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Dark Matter Phenomenology in Astrophysical Systems
KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. , p. 95
Series
TRITA-SCI-FOU ; 2019:35
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-251394ISBN: 978-91-7873-242-5 (print)OAI: oai:DiVA.org:kth-251394DiVA, id: diva2:1316215
Public defence
2019-06-13, FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Göran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of Technology, 1305BGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of Technology, 1404AGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of Technology, 1503Göran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of Technology, 1616
Note

QC20190517

Available from: 2019-05-17 Created: 2019-05-16 Last updated: 2019-05-17Bibliographically approved
List of papers
1. Asymmetric capture of Dirac dark matter by the Sun
Open this publication in new window or tab >>Asymmetric capture of Dirac dark matter by the Sun
2015 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2015, no 8, article id 036Article in journal (Refereed) Published
Abstract [en]

Current problems with the solar model may be alleviated if a significant amount of dark matter from the galactic halo is captured in the Sun. We discuss the capture process in the case where the dark matter is a Dirac fermion and the background halo consists of equal amounts of dark matter and anti-dark matter. By considering the case where dark matter and anti-dark matter have different cross sections on solar nuclei as well as the case where the capture process is considered to be a Poisson process, we find that a significant asymmetry between the captured dark particles and anti-particles is possible even for an annihilation cross section in the range expected for thermal relic dark matter. Since the captured number of particles are competitive with asymmetric dark matter models in a large range of parameter space, one may expect solar physics to be altered by the capture of Dirac dark matter. It is thus possible that solutions to the solar composition problem may be searched for in these type of models.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2015
Keywords
dark matter simulations, dark matter theory
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-175014 (URN)10.1088/1475-7516/2015/08/036 (DOI)000365046600036 ()2-s2.0-84940868751 (Scopus ID)
Note

QC 20151130

Available from: 2015-11-30 Created: 2015-10-09 Last updated: 2019-09-30Bibliographically approved
2. Pinning down inelastic dark matter in the Sun and in direct detection
Open this publication in new window or tab >>Pinning down inelastic dark matter in the Sun and in direct detection
2016 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2016, no 4, article id 004Article in journal (Refereed) Published
Abstract [en]

We study the solar capture rate of inelastic dark matter with endothermic and/or exothermic interactions. By assuming that an inelastic dark matter signal will be observed in next generation direct detection experiments we can set a lower bound on the capture rate that is independent of the local dark matter density, the velocity distribution, the galactic escape velocity as well as the scattering cross section. In combination with upper limits from neutrino observatories we can place upper bounds on the annihilation channels leading to neutrinos. We find that, while endothermic scattering limits are weak in the isospin-conserving case, strong bounds may be set for exothermic interactions, in particular in the spin-dependent case. Furthermore, we study the implications of observing two direct detection signals, in which case one can halo-independently obtain the dark matter mass and the mass splitting, and disentangle the endothermic/exothermic nature of the scattering. Finally we discuss isospin violation.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2016
Keywords
dark matter experiments, dark matter theory
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-187090 (URN)10.1088/1475-7516/2016/04/004 (DOI)000393286400012 ()2-s2.0-84963705514 (Scopus ID)
Note

QC 20160517

Available from: 2016-05-17 Created: 2016-05-17 Last updated: 2019-05-16Bibliographically approved
3. Self-interacting inelastic dark matter: A viable solution to the small scale structure problems
Open this publication in new window or tab >>Self-interacting inelastic dark matter: A viable solution to the small scale structure problems
2017 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2017, no 3, article id 048Article in journal (Refereed) Published
Abstract [en]

Self-interacting dark matter has been proposed as a solution to the small-scale structure problems, such as the observed flat cores in dwarf and low surface brightness galaxies. If scattering takes place through light mediators, the scattering cross section relevant to solve these problems may fall into the non-perturbative regime leading to a non-trivial velocity dependence, which allows compatibility with limits stemming from cluster-size objects. However, these models are strongly constrained by different observations, in particular from the requirements that the decay of the light mediator is sufficiently rapid (before Big Bang Nucleosynthesis) and from direct detection. A natural solution to reconcile both requirements are inelastic endothermic interactions, such that scatterings in direct detection experiments are suppressed or even kinematically forbidden if the mass splitting between the two-states is sufficiently large. Using an exact solution when numerically solving the Schrödinger equation, we study such scenarios and find regions in the parameter space of dark matter and mediator masses, and the mass splitting of the states, where the small scale structure problems can be solved, the dark matter has the correct relic abundance and direct detection limits can be evaded.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2017
Keywords
dark matter simulations, dark matter theory, particle physics - cosmology connection
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-210140 (URN)10.1088/1475-7516/2017/03/048 (DOI)000405653700011 ()2-s2.0-85016973980 (Scopus ID)
Note

QC 20170630

Available from: 2017-06-30 Created: 2017-06-30 Last updated: 2019-10-01Bibliographically approved
4. The distribution of inelastic dark matter in the Sun
Open this publication in new window or tab >>The distribution of inelastic dark matter in the Sun
2018 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 78, no 5, article id 386Article in journal (Refereed) Published
Abstract [en]

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 (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 (≲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.

Place, publisher, year, edition, pages
Springer-Verlag New York, 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-229624 (URN)10.1140/epjc/s10052-018-5863-4 (DOI)000432927600001 ()2-s2.0-85047251363 (Scopus ID)
Funder
Göran Gustafsson Foundation for Research in Natural Sciences and Medicine
Note

QC 20180605

Available from: 2018-06-05 Created: 2018-06-05 Last updated: 2019-05-16Bibliographically approved

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