Equidistribution of Dynamically Small Subvarieties over the Function Field of a Curve

For a projective variety X defined over a field K, there is a special class of self-morphisms of X called algebraic dynamical systems. In this paper we take K to be the function field of a smooth curve and prove that at each place of K, subvarieties of X of dynamically small height are equidistributed on the associated Berkovich analytic space. We carefully develop all of the arithmetic intersection theory needed to state and prove this theorem, and we present several applications on the non-Zariski density of preperiodic points and of points of small height in field extensions of bounded degree.Comment: v2: Various typos fixed; statement and proof of auxiliary Prop. 6.1 corrected. During the process of preparing this manuscript for submission, it came to the author's attention that Walter Gubler has recently proved many of the same results. See arXiv:0801.4508v3. v3: References updated and a few more typos corrected. To appear in Acta Arithmetic

A Remark on the Effective Mordell Conjecture and Rational Pre-Images under Quadratic Dynamical Systems

Fix a rational basepoint b and a rational number c. For the quadratic dynamical system f_c(x) = x^2+c, it has been shown that the number of rational points in the backward orbit of b is bounded independent of the choice of rational parameter c. In this short note we investigate the dependence of the bound on the basepoint b, assuming a strong form of the Mordell Conjecture.Comment: 5 pages; Final version to appear in Comptes Rendus Mathematiqu

Tautological and non-tautological cohomology of the moduli space of curves

After a short exposition of the basic properties of the tautological ring of the moduli space of genus g Deligne-Mumford stable curves with n markings, we explain three methods of detecting non-tautological classes in cohomology. The first is via curve counting over finite fields. The second is by obtaining length bounds on the action of the symmetric group S_n on tautological classes. The third is via classical boundary geometry. Several new non-tautological classes are found.Comment: 40 page

Hodge integrals, partition matrices, and the lambda_g conjecture

We prove a closed formula for integrals of the cotangent line classes against the top Chern class of the Hodge bundle on the moduli space of stable pointed curves. These integrals are computed via relations obtained from virtual localization in Gromov-Witten theory. An analysis of several natural matrices indexed by partitions is required.Comment: 28 pages, published versio

Covariants of binary sextics and vector-valued Siegel modular forms of genus two

We extend Igusa’s description of the relation between invariants of binary sextics and Siegel modular forms of degree 2 to a relation between covariants and vector-valued Siegel modular forms of degree 2. We show how this relation can be used to effectively calculate the Fourier expansions of Siegel modular forms of degree 2