Title: Decay of Magnetic Fields in the Early Universe Show Chinese title

Title: 早期宇宙中磁场的衰减

Abstract: We study the evolution of a stochastic helical magnetic field generated in the early Universe after the electroweak phase transition, using standard magnetohydrodynamics (MHD). We find how the coherence length xi, magnetic energy E_M and magnetic helicity H evolve with time. We show that the self-similarity of the magnetic power spectrum alone implies that xi ~ t^{1/2}. This in turn implies that magnetic helicity decays as H ~ t^{-2s}, and that the magnetic energy decays as E_M ~ t^{-0.5-2s}, where s is inversely proportional to the magnetic Reynolds number Re_M. These laws improve on several previous estimates. Show Chinese abstract

Abstract: 我们研究了早期宇宙中电弱相变后产生的随机螺旋磁场的演化，使用的是标准磁流体力学（MHD）。 我们发现相干长度 ξ、磁场能量 EM 和磁场螺旋度 H 随时间如何演化。 我们表明，磁场功率谱的自相似性本身就意味着 ξ ~ t^{1/2}。 这反过来意味着磁场螺旋度以 H ~ t^{-2s}的方式衰减，并且磁场能量以 EM ~ t^{-0.5-2s}的方式衰减，其中 s 与磁雷诺数 Re_M 成反比。 这些规律改进了多个先前的估计。