宇宙学模型中的摩擦力
Friction forces in cosmological models
摘要：
我们研究了在Friedmann-Robertson-Walker（FRW）时空中受摩擦力作用的测试粒子的动力学。通过在运动方程中引入类似坡印廷-罗伯逊的摩擦力来模拟与背景流体的相互作用，从而导致颗粒轨迹与测地线运动的可测量的（至少在原则上）偏差。研究了不同背景流体状态方程和不同标准宇宙学模型对粒子奇异速度的影响。摩擦力被发现对封闭FRW宇宙中的粒子运动有重大影响，在那里它将特殊粒子速度的时间渐近值（接近于光速）从超相对论性（接近光速）转变为共同运动，即，零特殊速度另一方面，对于开放或平坦的宇宙，摩擦的影响并不那么显著，因为时间渐近的特殊粒子速度在测地线的情况下也基本上是非相对论的。
英文摘要：
We investigate the dynamics of test particles undergoing friction forces in a Friedmann-Robertson-Walker (FRW) spacetime. The interaction with the background fluid is modeled by introducing a Poynting-Robertson-like friction force in the equations of motion, leading to measurable (at least in principle) deviations of the particle trajectories from geodesic motion. The effect on the peculiar velocities of the particles is investigated for various equations of state of the background fluid and different standard cosmological models. The friction force is found to have major effects on particle motion in closed FRW universes, where it turns the time-asymptotic value (approaching the recollapse) of the peculiar particle velocity from ultra-relativistic (close to light speed) to a co-moving one, i.e., zero peculiar speed. On the other hand, for open or flat universes the effect of the friction is not so significant, because the time-asymptotic peculiar particle speed is largely non-relativistic also in the geodesic case.
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