The dipole of the galaxy bispectrum

TL;DR

This paper demonstrates that relativistic effects induce a significant dipole in the galaxy bispectrum, providing a new observable to test relativistic corrections in large-scale structure surveys.

Contribution

It is the first to show that relativistic distortions produce a notable dipole in the galaxy bispectrum, highlighting a new signature of relativistic effects.

Findings

Relativistic redshift space distortions generate a dipole in the bispectrum.

The dipole amplitude can exceed 10% of the monopole on large scales.

The dipole is absent in the Newtonian approximation, serving as a relativistic signature.

Abstract

The bispectrum will play an important role in future galaxy surveys. On large scales it is a key probe for measuring primordial non-Gaussianity which can help differentiate between different inflationary models and other theories of the early universe. On these scales a variety of relativistic effects come into play once the galaxy number-count fluctuation is projected onto our past lightcone. We show for the first time that the leading relativistic correction from these distortions in the galaxy bispectrum generates a significant dipole, mainly from relativistic redshift space distortions. The amplitude of the dipole can be more than 10% of the monopole even on equality scales. Such a dipole is absent in the Newtonian approximation to the redshift space bispectrum, so it offers a clear signature of relativistic effects on cosmological scales in large scale structure.