THE ISOTROPIC DIFFUSION SOURCE APPROXIMATION FOR SUPERNOVA NEUTRINO TRANSPORT
THE ISOTROPIC DIFFUSION SOURCE APPROXIMATION FOR SUPERNOVA NEUTRINO TRANSPORT
复制标题
超新星中微子输运的各向同性扩散源近似
DOI：
10.1088/0004-637x/698/2/1174
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
Tobias Fischer
中科院分区：
文献类型：
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作者：
M. Liebendörfer;S. Whitehouse;Tobias Fischer
天体物理观测来源于与辐射或传输粒子相互作用的物质。我们开发了一个实用的近似，以便在可用的计算资源不足以解决完整的玻尔兹曼输运方程时，实现具有基本光谱辐射传输的多维模拟。将输运粒子的分布函数分解为捕获粒子分量和流动粒子分量。它们各自独立的演化方程由一个源项耦合，该源项将捕获的粒子转换为流动的粒子。我们通过要求捕获粒子组分演化的正确扩散极限来确定源项。为了平稳过渡到自由流状态，这种“扩散源”受到物质发射率的限制。将得到的流粒子发射率在空间上积分以得到流粒子通量。最后，利用通量因子的几何估计将粒子通量转换为流动粒子密度，从而进入流动粒子-物质相互作用的评估。该方案的效率源于对每个粒子分量使用不同近似的自由。例如，在超新星中，在快速时间尺度上与捕获粒子的反应建立了平衡，减少了进化捕获粒子成分所需的原始变量的数量。另一方面，稳态近似极大地促进了流粒子分量的处理。不同的近似可以应用于恒星大气、恒星形成或宇宙辐射转移。我们比较了球对称超新星模型中电子味中微子的各向同性扩散源近似和玻尔兹曼中微子输运，发现了很好的一致性。本文还讨论了该方法在多维情况下的推广。
Astrophysical observations originate from matter that interacts with radiation or transported particles. We develop a pragmatic approximation in order to enable multidimensional simulations with basic spectral radiative transfer when the available computational resources are not sufficient to solve the complete Boltzmann transport equation. The distribution function of the transported particles is decomposed into a trapped particle component and a streaming particle component. Their separate evolution equations are coupled by a source term that converts trapped particles into streaming particles. We determine this source term by requiring the correct diffusion limit for the evolution of the trapped particle component. For a smooth transition to the free streaming regime, this “diffusion source” is limited by the matter emissivity. The resulting streaming particle emission rates are integrated over space to obtain the streaming particle flux. Finally, a geometric estimate of the flux factor is used to convert the particle flux to the streaming particle density, which enters the evaluation of streaming particle–matter interactions. The efficiency of the scheme results from the freedom to use different approximations for each particle component. In supernovae, for example, reactions with trapped particles on fast timescales establish equilibria that reduce the number of primitive variables required to evolve the trapped particle component. On the other hand, a stationary-state approximation considerably facilitates the treatment of the streaming particle component. Different approximations may apply in applications to stellar atmospheres, star formation, or cosmological radiative transfer. We compare the isotropic diffusion source approximation with Boltzmann neutrino transport of electron flavor neutrinos in spherically symmetric supernova models and find good agreement. An extension of the scheme to the multidimensional case is also discussed.
DOI：
10.1088/0004-637x/694/1/664
发表时间：
2007-08
期刊：
The Astrophysical Journal
影响因子：
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作者：
A. Marek;H. Janka
通讯作者：
A. Marek;H. Janka