Automorphic forms with singularities on Grassmannians

Oblatum 30-IX-1996 & 17-VI-1997     

Automorphic forms and differentiability properties

We consider Fourier series given by a type of fractional integral of automorphic forms, and we study their local and global properties, especially differentiability and fractal dimension of the graph of their real and imaginary parts. In this way we can construct fractal objects and continuous non-differentiable functions associated with elliptic curves and theta functions.

     

Automorphic forms for elliptic function fields

Let F be the function field of an elliptic curve X over ${\mathbb{F}_q}$ . In this paper, we calculate explicit formulas for unramified Hecke operators acting on automorphic forms over F. We determine these formulas in the language of the graph of an Hecke operator, for which we use its interpretation in terms of ${\mathbb{P}^1}$ -bundles on X. This allows a purely geometric approach, which involves, amongst others, a classification of the ${\mathbb{P}^1}$ -bundles on X. We apply the computed formulas to calculate the dimension of the space of unramified cusp forms and the support of a cusp form. We show that a cuspidal Hecke eigenform does not vanish in the trivial ${\mathbb{P}^1}$ -bundle. Further, we determine the space of unramified F′-toroidal automorphic forms where F′ is the quadratic constant field extension of F. It does not contain non-trivial cusp forms. An investigation of zeros of certain Hecke L-series leads to the conclusion that the space of unramified toroidal automorphic forms is spanned by the Eisenstein series E( · , s) where s?+?1/2 is a zero of the zeta function of X—with one possible exception in the case that q is even and the class number h equals q?+?1.     

Automorphic forms and the distribution of points on odd-dimensional spheres

We discuss standard pairs of generators of cyclic divisionp-algebras of degreep, and prove forp=3 that any two Artin-Schreier elements are connected by a chain of standard pairs. This result has immediate applications to the presentations of such algebras.     

Automorphic forms for subgroups of the modular group

The theory of theta constants with rational characteristics is developed from the point of view of automorphic functions for the principal congruence subgroups of the modular group PSL(2, ℤ). New identities are derived and particular emphasis is given to the level 3 case where a striking generalization of the classical λ-function is obtained. This paper is dedicated to Prof. J. Thompson in recognition of his many contributions to mathematics and of his being the recipient of the Wolf Prize in Mathematics Research by HMF supported in part by the Paul and Gabriella Rosenbaum Foundation and partially sponsored by the Edmund Landau Center for Research in Mathematical Analysis, supported by the Minerva Foundation (Germany). Research by IK supported in part by NSF Grants DMS 9003361 and 9204092.     

Building ofGL(m, D) and centralizers

LetG=GL(m, D) whereD is a central division algebra over a commutative nonarchimedean local fieldF. LetE/F be a field extension contained inM(m, D). We denote byI (resp.I _E) the nonextended affine building ofG (resp. of the centralizer ofE ^x inG). In this paper we prove that there exists a uniqueG _E-equivariant affine mapj _EI_EI. It is injective and its image coincides with the set ofE ^x-fixed points inI. Moreover, we prove thatj _E is compatible with the Moy-Prasad filtrations.This author's contribution was written while he was a post-doctoral student at King's College London and supported by an european TMR grant     

Automorphic forms and cohomology theories on Shimura curves of small discriminant

We apply Lurie's theorem to produce spectra associated to 1-dimensional formal group laws on the Shimura curves of discriminants 6, 10, and 14. We compute rings of automorphic forms on these curves and the homotopy of the associated spectra. At p=3, we find that the curve of discriminant 10 recovers much the same as the topological modular forms spectrum, and the curve of discriminant 14 gives rise to a model of a truncated Brown-Peterson spectrum as an E_∞ ring spectrum.     

Fractional Moments of Automorphic L-Functions on GL（m）

Let π be an irreducible unitary cuspidal representation of GLm(AQ), m ≥ 2. Assume that π is self-contragredient. The author gets upper and lower bounds of the same order for fractional moments of automorphic L-function L(s, π) on the critical line under Generalized Ramanujan Conjecture; the upper bound being conditionally subject to the truth of Generalized Riemann Hypothesis.