Dwarf Spheroidal J-factors with Self-interacting Dark Matter

Abstract

The next decade of searches in the field of dark matter will focus on the detection of gamma rays from dark matter annihilation in dwarf spheroidal galaxies. This dark matter-induced gamma ray flux crucially depends on a quantity known as the Jfactor. In current research, the J-factor calculations does not include self-interaction between the dark matter particles, but there are indications on galactic scales that dark matter is self-interacting. The purpose of this thesis is to introduce a thorough generalisation of the J-factor to include a self-interacting effect and to compute the factor for 20 dwarf spheroidal galaxies orbiting the Milky Way. We thoroughly study the fundamental theory needed to compute the J-factor, based on Newtonian dynamics and non-relativistic quantum mechanics. A maximum likelihood formalism is applied to velocity data from dwarf spheroidal galaxies, assuming a Gaussian distribution for the line of sight velocity data. From this we extract galactic length and density scale parameters. The acquired parameters are then used to compute the J-factor. Using a binning approach, we present an error estimate in J. The used method is compared to previously published results, by neglecting self-interaction. We perform the first fully rigorous calculation for the J-factor, properly taking into account the dark matter velocity distribution. We can deduce that a previously used approximation of the self-interaction overestimates the J-factor by 1.5 orders of magnitude. Furthermore, we confirm that our method produces three to four orders of magnitudes larger values compared to J-factors without self-interaction.