Astrophysical observations — galaxy rotation curves, gravitational lensing, and CMB anisotropies — provide strong evidence for dark matter (DM), with PLANCK and WMAP data indicating DM makes up ~85% of the Universe’s matter content and ~26.7% of its total energy budget. Yet DM’s particle nature remains unknown, and since the SM offers no viable candidate, various BSM scenarios have been proposed, with WIMPs being the most popular. Null results from terrestrial WIMP searches motivate looking beyond minimal WIMP scenarios.

The Standard Model lacks right-handed neutrino (RHN) fields, so neutrinos remain massless without a Yukawa coupling involving the Higgs, leptons, and RHNs. However, solar and atmospheric neutrino oscillation experiments confirm that at least two neutrino states are massive, though tiny. So what is the origin of this tiny neutrino mass? Whether neutrinos are Dirac or Majorana particles also remains unresolved. Treating light neutrinos as Majorana, various BSM frameworks, popularly known as seesaw mechanisms have been proposed to explain their mass. 

The matter–antimatter (baryon) asymmetry problem in cosmology refers to the observed imbalance between baryonic and antibaryonic matter in the universe. Neither the Standard Model nor General Relativity explains this, despite the natural expectation of a charge-neutral universe where the Big Bang would have produced equal amounts of matter and antimatter. Since this isn’t observed, physical laws likely acted differently for matter and antimatter. Various competing hypotheses attempt to explain this imbalance through baryogenesis, but no consensus theory yet exists.