Kavli Affiliate: Toshiya Namikawa
| First 5 Authors: Hongbo Cai, Yilun Guan, Toshiya Namikawa, Arthur Kosowsky,
| Summary:
The cosmic microwave background (CMB) lensing power spectrum is a powerful
probe of the late-time universe, encoding valuable information about
cosmological parameters such as the sum of neutrino masses and dark energy
equation of state. However, the presence of anisotropic cosmic birefringence
can bias the reconstructed CMB lensing power spectrum using CMB polarization
maps, particularly at small scales, and affect the constraints on these
parameters. Upcoming experiments, which will be dominated by the polarization
lensing signal, are especially susceptible to this bias. We identify the
dominant contribution to this bias as an $N_L^{(1)}$-like noise, caused by
anisotropic rotation instead of lensing. We show that, for an CMB-S4-like
experiment, a scale-invariant anisotropic rotation field with a standard
deviation of 0.05 degrees can suppress the small-scale lensing power spectrum
($Lgtrsim 2000$) at a comparable level to the effect of massive neutrino with
$sum_i m_{nu_{i}}=50~rm{meV}$, making rotation field an important source of
degeneracy in neutrino mass measurement for future CMB experiments. We provide
an analytic expression and a simulation-based estimator for this
$N_L^{(1)}$-like noise, which allows for efficient forecasting and mitigation
of the bias in future experiments. Furthermore, we investigate the impact of a
non-scale-invariant rotation power spectrum on the reconstructed lensing power
spectrum and find that an excess of power in the small-scale rotation power
spectrum leads to a larger bias. Our work provides an effective numeric
framework to accurately model and account for the bias caused by anisotropic
rotation in future CMB lensing measurements.
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