There’s work ongoing on figuring out why neutrinos have mass. What’s in dark matter is also still a big mystery, and there’s experiments ongoing to pin down a few miscellaneous interactions that just work a bit funny.
Beyond that, there’s all kinds of ideas about very high energy physics: unification of the three forces of nature, what happened during the big bang, supersymmetry, string theory and so on. At this point it’s looking like no particle accelerator that fits on Earth will be strong enough to find anything like that, though.
https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics#High-energy/particle_physics
There’s work ongoing on figuring out why neutrinos have mass. What’s in dark matter is also still a big mystery, and there’s experiments ongoing to pin down a few miscellaneous interactions that just work a bit funny.
Beyond that, there’s all kinds of ideas about very high energy physics: unification of the three forces of nature, what happened during the big bang, supersymmetry, string theory and so on. At this point it’s looking like no particle accelerator that fits on Earth will be strong enough to find anything like that, though.