Decomposition of reductive regular prehomogeneous vector spaces

Let (G,V) be a regular prehomogeneous vector space (abbreviated to PV), where G is a connected reductive algebraic group over C. If $V= \oplus_{i=0}^{n}V_{i}$ is a decomposition of V into irreducible representations, then, in general, the PV's $(G,V_{i})$ are no longer regular. In this paper we introduce the notion of quasi-irreducible PV (abbreviated to Q-irreducible), and show first that for completely Q-reducible PV's, the Q-isotopic components are intrinsically defined, as in ordinary representation theory. We also show that, in an appropriate sense, any regular PV is a direct sum of quasi-irreducible PV's. Finally we classify the quasi-irreducible PV's of parabolic type

Algebras of invariant differential operators on a class of multiplicity free spaces

Let G be a connected reductive algebraic group and let G'=[G,G] be its derived subgroup. Let (G,V) be a multiplicity free representation with a one dimensional quotient (see definition below). We prove that the algebra D(V)^{G'} of G'-invariant differential operators with polynomial coefficients on V, is a quotient of a so-called Smith algebra over its center. Over C this class of algebras was introduced by S.P. Smith as a class of algebras similar to the enveloping algebra U(sl(2)) of sl(2). Our result generalizes the case of the Weil representation, where the associative algebra generated by Q(x) and Q(?) (Q being a non degenerate quadratic form on V) is a quotient of U(sl(2)) Other structure results are obtained when (G,V) is a regular prehomogeneous vector space of commutative parabolic type

Invariant differential operators on a class of multiplicity free spaces

If $(G,V)$ is a multiplity free space with a one dimensional quotient we give generators and relations for the non-commutative algebra $D(V)^{G'}$ of invariant differential operators under the semi-simple part $G'$ of the reductive group $G$. More precisely we show that $D(V)^{G'}$ is the quotient of a Smith algebra by a completely described two-sided ideal.Comment: 31 page

Non-parabolic prehomogeneous vector spaces and exceptional Lie algebras

AbstractAmong the classification of irreducible regular and reduced prehomogeneous vector spaces, there are only a few one which are not of parabolic type. In this paper we investigate this family of prehomogeneous vector and show that they nevertheless all occur inside the exceptional Lie algebras and are in some sense close to the parabolic family. Moreover we give a Lie theoretical description of their relative invariants and the corresponding characters