Dark Matter Phenomenology in Astrophysical Systems

There is now a great deal of evidence in support of the existence of a large amount of unseen gravitational mass, commonly called dark matter, from observations in astrophysical systems of sizes ranging from that of dwarf galaxies to the scale of the entire Universe. One of the most promising explanations for this unseen mass is that it consists of a species of unobserved elementary particles. An expected feature of particle dark matter is that it should form halos in the early Universe that cannot collapse due to its weak interactions with itself and baryonic matter. It is within these halos that galaxies, including the Milky Way, which is the galaxy that we inhabit, are thought to be born.Different methods to detect dark matter that originates from the galactic halo have been devised and these generally fall into the categories of direct and indirect detection. On Earth, direct detection experiments are employed to detect the recoiling atoms that are generated through the occasional scattering between halo dark matter particles with the detector material. The indirect search for dark matter is conducted by attempting to detect the standard model particles that may be produced as dark matter annihilates or decays and by looking for the effects that dark matter may have on astrophysical bodies. The aim of this thesis is to study the effects that dark matter may have in different astrophysical systems and how its properties can be determined should an effect that is due to dark matter be detected.The Sun currently experiences the solar composition problem, which is a mismatch between simulated and observed helioseismological properties of the Sun. A large abundance of dark matter introduces a new heat transfer mechanism that has been shown to offer a viable solution. This problem is discussed here in a particular model of dark matter where the dark matter halo is made up of equal numbers of particles and antiparticles. It is shown that dark matter arising from the thermal freeze-out mechanism might alleviate the problem, whereas only asymmetric dark matter models have previously been considered.If a dark matter signal is seen in a direct detection experiment, the determination of the dark matter properties will be plagued by numerous uncertainties related to the halo. It has been shown that many of these uncertainties can be eliminated by comparing signals in different direct detection experiments in what is called ``halo-independent" methods. These methods can also be used to predict the neutrino signal from dark matter annihilating in the Sun, further constraining DM properties, if a direct detection experiment detects a signal. This framework is here generalized to inelastic dark matter and the information concerning dark matter properties in a direct detection signal is discussed.When the Sun captures dark matter, thermalization is a process where dark matter particles lose their remaining kinetic energy after being captured and sink into the solar core. Evaporation due to collisions with high-energy solar atoms is also possible. For inelastic dark matter, it is expected that the thermalization process stops prematurely, which will have an effect on the expected neutrino signal from its annihilation. Moreover, evaporation may also be significant due transitions from the heavier to the lighter state. Here, the thermalization problem is discussed, and results from numerical simulations are presented that show the extent to which inelastic dark matter thermalizes and if evaporation has to be taken into account.A number of issues have been observed in dark matter halos at smaller scales when compared to results from large simulations. Dark matter that interacts strongly with itself has been proposed as a solution. There are a number of problems associated with these models that are excluded by other means. A particular model of inelastic dark matter interacting via a light mediator is analyzed here and shown to possible alleviate at least some of the problems associated with models of this kind.QC20190517</p

Effects of Dark Matter in Astrophysical Systems

When studying astrophysical structures with sizes ranging from dwarf galaxies to galaxy clusters, it becomes clear that there are vast amounts of unobservable gravitating mass. A compelling hypothesis is that this missing mass, which we call dark matter, consists of elementary particles that can be described in the same manner as those of the standard model of particle physics. This thesis is dedicated to the study of particle dark matter in astrophysical systems. The solar composition problem refers to the current mismatch between theoretical predictions and observations of the solar convection zone depth and sound speed profile. It has been shown that heat transfer by dark matter in the Sun may cool the solar core and alleviate the problem. We discuss solar capture of a self-interacting Dirac fermion dark matter candidate and show that, even though particles and antiparticles annihilate, the abundance of such a particle may be large enough to influence solar physics. Currently, direct and indirect methods are employed in searches for dark matter. In this context, we study inelastic dark matter, where a small mass splitting separates two dark matter particles and scattering takes one into the other. This affects the scattering kinematics, which in turn affects direct detection and solar capture rates. We also discuss the information contained in a direct detection signal and how it can be used to infer a minimal solar capture rate of dark matter. When comparing simulated dark matter halos with collisionless dark matter with dark matter halos inferred from observations, problems appear in the smallest structures. A proposed solution is self-interacting dark matter with long range forces. As the simplest models are under severe constraints, we study self-interactions in a model of inelastic dark matter.QC 20170309</p

Dark Matter Phenomenology in Astrophysical Systems

There is now a great deal of evidence in support of the existence of a large amount of unseen gravitational mass, commonly called dark matter, from observations in astrophysical systems of sizes ranging from that of dwarf galaxies to the scale of the entire Universe. One of the most promising explanations for this unseen mass is that it consists of a species of unobserved elementary particles. An expected feature of particle dark matter is that it should form halos in the early Universe that cannot collapse due to its weak interactions with itself and baryonic matter. It is within these halos that galaxies, including the Milky Way, which is the galaxy that we inhabit, are thought to be born.Different methods to detect dark matter that originates from the galactic halo have been devised and these generally fall into the categories of direct and indirect detection. On Earth, direct detection experiments are employed to detect the recoiling atoms that are generated through the occasional scattering between halo dark matter particles with the detector material. The indirect search for dark matter is conducted by attempting to detect the standard model particles that may be produced as dark matter annihilates or decays and by looking for the effects that dark matter may have on astrophysical bodies. The aim of this thesis is to study the effects that dark matter may have in different astrophysical systems and how its properties can be determined should an effect that is due to dark matter be detected.The Sun currently experiences the solar composition problem, which is a mismatch between simulated and observed helioseismological properties of the Sun. A large abundance of dark matter introduces a new heat transfer mechanism that has been shown to offer a viable solution. This problem is discussed here in a particular model of dark matter where the dark matter halo is made up of equal numbers of particles and antiparticles. It is shown that dark matter arising from the thermal freeze-out mechanism might alleviate the problem, whereas only asymmetric dark matter models have previously been considered.If a dark matter signal is seen in a direct detection experiment, the determination of the dark matter properties will be plagued by numerous uncertainties related to the halo. It has been shown that many of these uncertainties can be eliminated by comparing signals in different direct detection experiments in what is called ``halo-independent" methods. These methods can also be used to predict the neutrino signal from dark matter annihilating in the Sun, further constraining DM properties, if a direct detection experiment detects a signal. This framework is here generalized to inelastic dark matter and the information concerning dark matter properties in a direct detection signal is discussed.When the Sun captures dark matter, thermalization is a process where dark matter particles lose their remaining kinetic energy after being captured and sink into the solar core. Evaporation due to collisions with high-energy solar atoms is also possible. For inelastic dark matter, it is expected that the thermalization process stops prematurely, which will have an effect on the expected neutrino signal from its annihilation. Moreover, evaporation may also be significant due transitions from the heavier to the lighter state. Here, the thermalization problem is discussed, and results from numerical simulations are presented that show the extent to which inelastic dark matter thermalizes and if evaporation has to be taken into account.A number of issues have been observed in dark matter halos at smaller scales when compared to results from large simulations. Dark matter that interacts strongly with itself has been proposed as a solution. There are a number of problems associated with these models that are excluded by other means. A particular model of inelastic dark matter interacting via a light mediator is analyzed here and shown to possible alleviate at least some of the problems associated with models of this kind.QC20190517</p

Dark Matter Phenomenology in Astrophysical Systems

There is now a great deal of evidence in support of the existence of a large amount of unseen gravitational mass, commonly called dark matter, from observations in astrophysical systems of sizes ranging from that of dwarf galaxies to the scale of the entire Universe. One of the most promising explanations for this unseen mass is that it consists of a species of unobserved elementary particles. An expected feature of particle dark matter is that it should form halos in the early Universe that cannot collapse due to its weak interactions with itself and baryonic matter. It is within these halos that galaxies, including the Milky Way, which is the galaxy that we inhabit, are thought to be born.Different methods to detect dark matter that originates from the galactic halo have been devised and these generally fall into the categories of direct and indirect detection. On Earth, direct detection experiments are employed to detect the recoiling atoms that are generated through the occasional scattering between halo dark matter particles with the detector material. The indirect search for dark matter is conducted by attempting to detect the standard model particles that may be produced as dark matter annihilates or decays and by looking for the effects that dark matter may have on astrophysical bodies. The aim of this thesis is to study the effects that dark matter may have in different astrophysical systems and how its properties can be determined should an effect that is due to dark matter be detected.The Sun currently experiences the solar composition problem, which is a mismatch between simulated and observed helioseismological properties of the Sun. A large abundance of dark matter introduces a new heat transfer mechanism that has been shown to offer a viable solution. This problem is discussed here in a particular model of dark matter where the dark matter halo is made up of equal numbers of particles and antiparticles. It is shown that dark matter arising from the thermal freeze-out mechanism might alleviate the problem, whereas only asymmetric dark matter models have previously been considered.If a dark matter signal is seen in a direct detection experiment, the determination of the dark matter properties will be plagued by numerous uncertainties related to the halo. It has been shown that many of these uncertainties can be eliminated by comparing signals in different direct detection experiments in what is called ``halo-independent" methods. These methods can also be used to predict the neutrino signal from dark matter annihilating in the Sun, further constraining DM properties, if a direct detection experiment detects a signal. This framework is here generalized to inelastic dark matter and the information concerning dark matter properties in a direct detection signal is discussed.When the Sun captures dark matter, thermalization is a process where dark matter particles lose their remaining kinetic energy after being captured and sink into the solar core. Evaporation due to collisions with high-energy solar atoms is also possible. For inelastic dark matter, it is expected that the thermalization process stops prematurely, which will have an effect on the expected neutrino signal from its annihilation. Moreover, evaporation may also be significant due transitions from the heavier to the lighter state. Here, the thermalization problem is discussed, and results from numerical simulations are presented that show the extent to which inelastic dark matter thermalizes and if evaporation has to be taken into account.A number of issues have been observed in dark matter halos at smaller scales when compared to results from large simulations. Dark matter that interacts strongly with itself has been proposed as a solution. There are a number of problems associated with these models that are excluded by other means. A particular model of inelastic dark matter interacting via a light mediator is analyzed here and shown to possible alleviate at least some of the problems associated with models of this kind.QC20190517</p

Erratum to: The distribution of inelastic dark matter in the Sun

The annihilation rates in Fig. 9 of the original article were incorrectly calculate

The distribution of inelastic dark matter in the Sun

Abstract If dark matter is composed of new particles, these may become captured after scattering with nuclei in the Sun, thermalize through additional scattering, and finally annihilate into neutrinos that can be detected on Earth. If dark matter scatters inelastically into a slightly heavier ($${\mathcal {O}} (10-100)\,\hbox {keV}$$ O(10-100)keV ) state it is unclear whether thermalization occurs. One issue is that up-scattering from the lower mass state may be kinematically forbidden, at which point the thermalization process effectively stops. A larger evaporation rate is also expected due to down-scattering. In this work, we perform a numerical simulation of the capture and thermalization process in order to study the evolution of the dark matter distribution. We then calculate and compare the annihilation rate with that of the often assumed Maxwell–Boltzmann distribution. We also check if equilibrium between capture and annihilation is reached. We find that, unless the mass splitting is very small ($$\lesssim 50\,\hbox { keV}$$ ≲50keV ) and/or the dark matter has a sub-dominant elastic cross section, the dark matter distribution does not reach a stationary state, it is not isothermal, annihilation is severely suppressed, and equilibrium is generally not reached. We also find that evaporation induced by down-scattering is not effective in reducing the total dark matter abundance