B-mode forecast of CMB-Bhārat

Abstract

ABSTRACT Exploring Cosmic History and Origin (ECHO), popularly known as ‘CMB-Bh$\overline{a}$rat’, is a space mission that has been proposed to the Indian Space Research Organisation for the scientific exploitation of the cosmic microwave background (CMB) at the next level of precision and accuracy. The quest for the CMB polarization B-mode signals, generated by inflationary gravitational waves in the very early universe, is one of the key scientific goals of its experimental design. This work studies the potential of the proposed ECHO instrumental configuration to detect the target tensor-to-scalar ratio r ∼ 10−3 at 3σ significance level, which covers the predictions of a large class of inflationary models. We investigate the performance of two different component separation pipelines, ${\mathtt {NILC}}$ and ${\mathtt {Commander}}$, for the measurement of r in the presence of different physically motivated models of astrophysical foregrounds. For a simplistic foreground model (only polarized dust and synchrotron), both component separation pipelines can achieve the desired sensitivity of ECHO, i.e. σ(r = 0) ∼ (0.4–0.7) × 10−3. ${\mathtt {NILC}}$ performs better than ${\mathtt {Commander}}$ in terms of bias on recovered r for complex spectral models (power law and curved power law) of the synchrotron emission and complex dust models (dust decorrelation). Assuming 84 per cent delensing, we can achieve an improvement of σ(r = 0) by approximately 50 per cent as compared to the results obtained for the same configuration without any lensing correction.