How precisely do we know the research topics of the scientists in TBBT?

Question

I believe the general research areas/specialties of each of the main scientists in The Big Bang Theory are well known to viewers, as follows:

• Sheldon: theoretical physics
• Leonard: experimental physics
• Raj: astrophysics
• Howard: mechanical/electrical engineering
  (but I count him as a scientist for this question because it's easy)
• Amy: neuroscience
• Bernadette: microbiology

How much more precisely can we identify the specific subfields they work in? What evidence exists in the show that one would use to make such an identification?

Of course, I'm aware that if one looks too closely, the evidence will be inconsistent, e.g. Sheldon usually works on string theory and particle physics but spends a whole episode on the motion of electrons through a crystal lattice, which is only vaguely related. But I'm willing to excuse an occasional diversion into a different research topic (which is plausible). I would imagine the majority of each character's work in the show centers around some topic which can be identified more specifically than just e.g. "experimental physics," and that's what I'm curious to know about.

Answer 1

Well, we do have at least one clue for Sheldon Cooper and Leonard Hofstadter, in that in episode 1.9 "The Cooper-Hofstadter Polarization", they were invited to co-present a paper on super solids, which comes from the quantum field. Leonard was also awarded dissertation of the year for his doctoral thesis on experimental particle physics. Sheldon concentrates more on string theory and M-theory.

Rajesh Koothrappali is in astrophysics, and at one point in the series fears being deported because of failed research in trans Neptunian objects, so astral body research can be intimated from this reference, and he also does research with Sheldon on gamma rays and dark matter annihilation.

Howard Wolowitz is pretty much an engineer, as shown by his creation of a toilet for the space station, and other physical objects.

Amy Farrah Fowler is engaged in research on primates and invertebrates, which is sprinkled in through many episodes, usually centered around jokes during her work. (As an aside, Mayim Bialik, the actress that portrays Dr. Amy Fowler has a Ph.D in neuroscience.)

Bernadette Marian Rostenkowski Wolowitz (formerly Bernadette Marian Rostenkowski), for some of the series was in graduate school, and when she graduated was hired by a large pharmaceutical company, presumably in drug research.