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Effects of Dark Matter in Astrophysical Systems
KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. , p. 68
Series
TRITA-FYS, ISSN 0280-316X ; 2017:13
Keyword [en]
Dark matter, Self-interactions, solar capture, helioseismology, inelastic dark matter, direct detection, indirect detection
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-202956ISBN: 978-91-7729-307-1 (print)OAI: oai:DiVA.org:kth-202956DiVA, id: diva2:1079603
Presentation
2017-04-07, FB54, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20170309

Available from: 2017-03-09 Created: 2017-03-08 Last updated: 2017-03-09Bibliographically 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
Keyword
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)2-s2.0-84940868751 (Scopus ID)
Note

QC 20151130

Available from: 2015-11-30 Created: 2015-10-09 Last updated: 2017-12-01Bibliographically 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
Keyword
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: 2017-11-30Bibliographically 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
(English)Manuscript (preprint) (Other academic)
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 Schr\"odinger 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.

Keyword
Dark matter theory, self-interactions, small scale structure problems
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-202949 (URN)
Note

QC 20170309

Available from: 2017-03-08 Created: 2017-03-08 Last updated: 2017-03-09Bibliographically approved

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