School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540, USA.
Phys Rev Lett. 2011 Dec 23;107(26):261301. doi: 10.1103/PhysRevLett.107.261301. Epub 2011 Dec 22.
Baryon-density perturbations of large amplitude may exist if they are compensated by dark-matter perturbations such that the total density is unchanged. Primordial abundances and galaxy clusters allow these compensated isocurvature perturbations (CIPs) to have amplitudes as large as ~10%. CIPs will modulate the power spectrum of cosmic microwave background (CMB) fluctuations--those due to the usual adiabatic perturbations--as a function of position on the sky. This leads to correlations between different spherical-harmonic coefficients of the temperature and/or polarization maps, and induces polarization B modes. Here, the magnitude of these effects is calculated and techniques to measure them are introduced. While a CIP of this amplitude can be probed on large scales with existing data, forthcoming CMB experiments should improve the sensitivity to CIPs by at least an order of magnitude.
如果大振幅重子密度涨落被暗物质密度涨落所补偿，从而使总密度保持不变，则可能存在大振幅重子密度涨落。原初丰度和星系团允许这些补偿的非绝热密度涨落（CIP）的幅度达到~10%。CIP 会调制宇宙微波背景（CMB）涨落的功率谱——这些涨落归因于通常的绝热涨落——作为天区的函数。这导致了温度和/或极化图的不同球谐系数之间的相关性，并诱导出极化 B 模式。在这里，计算了这些效应的大小，并介绍了测量它们的技术。虽然现有的数据可以在大尺度上探测到这种幅度的 CIP，但即将到来的 CMB 实验应该至少提高一个数量级来探测 CIP。
