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Studies of dark matter annihilation and production in the Universe
Stockholm University, Faculty of Science, Department of Physics.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this PhD thesis we investigate various aspects of particle dark matter. The proper identification of dark matter developed during the second half of the twentieth century to become one of the biggest endeavours in modern physics and astronomy. Although observations currently favour the explanation that dark matter consists of a new form of particle, no experimental search has yet provided unequivocal evidence of such a particle. 

Of particular importance in this thesis is the field of indirect detection of dark matter, where one searches for the particles emerging from annihilations of dark matter particles out in the Universe. Specifically, we consider dark matter annihilations in the centre of the Sun. As the Sun moves through the galaxy, some dark matter particles scatter in the Sun and lose enough energy to become bound to the Sun. They settle in the solar core and begin to annihilate, which leads to an annihilation signal from the solar direction.

The thesis is built on novel research consisting of three papers and a monograph-type chapter. In the first paper we calculate the flux of high energy neutrinos coming from cosmic ray cascades in the solar atmosphere and investigate the role it plays as a background in solar dark matter searches. In the second paper we consider dark matter annihilating into long-lived mediators in the Sun, which leads to interesting new detection possibilities. A third paper explores more generally the fluxes of secondary particles from dark matter annihilations that are searched for in indirect detection. We look at the effects of changing the Monte Carlo event generator that generates the fluxes and of having polarized final states in the annihilations. Finally, we consider in a monograph-type chapter the production of dark matter in the early Universe through the freeze-out mechanism, looking at effects of higher order corrections in the calculation of the relic abundance in the minimal supersymmetric standard model.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2019. , p. 132
Keywords [en]
dark matter, neutrinos, astroparticle physics, indirect detection
National Category
Astronomy, Astrophysics and Cosmology Subatomic Physics
Research subject
Theoretical Physics
Identifiers
URN: urn:nbn:se:su:diva-169786ISBN: 978-91-7797-739-1 (print)ISBN: 978-91-7797-740-7 (electronic)OAI: oai:DiVA.org:su-169786DiVA, id: diva2:1326001
Public defence
2019-09-06, FB53, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Manuscript.

Available from: 2019-08-14 Created: 2019-06-17 Last updated: 2019-08-07Bibliographically approved
List of papers
1. Neutrinos from cosmic ray interactions in the Sun
Open this publication in new window or tab >>Neutrinos from cosmic ray interactions in the Sun
2017 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 6, article id 033Article in journal (Refereed) Published
Abstract [en]

Cosmic rays hitting the solar atmosphere generate neutrinos that interact and oscillate in the Sun and oscillate on the way to Earth. These neutrinos could potentially be detected with neutrino telescopes and will be a background for searches for neutrinos from dark matter annihilation in the Sun. We calculate the flux of neutrinos from these cosmic ray interactions in the Sun and also investigate the interactions near a detector on Earth that give rise to muons. We compare this background with both regular Earth-atmospheric neutrinos and signals from dark matter annihilation in the Sun. Our calculation is performed with an event-based Monte Carlo approach that should be suitable as a simulation tool for experimental collaborations. Our program package is released publicly along with this paper.

Keywords
solar and atmospheric neutrinos, neutrino experiments, cosmic ray theory, dark matter experiments
National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-147962 (URN)10.1088/1475-7516/2017/06/033 (DOI)000408310600003 ()
Available from: 2017-10-16 Created: 2017-10-16 Last updated: 2019-06-17Bibliographically approved
2. Neutrinos and gamma rays from long-lived mediator decays in the Sun
Open this publication in new window or tab >>Neutrinos and gamma rays from long-lived mediator decays in the Sun
(English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516Article in journal (Refereed) Submitted
Abstract [en]

We investigate a scenario where dark matter (DM) particles can be captured and accumulate in the Sun, and subsequently annihilate into a pair of long-lived mediators. These mediators can decay further out in the Sun or outside of the Sun. Compared to the standard scenario where DM particles annihilate directly into Standard Model particles close to the solar core, here we also obtain fluxes of gamma rays and charged cosmic rays. We simulate this scenario using a full three-dimensional model of the Sun, and include interactions and neutrino oscillations. In particular, we perform a model-independent study of the complementarity between neutrino and gamma ray fluxes by comparing the recent searches from IceCube, Super-Kamiokande, Fermi-LAT, ARGO and HAWC.

We find that the resulting neutrino fluxes are significantly higher at high energy when the mediators decay further out in the Sun. We also find that gamma ray searches place stronger constraints than neutrino searches on these models even in cases where the mediators decay mainly inside the Sun, except in the approximately inner 10% of the Sun where neutrino searches are more powerful. We present our results in a model-independent manner and release a new version of the WimpSim code that can be used to simulate this scenario for arbitrary mediator models.

National Category
Astronomy, Astrophysics and Cosmology Subatomic Physics
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-169711 (URN)
Available from: 2019-06-17 Created: 2019-06-17 Last updated: 2019-06-17Bibliographically approved
3. Effect of polarisation and change of event generator on dark matter annihilation fluxes
Open this publication in new window or tab >>Effect of polarisation and change of event generator on dark matter annihilation fluxes
(English)Manuscript (preprint) (Other academic)
Abstract [en]

If indirect detection searches are to be used to discriminate between dark matter particle models, it is crucial to understand the expected energy spectra of secondary particles such as neutrinos, charged antiparticles and gamma rays emerging from dark matter annihilations in the local Universe. We simulate the dark matter annihilation processes and collect the fluxes of the stable end products in the annihilation. In order to get an estimate of the impact of different modelling of the physics in the annihilation process, we compare fluxes obtained with two popular event generators, Pythia8 and Herwig7. We also consider the possible impact of polarisation of the final state in the annihilation, with a specific focuson the impact on neutrino fluxes from dark matter annihilations in the centre of the Sun. We find that differences between the event generators are larger for yields of hadronic end products such as antiprotons, than for leptonic end products. Concerning polarisation, we conversely find the largest differences in the leptonic spectra. We find that for neutrino fluxes from dark matter annihilations in the Sun, differences between the polarisations of the final state are to some extent washed out by neutrino oscillations and interactions in the Sun.

National Category
Astronomy, Astrophysics and Cosmology Subatomic Physics
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-169714 (URN)
Available from: 2019-06-17 Created: 2019-06-17 Last updated: 2019-06-17Bibliographically approved

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