# Towards detection of relativistic effects in galaxy number counts using kSZ Tomography

## TL;DR

This paper explores how future high-resolution CMB and galaxy surveys can detect relativistic effects in galaxy counts through kSZ tomography, revealing biases in primordial non-Gaussianity estimates and improving bias parameter constraints.

## Contribution

It demonstrates the potential of using correlations between the remote dipole field and galaxy counts to detect relativistic corrections and improve cosmological parameter estimation.

## Key findings

- Neglecting relativistic corrections biases primordial non-Gaussianity measurements.
- Correlations can detect relativistic effects in galaxy counts.
- Remote dipole field helps constrain bias parameters and reduce alignment bias.

## Abstract

High-resolution, low-noise observations of the cosmic microwave background (CMB) planned for the near-future will enable new cosmological probes based on re-scattered CMB photons -- the secondary CMB. At the same time, enormous galaxy surveys will map out huge volumes of the observable Universe. Using the technique of kinetic Sunyaev Zel'dovich (kSZ) tomography these new probes can be combined to reconstruct the remote dipole field, the CMB dipole as observed from different vantage points in our Universe. The volume accessible to future galaxy surveys is large enough that general relativistic corrections to the observed distribution of galaxies must be taken into account. These corrections are interesting probes of gravity in their own right, but can also obscure potential signatures of primordial non-Gaussianity. In this paper, we demonstrate that correlations between the reconstructed remote dipole field and the observed galaxy number counts can in principle be used to detect general relativistic corrections. We show that neglecting general relativistic corrections leads to an $\mathcal{O}(1)$ bias on the inferred amplitude of primordial non-Gaussianity, $f_{\rm NL}$. In addition, we demonstrate that the reconstructed remote dipole field can provide useful constraining power on various bias parameters appearing in the galaxy number counts, and can significantly mitigate the effects of alignment bias.