(Experts might skip right to my publications here)
Theorist (th¨¥-e-rist,thir-ist) n. you think you're right but no one else does.
Experimentalist (ik-sper-e-ment-te-lest) n. you think you're wrong but no one else does.
My formal training is in theoretical particle physicis with experimental leanings: I am interested in the fundamental constituents and rules of Nature that we can actually measure.
The accepted paradigm is as follows: currently, there are known to be a number of basic particles (like lego bricks, these can be used to build more complicated objects such as atoms), as shown in the table below.
Thus, you could say there are 16 fundamental particles, divided into 4 "bosons" and 12 "fermions" (strictly speaking there are more, because each particle can have L- or R-handed varieties and/or "colors"). The bosons are understood to be force carriers of three of the four known forces in Nature: the gluon mediates the "strong" force (responsible for nuclear interactions), the W and Z mediate the "weak force" (important for nuclear decay) while the photon mediates good old electromagnetism. Together with a collection of rules for describing how all these particles interact with each other, called quantum field theory, this constitutes what's known as the Standard Model of Particle Physics, and it's thus far been highly successful in describing results of experiments where some of these particles are smashed into others.
But there are some things missing or needing further explanation in the Standard Model, e.g. why there are three generations, what is the pattern of the particles' masses, why there are different quarks and leptons to begin with. Also, the most glaring omission in the above is gravity. Nobody has figured out the fundamental reason why the Earth goes around the Sun! My research is concerned with all of these questions and much more, for which it is probably better to refer you to a primer on the subject.
Though I had been looking at direct answers to these questions in the context of quantum field theory, which is based on continuous mathematics, I am now poking around with a discrete formalism (i.e. make spacetime a lattice of points instead of a continuous manifold).