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Supersymmetry vis-à-vis Observation: Dark Matter Constraints, Global Fits and Statistical Issues
Stockholm University, Faculty of Science, Department of Physics. (Cosmology, Particle Astrophysics and String Theory)
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Weak-scale supersymmetry is one of the most favoured theories beyond the Standard Model of particle physics that elegantly solves various theoretical and observational problems in both particle physics and cosmology. In this thesis, I describe the theoretical foundations of supersymmetry, issues that it can address and concrete supersymmetric models that are widely used in phenomenological studies. I discuss how the predictions of supersymmetric models may be compared with observational data from both colliders and cosmology. I show why constraints on supersymmetric parameters by direct and indirect searches of particle dark matter are of particular interest in this respect. Gamma-ray observations of astrophysical sources, in particular dwarf spheroidal galaxies, by the Fermi satellite, and recording nuclear recoil events and energies by future ton-scale direct detection experiments are shown to provide powerful tools in searches for supersymmetric dark matter and estimating supersymmetric parameters. I discuss some major statistical issues in supersymmetric global fits to experimental data. In particular, I further demonstrate that existing advanced scanning techniques may fail in correctly mapping the statistical properties of the parameter spaces even for the simplest supersymmetric models. Complementary scanning methods based on Genetic Algorithms are proposed.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2011. , 142 p.
Keyword [en]
supersymmetry, cosmology of theories beyond the Standard Model, dark matter, gamma rays, dwarf galaxies, direct detection, statistical techniques, scanning algorithms, genetic algorithms, statistical coverage
National Category
Subatomic Physics Astronomy, Astrophysics and Cosmology Subatomic Physics
Research subject
Theoretical Physics
Identifiers
URN: urn:nbn:se:su:diva-57194ISBN: 978-91-7447-312-4OAI: oai:DiVA.org:su-57194DiVA: diva2:414563
Public defence
2011-06-07, room FA32, AlbaNova University Center, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.Available from: 2011-05-12 Created: 2011-05-03 Last updated: 2011-06-28Bibliographically approved
List of papers
1. 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
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2010 (English)In: Journal of Cosmology and Astroparticle Physics, 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: 2011-05-09Bibliographically approved
2. 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
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2010 (English)In: Journal of High Energy Physics (JHEP), ISSN 1029-8479, E-ISSN 1126-6708, 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: 2011-12-05Bibliographically approved
3. How well will ton-scale dark matter direct detection experiments constrain minimal supersymmetry?
Open this publication in new window or tab >>How well will ton-scale dark matter direct detection experiments constrain minimal supersymmetry?
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2011 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, no 4, 012- p.Article in journal (Refereed) Published
Abstract [en]

Weakly interacting massive particles (WIMPs) are amongst the most interesting dark matter (DM) candidates. Many DM candidates naturally arise in theories beyond the standard model (SM) of particle physics, like weak-scale supersymmetry (SUSY). Experiments aim to detect WIMPs by scattering, annihilation or direct production, and thereby determine the underlying theory to which they belong, along with its parameters. Here we examine the prospects for further constraining the Constrained Minimal Supersymmetric Standard Model (CMSSM) with future ton-scale direct detection experiments. We consider ton-scale extrapolations of three current experiments: CDMS, XENON and COUPP, with 1000 kg-years of raw exposure each. We assume energy resolutions, energy ranges and efficiencies similar to the current versions of the experiments, and include backgrounds at target levels. Our analysis is based on full likelihood constructions for the experiments. We also take into account present uncertainties on hadronic matrix elements for neutralino-quark couplings, and on halo model parameters. We generate synthetic data based on four benchmark points and scan over the CMSSM parameter space using nested sampling. We construct both Bayesian posterior PDFs and frequentist profile likelihoods for the model parameters, as well as the mass and various cross-sections of the lightest neutralino. Future ton-scale experiments will help substantially in constraining supersymmetry, especially when results of experiments primarily targeting spin-dependent nuclear scattering are combined with those directed more toward spin-independent interactions.

Keyword
dark matter theory, dark matter experiments, cosmology of theories beyond the SM, supersymmetry and cosmology
National Category
Subatomic Physics Astronomy, Astrophysics and Cosmology
Research subject
Theoretical Physics; High Energy Physics; Theoretical Astrophysics
Identifiers
urn:nbn:se:su:diva-57171 (URN)10.1088/1475-7516/2011/04/012 (DOI)000291259000012 ()
Available from: 2011-05-03 Created: 2011-05-03 Last updated: 2012-01-25Bibliographically approved
4. Statistical coverage for supersymmetric parameter estimation: a case study with direct detection of dark matter
Open this publication in new window or tab >>Statistical coverage for supersymmetric parameter estimation: a case study with direct detection of dark matter
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2011 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, no 7, 002- p.Article in journal (Refereed) Published
Abstract [en]

Models of weak-scale supersymmetry offer viable dark matter (DM) candidates. Their parameter spaces are however rather large and complex, such that pinning down the actual parameter values from experimental data can depend strongly on the employed statistical framework and scanning algorithm. In frequentist parameter estimation, a central requirement for properly constructed confidence intervals is that they cover true parameter values, preferably at exactly the stated confidence level when experiments are repeated infinitely many times. Since most widely-used scanning techniques are optimised for Bayesian statistics, one needs to assess their abilities in providing correct confidence intervals in terms of the statistical coverage. Here we investigate this for the Constrained Minimal Supersymmetric Standard Model (CMSSM) when only constrained by data from direct searches for dark matter. We construct confidence intervals from one-dimensional profile likelihoods and study the coverage by generating several pseudo-experiments for two benchmark sets of pseudo-true parameters. We use nested sampling to scan the parameter space and evaluate the coverage for the two benchmarks when either flat or logarithmic priors are imposed on gaugino and scalar mass parameters. We observe both under- and over-coverage, which in some cases vary quite dramatically when benchmarks or priors are modified. We show how most of the variation can be explained as the impact of explicit and implicit priors, where the latter are indirectly imposed by physicality conditions. For comparison, we also evaluate the coverage for Bayesian credible intervals, and (predictably) observe significant under-coverage in those cases.

Keyword
dark matter theory, dark matter experiments, cosmology of theories beyond the SM, supersymmetry and cosmology
National Category
Subatomic Physics Astronomy, Astrophysics and Cosmology Subatomic Physics
Research subject
Theoretical Physics; High Energy Physics; Theoretical Astrophysics
Identifiers
urn:nbn:se:su:diva-57193 (URN)10.1088/1475-7516/2011/07/002 (DOI)000297541000003 ()
Available from: 2011-05-03 Created: 2011-05-03 Last updated: 2012-03-01Bibliographically approved

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