Study of Dark Matter Models in Astrophysics and Particle Physics

Abstract

From astrophysical and cosmological observations, it is known that most of the matter in the Universe is dark. This matter could be explainable by new particles, not included in the Standard Model of Particle Physics. This work assumes that there exists an interaction between dark matter and Standard Model particles, and investigates if the present relic density of dark matter in the Universe could be satisfied by a model with a vector mediator Z' for a variety of mediator and dark matter masses, as well as coupling constants to dark matter and Standard Model fermions, distinguishing between quark and lepton couplings.
The relic density is computed in the standard thermal freeze-out scenario using MadDM, and in the freeze-in scenario using micrOMEGAs. The freeze-out scenario assumes that all dark matter is produced in the early Universe, and then partially annihilates, i.e. “freezes out", to the current amount. In the freeze-in scenario, it is assumed there that is no dark matter in the early Universe and it is produced over time from Standard Model particle annihilations. In this work, it is also shown how the reheating temperature affects the freeze-in relic density. These couplings and masses tested here are chosen so that they could be produced at the LHC. While the relic density can be satisfied by these models in the freeze-out scenario, the freeze-in mechanism requires a very low reheating temperature in order to obtain couplings that the LHC is sensitive to.
In a second part, this work turns to the comparison of dark matter exclusion limits from LHC searches and results from direct detection experiments, concentrating on the latter. Direct detection experiments can detect these relic dark matter particles, and therefore their event rate depends on the local dark matter density and the velocity distribution. These are both uncertain parameters. Using uncertainty calculation methods from different analyses that choose assumptions alternative to the common assumptions made in the Standard Halo Model, deviations of the direct detection experiment exclusion limits are investigated and discussed.

Popular Abstract

Astrophysical observations indicate that most of the matter in the Universe is invisible to us, and we do not know what this matter is made of. One explanation is that, just like ordinary matter, this dark matter is made up of fundamental particles, and many efforts are made to detect these particles. This work looks at simple dark matter particle models and how they can account for the astrophysical observations.
Ordinary matter, made up from elementary particles, only accounts for 5% of the total energy content of the Universe, 27% are dark matter, and the remaining 68% are dark energy of which is even less known. The Standard Model of particle physics, that describes these ordinary matter particles and their interactions, is incomplete, and more particles are expected to exist. Some of these could have properties expected for dark matter particles. Assuming that there also exists an interaction that links dark matter particles to ordinary matter particles, experiments are designed to observe these interactions.
Astrophysical observations provide constraints on the particle models. In this work, the relic density is investigated, which is a measure of the amount of dark matter currently present in the Universe. A dark matter particle model should reproduce this amount of dark matter to be a viable candidate. From this, constraints on the possible dark matter mass and interaction strength to ordinary matter are gained, which in turn can be tested at collider experiments. There, particles are accelerated to extremely high energies and collided with each other. This produces new particles, some of which could be dark matter.
Other experiments, called direct detection experiments, aim to detect dark matter particles coming from space. For this, large tanks with a liquid target material are needed since the interactions of dark matter particles are rare. A traversing dark matter particle can scatter with a nucleus of the target material, and the bouncing off this nucleus can be measured, indicating the discovery of a dark matter particle. It is necessary to know the amount of incoming dark matter particles and their velocities, as this determines the expected detection rate of the experiment. The interpretation of the experimental results depends on these properties, but they are not well known. In this work, it is investigated how different assumptions affect the results.
So far, no dark matter particles have been found, but with the combined efforts of the many different experiments and advancing technology, it should only be a matter of time until the mystery of dark matter will be solved.

• author: John, Isabelle
• supervisor: Caterina Doglioni; Antonio Boveia
• organization: Particle and nuclear physics; Department of Physics
• course: FYSM60 20191
• year: 2019
• type: H2 - Master's Degree (Two Years)
• subject: Physics and Astronomy
• language: English
• id: 8992402
• date added to LUP: 2019-08-20 09:27:31
• date last changed: 2019-11-29 09:36:38