  This theoretical particle physics thesis is an investigation into old and new
symmetries of Nature. Known symmetries and conservation laws serve as a guide
for dark and visible sector model building. New symmetries of Nature are
proposed, broken and subsequently reinstated at high temperatures in order to
discover well-motivated particle physics models for cosmological observations
implying the existence of a dark sector. Candidate processes for creation of a
non-primordial matter/antimatter asymmetry result from out of equilibrium
spontaneous breaking of these symmetries in the early Universe. Using the
Standard Model of particle physics as a foundation with minimal new degrees of
freedom, minicharged and millicharged particles emerge from a proposed
spontaneous breaking of known symmetries. Experimental predictions and
constraints for such dark matter candidates are given briefly here and outlined
for future work. Constraints on neutrino-like particles found in the debris of
broken local (gauge) symmetries are given, a subset of which are sterile and
appear to be viable particle dark matter candidates. A failed baryonic dark
matter candidate became a candidate to solve an outstanding nuclear structure
problem, the EMC effect.
