I've just started working on my first particle theory project in graduate school, and I'm finding it very exciting and challenging. Having just recently finished my first year of QFT, I still have a lot more to learn. But it's already sinking in pretty fast.
I'm working with BFSS Matrix Theory, the discrete light cone quantized 11-dimensional theory of interacting D0-branes which in the large N limit might be the full non-perturbative description of M-Theory. (N here is the size of the matrices, which replace coordinates leading to a non-commutative geometry at short distances). It seems very promising to me so far, but everything I hear about it is from Tom Banks who of course has a lot invested. One thing I'd be curious about, if anyone knows more about the history behind this, is if it's my imagination or if work on this and excitement for this dropped off a bit after around '99 or so. If it did, I'd be interested in hearing why. Are there any good reasons to be skeptical of it, or is it just a matter of people getting stuck and spending time on other things?
I'm trying to get quantum corrections to a classical solution for Matrix Theory which appears to have the proper spectrum for supergravity. Hopefully the corrections don't screw anything up. I'm doing everything at finite temperature, which has caused me to have to quickly learn "QFT at finite temp" which we never covered in my first year of QFT. It's simpler than I'd expected though, and seems pretty similar to how regular Green functions work aside from the periodic time variable which "threw me for a loop" at first. The Matrix Theory Lagrangian itself is also surprisingly simple, and works essentially like non-relativistic quantum mechanics, but with a variable mass given by the discrete momentum in the longitudinal direction of the compactified light-cone dimension.
If anyone is more curious about this, or wants a quick run-down on how Matrix Theory works, I'd love to discuss it... to the extent that I understand it (which is not that much yet, but quickly improving!) I'm very much enjoying this so far, but I'd be curious to hear any positive or negative comments about this direction of research. Since I'll soon have to figure out whether I want to stick with this or look into something else.