Local bursts model of primordial CMB temperature fluctuations: scattering in hydrogen lines

TL;DR

This paper models the propagation of primordial radiation bursts through the early universe, analyzing hydrogen line scattering effects on CMB temperature fluctuations and their spectral profiles.

Contribution

It introduces a detailed model of hydrogen line scattering effects on primordial radiation bursts, including absorption and emission features, and assesses their impact on CMB temperature fluctuations.

Findings

Hydrogen lines can cause absorption of up to 2e-4 in the CMB spectrum.

Emission components may appear at smaller distances, weakening absorption.

Temperature fluctuations due to these effects range between 1e-7 and 1e-9.

Abstract

Within the framework of a flat cosmological model a propagation of an instantaneous burst of isotropic radiation is considered from the moment of its beginning at some initial redshift z0 to the moment of its registration now (at z=0). Thomson scattering by free electrons and scattering in primordial hydrogen lines Ha, Hb, Pa and Pb are considered as the sources of opacity and when calculating an albedo of a single scattering in the lines we take into account deactivation of the upper levels of transitions by background blackbody radiation. Profiles for these lines in a burst spectrum are calculated for different distances from the center of the burst and different values of z0. In the first approximation these profiles do not depend on spectrum and intensity of a burst radiation. It is shown that lines are in absorption at sufficiently large distance but emission components may appear as a distance decreases and it becomes stronger while absorption component weakens with a further distance decrease. For the sum of Ha and Hb lines the depth of absorption can reach 2e-4 while for the sum of Pa and Pb lines the maximum absorption is about 7e-6. So that the relative magnitude of temperature fluctuations lies between 1e-7 and 1e-9. The calculations were fulfiled for bursts with different initial sizes. For the same z0 the profiles of hydrogen lines are practically coinside for burst sizes lower than someone and for greater ones the lines weaken as the burst size grows.