Let A be a homogeneous K-algebra where K is a field of characteristic 0, and h ∈ A a generic form. We bound the Hilbert function H(A/(h),-) in terms of H(A,-) which extends the bound given by M. Green for generic linear forms. We apply this to some conjectures from Higher Castelnuovo Theory and Cayley-Bacharach Theory.

Let (C,G) be a smooth irreducible projective curve of genus g over an algebraically closed field k of chararacteristic p>0 and G be a finite group of automorphisms of C. It is well known that here, contrary to the characteristic 0 case, Hurwitz‘s bound |G|[les ] 84(g-1) doesn‘t hold in general; in such cases this gives an obstruction to obtaining a smooth galois lifting of (C,G) to characteristic 0. We shall give new obstructions of local nature to the lifting problem, even in the case where G is abelian. In the case where the inertia groups are p$^ae$-cyclic with a[les ] 2 and (e,p)=1, we shall prove that smooth galois liftings exist over W(k)[$^p^^2$√1].

We give a short proof of the inner product conjecture for the symmetric Macdonald polynomials of type A$_n-1$. As a special case, the corresponding constant term conjecture is also proved.

Let G be a complex linear algebraic group and ρ:G → GL(V) a finite dimensional rational representation. Assume that G is connected and reductive, and that V has an open G-orbit. Let f in C[V] be a non-zero relative invariant with character ϕ ∈ Hom (G, C$^×$), meaning that f ˆ ρ (g) =ϕ (g) f for all g in G. Choose a non-zero relative invariant f$^v$ in C[V$^v$], with character ϕ$^-1$, for the dual representation ρ$^v$:G → GL(V$^v$). Roughly, the fundamental theorem of the theory of prehomogeneous vector spaces due to M. Sato says that the Fourier transform of |f|$^s$equals |f$^v$|$^-s$ up to some factors. The purpose of the present paper is to study a finite field analogue of Sato‘s theorem and to give a completely explicit description of the Fourier transform assuming that the characteristic of the base field F$_q$ is large enough. Now |f|$^s$ is replaced by χ (f), with χ in Hom (F$_q$$^×$, C$^×$), and the factors involve Gauss sums, the Bernstein–Sato polynomial b(s) of f, and the parity of the split rank of the isotropy group at v$^v$∈ V$^v(F<math>_q$). We also express this parity in terms of the quadratic residue of the discriminant of the Hessian of log f$^v$ (v$^v$). Moreover we prove a conjecture of N. Kawanaka on the number of integer roots of b(s).

This paper determines the θ–correspondence for the dual pairs (O(p, q), Sp(2n, R)) when p+q=2n+1. As a consequence, there is a natural bijection between genuine irreducible representations of the metaplectic group Mp(2n, R) and irreducible representations of SO(p, q) with p+q=2n+1.

In this paper we examine the Iwasawa theory of modular elliptic curves E defined over Q without semi-stable reduction at p. By constructing p-adic L-functions at primes of additive reduction, we formulate a “Main Conjecture” linking this L-function with a certain Selmer group for E over the Zp-extension. Thus the leading term is expressible in terms of III$_E$, E(Q)$_tors$ and a p-adic regulator term.

Let S be a smooth, minimal rational surface. The geometry of the Severi variety parametrising irreducible, rational curves in a given linear system on S is studied. The results obtained are applied to enumerative geometry, in combination with ideas from Quantum Cohomology. Formulas enumerating rational curves are found, some of which generalised Kontsevich‘s formula for plane curves.

In this paper we give explicit equations for determinantal rational surface singularities and prove dimension formulas for the t$^1$ and T$^2$ for those singularities.

A new method to approach enumerative questions about rational curves on algebraic varieties is described. The idea is to reduce the counting problems to computations on the Néron-Severi group of a ruled surface. Applications include a short proof of Kontsevich‘s formula for plane curves and the solution of the analogous problem for the Hirzebruch surface F$_3$.

We build a theory of Λ-adic Siegel modular forms related to the Klingen parabolic subgroup of GSp(4). These correspond to families of cohomology classes of increasing levels whose Hecke eigenvalues enjoy strong congruence properties. In the spirit of Hida‘s theory, a control theorem to relate the family to finite-level members is proved for almost all primes p; in particular we show that the error term appearing in degree one cohomology is killed by the ordinary idempotent.