|M.Sc Student||Biran Eyal|
|Subject||Testing the Weak Equivalence Principle in the Dark Sector|
using Satellite Galaxies of the Milky Way
|Department||Department of Physics||Supervisor||Professor Adi Nusser|
|Full Thesis text|
We consider breaking of the Weak Equivalence Principle (WEP) in the dark sector by
means of long range scalar interactions (LRSI) acting between dark matter (DM) particles only. Laboratory experiments put stringent constraints on WEP violating forces for visible baryonic matter (BM) only and are incapable of probing the dark sector. The dynamics of a DM dominated dwarf galaxy bound to the Milky Way (MW) can provide an interesting scenario for exploring this theoretical interaction. Considering this scenario, the stellar component of a dwarf galaxy orbiting the MW is governed by gravity alone, while its DM is also affected by the LRSI force generated by the interaction with the MW dark halo. This leads to important observable consequences, the most extreme form of which is a total disruption of the stellar component from the DM halo. Out of several MW dwarf spheroidal (dSph) galaxies, we pinpoint Draco as currently the most suitable for studying dark sector WEP violation for the following reasons. i) good quality observations of the stellar distribution and internal velocity dispersion, ii) it has a high mass-to-light ratio of
(M/L)i = 146±42Mʘ/Lʘ which is most likely due to DM abundance, and iii) its proximity to the Galactic center of a current Galactic distance of D = 82.4±5.8 kpc . These last two facts enhance observational signatures of LRSI forces. Our goal is to constrain the relative strength of the LRSI force to gravity, β, using numerical simulation of Draco orbiting the MW. We present a physical scenario which is consistent with WEP violation namely, a value for β which generates a stable system that resembles Draco as observed today. We consider two possible Galactic orbits for Draco, the first with a pericenters of ~ 20 kpc and the second with ~ 60 kpc , obtained from two different proper motion measurements for Draco. By studying the evolution of Draco's internal properties, as surface density and line-of-sight velocity dispersion profiles, we were able to derive the constraints of β<0.3 and β<0.5, which pass observational demands for these two orbits, respectively.