μ子对中子星物质metamodels bulk黏度的影响
Impact of muons on the bulk viscosity of neutron star matter metamodels
AI总结：
本文研究μ子对中子星物质bulk黏度的影响，分析了对称能量斜率L变化时的黏性 dissipation 变化，发现L增加对黏度有显著影响，并在某些密度下出现双峰结构。
摘要：
近期研究利用metamodels统一描述不同中子星观测数据，通过几个核参数参数化中子星物质的方程状态(EoS)。在此背景下，中子、质子和电子组成的密集核物质在中微子透明区域的bulk黏度主要受对称能量值影响。由于μ子在核饱和密度附近也存在，本文进一步分析其对这一传输系数的影响，作为对称能量斜率L函数。发现μ子对bulk黏性 dissipation 引入了显著的定性和定量影响。L增加一倍使频率无关的bulk黏度变化达几个数量级。此外，对于所有L值，在某些密度下，频率依赖的bulk黏度呈现双峰结构，这在无μ子时不存在。这代表了在中子星可达到的密度范围内，黏度在狭窄密度窗口内可能有数量级变化，当L足够高时。本文系统分析了第二阶传输系数、频率依赖的bulk黏度以及密度振荡的阻尼时间，作为密度和斜率函数，并发现这些在中子星并合动态中可能相关。
英文摘要：
Recent studies invoke a unified description of different neutron star observables using metamodels, which parametrize the equation of state of neutron star matter close to nuclear saturation density in terms of few nuclear parameters. In this light, the bulk viscosity in the neutrino-transparent regime of dense nuclear matter composed of neutrons, protons and electrons has been recently shown to be mostly sensitive to the value of the nuclear symmetry energy. As muons are also present at densities around nuclear saturation, we further analyze in this manuscript their impact on this transport coefficient as a function of the slope $L$ of the symmetry energy. We find that muons introduce both relevant qualitative and quantitative effects in the bulk viscous dissipation. Increasing $L$ by a factor two has an effect of several orders of magnitude on the (frequency-independent) bulk viscosity. We also find that for all values of $L$ the frequency-dependent bulk viscosity presents a double peak structure for some values of the density, absent without muons. This also represents changes in orders of magnitude of the viscosity in narrow windows of densities that could be attainable in a neutron star for enough high values of $L$. The double-peak structure is due to the fact that direct Urca processes open up at different densities for electrons and muons, the critical values depending on $L$. We present a systematic numerical analysis of both second-order transport coefficients, frequency-dependent bulk viscosity, and damping times of density oscillations as a function of the density and the slope, and find when these could be relevant for the dynamics of the merger of neutrons stars.
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