Though Raj expressed the desire to become the Indira Gandhi of particle astrophysics in the first season's The Grasshopper Experiment, his research as of The Griffin Equivalency had been planetary astronomy until The Pirate Solution, when he begins research on dark matter with Sheldon once his prospect for stellar astrophysics fails. Koothrappali expresses heliophysics interest in The Spaghetti Catalyst, and along with his work for Sheldon, he renews his focus on planetary astronomy in The Boyfriend Complexity. His expertise in the latter field is again expanded upon in The Higgs Boson Observation and The Sales Call Sublimation. He references published space physics literature, still within the purview of planetology, in The Hofstadter Insufficiency.
An enumeration of the research fields of Rajesh Koothrappali follows thusly:
Observational and Numerical Planetary Astronomy – Trans-Neptunian Objects, Trojan Asteroids, Van Allen Belts, Exoplanets, Rogue Planets
Phenomenology of Particle Astrophysics – Dark Matter
For the sake of completeness (and in an effort to be self-contained), the research areas of the other primary characters are also classified and listed here.
An enumeration of the research fields of Sheldon Cooper follows thusly:
Theoretical Nuclear and Particle Physics – Superstrings and Quantum Gravity, Particle Cosmology, Collider Phenomenology, Superheavy Elements
Theoretical Cosmology – Dark Matter, Spacetime Analogue, Penrose Conjecture
Theoretical Condensed Matter Physics – Bose-Einstein Condensates, Superfluids, Graphene Quasiparticles, Topological Insulators, Thermodynamic Fluctuations, Polymer Degradation
Theoretical Plasma Physics – Turbulent Diffusion in Fusion Devices
Philosophy of Physics – Quantum Measurement Problem
An enumeration of the research fields of Leonard Hofstadter follows thusly:
Experimental Particle and Astroparticle Physics – Dark Matter, Cosmic Rays, Neutrinos, Unruh Radiation, Antiproton Decay, Accelerator Physics
Experimental Condensed Matter and Materials Physics– Supersolids, Superfluid Helium, Gels, Nanoelectronics, X-Ray Diffraction
Applied Optics and Photonics – High Energy Lasers, Holographic Displays
An enumeration of the research fields of Howard Wolowitz follows thusly:
Space Systems Engineering – Satellite Systems, Aerospace Robotics, Spaceflight Hardware Design, Astronomical Instrumentation