An analytical approach to the CMB anisotropies in a Spatially Closed background

TL;DR

This paper derives an analytic expression for CMB temperature fluctuations in a closed universe, comparing it with numerical results and observational data, showing good agreement in peak positions and heights within approximations.

Contribution

It provides a novel analytic approach to compute CMB anisotropies in a closed universe, validated against numerical simulations and observational data.

Findings

Analytic expression matches numerical results on most scales.

Peak positions in the power spectrum are accurately predicted.

Peak heights are within 10% of numerical results due to approximations.

Abstract

The scalar mode temperature fluctuations of the cosmic microwave background has been derived in a spatially closed universe from two different methods. First, by following the photon trajectory after the last scattering and then from the Boltzmann equation in a closed background and the line of sight integral method. An analytic expression for the temperature multipole coefficient has been extracted at the hydrodynamical limit, where we have considered some tolerable approximations. By considering a realistic set of cosmological parameters taken from a fit to data from Planck, the TT power spectrum in the scalar mode for the closed universe has been compared with numerical one by using the CAMB code and also latest observational data. The analytic result agrees with the numerical one on almost all scales. The peak positions are in very good agreement with numerical result while the peak heights agree with that to within 10% due to the approximations have been considered for this derivation.