We perform a joint analysis of the power spectrum and the bispectrum of the CMB temperature and polarization anisotropies to improve the constraints on isocurvature modes. We construct joint likelihoods, both for the existing Planck data, and to make forecasts for the future LiteBIRD and CMB-S4 experiments. We assume a general two-field inflation model with five free parameters, leading to one isocurvature mode (which can be CDM density, neutrino density or neutrino velocity) arbitrarily correlated with the adiabatic mode. We theoretically assess in which cases (of detecting and/or fixing parameters) improvements can be expected, to guide our subsequent numerical analyses. We find that for Planck, which detected neither isocurvature modes nor primordial non-Gaussianity, the joint analysis does not improve the constraints in the general case. However, if we fix additional parameters in the model, the improvements can be highly significant depending on the chosen parameter values. For LiteBIRD+CMB-S4 we study in which regions of parameter space compatible with the Planck results the joint analysis will improve the constraints or the significance of a detection. We find that, while for CDM isocurvature this region is very small, for the neutrino isocurvature modes it is much larger. In particular for neutrino velocity it can be about half of the Planck-allowed region, where the joint analysis reduces the isocurvature error bars by up to 70%. In addition the joint analysis can also improve the error bars of some of the standard cosmological parameters, by up to 30% for $\theta_{MC}$ for example, by breaking the degeneracies with the correlation parameter between adiabatic and isocurvature modes.

中文翻译：

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等曲率模式：CMB 功率谱和双谱的联合分析

我们对功率谱和 CMB 温度和极化各向异性的双谱进行联合分析，以改善对等曲率模式的约束。我们为现有的普朗克数据构建联合似然，并对未来的 LiteBIRD 和 CMB-S4 实验进行预测。我们假设一个具有五个自由参数的通用双场膨胀模型，导致一个等曲率模式（可以是 CDM 密度、中微子密度或中微子速度）与绝热模式任意相关。我们从理论上评估在哪些情况下（检测和/或固定参数）可以预期改进，以指导我们随后的数值分析。我们发现，对于既没有检测到等曲率模式也没有检测到原始非高斯性的普朗克，联合分析并没有改善一般情况下的约束。但是，如果我们修复模型中的其他参数，则取决于所选参数值，改进可能非常显着。对于 LiteBIRD+CMB-S4，我们研究了与普朗克结果兼容的参数空间区域，联合分析将改善检测的约束或重要性。我们发现，虽然对于 CDM 等曲率，这个区域非常小，但对于中微子等曲率模式，它要大得多。特别是对于中微子速度，它可以是普朗克允许区域的大约一半，联合分析将等曲率误差条减少了 70%。此外联合分析还可以改善一些标准宇宙学参数的误差线，例如$\theta_{MC}$ 最多可改善30%，