Description
Primordial power spectra with low power at long wavelengths can
alleviate lensing anomaly. However, the extent to which data favours such a
primordial spectra is not clear. In this work, we investigate power suppression and
related mitigation of lensing anomaly with the help of phenomenological models
which are valid over scales of interest. We consider simple extensions to nearly
scale invariant power spectra such as those which includes running and running of
running of spectral index. We perform Bayesian analysis of these models, which
are agnostic about power suppression, with Planck legacy data and show that data
tend to choose parameters which leads to power suppression at low multipoles.
We then investigate the connection between power suppression and alleviation of
lensing anomaly and show that lensing anomaly is mitigated the most in models
with maximum suppression of power at low multipoles. We also analyse the
significance of these findings using information criteria. These results are further
analyzed in the light of Planck Release 4 data using CamSpec, HiLLiPoP and
LoLLiPoP likelihoods in which departure of lensing parameter from one is
significantly reduced. Furthermore, we investigate the ability of near-ultimate future
CMB missions such as ECHO to put tighter constraints on these models and to
settle the issue. We conclude that we can make stronger conclusions about the
presence of power suppression in the future by studying such simple
phenomenological models. This talk is based on our recent paper
https://arxiv.org/abs/2504.21386
