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Type: Theses
Title: Collider constraints applied to simplified models of dark matter fitted to the Fermi- LAT gamma ray excess using Bayesian techniques
Author: Pitman, Guy Hamilton Massey
Issue Date: 2016
School/Discipline: School of Physical Sciences
Abstract: The Fermi gamma ray space telescope has over the past few years detected a gamma ray signal from the inner few degrees around the galactic centre, corresponding to a region several hundred parsecs in radius. The spectrum and angular distribution are compatible with that from annihilating dark matter particles. A number of papers have recently attempted to explain the Gamma Ray excess in terms of extensions to the Standard Model, taking into account constraints from ATLAS and CMS collider experiments , direct detection of dark matter colliding off nucleii in well shielded detectors (e.g. LUX), as well as other indirect measurements (astrophysical observations). These papers take the approach of simplified models which describe the contact interactions of a mediator between DM and ordinary matter using an effective field theory approach (EFT). Until recently it has been difficult to discriminate between the results of these papers, which look at different models and produce different statistical results. A recent paper [19] "Simplified Dark Matter Models Confront the Gamma Ray Excess", used a Bayesian inference tool to compare a variety of simplified models using the Bayesian evidence values calculated for each model to find the most preferred explanation. The motivation for the chosen models is discussed in section 1.2.1. A subsequent paper [20], "Interpreting the Fermi-LAT gamma ray excess in the simplified framework", studied the most likely model, again using Bayesian inference to find the most likely parameters for the (most likely) model. The data inputs (observables) to the scan were the Planck measurement of the dark matter relic density [21], Fermi-LAT gamma ray flux data from the galactic center [17], cosmic positron flux data [22], cosmic anti-proton flux data [18], cosmic microwave background data, and direct detection data from the LUX experiment [16]. The result of the scan was a posterior probability density function in the parameter space of the model. This paper extends the findings in [19] by adding collider constraints to the likelihood estimations for the three models. It is not a simple matter to add collider constraints because each point in parameter space demands a significant amount of computing to calculate the expected excess amount of observable particles corresponding to the particular experiment, given the proposed simplified model. A sampling method has been employed to calculate the collider constraints using the probability of the parameters based on the astrophysical observables.
Advisor: Williams, Anthony Gordon
White, Martin
Balasz, Csaba
Dissertation Note: Thesis (M.Phil..) -- University of Adelaide, School of Physical Sciences, 2016.
Keywords: dark matter
Fermi-LAT
collider constraints
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legals
DOI: 10.4225/55/58b7b9153a142
Appears in Collections:Research Theses

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