$B$-mode forecast of CMB-Bh$\overline{a}$rat

Abstract

Exploring Cosmic History and Origins (ECHO), popularly known as 'CMB-Bharat', is a space mission that has been proposed to the Indian Space Research Organisation (ISRO) 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, NILC and Commander, for the measurement of r in 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 . NILC performs better than 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% delensing, we can achieve an improvement of σ(r = 0) by approximately 50% as compared to the results obtained for the same configuration without any lensing correction.

Tensor Fluctuations in the Early Universe

“…where v q k is the solution to Equation ( 29), with a time-varying frequency and an initial amplitude 1/ √ 2k. The power spectrum for each polarization mode is thus extracted from an expression analogous to Equation (18),…”

“…In previous work [11,12,13], we demonstrated how scalar fluctuations created and amplified by a numen field naturally account for the first three of these observational constraints. The primary goal of this Letter is to address the fourth, given that a focus of several upcoming observational campaigns will be to detect and measure the so-called B-mode polarization in the CMB (e.g., LiteBIRD [14]; COrE [15]; PRISM [16]; PICO [17]; and, more recently, ECHO [18]). This signal is widely believed to be a tell-tale signature of gravity waves produced during inflation, and is thus greatly anticipated to provide concrete evidence for the role played by an inflaton field in the early Universe.…”