Astrophysics Seminar: Luca Boccioli and Atul Kedia, University of Notre Dame

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How to incorporate turbulence in one-dimensional core-collapse supernovae simulations

Luca Boccioli
Graduate Student, University of Notre Dame

Convection and turbulence in core collapse supernovae (CCSN)  are inherently three-dimensional in nature. Hence, it is valuable to modify simulations in spherical symmetry to incorporate 3D effects. This permits exploration of the parameter dependence of CCSN with a minimum of computational resources. In this talk I will present the formulation and implementation of general relativistic (GR) neutrino driven convective turbulence in the spherical relativistic core-collapse supernova code \texttt{GR1D}. This is based upon the recently proposed method of Supernova Turbulence in Reduced-dimensionality (\STIR/) in Newtonian simulations. When the parameters of this approach are calibrated to 3D simulations, we find that in GR one needs larger turbulent eddies to achieve a shock evolution similar to the original \STIR/ model. We also find that the GR formulation significantly alters the correspondence  between progenitor mass and explosion vs. black-hole formation.

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Relativistic thermodynamics in Big bang nucleosynthesis

Atul Kedia
Graduate Student, University of Notre Dame

Big-bang nucleosynthesis (BBN) is a valuable means to constrain the physics of the early universe. A fundamental assumption in BBN nuclear reaction calculations is that the nuclear velocity distributions obey Maxwell-Boltzmann (MB) statistics as they do in stars. There exists a difference in these environments specifically in that the BBN epoch is characterized by a dilute baryon plasma for which the nuclear velocity distribution is mainly determined by the dominant Coulomb elastic scattering with the mildly relativistic electrons present in the background. One must therefore simulate or solve analytically for the thermalization of a dilute heavy particle (in our case baryons) in an environment filled with light particles (in our case electrons and positrons) that follow a relativistic-MB distribution to obtain the baryon equilibrium distribution. The baryon distribution thus obtained, if different from the classical MB distribution, could alter the abundances of resultant light nuclei.

In this talk I would firstly like to give an introduction to BBN and motivate our research with a discussion on the cosmic Lithium abundance problem. Following that I will show the workings of our Monte-Carlo scattering simulation we built to replicate the thermalization (i.e. equilibration) process and the Boltzmann equation solution we found that solves for the equilibrium distribution. Then I will discuss what our results mean specifically for the Lithium problem and BBN and in general for Monte-Carlo thermalization simulations of multiple different species when mixed and its potential application to various other physical systems.

Hosted by Prof. Mathews

All interested persons are invited to attend remotely—email physics@nd.edu for information.

Originally published at physics.nd.edu.

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