  In this thesis, we investigate some aspects of dark matter phenomenology and
its predictive power in explaining the flattening of galaxy rotation curves at
large distances. After outlining the Standard Model of particle physics, its
symmetries and possible extensions in Chapter 2, we review key facts about dark
matter and various types of dark matter models in Chapter 3. In Chapter 4 we
discuss some alternatives to cold dark matter, which include modified Newtonian
dynamics (MOND), superfluid dark matter and emergent gravity, and highlight the
difficulties that are encountered in attempts to extend these frameworks to
full-fledged relativistic settings. In Chapter 5 we turn to explore a
completely different option, namely that flattened rotation curves reflect the
presence of prolate dark-matter bulges or string-like objects around galaxies,
without the need for any infrared modification of gravity. To test this model,
we fit a number of galaxy rotation curves and find that the presence of a
string-like filament yields improvement in fit quality of about 40-70 % in some
cases, while the deformation of a dark halo yields only modest improvement by
about 6-7 %. In Chapter 6 we collect some concluding remarks.
