Seeking the Light in the Dark: Quests for Identifying Dark Matter

The night sky is a beautiful display of stars and galaxies.We have come a long way to realize that they are made with substances that can be produced and studied on Earth.However, it has been discovered that those substances make up only 5% of the observable Universe, with the remaining 95% being mysterious substances called dark matter and dark energy, both of which have never been observed directly.Their nature is among the most profound questions in modern science, and unquestionably holds the key to the fundamentals of the Universe and laws of physics.In this dissertation, I discuss a series of papers related to studies of dark matter.I revisit the problem of dark matter annihilation in the extragalactic background radiation, and show that they are sensitive to the properties of the smallest dark matter halos.I show that the newly discovered high-energy astrophysical neutrinos can be used to test secret neutrino interactions through their propagation in the Cosmic Neutrino Background.I discuss how we use the Fermi-GBM to search for sterile neutrino dark matter in a region of parameter space that is not probed otherwise.I discuss a novel method for testing dark matter annihilation/decay signals with a line spectrum.Lastly, I discuss new and interesting results from gamma-ray observations of the Sun, and how this is related to future dark matter searches from the Sun.May it be a light for you in dark places, when all other lights go out. GaladrielThanks to all the people whom I had the pleasure to meet during graduate school, OSU will always be a special place to me.Among fellow graduate students, I probably spent too much time debating with Ranjan Laha, but at least some of that was about physics.Shirley Li was always incredibly helpful and constructive, especially when I was most desperate.I also had the privilege of working closely with three younger students, Eric Speckhard, Bei Zhou, and Chris Cappiello, who always reminded me of the old Chinese saying, "fear the young."I thank Andrea Albert for introducing me to CCAPP; joining CCAPP ended up being one of the best decision I have ever made.And I could not have imagined that the first student I interacted with at OSU would teach me, among other things, about the superbowl and Thanksgiving, and then ended up being my academic neighbor.It is a pleasure meeting you, Joe McEwen.I am also indebted to the kindness of many CCAPP postdocs (many are professors now!), especially when I just started.