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Studies of dark matter in and around stars
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

There is by now compelling evidence that most of the matter in the Universe is in the form of dark matter, a form of matter quite different from the matter we experience in every day life. The gravitational effects of this dark matter have been observed in many different ways but its true nature is still unknown. In most models, dark matter particles can annihilate with each other into standard model particles; the direct or indirect observation of such annihilation products could give important clues for the dark matter puzzle. For signals from dark matter annihilations to be detectable, typically high dark matter densities are required. Massive objects, such as stars, can increase the local dark matter density both via scattering off nucleons and by pulling in dark matter gravitationally as a star forms. Annihilations within this kind of dark matter population gravitationally bound to a star, like the Sun, give rise to a gamma ray flux. For a star which has a planetary system, dark matter can become gravitationally bound also through gravitational interactions with the planets. The interplay between the different dark matter populations in the solar system is analyzed, shedding new light on dark matter annihilations inside celestial bodies and improving the predicted experimental reach. Dark matter annihilations inside a star would also deposit energy in the star which, if abundant enough, could alter the stellar evolution. This is investigated for the very first stars in the Universe. Finally, there is a possibility for abundant small scale dark matter overdensities to have formed in the early Universe. Prospects of detecting gamma rays from such minihalos, which have survived until the present day, are discussed.

Abstract [sv]

Kosmologiska observationer har visat att större delen av materian i universum består av mörk materia, en form av materia med helt andra egenskaper än den vi upplever i vardagslivet. Effekterna av denna mörka materia har observerats gravitationellt på många olika sätt men vad den egentligen består av är fortfarande okänt. I de flesta modeller kan mörk materia-partiklar annihilera med varandra till standardmodellpartiklar. Att direkt eller indirekt observera sådana annihilationsprodukter kan ge viktiga ledtrådar om vad den mörka materian består av. För att kunna detektera sådana signaler fordras typiskt höga densiteter av mörk materia. Stjärnor kan lokalt öka densiteten av mörk materia, både via spridning mot atomkärnor i stjärnan och genom den ökande gravitationskraften i samband med att en stjärna föds. Annihilationer inom en sådan mörk materia-population gravitationellt bunden till en stjärna, till exempel solen, ger upphov till ett flöde av gammastrålning, som beräknas. För en stjärna som har ett planetsystem kan mörk materia även bli infångad genom gravitationell växelverkan med planeterna. Samspelet mellan de två mörk materia-populationerna i solsystemet analyseras, vilket ger nya insikter om mörk materia-annihilationer inuti himlakroppar och förbättrar de experimentella möjligheterna att detektera dem. Mörk materia-annihilationer inuti en stjärna utgör också en extra energikälla för stjärnan, vilket kan påverka stjärnans utveckling om mörk materia-densiteten blir tillräckligt stor. Denna effekt undersöks för de allra första stjärnorna i universum. Slutligen finns det också en möjlighet att det i det tidiga universum skapades mörk materia-ansamlingar som fortfarande finns kvar idag. Utsikterna att upptäcka dessa genom mätning av gammastrålning diskuteras.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , x, 73 p.
Series
Trita-FYS, ISSN 0280-316X ; 2012:04
Keyword [en]
Dark matter, particle astrophysics
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-64245ISBN: 987-91-7501-251-3 OAI: oai:DiVA.org:kth-64245DiVA: diva2:484625
Public defence
2012-02-17, FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, AlbaNova, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20120130Available from: 2012-01-30 Created: 2012-01-24 Last updated: 2012-01-30Bibliographically approved
List of papers
1. Accurate calculations of the WIMP halo around the Sun and prospects for its gamma-ray detection
Open this publication in new window or tab >>Accurate calculations of the WIMP halo around the Sun and prospects for its gamma-ray detection
2010 (English)In: Physical Review D, ISSN 1550-7998, Vol. 81, no 6, 063502-1-063502-14 p.Article in journal (Refereed) Published
Abstract [en]

Galactic weakly interacting massive particles (WIMPs) may scatter off solar nuclei to orbits gravitationally bound to the Sun. Once bound, the WIMPs continue to lose energy by repeated scatters in the Sun, eventually leading to complete entrapment in the solar interior. While the density of the bound population is highest at the center of the Sun, the only observable signature of WIMP annihilations inside the Sun is neutrinos. It has been previously suggested that although the density of WIMPs just outside the Sun is lower than deep inside, gamma rays from WIMP annihilation just outside the surface of the Sun, in the so-called WIMP halo around the Sun, may be more easily detected. We here revisit this problem using detailed Monte Carlo simulations and detailed composition and structure information about the Sun to estimate the size of the gamma-ray flux. Compared to earlier simpler estimates, we find that the gamma-ray flux from WIMP annihilations in the solar WIMP halo would be negligible; no current or planned detectors would be able to detect this flux.

Place, publisher, year, edition, pages
The American Physical Society, 2010
Keyword
DARK-MATTER CANDIDATES, MASSIVE PARTICLES, SOLAR, NEUTRINOS, POPULATION, SIGNATURES, CAPTURE
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-25799 (URN)10.1103/PhysRevD.81.063502 (DOI)000276195700019 ()2-s2.0-77951526943 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20101101 QC 20111209Available from: 2011-12-09 Created: 2010-11-01 Last updated: 2012-01-30Bibliographically approved
2. The WIMP capture process for dark stars in the early universe
Open this publication in new window or tab >>The WIMP capture process for dark stars in the early universe
2011 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 729, no 1, 51-1-51-11 p.Article in journal (Refereed) Published
Abstract [en]

The first stars to form in the universe may have been dark stars, powered by dark matter annihilation instead of nuclear fusion. The initial amount of dark matter gathered by the star gravitationally can sustain it only for a limited period of time. It has been suggested that capture of additional dark matter from the environment can prolong the dark star phase even to the present day. Here we show that this capture process is ineffective to prolong the life of the first generation of dark stars. We construct a Monte-Carlo simulation that follows each Weakly Interacting Massive Particle (WIMP) in the dark matter halo as its orbit responds to the formation and evolution of the dark star, as it scatters off the star's nuclei, and as it annihilates inside the star. A rapid depletion of the WIMPs on orbits that cross the star causes the demise of the first generation of dark stars. We suggest that a second generation of dark stars may in principle survive much longer through capture. We comment on the effect of relaxing our assumptions.

Place, publisher, year, edition, pages
The American Astronomical Society, 2011
Keyword
dark matter, stars, formation
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-25801 (URN)10.1088/0004-637X/729/1/51 (DOI)000287255300051 ()2-s2.0-79952174178 (Scopus ID)
Funder
Swedish Research Council, 315-2004-6519
Note
QC 20101101 Uppdaterad från submitted till published (20110315).Available from: 2011-12-09 Created: 2010-11-01 Last updated: 2012-01-30Bibliographically approved
3. Gamma Rays from Ultracompact Primordial Dark Matter Minihalos
Open this publication in new window or tab >>Gamma Rays from Ultracompact Primordial Dark Matter Minihalos
2009 (English)In: Physical Review Letters, ISSN 0031-9007, Vol. 103, no 21, 211301-1-211301-4 p.Article in journal (Refereed) Published
Abstract [en]

Ultracompact minihalos have been proposed as a new class of dark matter structure. They would be produced by phase transitions in the early Universe or features in the inflaton potential, and constitute nonbaryonic massive compact halo objects today. We examine the prospects of detecting these minihalos in gamma rays if dark matter can self-annihilate. We compute present-day fluxes from minihalos produced in the e(+)e(-) annihilation epoch and the QCD and electroweak phase transitions. Even at a distance of 4 kpc, minihalos from the e(+)e(-) epoch would be eminently detectable today by the Fermi satellite or air Ccerenkov telescopes, or even in archival EGRET data. Within 2 kpc, they would appear as extended sources to Fermi. At 4 kpc, minihalos from the QCD transition have similar predicted fluxes to dwarf spheroidal galaxies, so might also be detectable by present or upcoming experiments.

Place, publisher, year, edition, pages
The American Physical Society, 2009
Keyword
Dark matter, E+e- annihilation, Early universe, Electroweak phase transition, Extended sources
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-25803 (URN)10.1103/PhysRevLett.103.211301 (DOI)000272054300008 ()2-s2.0-70450190446 (Scopus ID)
Funder
Swedish Research Council
Note
A correction of this article occurs in Phys. Rev. Lett. 105, 119902(E) (2010).QC 20111208Available from: 2011-12-08 Created: 2010-11-01 Last updated: 2012-01-30Bibliographically approved
4. WIMP diffusion in the Solar System including solar WIMP-nucleon scattering
Open this publication in new window or tab >>WIMP diffusion in the Solar System including solar WIMP-nucleon scattering
2012 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 85, no 12, 123514- p.Article in journal (Refereed) Published
Abstract [en]

Dark matter in the form of Weakly Interacting Massive Particles (WIMPs) can be captured by the Sun and the Earth, sink to their cores, annihilate and produce neutrinos that can be searched for with neutrino telescopes. The calculation of the capture rates of WIMPs in the Sun and especially the Earth are affected by large uncertainties coming mainly from effects of the planets in the Solar System, reducing the capture rates by up to an order of magnitude (or even more in some cases). We show that the WIMPs captured by weak scatterings in the Sun also constitute an important bound WIMP population in the Solar System. Taking this population and its interplay with the population bound through gravitational diffusion into account cancel the planetary effects on the capture rates, and the capture essentially proceeds as if the Sun and the Earth were free in the galactic halo. The neutrino signals from the Sun and the Earth are thus significantly higher than claimed in the scenarios with reduced capture rates.

Keyword
DARK-MATTER CANDIDATES, CAPTURE, EARTH
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-70238 (URN)10.1103/PhysRevD.85.123514 (DOI)000304941200005 ()2-s2.0-84862285317 (Scopus ID)
Funder
Swedish Research Council, 621-2010-3301Swedish Research Council, 315-2004-6519
Note
QC 20120130. Updated from submitted to published.Available from: 2012-01-30 Created: 2012-01-30 Last updated: 2017-12-08Bibliographically approved

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