The CMB Cold Spot under the lens II: Lensing signatures in polarization and cosmic texture footprints

TL;DR

This paper forecasts the detectability of lensing signatures from a cosmic texture related to the CMB Cold Spot using polarization data, proposing a specialized estimator for localized lensing footprints.

Contribution

It introduces a quadratic estimator targeting localized, azimuthally symmetric lensing profiles, enhancing detection prospects with polarization data in upcoming surveys.

Findings

Potential 2.3σ detection of cosmic texture lensing signature with future data.

Polarization data increases detection sensitivity by approximately 67%.

Detection sensitivity is feasible for deflections below 6 arcseconds.

Abstract

We forecast the detectability of the lensing footprint of a collapsing cosmic texture, a topological defect proposed as an explanation of the CMB Cold Spot. Our pipeline is a quadratic, template-amplitude estimator for localized, azimuthally symmetric lensing profiles: it projects the standard off-diagonal covariance response of lensed CMB fields onto a physically motivated template. Rather than reconstructing an arbitrary lensing field, the method targets weak but coherent localized footprints from sources such as voids, clusters and topological defects. Using the temperature/polarization pairs TT, TE+ET, EE, TB+BT and EB+BE for forthcoming Simons Observatory data, we estimate a $2.3\sigma$ detection if the texture amplitude reaches the current Planck 2018 $2\sigma$ upper limit, and a $1.5\sigma$ measurement for the best-fit texture parameters. This sensitivity is notable given the expected typical deflection angle below $6''$. The inclusion of polarization substantially increases the cumulative signal-to-noise ratio, by $\sim67\%$ relative to temperature alone, making sub-$10''$ localized lensing footprints accessible to SO-like surveys.