Refining the chemical and kinetic decoupling description of thermally produced dark matter

by Tobias Binder
Doctoral thesis
Date of Examination:2019-03-13
Date of issue:2019-03-26
Advisor:Prof. Dr. Laura Covi
Referee:Prof. Dr. Karl-Henning Rehren
Referee:Prof. Dr. Björn Garbrecht
Referee:Prof. Dr. Steffen Schumann
Referee:Prof. Dr. Marcus Müller
Referee:Prof. Dr. Stan Lai
Referee:Prof. Dr. David Marsh
Persistent Address: http://dx.doi.org/10.53846/goediss-7369

 

 

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Abstract

English

The first part of this thesis deals with refined theoretical predictions of the thermal relic abundance for weakly interacting massive particles (WIMPs). Methods are developed in a model independent way to describe the discovered exception where kinetic equilibrium, the main assumption entering the standard prediction, is not maintained during the chemical decoupling process. The impact of early kinetic decoupling is quantified for the Scalar Singlet model and the results show that the refined prediction can differ from the standard computation of the thermal relic abundance by up to an order of magnitude. Furthermore, many previous works show within the classical Boltzmann approach that attractive long-range interactions can lead to an enhancement of the annihilation cross-section at the time of chemical decoupling. In this thesis, it is investigated how to describe long-range interactions in the presence of a hot and dense plasma background in the framework of non-equilibrium quantum field theory. The main result is a novel number density equation expressed in terms of thermal correlation functions which allows to study chemical decoupling including various long-range effects and plasma background corrections in a self-consistent way. Consistency is proven with previous literature results under certain limits. The second part of the thesis deals with long-range forces in the context of Self-Interacting Dark Matter (SIDM), considered in literature as a possible solution of structure formation problems at small scales. In this thesis, new types of long-range interactions are identified which could alleviate in a similar parameter region several structure formation issues simultaneously. It is shown that a particular type of long-range force could additionally relax tensions between the cosmic microwave background and low-redshift astronomical observations.
Keywords: Dark Matter; Non-equilibrium quantum field theory; Boltzmann equation; Thermal decoupling; Self-interacting dark matter
 
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