| Abstract : | The large-scale B-mode polarization of CMB serves the upcoming CMB experiments a unique observational window for detecting the primordial Gravitational Waves(GW). This detection is tied to constraining the tensor-to-scalar ratio, r, which determines the amplitude of the GW signal. The weak nature of the GW signal necessitates accurate modelling of foregrounds. Besides lensing contribution, the B-mode signal arising from the `patchy' ionization fields during reionization era is a primary contributor to these foregrounds. With the upcoming CMB experiments, it becomes crucial to understand, how being negligent of this `patchy' reionization contribution biases our inference of r. Models neglecting this contribution overestimate the actual value of r, leading to a bias. We present the quantification of this bias through Bayesian inference of r for a physically motivated model of reionization based on an explicitly photon-conserving scheme SCRIPT (Semi-numerical Code for ReIonization with PhoTon-conservation). SCRIPT leads to large-scale numerical convergence of electron fluctuation power spectra, allowing efficient simulation of B-modes from the reionization era. We find that a de-lensed B mode observation from observatories, like CMBS4, CMB-Bharat, and PICO, will suffer a bias of order of 1-sigma if we fail to correct for the reionization foregrounds. Any further increase in reionization contribution in the B-mode power will worsen our ability to establish the nature of the measured signal. Inferring from the results we make the case as to when and why it becomes important to account for the physics of reionization era if we wish to further our understanding of the primordial GW.
|
