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Multipoles of the relativistic galaxy bispectrum

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Above the equality scale the galaxy bispectrum will be 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. By decomposing the Fourier-space bispectrum into invariant multipoles about the observer's line of sight we examine in detail how the relativistic effects contribute to these. We show how to perform this decomposition analytically, which is significantly faster for subsequent computations. While all multipoles receive a contribution from the relativistic part, odd multipoles arising from the imaginary part of the bispectrum have no Newtonian contribution, making the odd multipoles a smoking gun for a relativistic signature in the bispectrum for single tracers. The dipole and the octopole are significant on equality scales and above where the Newtonian approximation breaks down. This breakdown is further signified by the fact that the even multipoles receive a significant correction on very large scales.
Original languageEnglish
Article number018
Pages (from-to)1-36
Number of pages36
JournalJournal of Cosmology and Astroparticle Physics
Issue number05
Publication statusPublished - 11 May 2020


  • 1912.11016v3

    Rights statement: This Accepted Manuscript is available for reuse under a CC BY-NC-ND 3.0 licence after the 12 month embargo period provided that all the terms and conditions of the licence are adhered to

    Accepted author manuscript (Post-print), 2.84 MB, PDF document

    Due to publisher’s copyright restrictions, this document is not freely available to download from this website until: 11/05/21

    Licence: CC BY-NC-ND

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