| 1. |
- Scott, Pat, et al.
(författare)
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Gamma Rays from Ultracompact Primordial Dark Matter Minihalos
- 2009
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Ingår i: Physical Review Letters. - : The American Physical Society. - 0031-9007 .- 1079-7114. ; 103:21, s. 211301-1-211301-4
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Sivertsson, Sofia, 1982-, et al.
(författare)
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Accurate calculations of the WIMP halo around the Sun and prospects for gamma ray detection
- 2008
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Ingår i: Identification of dark matter 2008. - : SISSA. ; , s. 112-
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Konferensbidrag (refereegranskat)abstract
- Weakly interacting massive particles (WIMPs) can be captured by heavenly objects, like the Sun.Under the process of being captured by the Sun, they will build up a population of WIMPs aroundit, that will eventually sink to the core of the Sun. It has been argued with simpler estimatesbefore that this halo of WIMPs around the Sun could be a strong enough gamma ray source to bea detectable signature for WIMP dark matter. We here revisit the problem using detailed MonteCarlo simulations and detailed composition and structure information about the Sun to estimatethe size of the gamma ray flux. Compared to earlier estimates, we find that the gamma ray fluxfrom WIMP annihilations in the Sun halo would be negligible and no current or planned detectorswould even be able to detect this flux.
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| 3. |
- Sivertsson, Sofia, 1982-, et al.
(författare)
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Accurate calculations of the WIMP halo around the Sun and prospects for its gamma-ray detection
- 2010
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Ingår i: Physical Review D. - : The American Physical Society. - 1550-7998 .- 1550-2368. ; 81:6, s. 63502-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Sivertsson, Sofia, 1982-
(författare)
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Studies of dark matter in and around stars
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 5. |
- Sivertsson, Sofia, 1982-, et al.
(författare)
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The WIMP capture process for dark stars in the early universe
- 2011
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Ingår i: Astrophysical Journal. - : The American Astronomical Society. - 0004-637X .- 1538-4357. ; 729:1, s. 51-1-51-11
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Zackrisson, Erik, et al.
(författare)
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Finding high-redshift dark stars with the James Webb Space Telescope
- 2010
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Ingår i: Astrophysical Journal. - : The American Astronomical Society. - 0004-637X .- 1538-4357. ; 717:1, s. 257-267
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Tidskriftsartikel (refereegranskat)abstract
- The first stars in the history of the universe are likely to form in the dense central regions of similar to 10(5)-10(6) M-circle dot cold dark matter halos at z approximate to 10-50. The annihilation of dark matter particles in these environments may lead to the formation of so-called dark stars, which are predicted to be cooler, larger, more massive, and potentially more long-lived than conventional population III stars. Here, we investigate the prospects of detecting high-redshift dark stars with the upcoming James Webb Space Telescope (JWST). We find that all dark stars with masses up to 10(3) M-circle dot are intrinsically too faint to be detected by JWST at z > 6. However, by exploiting foreground galaxy clusters as gravitational telescopes do, certain varieties of cool (T-eff <= 30,000 K) dark stars should be within reach at redshifts up to z approximate to 10. If the lifetimes of dark stars are sufficiently long, many such objects may also congregate inside the first galaxies. We demonstrate that this could give rise to peculiar features in the integrated spectra of galaxies at high redshifts, provided that dark stars make up at least similar to 1% of the total stellar mass in such objects.
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| 7. |
- Zackrisson, Erik, et al.
(författare)
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Observational constraints on supermassive dark stars
- 2010
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1745-3925 .- 1365-2966. ; 407:1, s. L74-L78
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Tidskriftsartikel (refereegranskat)abstract
- Some of the first stars could be cooler and more massive than standard stellar models would suggest, due to the effects of dark matter annihilation in their cores. It has recently been argued that such objects may attain masses in the 104-107Msolar range and that such supermassive dark stars should be within reach of the upcoming James Webb Space Telescope. Notwithstanding theoretical difficulties with this proposal, we argue here that some of these objects should also be readily detectable with both the Hubble Space Telescope and ground-based 8-10 m class telescopes. Existing survey data already place strong constraints on 107Msolar dark stars at z ~ 10. We show that such objects must be exceedingly rare or short lived to have avoided detection.
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