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Searches for Particle Dark Matter: Dark stars, dark galaxies, dark halos and global supersymmetric fits
Stockholm University, Faculty of Science, Department of Physics. (Cosmology, Particle Astrophysics and String Theory)
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The identity of dark matter is one of the key outstanding problems in both particle and astrophysics. In this thesis, I describe a number of complementary searches for particle dark matter. I discuss how the impact of dark matter on stars can constrain its interaction with nuclei, focussing on main sequence stars close to the Galactic Centre, and on the first stars as seen through the upcoming James Webb Space Telescope. The mass and annihilation cross-section of dark matter particles can be probed with searches for gamma rays produced in astronomical targets. Dwarf galaxies and ultracompact, primordially-produced dark matter minihalos turn out to be especially promising in this respect. I illustrate how the results of these searches can be combined with constraints from accelerators and cosmology to produce a single global fit to all available data. Global fits in supersymmetry turn out to be quite technically demanding, even with the simplest predictive models and the addition of complementary data from a bevy of astronomical and terrestrial experiments; I show how genetic algorithms can help in overcoming these challenges.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2010. , 84 p.
Keyword [en]
dark matter, supersymmetry, gamma rays, dwarf galaxies, stellar evolution, cosmological perturbations, phase transitions, statistical techniques
National Category
Subatomic Physics Subatomic Physics Astronomy, Astrophysics and Cosmology Subatomic Physics Other Physics Topics Astronomy, Astrophysics and Cosmology Astronomy, Astrophysics and Cosmology
Research subject
Theoretical Physics
Identifiers
URN: urn:nbn:se:su:diva-38221ISBN: 978-91-7447-031-4 (print)OAI: oai:DiVA.org:su-38221DiVA: diva2:308048
Public defence
2010-05-04, FD5, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 15:15 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Accepted. Paper 6: Submitted. Available from: 2010-04-12 Created: 2010-04-01 Last updated: 2010-04-07Bibliographically approved
List of papers
1. The zero age main sequence of WIMP burners
Open this publication in new window or tab >>The zero age main sequence of WIMP burners
2008 (English)In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 77, 047301- p.Article in journal (Refereed) Published
Abstract [en]

We modify a stellar structure code to estimate the effect upon the main sequence of the accretion of weakly-interacting dark matter onto stars and its subsequent annihilation. The effect upon the stars depends upon whether the energy generation rate from dark matter annihilation is large enough to shut off the nuclear burning in the star. Main sequence weakly-interacting massive particles (WIMP) burners look much like proto-stars moving on the Hayashi track, although they are in principle completely stable. We make some brief comments about where such stars could be found, how they might be observed and more detailed simulations which are currently in progress. Finally we comment on whether or not it is possible to link the paradoxically hot, young stars found at the galactic center with WIMP burners.

Identifiers
urn:nbn:se:su:diva-38212 (URN)10.1103/PhysRevD.77.047301 (DOI)000253764800140 ()
Available from: 2010-04-01 Created: 2010-04-01 Last updated: 2017-12-12Bibliographically approved
2. Dark stars at the Galactic Centre: the main sequence
Open this publication in new window or tab >>Dark stars at the Galactic Centre: the main sequence
2009 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 394, no 1, 82-104 p.Article in journal (Refereed) Published
Abstract [en]

In regions of very high dark matter density such as the Galactic Centre, the capture and annihilation of WIMP dark matter by stars has the potential to significantly alter their evolution. We describe the dark stellar evolution code DarkStars, and present a series of detailed grids of WIMP-influenced stellar models for main-sequence stars. We describe the changes in stellar structure and main-sequence evolution which occur as a function of the rate of energy injection by WIMPs, for masses of 0.3–2.0 M⊙ and metallicities Z= 0.0003–0.02 . We show what rates of energy injection can be obtained using realistic orbital parameters for stars at the Galactic Centre, including detailed consideration of the velocity and density profiles of dark matter. Capture and annihilation rates are strongly boosted when stars follow elliptical rather than circular orbits. If there is a spike of dark matter induced by the supermassive black hole at the Galactic Centre, single solar mass stars following orbits with periods as long as 50 yr and eccentricities as low as 0.9 could be significantly affected. Binary systems with similar periods about the Galactic Centre could be affected on even less eccentric orbits. The most striking observational effect of this scenario would be the existence of a binary consisting of a low-mass protostar and a higher mass evolved star. The observation of low-mass stars and/or binaries on such orbits would either provide a detection of WIMP dark matter, or place stringent limits on the combination of the WIMP mass, spin-dependent nuclear-scattering cross-section, halo density and velocity distribution near the Galactic Centre. In some cases, the derived limits on the WIMP mass and spin-dependent nuclear-scattering cross-section would be of comparable sensitivity to current direct-detection experiments.

Keyword
elementary particles, stars: evolution, stars: fundamental parameters, stars: interiors, Galaxy: centre, dark matter
Identifiers
urn:nbn:se:su:diva-38215 (URN)10.1111/j.1365-2966.2008.14282.x (DOI)000263967700007 ()
Available from: 2010-04-01 Created: 2010-04-01 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, 211301- 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 Čerenkov 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.

Keyword
Astrophysics - Cosmology and Extragalactic Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, High Energy Physics - Phenomenology
Identifiers
urn:nbn:se:su:diva-38211 (URN)10.1103/PhysRevLett.103.211301 (DOI)000272054300008 ()
Available from: 2010-04-01 Created: 2010-04-01 Last updated: 2017-12-12Bibliographically approved
4. Direct constraints on minimal supersymmetry from Fermi-LAT observations of the dwarf galaxy Segue 1
Open this publication in new window or tab >>Direct constraints on minimal supersymmetry from Fermi-LAT observations of the dwarf galaxy Segue 1
Show others...
2010 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 1, 31-50 p.Article in journal (Refereed) Published
Abstract [en]

The dwarf galaxy Segue 1 is one of the most promising targets for the indirect detection of dark matter. Here we examine what constraints 9 months of Fermi-LAT gamma-ray observations of Segue 1 place upon the Constrained Minimal Supersymmetric Standard Model (CMSSM), with the lightest neutralino as the dark matter particle. We use nested sampling to explore the CMSSM parameter space, simultaneously fitting other relevant constraints from accelerator bounds, the relic density, electroweak precision observables, the anomalous magnetic moment of the muon and B-physics. We include spectral and spatial fits to the Fermi observations, a full treatment of the instrumental response and its related uncertainty, and detailed background models. We also perform an extrapolation to 5 years of observations, assuming no signal is observed from Segue 1 in that time. Results marginally disfavour models with low neutralino masses and high annihilation cross-sections. Virtually all of these models are however already disfavoured by existing experimental or relic density constraints.

Keyword
dark matter theory, dwarfs galaxies, supersymmetry and cosmology, gamma ray theory
National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-38209 (URN)10.1088/1475-7516/2010/01/031 (DOI)
Available from: 2010-04-01 Created: 2010-04-01 Last updated: 2017-12-12Bibliographically approved
5. A Profile Likelihood Analysis of the Constrained MSSM with Genetic Algorithms
Open this publication in new window or tab >>A Profile Likelihood Analysis of the Constrained MSSM with Genetic Algorithms
Show others...
2010 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 4, 057- p.Article in journal (Refereed) Published
Abstract [en]

The Constrained Minimal Supersymmetric Standard Model (CMSSM) is one of the simplest and most widely-studied supersymmetric extensions to the standard model of particle physics. Nevertheless, current data do not sufficiently constrain the model parameters in a way completely independent of priors, statistical measures and scanning techniques. We present a new technique for scanning supersymmetric parameter spaces, optimised for frequentist profile likelihood analyses and based on Genetic Algorithms. We apply this technique to the CMSSM, taking into account existing collider and cosmological data in our global fit. We compare our method to the MultiNest algorithm, an efficient Bayesian technique, paying particular attention to the best-fit points and implications for particle masses at the LHC and dark matter searches. Our global best-fit point lies in the focus point region. We find many high-likelihood points in both the stau co-annihilation and focus point regions, including a previously neglected section of the co-annihilation region at large m 0. We show that there are many high-likelihood points in the CMSSM parameter space commonly missed by existing scanning techniques, especially at high masses. This has a significant influence on the derived confidence regions for parameters and observables, and can dramatically change the entire statistical inference of such scans.

Keyword
High Energy Physics - Phenomenology, Astrophysics - Cosmology and Extragalactic Astrophysics
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-38220 (URN)10.1007/JHEP04(2010)057 (DOI)000277473100013 ()
Available from: 2010-04-01 Created: 2010-04-01 Last updated: 2017-12-12Bibliographically approved
6. Finding high-redshift dark stars with the James Webb Space Telescope
Open this publication in new window or tab >>Finding high-redshift dark stars with the James Webb Space Telescope
Show others...
2010 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 717, no 1, 257-267 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
dark ages, reionization, first stars; dark matter; galaxies: high-redshift; stars: Population III
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-38219 (URN)10.1088/0004-637X/717/1/257 (DOI)000278777900023 ()
Available from: 2010-04-01 Created: 2010-04-01 Last updated: 2017-12-12Bibliographically approved

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