Local Bursts Model of CMB Temperature Fluctuations: Scattering in Resonance Lines of Primordial Hydrogen and Helium

TL;DR

This paper models how primordial hydrogen and helium resonance line scattering significantly distort the CMB spectrum from an early burst, revealing large amplitude absorption features that depend on the burst's redshift.

Contribution

It introduces a detailed model of CMB spectrum distortions caused by resonance line scattering in primordial hydrogen and helium, showing these effects are much larger than previously considered.

Findings

Resonance line scattering causes spectrum distortions 1000-10000 times greater than subordinate lines.

Profiles of distortions are purely in absorption and independent of burst direction and distance.

Jumps in the spectrum occur at specific frequencies related to the burst redshift.

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). We take into account Thomson scattering by free electrons and scattering in La and Lb lines of primordial hydrogen and in lines 1s2 - 1s2p, 1s3p (1S-1P*) of HeI. It is shown that relative amplitude of spectrum distortions caused by scattering in these lines may be from 1000 to 10000 times greater than maximum possible amplitude due to scattering in subordinate lines considered in our previous paper (Dubrovich, Grachev, 2015). In a linear approximation on the optical thickness in the lines the profiles of distortions in resonance lines turn out to be purely in absorption and do not depend on both direction and distance to the burst center in contradistinction to the profiles in subordinate lines. The profiles contain jumps on frequencies corresponding to appearance of a source (burst) at a given redshift z=z0. For z0=5000 the jumps in hydrogen La and Lb lines are on frequencies 493 and 584 GHz respectively and jumps in two HeI lines are on 855 and 930 GHz for z0=6000. Relative magnitude of jumps amounts to 1e-4 - 3e-3.