302 research outputs found
Improving small-scale CMB lensing reconstruction
Over the past decade, the gravitational lensing of the Cosmic Microwave
Background (CMB) has become a powerful tool for probing the matter distribution
in the Universe. The standard technique used to reconstruct the CMB lensing
signal employs the quadratic estimator (QE) method, which has recently been
shown to be suboptimal for lensing measurements on very small scales in
temperature and polarization data. We implement a simple, more optimal method
for the small-scale regime, which involves taking the direct inverse of the
background gradient. We derive new techniques to make continuous maps of
lensing using this "Gradient-Inversion" (GI) method and validate our method
with simulated data, finding good agreement with predictions. For idealized
simulations of lensing cross- and autospectra that neglect foregrounds, we
demonstrate that our method performs significantly better than previous
quadratic estimator methods in temperature; at , it reduces errors
on the lensing auto-power spectrum by a factor of for both idealized
CMB-S4 and Simons Observatory-like experiments and by a factor of
for cross-correlations of CMB-S4-like lensing reconstruction and the true
lensing field. We caution that the level of the neglected small-scale
foreground power, while low in polarization, is very high in temperature;
though we briefly outline foreground mitigation methods, further work on this
topic is required. Nevertheless, our results show the future potential for
improved small-scale CMB lensing measurements, which could provide stronger
constraints on cosmological parameters and astrophysics at high redshifts
KSZ tomography and the bispectrum
Several statistics have been proposed for measuring the kSZ effect by
combining the small-scale CMB with galaxy surveys. We review five such
statistics, and show that they are all mathematically equivalent to the optimal
bispectrum estimator of type . Reinterpreting these kSZ
statistics as special cases of bispectrum estimation makes many aspects
transparent, for example optimally weighting the estimator, or incorporating
photometric redshift errors. We analyze the information content of the
bispectrum and show that there are two observables: the small-scale
galaxy-electron power spectrum , and the large-scale
galaxy-velocity power spectrum . The cosmological constraining power
of the kSZ arises from its sensitivity to fluctuations on large length scales,
where its effective noise level can be much better than galaxy surveys.Comment: 39 page
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