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Dark matter in and around stars
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
2009 (English)Licentiate 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 the star forms. Dark matter annihilations outside the star would give rise to gamma rays and this is discussed in the first paper. Furthermore dark matter annihilations inside the star would deposit energy inside the star which, if abundant enough, could alter the stellar evolution. Aspects of this are investigated in the second paper. Finally, local dark matter overdensities formed in the early universe could still be around today; prospects of detecting gamma rays from such clumps are discussed in the third paper.

Place, publisher, year, edition, pages
Stockholm: Universitetsservice US AB , 2009. , x, 28 p.
Series
Trita-FYS, ISSN 0280-316X ; 2009:49
Keyword [en]
Dark matter, early universe
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:kth:diva-11259ISBN: 978-91-7415-430-6 (print)OAI: oai:DiVA.org:kth-11259DiVA: diva2:271548
Presentation
2009-10-02, FA32, AlbaNova, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
Introduktionsdelen till en sammanläggningsavhandlingAvailable from: 2009-10-13 Created: 2009-10-12 Last updated: 2010-11-01Bibliographically 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, E-ISSN 1550-2368, 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: 2017-12-12Bibliographically 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: 2017-12-12Bibliographically 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, E-ISSN 1079-7114, 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: 2017-12-12Bibliographically approved

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