Pre-inflationary genesis with CMB B-mode polarization

Understand

Recent B-mode polarization observation seems to imply the tensor tilt $n_T\gtrsim 1$ at large angular scale, if the primordial signal is dominated.

• We show that for a primordial universe, which is in a slowly expanding genesis phase before the slow-roll inflation, the primordial tensor spectrum will get a large-scale cutoff, i.e.
• $n_T\gtrsim 1$ at large scales while $n_T\simeq 0$ at small scale.
• We find that this inflationary scenario not only may be consistent with the observation, but also predicts a large-scale anomaly in BB power spectrum, i.e.