Dissertation/Thesis Abstract

Placing Limits on Experimental Signatures of Dark Matter Model Predictions
by Sharma, Arjun, Ph.D., The University of Chicago, 2018, 44; 10807985
Abstract (Summary)

In this work, we consider two different models of dark matter and set limits on results of experiments. One is a dynamic dark matter scenario where we put limits on parameters observable by experiments DAMA and XMASS through nuclear recoil of detector atoms (direct detection). The second is a case of dark matter annihilation into positrons and electrons and the signal this would produce on measured values of positron flux and ratio of electron to positron (indirect detection). The values of these quantities as measured by FERMI and PAMELA experiments are observed and an explanation using a dark matter annihilation is presented vs astrophysical sources of particles.

We explore a dynamic dark matter scenario with an ensemble of dark matter particles that starts at m0 and spans a comb of particles separated by jδΔ m. We verify the model by using Δm = ∞ and comparing the predictions to a non dynamic model for the same mass m0. We then observe the wider set of possibilities available with the dynamic dark matter model compared with the single mass case vis a vis constraints set by NaI and Xe detectors published by the DAMA and XMASS collaborations and check for validity of model against these measurements.

The Fermi experiment has measured the cosmic ray electron+positron spectrum and positron fraction [фe+/(фe++e)], and PAMELA has measured the positron fraction with better precision. While the majority of cosmic ray electrons and positrons are of astrophysical origin, there may also be a contribution from dark matter annihilation in the galactic halo. The upcoming results of the AMS experiment will show measurements of these quantities with far greater precision. One dark matter annihilation scenario is where two dark matter particles annihilate directly to e + and e final states. In this article, we calculate the signature “bumps” in these measurements assuming a given density profile (NFW profile). If the dark matter annihilates to electrons and positrons with a cross section σv ∼ 10−26 cm3/s or greater, this feature may be discernible by AMS. However, we demonstrate that such a prominent spectral feature is already ruled out by the relative smoothness of the positron + electron cosmic ray spectrum as measured by Fermi. Hence we conclude that such a feature is undetectable unless the mass is less than ∼40 GeV.

Indexing (document details)
Advisor: Wah, Yau, Kim, Young-Kee
Commitee: Kelso, Christopher, Reid, David
School: The University of Chicago
Department: Physics
School Location: United States -- Illinois
Source: DAI-B 80/01(E), Dissertation Abstracts International
Source Type: DISSERTATION
Subjects: Astrophysics, Physics, Particle physics
Keywords: Dark matter, Direct detection, Form factor, Nuclear recoil, Quenching, Scintillation
Publication Number: 10807985
ISBN: 9780438370142
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