Is there any classification for coadjoint orbits of lower or upper triangular matrices in general case $n\times n$. Is there any reference?

Consider algebraic group G over some field "k". Consider the SET of all its complex irreducible representations (I think I need unitary also). Question Is there some way to put …

Given a complex Lie algebra $\mathfrak g$, we can form its universal enveloping algebra and interpret it as a noncommutative space. Is this perspective useful? What does this spa …