A perspective on the CMB acoustic peak

2002/03/11 by Tobias A. Marriage, T. A. Marriage, Marriage, T. A.
Computer Science · Earth and Planetary Sciences · Physics and Astronomy · #Astrophysics (astro-ph) #Computational Physics and Python Applications #Cosmology and Gravitation Theories #FOS: Physical sciences #Geophysics and Gravity Measurements #astro-ph

paper · pdf · doi:10.48550/arxiv.astro-ph/0203153

4 pages; submitted to ApJ Letters

arxiv created 2002/03/11 · openalex publication_date 2002/03/11 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28

Abstract

CMB angular spectrum measurements suggest a flat universe. This paper clarifies the relation between geometry and the spherical harmonic index of the first acoustic peak (ℓ_peak). Numerical and analytic calculations show that ℓ_peak is approximately a function of Ω_K/Ω_M where Ω_K and Ω_M are the curvature (Ω_K > 0 implies an open geometry) and mass density today in units of critical density. Assuming Ω_K/Ω_M ≪ 1, one obtains a simple formula for ℓ_peak, the derivation of which gives another perspective on the widely-recognized Ω_M-Ω_Λ degeneracy in flat models. This formula for near-flat cosmogonies together with current angular spectrum data yields familiar parameter constraints.

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