标题： II型超新星中的中微子输运：Boltzmann求解器与Monte Carlo方法 显示英文标题

标题： Neutrino transport in type II supernovae: Boltzmann solver vs. Monte Carlo method

摘要： 我们基于有限差分格式（S_N 方法）编写了一个玻尔兹曼求解器，旨在计算II型超新星中的中微子输运。 在假设静态背景的情况下，对反弹后核心模型的真实大气进行了玻尔兹曼求解器与蒙特卡罗输运代码之间的密切比较。 我们还详细研究了结果对径向、角向和能量网格点数量的依赖性，以及玻尔兹曼求解器中用于离散化空间对流项的方式的影响。 其中的一个模型已经进行了广义相对论计算。 我们发现两种方法之间总体上具有良好的一致性。 然而，由于角向网格点数量相对较少（这是由于计算时间限制所不可避免的），玻尔兹曼求解器倾向于在中微子角分布变得高度各向异性之外的（平均）“中微子球”区域低估通量因子和埃丁顿因子。 这一事实表明，在应用玻尔兹曼求解器计算热气泡区域的中微子加热时需要谨慎，因为它可能会高估局部能量沉积率。 对比显示，这种趋势与使用多群组通量限制扩散近似方法得到的结果相反。 通过使用可变角网格以提高半透明区域的角分辨率，可以显著改善玻尔兹曼求解器的精度。 显示英文摘要

摘要： We have coded a Boltzmann solver based on a finite difference scheme (S_N method) aiming at calculations of neutrino transport in type II supernovae. Close comparison between the Boltzmann solver and a Monte Carlo transport code has been made for realistic atmospheres of post bounce core models under the assumption of a static background. We have also investigated in detail the dependence of the results on the numbers of radial, angular, and energy grid points and the way to discretize the spatial advection term which is used in the Boltzmann solver. A general relativistic calculation has been done for one of the models. We find overall good agreement between the two methods. However, because of a relatively small number of angular grid points (which is inevitable due to limitations of the computation time) the Boltzmann solver tends to underestimate the flux factor and the Eddington factor outside the (mean) ``neutrinosphere'' where the angular distribution of the neutrinos becomes highly anisotropic. This fact suggests that one has to be cautious in applying the Boltzmann solver to a calculation of the neutrino heating in the hot-bubble region because it might tend to overestimate the local energy deposition rate. A comparison shows that this trend is opposite to the results obtained with a multi-group flux-limited diffusion approximation of neutrino transport. The accuracy of the Boltzmann solver can be considerably improved by using a variable angular mesh to increase the angular resolution in the semi-transparent regime.