences in the timing (up to 50%) and location (up to 20%) of shock stall. Our analysis also revealed the importance of compositional differences in the sub-nuclear regime, which couple to the neutrino transport to affect the electron fraction and entropy of the matter and therefore the progress of the shock.

Terrestial Neutrino Signatures (Messer, Lentz, Mezzacappa)

We have worked with UTK undergraduate Adrian Sanchez to produce a library of SN neutrino signature templates for terrestrial detectors using Agile-BOLTZTRAN. A workflow for this post-processing of neutrino data has been established and is now being applied to 2-dimensional CHIMERA neutrino data as well.  This will allow us to explore line-of-sight effects in asymmetric explosions, which is essentially a unique capability.

Sensitivity to Neutrino Opacities (Lentz, Messer, Mezzacappa, Hix with Liebendoerfer)

A comprehensive study of effects of neutrino opacities is underway, building on Lentz prior efforts to update the neutrino opacities included within BOLTZTRAN and restructure BOLTZTRAN to allow solution of the transport of multiple neutrino flavors simultaneously, enabling the inclusion of neutrino interactions that involve more than one neutrino flavor and allowing for flexibility and extensibility in the number of neutrino flavors treated. In future this will permit the treatment of neutrino flavor mixing much more effectively than prior versions of BOLTZTRAN.