Searches for the imprint of primordial gravitational waves in degree-scale CMB B-mode polarisation data must account for significant contamination from gravitational lensing. Fortunately, the lensing effects can be partially removed by combining high-resolution E-mode measurements with an estimate of the projected matter distribution. In the near future, experimental characteristics will be such that the latter can be reconstructed internally with high fidelity from the observed CMB, with the EB quadratic estimator providing a large fraction of the signal-to-noise. It is a well-known phenomenon in this context that any overlap in modes between the B-field to be delensed and the B-field from which the reconstruction is derived leads to a suppression of delensed power going beyond that which can be attributed to a mitigation of the lensing effects. More importantly, the variance associated with this spectrum is also reduced, posing the question of whether the additional power suppression could help better constrain the tensor-to-scalar ratio, r. In this paper, we show this is not the case, as suggested but not quantified in previous work. We develop an analytic model for the biased delensed B-mode angular power spectrum, which suggests a simple renormalisation prescription to avoid bias on the inferred tensor-to-scalar ratio. With this approach, we learn that the bias necessarily leads to a degradation of the signal-to-noise on a primordial component compared to “unbiased delensing”. Next, we assess the impact of removing from the lensing reconstruction any overlapping B-modes on our ability to constrain r, showing that it is in general advantageous to do this rather than modelling or renormalising the bias. Finally, we verify these results within a maximum-likelihood inference framework applied to simulations.

在度数级CMB B模式极化数据中搜索原始引力波的烙印必须说明引力透镜造成的严重污染。幸运的是，通过结合高分辨率E模式测量值和投影物质分布的估计值，可以部分消除透镜效应。在不久的将来，实验特性将使后者可以从观察到的CMB以高保真度在内部进行重建，而EB二次估计器将提供很大一部分信噪比。在这种情况下，众所周知的现象是，要被去视化的B场与从中获得重构的B场之间的任何模式重叠，都会导致对去视力的抑制超出可归因于A的范围。减轻透镜效应。更重要的是，与该频谱相关的方差也减小了，提出了一个问题，即附加的功率抑制是否可以帮助更好地限制张量与标量之比r。在本文中，我们表明情况并非如此，正如建议的那样，但在先前的工作中并未量化。我们为有偏差的B模式角功率谱开发了一个解析模型，该模型建议了一个简单的重新规范化处方，以避免对推断的张量/标量比产生偏见。通过这种方法，我们了解到偏差必然会导致 我们为有偏差的B模式角功率谱开发了一个解析模型，该模型建议了一个简单的重新规范化处方，以避免对推断的张量/标量比产生偏见。通过这种方法，我们了解到偏差必然会导致 我们为有偏差的B模式角功率谱开发了一个解析模型，该模型建议了一个简单的重新规范化处方，以避免对推断的张量/标量比产生偏见。通过这种方法，我们了解到偏差必然会导致降解的信号-噪声一个原始部件上相比，“无偏脱镜片”的。接下来，我们评估了从镜头重建中删除任何重叠的B模式对我们约束r的能力的影响，表明这样做通常比对偏差进行建模或重新归一化更为有利。最后，我们在应用于模拟的最大似然推断框架内验证了这些结果。